Photophysics of phenol and pentafluorophenol: The role of nonadiabaticity in the optical transition to the lowest bright 1ππ* state

NASA Astrophysics Data System (ADS)

Rajak, Karunamoy; Ghosh, Arpita; Mahapatra, S.

2018-02-01

We report multimode vibronic coupling of the energetically low-lying electronic states of phenol and pentafluorophenol in this article. First principles nuclear dynamics calculations are carried out to elucidate the optical absorption spectrum of both of the molecules. This is motivated by the recent experimental measurements [S. Karmakar et al., J. Chem. Phys. 142, 184303 (2015)] on these systems. Diabatic vibronic coupling models are developed with the aid of adiabatic electronic energies calculated ab initio by the equation of motion coupled cluster quantum chemistry method. A nuclear dynamics study on the constructed electronic states is carried out by both the time-independent and time-dependent quantum mechanical methods. It is found that the nature of low-energy πσ* transition changes, and in pentafluorophenol the energy of the first two 1πσ* states, is lowered by about half an eV (vertically, relative to those in phenol), and they become energetically close to the optically bright first excited 1ππ* (S1) state. This results in strong vibronic coupling and multiple multi-state conical intersections among the ππ* and πσ* electronic states of pentafluorophenol. The impact of associated nonadiabatic effects on the vibronic structure and dynamics of the 1ππ* state is examined at length. The structured vibronic band of phenol becomes structureless in pentafluorophenol. The theoretical results are found to be in good accord with the experimental finding at both high energy resolution and low energy resolution.

Vibronic coupling effect on the electron transport through molecules

NASA Astrophysics Data System (ADS)

Tsukada, Masaru; Mitsutake, Kunihiro

2007-03-01

Electron transport through molecular bridges or molecular layers connected to nano-electrodes is determined by the combination of coherent and dissipative processes, controlled by the electron-vibron coupling, transfer integrals between the molecular orbitals, applied electric field and temperature. We propose a novel theoretical approach, which combines ab initio molecular orbital method with analytical many-boson model. As a case study, the long chain model of the thiophene oligomer is solved by a variation approach. Mixed states of moderately extended molecular orbital states mediated and localised by dress of vibron cloud are found as eigen-states. All the excited states accompanied by multiple quanta of vibration can be solved, and the overall carrier transport properties including the conductance, mobility, dissipation spectra are analyzed by solving the master equation with the transition rates estimated by the golden rule. We clarify obtained in a uniform systematic way, how the transport mode changes from a dominantly coherent transport to the dissipative hopping transport.

Vibronic coupling effect on circular dichroism spectrum: Carotenoid-retinal interaction in xanthorhodopsin

NASA Astrophysics Data System (ADS)

Fujimoto, Kazuhiro J.; Balashov, Sergei P.

2017-03-01

The role of vibronic coupling of antenna carotenoid and retinal in xanthorhodopsin (XR) in its circular dichroism (CD) spectrum is examined computationally. A vibronic exciton model combined with a transition-density-fragment interaction (TDFI) method is developed, and applied to absorption and CD spectral calculations of XR. The TDFI method is based on the electronic Coulomb and exchange interactions between transition densities for individual chromophores [K. J. Fujimoto, J. Chem. Phys. 137, 034101 (2012)], which provides a quantitative description of electronic coupling energy. The TDFI calculation reveals a dominant contribution of the Coulomb interaction to the electronic coupling energy and a negligible contribution of the exchange interaction, indicating that the antenna function of carotenoid results from the Förster type of excitation-energy transfer, not from the Dexter one. The calculated absorption and CD spectra successfully reproduce the main features of the experimental results, which allow us to investigate the mechanism of biphasic CD spectrum observed in XR. The results indicate that vibronic coupling between carotenoid and retinal plays a significant role in the shape of the CD spectrum. Further analysis reveals that the negative value of electronic coupling directly contributes to the biphasic shape of CD spectrum. This study also reveals that the C6—C7 bond rotation of salinixanthin is not the main factor for the biphasic CD spectrum although it gives a non-negligible contribution to the spectral shift. The present method is useful for analyzing the molecular mechanisms underlying the chromophore-chromophore interactions in biological systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wykes, M., E-mail: mikewykes@gmail.com; Parambil, R.; Gierschner, J.

Here, we present a general approach to treating vibronic coupling in molecular crystals based on atomistic simulations of large clusters. Such clusters comprise model aggregates treated at the quantum chemical level embedded within a realistic environment treated at the molecular mechanics level. As we calculate ground and excited state equilibrium geometries and vibrational modes of model aggregates, our approach is able to capture effects arising from coupling to intermolecular degrees of freedom, absent from existing models relying on geometries and normal modes of single molecules. Using the geometries and vibrational modes of clusters, we are able to simulate the fluorescencemore » spectra of aggregates for which the lowest excited state bears negligible oscillator strength (as is the case, e.g., ideal H-aggregates) by including both Franck-Condon (FC) and Herzberg-Teller (HT) vibronic transitions. The latter terms allow the adiabatic excited state of the cluster to couple with vibrations in a perturbative fashion via derivatives of the transition dipole moment along nuclear coordinates. While vibronic coupling simulations employing FC and HT terms are well established for single-molecules, to our knowledge this is the first time they are applied to molecular aggregates. Here, we apply this approach to the simulation of the low-temperature fluorescence spectrum of para-distyrylbenzene single-crystal H-aggregates and draw comparisons with coarse-grained Frenkel-Holstein approaches previously extensively applied to such systems.« less

Theory of Excitonic Delocalization for Robust Vibronic Dynamics in LH2.

PubMed

Caycedo-Soler, Felipe; Lim, James; Oviedo-Casado, Santiago; van Hulst, Niek F; Huelga, Susana F; Plenio, Martin B

2018-06-11

Nonlinear spectroscopy has revealed long-lasting oscillations in the optical response of a variety of photosynthetic complexes. Different theoretical models that involve the coherent coupling of electronic (excitonic) or electronic-vibrational (vibronic) degrees of freedom have been put forward to explain these observations. The ensuing debate concerning the relevance of either mechanism may have obscured their complementarity. To illustrate this balance, we quantify how the excitonic delocalization in the LH2 unit of Rhodopseudomonas acidophila purple bacterium leads to correlations of excitonic energy fluctuations, relevant coherent vibronic coupling, and importantly, a decrease in the excitonic dephasing rates. Combining these effects, we identify a feasible origin for the long-lasting oscillations observed in fluorescent traces from time-delayed two-pulse single-molecule experiments performed on this photosynthetic complex and use this approach to discuss the role of this complementarity in other photosynthetic systems.

Full-dimensional treatment of short-time vibronic dynamics in a molecular high-order-harmonic-generation process in methane

NASA Astrophysics Data System (ADS)

Patchkovskii, Serguei; Schuurman, Michael S.

2017-11-01

We present derivation and implementation of the multiconfigurational strong-field approximation with Gaussian nuclear wave packets (MC-SFA-GWP)—a version of the molecular strong-field approximation which treats all electronic and nuclear degrees of freedom, including their correlations, quantum mechanically. The technique allows realistic simulation of high-order-harmonic emission in polyatomic molecules without invoking reduced-dimensionality models for the nuclear motion or the electronic structure. We use MC-SFA-GWP to model isotope effects in high-order-harmonic-generation (HHG) spectroscopy of methane. The HHG emission in this molecule transiently involves the strongly vibronically coupled F22 electronic state of the CH4+ cation. We show that the isotopic HHG ratio in methane contains signatures of (a) field-free vibronic dynamics at the conical intersection (CI); (b) resonant features in the recombination cross sections; (c) laser-driven bound-state dynamics; as well as (d) the well-known short-time Gaussian decay of the emission. We assign the intrinsic vibronic feature (a) to a relatively long-lived (≥4 fs) vibronic wave packet of the singly excited ν4 (t2) and ν2 (e ) vibrational modes, strongly coupled to the components of the F22 electronic state. We demonstrate that these physical effects differ in their dependence on the wavelength, intensity, and duration of the driving pulse, allowing them to be disentangled. We thus show that HHG spectroscopy provides a versatile tool for exploring both conical intersections and resonant features in photorecombination matrix elements in the regime not easily accessible with other techniques.

Vibronic Wavepackets and Energy Transfer in Cryptophyte Light-Harvesting Complexes.

PubMed

Jumper, Chanelle C; van Stokkum, Ivo H M; Mirkovic, Tihana; Scholes, Gregory D

2018-06-21

Determining the key features of high-efficiency photosynthetic energy transfer remains an ongoing task. Recently, there has been evidence for the role of vibronic coherence in linking donor and acceptor states to redistribute oscillator strength for enhanced energy transfer. To gain further insights into the interplay between vibronic wavepackets and energy-transfer dynamics, we systematically compare four structurally related phycobiliproteins from cryptophyte algae by broad-band pump-probe spectroscopy and extend a parametric model based on global analysis to include vibrational wavepacket characterization. The four phycobiliproteins isolated from cryptophyte algae are two "open" structures and two "closed" structures. The closed structures exhibit strong exciton coupling in the central dimer. The dominant energy-transfer pathway occurs on the subpicosecond timescale across the largest energy gap in each of the proteins, from central to peripheral chromophores. All proteins exhibit a strong 1585 cm -1 coherent oscillation whose relative amplitude, a measure of vibronic intensity borrowing from resonance between donor and acceptor states, scales with both energy-transfer rates and damping rates. Central exciton splitting may aid in bringing the vibronically linked donor and acceptor states into better resonance resulting in the observed doubled rate in the closed structures. Several excited-state vibrational wavepackets persist on timescales relevant to energy transfer, highlighting the importance of further investigation of the interplay between electronic coupling and nuclear degrees of freedom in studies on high-efficiency photosynthesis.

Low-lying vibronic level structure of the ground state of the methoxy radical: Slow electron velocity-map imaging (SEVI) spectra and Köppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weichman, Marissa L.; Cheng, Lan; Kim, Jongjin B.

A joint experimental and theoretical study is reported on the low-lying vibronic level structure of the ground state of the methoxy radical using slow photoelectron velocity-map imaging spectroscopy of cryogenically cooled, mass-selected anions (cryo-SEVI) and Köppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations. The KDC vibronic model Hamiltonian in the present study was parametrized using high-level quantum chemistry, allowing the assignment of the cryo-SEVI spectra for vibronic levels of CH 3O up to 2000 cm –1 and of CD 3O up to 1500 cm –1 above the vibrational origin, using calculated vibronic wave functions. The adiabatic electron affinities of CH 3O and CDmore » 3O are determined from the cryo-SEVI spectra to be 1.5689 ± 0.0007 eV and 1.5548 ± 0.0007 eV, respectively, demonstrating improved precision compared to previous work. Experimental peak splittings of <10 cm –1 are resolved between the e 1/2 and e 3/2 components of the 6 1 and 5 1 vibronic levels. A pair of spin-vibronic levels at 1638 and 1677 cm –1 were predicted in the calculation as the e 1/2 and e 3/2 components of 6 2 levels and experimentally resolved for the first time. The strong variation of the spin-orbit splittings with a vibrational quantum number is in excellent agreement between theory and experiment. In conclusion, the observation of signals from nominally forbidden a 1 vibronic levels in the cryo-SEVI spectra also provides direct evidence of vibronic coupling between ground and electronically excited states of methoxy.« less

Low-lying vibronic level structure of the ground state of the methoxy radical: Slow electron velocity-map imaging (SEVI) spectra and Köppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations

DOE PAGES

Weichman, Marissa L.; Cheng, Lan; Kim, Jongjin B.; ...

2017-06-12

A joint experimental and theoretical study is reported on the low-lying vibronic level structure of the ground state of the methoxy radical using slow photoelectron velocity-map imaging spectroscopy of cryogenically cooled, mass-selected anions (cryo-SEVI) and Köppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations. The KDC vibronic model Hamiltonian in the present study was parametrized using high-level quantum chemistry, allowing the assignment of the cryo-SEVI spectra for vibronic levels of CH 3O up to 2000 cm –1 and of CD 3O up to 1500 cm –1 above the vibrational origin, using calculated vibronic wave functions. The adiabatic electron affinities of CH 3O and CDmore » 3O are determined from the cryo-SEVI spectra to be 1.5689 ± 0.0007 eV and 1.5548 ± 0.0007 eV, respectively, demonstrating improved precision compared to previous work. Experimental peak splittings of <10 cm –1 are resolved between the e 1/2 and e 3/2 components of the 6 1 and 5 1 vibronic levels. A pair of spin-vibronic levels at 1638 and 1677 cm –1 were predicted in the calculation as the e 1/2 and e 3/2 components of 6 2 levels and experimentally resolved for the first time. The strong variation of the spin-orbit splittings with a vibrational quantum number is in excellent agreement between theory and experiment. In conclusion, the observation of signals from nominally forbidden a 1 vibronic levels in the cryo-SEVI spectra also provides direct evidence of vibronic coupling between ground and electronically excited states of methoxy.« less

Vibronic structure and coupling of higher excited electronic states in carotenoids

NASA Astrophysics Data System (ADS)

Krawczyk, Stanisław; Luchowski, Rafał

2013-03-01

Absorption spectra of all-trans carotenoids (lycopene, violaxanthin, ζ-carotene) at low temperature exhibit peculiar features in the UV range. The transition to the 11Ag+ state ('cis-band') weakens on cooling, indicating that it is induced by thermal deformations of the conjugated chain. The higher energy band has unique vibrational structure indicating the vibronic coupling of nBu with another electronic state. The electroabsorption spectra point to the electric field-induced mixing of the nBu state with the vibrational continuum of a lower-lying excited state (Fano effect). These observations widen the basis for elucidation of the vibronic coupling effects in the lower excited states.

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2015-11-21

Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at highmore » temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes.« less

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soudackov, Alexander; Hammes-Schiffer, Sharon

2015-11-17

Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency regimes for the proton donor-acceptor vibrational mode. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term does not significantly impact the rate constants derived using the cumulant expansion approachmore » in any of the regimes studied. The effects of the quadratic term may become significant when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant, however, particularly at high temperatures and for proton transfer interfaces with extremely soft proton donor-acceptor modes that are associated with extraordinarily weak hydrogen bonds. Even with the thermal averaging procedure, the effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances, and the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes. We are grateful for support from National Institutes of Health Grant GM056207 (applications to enzymes) and the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (applications to molecular electrocatalysts).« less

Zero-point fluctuations in naphthalene and their effect on charge transport parameters.

PubMed

Kwiatkowski, Joe J; Frost, Jarvist M; Kirkpatrick, James; Nelson, Jenny

2008-09-25

We calculate the effect of vibronic coupling on the charge transport parameters in crystalline naphthalene, between 0 and 400 K. We find that nuclear fluctuations can cause large changes in both the energy of a charge on a molecule and on the electronic coupling between molecules. As a result, nuclear fluctuations cause wide distributions of both energies and couplings. We show that these distributions have a small temperature dependence and that, even at high temperatures, vibronic coupling is dominated by the effect of zero-point fluctuations. Because of the importance of zero-point fluctuations, we find that the distributions of energies and couplings have substantial width, even at 0 K. Furthermore, vibronic coupling with high energy modes may be significant, even though these modes are never thermally activated. Our results have implications for the temperature dependence of charge mobilities in organic semiconductors.

Vibronic coupling simulations for linear and nonlinear optical processes: Simulation results

NASA Astrophysics Data System (ADS)

Silverstein, Daniel W.; Jensen, Lasse

2012-02-01

A vibronic coupling model based on time-dependent wavepacket approach is applied to simulate linear optical processes, such as one-photon absorbance and resonance Raman scattering, and nonlinear optical processes, such as two-photon absorbance and resonance hyper-Raman scattering, on a series of small molecules. Simulations employing both the long-range corrected approach in density functional theory and coupled cluster are compared and also examined based on available experimental data. Although many of the small molecules are prone to anharmonicity in their potential energy surfaces, the harmonic approach performs adequately. A detailed discussion of the non-Condon effects is illustrated by the molecules presented in this work. Linear and nonlinear Raman scattering simulations allow for the quantification of interference between the Franck-Condon and Herzberg-Teller terms for different molecules.

Multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) approach to the correlated exciton-vibrational dynamics in the FMO complex

NASA Astrophysics Data System (ADS)

Schulze, Jan; Shibl, Mohamed F.; Al-Marri, Mohammed J.; Kühn, Oliver

2016-05-01

The coupled quantum dynamics of excitonic and vibrational degrees of freedom is investigated for high-dimensional models of the Fenna-Matthews-Olson complex. This includes a seven- and an eight-site model with 518 and 592 harmonic vibrational modes, respectively. The coupling between local electronic transitions and vibrations is described within the Huang-Rhys model using parameters that are obtained by discretization of an experimental spectral density. Different pathways of excitation energy flow are analyzed in terms of the reduced one-exciton density matrix, focussing on the role of vibrational and vibronic excitations. Distinct features due to both competing time scales of vibrational and exciton motion and vibronically assisted transfer are observed. The question of the effect of initial state preparation is addressed by comparing the case of an instantaneous Franck-Condon excitation at a single site with that of a laser field excitation.

Effects of Charge-Transfer Excitons on the Photophysics of Organic Semiconductors

NASA Astrophysics Data System (ADS)

Hestand, Nicholas J.

The field of organic electronics has received considerable attention over the past several years due to the promise of novel electronic materials that are cheap, flexible and light weight. While some devices based on organic materials have already emerged on the market (e.g. organic light emitting diodes), a deeper understanding of the excited states within the condensed phase is necessary both to improve current commercial products and to develop new materials for applications that are currently in the commercial pipeline (e.g. organic photovoltaics, wearable displays, and field effect transistors). To this end, a model for pi-conjugated molecular aggregates and crystals is developed and analyzed. The model considers two types of electronic excitations, namely Frenkel and charge-transfer excitons, both of which play a prominent role in determining the nature of the excited states within tightly-packed organic systems. The former consist of an electron-hole pair bound to the same molecule while in the later the electron and hole are located on different molecules. The model also considers the important nuclear reorganization that occurs when the system switches between electronic states. This is achieved using a Holstein-style Hamiltonian that includes linear vibronic coupling of the electronic states to the nuclear motion associated with the high frequency vinyl-stretching and ring-breathing modes. Analysis of the model reveals spectroscopic signatures of charge-transfer mediated J- and H-aggregation in systems where the photophysical properties are determined primarily by charge-transfer interactions. Importantly, such signatures are found to be sensitive to the relative phase of the intermolecular electron and hole transfer integrals, and the relative energy of the Frenkel and charge-transfer states. When the charge-transfer integrals are in phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits J-aggregate characteristics including a positive band curvature, a red shifted main absorption peak, and an increase in the ratio of the first two vibronic peaks relative to the monomer. On the other hand, when the charge-transfer integrals are out of phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits H-aggregate characteristics including a negative band curvature, a blue shifted main absorption peak, and a decrease in the ratio of the first two vibronic peaks relative to the monomer. Notably, these signatures are consistent with those exhibited by Coulombically coupled J- and H-aggregates. Additional signatures of charge-transfer J- and H-aggregation are also discovered, the most notable of which is the appearance of a second absorption band when the charge-transfer integrals are in phase and the charge-transfer and Frenkel excitons are near resonance. In such instances, the peak-to-peak spacing is found to be proportional to the sum of the electron and hole transfer integrals. Further analysis of the charge-transfer interactions within the context of an effective Frenkel exciton coupling reveals that the charge-transfer interactions interfere directly with the intermolecular Coulombic coupling. The interference can be either constructive or destructive resulting in either enhanced or suppressed J- or H- aggregate behavior relative to what is expected based on Coulombic coupling alone. Such interferences result in four new aggregate types, namely HH-, HJ-, JH-, and JJ-aggregates, where the first letter indicates the nature of the Coulombic coupling and the second indicates the nature of the charge-transfer coupling. Vibronic signatures of such aggregates are developed and provide a means by which to rapidly screen materials for certain electronic characteristics. Notably, a large total (Coulombic plus charge-transfer) exciton coupling is associated with an absorption spectrum in which the ratio of the first two vibronic peaks deviates significantly from that of the unaggregated monomer. Hence, strongly coupled, high exciton mobility aggregates can be readily distinguished from low mobility aggregates by the ratio of their first two vibronic peaks. (Abstract shortened by ProQuest.).

Subtle spectral effects accompanying the assembly of bacteriochlorophylls into cyclic light harvesting complexes revealed by high-resolution fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Rätsep, Margus; Pajusalu, Mihkel; Linnanto, Juha Matti; Freiberg, Arvi

2014-10-01

We have observed that an assembly of the bacteriochloropyll a molecules into B850 and B875 groups of cyclic bacterial light-harvesting complexes LH2 and LH1, respectively, results an almost total loss of the intra-molecular vibronic structure in the fluorescence spectrum, and simultaneously, an essential enhancement of its phonon sideband due to electron-phonon coupling. While the suppression of the vibronic coupling in delocalized (excitonic) molecular systems is predictable, as also confirmed by our model calculations, a boost of the electron-phonon coupling is rather unexpected. The latter phenomenon is explained by exciton self-trapping, promoted by mixing the molecular exciton states with charge transfer states between the adjacent chromophores in the tightly packed B850 and B875 arrangements. Similar, although less dramatic trends were noted for the light-harvesting complexes containing chlorophyll pigments.

The coherence lifetime-borrowing effect in vibronically coupled molecular aggregates under non-perturbative system-environment interactions.

NASA Astrophysics Data System (ADS)

Yeh, Shu-Hao; Engel, Gregory S.; Kais, Sabre

Recently it has been suggested that the long-lived coherences in some photosynthetic pigment-protein systems, such as the Fenna-Matthews-Olson complex, could be attributed to the mixing of the pigments' electronic and vibrational degrees of freedom. In order to verify whether this is the case and to understand its underlying mechanism, a theoretical model capable of including both the electronic excitations and intramolecular vibrational modes of the pigments is necessary. Our model simultaneously considers the electronic and vibrational degrees of freedom, treating the system-environment interactions non-perturbatively by implementing the hierarchical equations of motion approach. Here we report the simulated two-dimensional electronic spectra of vibronically coupled molecular dimers to demonstrate how the electronic coherence lifetimes can be extended by borrowing the lifetime from the vibrational coherences. Funded by Qatar National Research Fund and Qatar Environment and Energy Research Institute.

Reassigning the CaH+ 11Σ → 21Σ vibronic transition with CaD+

NASA Astrophysics Data System (ADS)

Condoluci, J.; Janardan, S.; Calvin, A. T.; Rugango, R.; Shu, G.; Sherrill, C. D.; Brown, K. R.

2017-12-01

We observe vibronic transitions in CaD+ between the 11Σ and 21Σ electronic states by resonance enhanced multiphoton photodissociation spectroscopy in a Coulomb crystal. The vibronic transitions are compared with previous measurements on CaH+. The result is a revised assignment of the CaH+ vibronic levels and a disagreement with multi-state-complete-active-space second-order perturbation theory theoretical calculations by approximately 700 cm-1. Updated high-level coupled-cluster calculations that include core-valence correlations reduce the disagreement between theory and experiment to 300 cm-1.

Vibrons in finite size molecular lattices: a route for high-fidelity quantum state transfer at room temperature.

PubMed

Pouthier, Vincent

2012-11-07

A communication protocol is proposed in which vibron-mediated quantum state transfer takes place in a molecular lattice. We consider two distant molecular groups grafted on each side of the lattice. These groups form two quantum computers where vibrational qubits are implemented and received. The lattice defines the communication channel along which a vibron delocalizes and interacts with a phonon bath. Using quasi-degenerate perturbation theory, vibron-phonon entanglement is taken into account through the effective Hamiltonian concept. A vibron is thus dressed by a virtual phonon cloud whereas a phonon is clothed by virtual vibronic transitions. It is shown that three quasi-degenerate dressed states define the relevant paths followed by a vibron to tunnel between the computers. When the coupling between the computers and the lattice is judiciously chosen, constructive interference takes place between these paths. Phonon-induced decoherence is minimized and a high-fidelity quantum state transfer occurs over a broad temperature range.

Multi-State Vibronic Interactions in Fluorinated Benzene Radical Cations.

NASA Astrophysics Data System (ADS)

Faraji, S.; Köppel, H.

2009-06-01

Conical intersections of potential energy surfaces have emerged as paradigms for signalling strong nonadiabatic coupling effects. An important class of systems where some of these effects have been analyzed in the literature, are the benzene and benzenoid cations, where the electronic structure, spectroscopy, and dynamics have received great attention in the literature. In the present work a brief overview is given over our theoretical treatments of multi-mode and multi-state vibronic interactions in the benzene radical cation and some of its fluorinated derivatives. The fluorobenzene derivatives are of systematic interest for at least two different reasons. (1) The reduction of symmetry by incomplete fluorination leads to a disappearance of the Jahn-Teller effect present in the parent cation. (2) A specific, more chemical effect of fluorination consists in the energetic increase of the lowest σ-type electronic states of the radical cations. The multi-mode multi-state vibronic interactions between the five lowest electronic states of the fluorobenzene radical cations are investigated theoretically, based on ab initio electronic structure data, and employing the well-established linear vibronic coupling model, augmented by quadratic coupling terms for the totally symmetric vibrational modes. Low-energy conical intersections, and strong vibronic couplings are found to prevail within the set of tilde{X}-tilde{A} and tilde{B}-tilde{C}-tilde{D} cationic states, while the interactions between these two sets of states are found to be weaker and depend on the particular isomer. This is attributed to the different location of the minima of the various conical intersections occurring in these systems. Wave-packet dynamical simulations for these coupled potential energy surfaces, utilizing the powerful multi-configuration time-dependent Hartree method are performed. Ultrafast internal conversion processes and the analysis of the MATI and photo-electron spectra shed new light on the spectroscopy and fluorescence dynamics of these species. W. Domcke, D. R. Yarkony, and H. Köppel, Advanced Series in Physical Chemistry, World Scientific, Singapore (2004). M. H. Beck and A. Jäckle and G. A. Worth and H. -D. Meyer, Phys. Rep. 324, 1 (2000). S. Faraji, H. Köppel, (Part I) ; S. Faraji, H. Köppel, H.-D. Meyer, (Part II) J. Chem. Phys. 129, 074310 (2008).

Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study.

PubMed

Piech, Krzysztof; Bally, Thomas; Ichino, Takatoshi; Stanton, John

2014-02-07

The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40,000 cm(-1) are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ˙(+) exhibits a very conspicuous and complicated pattern of features above 1900 cm(-1) that is due to this electronic transition, and offers an unusually vivid demonstration of the effects of vibronic coupling in what would usually be a relatively simple region of the electromagnetic spectrum associated only with vibrational transitions. As expected, the intensities of most of the IR transitions leading to levels that couple the ground to the very low-lying first excited state of PBQ˙(+) increase by large factors upon ionization, due to "intensity borrowing" from the D0 → D1 electronic transition. A notable exception is the antisymmetric C=O stretching vibration, which contributes significantly to the vibronic coupling, but has nevertheless quite small intensity in the cation spectrum. This surprising feature is rationalized on the basis of a simple perturbation analysis.

Multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) approach to the correlated exciton-vibrational dynamics in the FMO complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulze, Jan; Kühn, Oliver, E-mail: oliver.kuehn@uni-rostock.de; Shibl, Mohamed F., E-mail: mfshibl@qu.edu.qa

2016-05-14

The coupled quantum dynamics of excitonic and vibrational degrees of freedom is investigated for high-dimensional models of the Fenna-Matthews-Olson complex. This includes a seven- and an eight-site model with 518 and 592 harmonic vibrational modes, respectively. The coupling between local electronic transitions and vibrations is described within the Huang-Rhys model using parameters that are obtained by discretization of an experimental spectral density. Different pathways of excitation energy flow are analyzed in terms of the reduced one-exciton density matrix, focussing on the role of vibrational and vibronic excitations. Distinct features due to both competing time scales of vibrational and exciton motionmore » and vibronically assisted transfer are observed. The question of the effect of initial state preparation is addressed by comparing the case of an instantaneous Franck-Condon excitation at a single site with that of a laser field excitation.« less

The vibronic level structure of the cyclopentadienyl radical

NASA Astrophysics Data System (ADS)

Ichino, Takatoshi; Wren, Scott W.; Vogelhuber, Kristen M.; Gianola, Adam J.; Lineberger, W. Carl; Stanton, John F.

2008-08-01

The 351.1 nm photoelectron spectrum of the cyclopentadienide ion has been measured, which reveals the vibronic structure of the X~ 2E1'' state of the cyclopentadienyl radical. Equation-of-motion ionization potential coupled-cluster (EOMIP-CCSD) calculations have been performed to construct a diabatic model potential of the X~ 2E1'' state, which takes into account linear Jahn-Teller effects along the e2' normal coordinates as well as bilinear Jahn-Teller effects along the e2' and ring-breathing a1' coordinates. A simulation based on this ab initio model potential reproduces the spectrum very well, identifying the vibronic levels with linear Jahn-Teller angular momentum quantum numbers of +/-1/2. The angular distributions of the photoelectrons for these vibronic levels are highly anisotropic with the photon energies used in the measurements. A few additional weak photoelectron peaks are observed when photoelectrons ejected parallel to the laser polarization are examined. These peaks correspond to the vibronic levels for out-of-plane modes in the ground X~ 2E1'' state, which arise due to several pseudo-Jahn-Teller interactions with excited states of the radical and quadratic Jahn-Teller interaction in the X~ 2E1'' state. A variant of the first derivative of the energy for the EOMIP-CCSD method has been utilized to evaluate the strength of these nonadiabatic couplings, which have subsequently been employed to construct the model potential of the X~ 2E1'' state with respect to the out-of-plane normal coordinates. Simulations based on the model potential successfully reproduce the weak features that become conspicuous in the 0° spectrum. The present study of the photoelectron spectrum complements a previous dispersed fluorescence spectroscopic study Miller and co-workers [J. Chem. Phys. 114, 4855 (2001); 4869 (2001) Miller and co-workers [J. Chem. Phys.114, 4869 (2001)] to provide a detailed account of the vibronic structure of X~ 2E1'' cyclopentadienyl. The electron affinity of the cyclopentadienyl radical is determined to be 1.808+/-0.006 eV. This electron affinity and the gas-phase acidity of cyclopentadiene have been combined in a negative ion thermochemical cycle to determine the C-H bond dissociation energy of cyclopentadiene; D0(C5H6,C-H)=81.5+/-1.3 kcal mol-1. The standard enthalpy of formation of the cyclopentadienyl radical has been determined to be ΔfH298(C5H5)=63.2+/-1.4 kcal mol-1.

One- and two-photon absorption spectra of the yellow fluorescent protein citrine: effects of intramolecular electron-vibrational coupling and intermolecular interactions

NASA Astrophysics Data System (ADS)

Chen, Fasheng; Zhao, Xinyi; Liang, WanZhen

2018-04-01

Both the vibrationally resolved and statistically averaged one-photon absorption (OPA) and two-photon absorption (TPA) spectra of the anionic form of chromophore (AC) in its micro-environment of yellow fluorescent protein (YFP) Citrine have been calculated. The result comparison has been made with those of the AC model compounds in vacuo and methanol solution, which allows us to allocate the individual contribution of the intramolecular electron-vibrational coupling, the electrostatic π-stacking interaction between Tyr203 and AC, and the interaction between AC and its micro-environment to the spectra. The results reveal that the non-Condon vibronic coupling effect is responsible for the blue shift of TPA absorption maximum compared with its OPA counterpart corresponding to S0 → S1, and that the π-stacking interaction between Tyr203 and AC alters the relative intensities of TPA maxima, which further enhances the higher-energy vibronic peaks and weakens the lowest-energy peak. The statically averaged OPA and TPA spectra calculated by quantum mechanics/molecular mechanics (QM/MM) methods based on Born-Oppenheimer molecular dynamics simulation largely deviate the experimental spectral lineshapes, which further verifies the significant contribution of non-Condon vibronic coupling effect on the spectra. The interaction of individual amino acid residue or water close to AC+Tyr203 has different effects on the spectra, which may increase/decrease the excitation energy depending on its position and electronic property.

Identification of the optically active vibrational modes in the photoluminescence of MEH-PPV films

NASA Astrophysics Data System (ADS)

da Silva, M. A. T.; Dias, I. F. L.; Duarte, J. L.; Laureto, E.; Silvestre, I.; Cury, L. A.; Guimara~Es, P. S. S.

2008-03-01

The temperature dependence of the photoluminescence properties of a thin film of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene-vinylene], MEH-PPV, fabricated by spin coating, is analyzed. The evolution with temperature of the peak energy of the purely electronic transition, of the first vibronic band, of the effective conjugation length, and of the Huang-Rhys factors are discussed. The asymmetric character of the pure electronic transition peak and the contribution of the individual vibrational modes to the first vibronic band line shape are considered by a model developed by Cury et al. [J. Chem. Phys. 121, 3836 (2004)]. The temperature dependence of the Huang-Rhys factors of the main vibrational modes pertaining to the first vibronic band allows us to identify two competing vibrational modes. These results show that the electron coupling to different vibrational modes depends on temperature via reduction of thermal disorder.

Vibrational and vibronic coherences in the dynamics of the FMO complex

NASA Astrophysics Data System (ADS)

Liu, Xiaomeng; Kühn, Oliver

2016-12-01

The coupled exciton-vibrational dynamics of a seven site Frenkel exciton model of the Fenna-Matthews-Olson (FMO) complex is investigated using a Quantum Master Equation approach. Thereby, one vibrational mode per monomer is treated explicitly as being part of the relevant system. Emphasis is put on the comparison of this model with that of a purely excitonic relevant system. Further, the effects of two different approximations to the exciton-vibrational basis are investigated, namely the one- and two-particle description. Analysis of the vibronic and vibrational density matrix in the site basis points to the importance of on- and inter-site coherences for the exciton transfer. Here, one- and two-particle approximations give rise to qualitatively different results.

Vibronic Coupling Investigation to Compute Phosphorescence Spectra of Pt(II) Complexes.

PubMed

Vazart, Fanny; Latouche, Camille; Bloino, Julien; Barone, Vincenzo

2015-06-01

The present paper reports a comprehensive quantum mechanical investigation on the luminescence properties of several mono- and dinuclear platinum(II) complexes. The electronic structures and geometric parameters are briefly analyzed together with the absorption bands of all complexes. In all cases agreement with experiment is remarkable. Next, emission (phosphorescence) spectra from the first triplet states have been investigated by comparing different computational approaches and taking into account also vibronic effects. Once again, agreement with experiment is good, especially using unrestricted electronic computations coupled to vibronic contributions. Together with the intrinsic interest of the results, the robustness and generality of the approach open the opportunity for computationally oriented chemists to provide accurate results for the screening of large targets which could be of interest in molecular materials design.

Dynamical Jahn-Teller effect of fullerene anions

NASA Astrophysics Data System (ADS)

Liu, Dan; Iwahara, Naoya; Chibotaru, Liviu F.

2018-03-01

The dynamical Jahn-Teller effect of C60n - anions (n =1 -5) is studied using the numerical diagonalization of the linear pn⊗8 d Jahn-Teller Hamiltonian with the currently established coupling parameters. It is found that in all anions the Jahn-Teller effect stabilizes the low-spin states, resulting in the violation of Hund's rule. The energy gain due to the Jahn-Teller dynamics is found to be comparable to the static Jahn-Teller stabilization. The Jahn-Teller dynamics influences the thermodynamic properties via strong variation of the density of vibronic states with energy. Thus the large vibronic entropy in the low-spin states enhances the effective spin gap of C603 - quenching the spin crossover. From the calculations of the effective spin gap as a function of the Hund's rule coupling, we found that the latter should amount 40 ±5 meV in order to cope with the violation of Hund's rule and to reproduce the large spin gap. With the obtained numerical solutions, the matrix elements of electronic operators for the low-lying vibronic levels and the vibronic reduction factors are calculated for all anions.

Spin-vibronic quantum dynamics for ultrafast excited-state processes.

PubMed

Eng, Julien; Gourlaouen, Christophe; Gindensperger, Etienne; Daniel, Chantal

2015-03-17

Ultrafast intersystem crossing (ISC) processes coupled to nuclear relaxation and solvation dynamics play a central role in the photophysics and photochemistry of a wide range of transition metal complexes. These phenomena occurring within a few hundred femtoseconds are investigated experimentally by ultrafast picosecond and femtosecond transient absorption or luminescence spectroscopies, and optical laser pump-X-ray probe techniques using picosecond and femtosecond X-ray pulses. The interpretation of ultrafast structural changes, time-resolved spectra, quantum yields, and time scales of elementary processes or transient lifetimes needs robust theoretical tools combining state-of-the-art quantum chemistry and developments in quantum dynamics for solving the electronic and nuclear problems. Multimode molecular dynamics beyond the Born-Oppenheimer approximation has been successfully applied to many small polyatomic systems. Its application to large molecules containing a transition metal atom is still a challenge because of the nuclear dimensionality of the problem, the high density of electronic excited states, and the spin-orbit coupling effects. Rhenium(I) α-diimine carbonyl complexes, [Re(L)(CO)3(N,N)](n+) are thermally and photochemically robust and highly flexible synthetically. Structural variations of the N,N and L ligands affect the spectroscopy, the photophysics, and the photochemistry of these chromophores easily incorporated into a complex environment. Visible light absorption opens the route to a wide range of applications such as sensors, probes, or emissive labels for imaging biomolecules. Halide complexes [Re(X)(CO)3(bpy)] (X = Cl, Br, or I; bpy = 2,2'-bipyridine) exhibit complex electronic structure and large spin-orbit effects that do not correlate with the heavy atom effects. Indeed, the (1)MLCT → (3)MLCT intersystem crossing (ISC) kinetics is slower than in [Ru(bpy)3](2+) or [Fe(bpy)3](2+) despite the presence of a third-row transition metal. Counterintuitively, singlet excited-state lifetime increases on going from Cl (85 fs) to Br (128 fs) and to I (152 fs). Moreover, correlation between the Re-X stretching mode and the rate of ISC is observed. In this Account, we emphasize on the role of spin-vibronic coupling on the mechanism of ultrafast ISC put in evidence in [Re(Br)(CO)3(bpy)]. For this purpose, we have developed a model Hamiltonian for solving an 11 electronic excited states multimode problem including vibronic and SO coupling within the linear vibronic coupling (LVC) approximation and the assumption of harmonic potentials. The presence of a central metal atom coupled to rigid ligands, such as α-diimine, ensures nuclear motion of small amplitudes and a priori justifies the use of the LVC model. The simulation of the ultrafast dynamics by wavepacket propagations using the multiconfiguration time-dependent Hartree (MCTDH) method is based on density functional theory (DFT), and its time-dependent extension to excited states (TD-DFT) electronic structure data. We believe that the interplay between time-resolved experiments and these pioneering simulations covering the first picoseconds and including spin-vibronic coupling will promote a number of quantum dynamical studies that will contribute to a better understanding of ultrafast processes in a wide range of organic and inorganic chromophores easily incorporated in biosystems or supramolecular devices for specific functions.

Tunneling Splittings in Vibronic Structure of CH_3F^+ ( X^2E): Studied by High Resolution Photoelectron Spectra and AB Initio Theoretical Method

NASA Astrophysics Data System (ADS)

Mo, Yuxiang; Gao, Shuming; Dai, Zuyang; Li, Hua

2013-06-01

We report a combined experimental and theoretical study on the vibronic structure of CH_3F^+. The results show that the tunneling splittings of vibrational energy levels occur in CH_3F^+ due to the Jahn-Teller effect. Experimentally, we have measured a high resolution ZEKE spectrum of CH_3F up to 3500 cm^-^1 above the ground state. Theoretically, we performed an ab initio calculation based on the diabatic model. The adiabatic potential energy surfaces (APES) of CH_3F^+ have been calculated at the MRCI/CAS/avq(t)z level and expressed by Taylor expansions with normal coordinates as variables. The energy gradients for the lower and upper APES, the derivative couplings between them and also the energies of the APES have been used to determine the coefficients in the Taylor expansion. The spin-vibronic energy levels have been calculated by accounting all six vibrational modes and their couplings. The experimental ZEKE spectra were assigned based on the theoretical calculations. W. Domcke, D. R. Yarkony, and H. Köpple (Eds.), Conical Intersections: Eletronic Structure, Dynamics and Spectroscopy (World Scientific, Singapore, 2004). M. S. Schuurman, D. E. Weinberg, and D. R. Yarkony, J. Chem. Phys. 127, 104309 (2007).

Raman dispersion spectroscopy on the highly saddled nickel(II)-octaethyltetraphenylporphyrin reveals the symmetry of nonplanar distortions and the vibronic coupling strength of normal modes

NASA Astrophysics Data System (ADS)

Schweitzer-Stenner, Reinhard; Stichternath, Andreas; Dreybrodt, Wolfgang; Jentzen, Walter; Song, Xing-Zhi; Shelnutt, John A.; Nielsen, Ole Faurskov; Medforth, Craig J.; Smith, Kevin M.

1997-08-01

We have measured the polarized Raman cross sections and depolarization ratios of 16 fundamental modes of nickel octaethyltetraphenylporphyrin in a CS2 solution for 16 fundamental modes, i.e., the A1g-type vibrations ν1, ν2, ν3, ν4, ν5, and φ8, the B1g vibrations ν11 and ν14, the B2g vibrations ν28, ν29, and ν30 and the antisymmetric A2g modes ν19, ν20, ν22, and ν23 as function of the excitation wavelength. The data cover the entire resonant regions of the Q- and B-bands. They were analyzed by use of a theory which describes intra- and intermolecular coupling in terms of a time-independent nonadiabatic perturbation theory [E. Unger, U. Bobinger, W. Dreybrodt, and R. Schweitzer-Stenner, J. Phys. Chem. 97, 9956 (1993)]. This approach explicitly accounts in a self-consistent way for multimode mixing with all Raman modes investigated. The vibronic coupling parameters obtained from this procedure were then used to successfully fit the vibronic side bands of the absorption spectrum and to calculate the resonance excitation profiles in absolute units. Our results show that the porphyrin macrocycle is subject to B2u-(saddling) and B1u-(ruffling) distortions which lower its symmetry to S4. Thus, evidence is provided that the porphyrin molecule maintains the nonplanar structure of its crystal phase in an organic solvent. The vibronic coupling parameters indicate a breakdown of the four-orbital model. This notion is corroborated by (ZINDO/S) calculations which reveal that significant configurational interaction occurs between the electronic transitions into |Q>- and |1B>-states and various porphyrin→porphyrin, metal→porphyrin, and porphyrin→metal transitions. The intrastate coupling parameters are used to estimate the excited electronic states' displacements along the normal coordinates with respect to the ground state and their contributions to the reorganization energy. It turns out that the |B>-state is predominantly affected by symmetric A1g-displacements, whereas the |Q>-state is subject to A2g, B1g, and B2g displacements of its equilibrium configuration. While the former is induced by the combined effect of ruffling and saddling, the latter arises from Jahn-Teller coupling within the degenerate states.

Jet cooled cavity ringdown spectroscopy of the A ˜ 2 E ″ ← X ˜ 2 A2 ' transition of the NO3 radical

NASA Astrophysics Data System (ADS)

Codd, Terrance; Chen, Ming-Wei; Roudjane, Mourad; Stanton, John F.; Miller, Terry A.

2015-05-01

The A ˜ 2 E ″ ← X ˜ 2 A2 ' spectrum of NO3 radical from 7550 cm-1 to 9750 cm-1 has been recorded and analyzed. Our spectrum differs from previously recorded spectra of this transition due to jet-cooling, which narrows the rotational contours and eliminates spectral interference from hot bands. Assignments of numerous vibronic features can be made based on both band contour and position including the previously unassigned 30 1 band and several associated combination bands. We have analyzed our spectrum first with an independent anharmonic oscillator model and then by a quadratic Jahn-Teller vibronic coupling model. The fit achieved with the quadratic Jahn-Teller model is excellent, but the potential energy surface obtained with the fitted parameters is in only qualitative agreement with one obtained from ab initio calculations.

Vibronic Assignments and Vibronic Coupling in the 1E’ State of Sym-Triazine by Two Photon Spectroscopy.

DTIC Science & Technology

1980-08-11

No. Copies Cepies Office of INaval Research U.S. Army Research Office Attn: Code 472 Attn: CRD-AA-IP 80 North Quincy Street P.O. Box 1211 Arlington...Marine Building 5, Cameron Station Sciences Division Alexaidria, Virginia 22314 12 San Diego, California 91232 Dr. Fred Saalfeld K:r. John Boyle Chemistry

Communication: Vibrational and vibronic coherences in the two dimensional spectroscopy of coupled electron-nuclear motion.

PubMed

Albert, Julian; Falge, Mirjam; Gomez, Sandra; Sola, Ignacio R; Hildenbrand, Heiko; Engel, Volker

2015-07-28

We theoretically investigate the photon-echo spectroscopy of coupled electron-nuclear quantum dynamics. Two situations are treated. In the first case, the Born-Oppenheimer (adiabatic) approximation holds. It is then possible to interpret the two-dimensional (2D) spectra in terms of vibrational motion taking place in different electronic states. In particular, pure vibrational coherences which are related to oscillations in the time-dependent third-order polarization can be identified. This concept fails in the second case, where strong non-adiabatic coupling leads to the breakdown of the Born-Oppenheimer-approximation. Then, the 2D-spectra reveal a complicated vibronic structure and vibrational coherences cannot be disentangled from the electronic motion.

Communication: Vibrational and vibronic coherences in the two dimensional spectroscopy of coupled electron-nuclear motion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Albert, Julian; Falge, Mirjam; Hildenbrand, Heiko

2015-07-28

We theoretically investigate the photon-echo spectroscopy of coupled electron-nuclear quantum dynamics. Two situations are treated. In the first case, the Born-Oppenheimer (adiabatic) approximation holds. It is then possible to interpret the two-dimensional (2D) spectra in terms of vibrational motion taking place in different electronic states. In particular, pure vibrational coherences which are related to oscillations in the time-dependent third-order polarization can be identified. This concept fails in the second case, where strong non-adiabatic coupling leads to the breakdown of the Born-Oppenheimer-approximation. Then, the 2D-spectra reveal a complicated vibronic structure and vibrational coherences cannot be disentangled from the electronic motion.

Solvent effects on the vibronic one-photon absorption profiles of dioxaborine heterocycles

NASA Astrophysics Data System (ADS)

Wang, Yan-Hua; Halik, Marcus; Wang, Chuan-Kui; Marder, Seth R.; Luo, Yi

2005-11-01

The vibronic profiles of one-photon absorption spectra of dioxaborine heterocycles in gas phase and solution have been calculated at the Hartree-Fock and density-functional-theory levels. The polarizable continuum model has been applied to simulate the solvent effect, while the linear coupling model is used to compute the Franck-Condon and Herzberg-Teller contributions. It is found that a good agreement between theory and experiment can be achieved when the solvent effect and electron correlation are taken into account simultaneously. For the first excited charge-transfer state, the maximum of its Herzberg-Teller profile is blueshifted from that of the Franck-Condon profile. The shifted energy is found to be around 0.2eV, which agrees well with the measured energy difference between two- and one-photon absorptions of the first excited state.

Vibronic bands in the HOMO-LUMO excitation of linear polyyne molecules

NASA Astrophysics Data System (ADS)

Wakabayashi, Tomonari; Wada, Yoriko; Iwahara, Naoya; Sato, Tohru

2013-04-01

Hydrogen-capped linear carbon chain molecules, namely polyynes H(C≡C)nH (n>=2), give rise to three excited states in the HOMO-LUMO excitation. Electric dipole transition from the ground state is fully allowed to one of the three excited states, while forbidden for the other two low-lying excited states. In addition to the strong absorption bands in the UV for the allowed transition, the molecules exhibit weak absorption and emission bands in the near UV and visible wavelength regions. The weak features are the vibronic bands in the forbidden transition. In this article, symmetry considerations are presented for the optical transitions in the centrosymmetric linear polyyne molecule. The argument includes Herzberg-Teller expansion for the state mixing induced by nuclear displacements along the normal coordinate of the molecule, intensity borrowing from fully allowed transitions, and inducing vibrational modes excited in the vibronic transition. The vibronic coupling considered here includes off-diagonal matrix elements for second derivatives along the normal coordinate. The vibronic selection rule for the forbidden transition is derived and associated with the transition moment with respect to the molecular axis. Experimental approaches are proposed for the assignment of the observed vibronic bands.

The Jahn-Teller effect in (hu+)2⊗hg systems

NASA Astrophysics Data System (ADS)

Hands, Ian D.; Diery, Wajood A.; Dunn, Janette L.; Bates, Colin A.

2007-07-01

A general consideration is made of the vibronic coupling in a (hu+)2⊗hg Jahn-Teller system, that is to say, a system in which two holes of Hu symmetry are coupled to vibrations of hg symmetry. We find that the resulting high-spin states may undergo spontaneous distortion into species exhibiting one of the following four possible symmetries: D5 d, D3 d, D2 h or C2 h. The system may be viewed as a first approximation to a C602+ ion, but our intention here is to make a general consideration of the model without application to any specific molecular system. Coulombic interactions between holes, which must be important in real systems, are therefore ignored throughout. However, they could be included in the model, if required, using the method described in an earlier work [I.D. Hands, J.L. Dunn, W.A. Diery, C.A. Bates, Phys. Rev. B 73 (2006) 115435]. For each of the different symmetry types, projection operators are used to create symmetry-adapted states (SASs) that give a good account of the states of the system over a wide range of coupling strengths. These SASs are used, in turn, to derive energies for the vibronic states.

Exciton-phonon coupling in diindenoperylene thin films

NASA Astrophysics Data System (ADS)

Heinemeyer, U.; Scholz, R.; Gisslén, L.; Alonso, M. I.; Ossó, J. O.; Garriga, M.; Hinderhofer, A.; Kytka, M.; Kowarik, S.; Gerlach, A.; Schreiber, F.

2008-08-01

We investigate exciton-phonon coupling and exciton transfer in diindenoperylene (DIP) thin films on oxidized Si substrates by analyzing the dielectric function determined by variable-angle spectroscopic ellipsometry. Since the molecules in the thin-film phase form crystallites that are randomly oriented azimuthally and highly oriented along the surface normal, DIP films exhibit strongly anisotropic optical properties with uniaxial symmetry. This anisotropy can be determined by multiple sample analysis. The thin-film spectrum is compared with a monomer spectrum in solution, which reveals similar vibronic subbands and a Huang-Rhys parameter of S≈0.87 for an effective internal vibration at ℏωeff=0.17eV . However, employing these parameters the observed dielectric function of the DIP films cannot be described by a pure Frenkel exciton model, and the inclusion of charge-transfer (CT) states becomes mandatory. A model Hamiltonian is parametrized with density-functional theory calculations of single DIP molecules and molecule pairs in the stacking geometry of the thin-film phase, revealing the vibronic coupling constants of DIP in its excited and charged states together with electron and hole transfer integrals along the stack. From a fit of the model calculation to the observed dielectric tensor, we find the lowest CT transition E00CT at 0.26±0.05eV above the neutral molecular excitation energy E00F , which is an important parameter for device applications.

Vibronic eigenstates and the geometric phase effect in the 2E″ state of NO3.

PubMed

Eisfeld, Wolfgang; Viel, Alexandra

2017-01-21

The 2 E″ state of NO 3 , a prototype for the Jahn-Teller effect, has been an enigma and a challenge for a long time for both experiment and theory. We present a detailed theoretical study of the vibronic quantum dynamics in this electronic state, uncovering the effects of tunnelling, geometric phase, and symmetry. To this end, 45 vibronic levels of NO 3 in the 2 E″ state are determined accurately and analyzed thoroughly. The computation is based on a high quality diabatic potential representation of the two-sheeted surface of the 2 E″ state developed by us [W. Eisfeld et al., J. Chem. Phys. 140, 224109 (2014)] and on the multi-configuration time dependent Hartree approach. The vibrational eigenstates of the NO 3 - anion are determined and analyzed as well to gain a deeper understanding of the symmetry properties of such D 3h symmetric systems. To this end, 61 eigenstates of the NO 3 - anion ground state are computed using the single sheeted potential surface of the 1 A 1 state published in the same reference quoted above. The assignments of both the vibrational and vibronic levels are discussed. A simple model is proposed to rationalize the computed NO 3 spectrum strongly influenced by the Jahn-Teller couplings, the associated geometric phase effect, and the tunnelling. Comparison with the available spectroscopic data is also presented.

Probing the Inelastic Interactions in Molecular Junctions by Scanning Tunneling Microscope

NASA Astrophysics Data System (ADS)

Xu, Chen

With a sub-Kelvin scanning tunneling microscope, the energy resolution of spectroscopy is improved dramatically. Detailed studies of finer features of spectrum become possible. The asymmetry in the line shape of carbon monoxide vibrational spectra is observed to correlate with the couplings of the molecule to the tip and substrates. The spin-vibronic coupling in the molecular junctions is revisited with two metal phthalocyanine molecules, unveiling sharp spin-vibronic peaks. Finally, thanks to the improved spectrum resolution, the bonding structure of the acyclic compounds molecules is surveyed with STM inelastic tunneling probe, expanding the capability of the innovative high resolution imaging technique.

Proton transfer mediated by the vibronic coupling in oxygen core ionized states of glyoxalmonoxime studied by infrared-X-ray pump-probe spectroscopy.

PubMed

Felicíssimo, V C; Guimarães, F F; Cesar, A; Gel'mukhanov, F; Agren, H

2006-11-30

The theory of IR-X-ray pump-probe spectroscopy beyond the Born-Oppenheimer approximation is developed and applied to the study of the dynamics of intramolecular proton transfer in glyoxalmonoxime leading to the formation of the tautomer 2-nitrosoethenol. Due to the IR pump pulses the molecule gains sufficient energy to promote a proton to a weakly bound well. A femtosecond X-ray pulse snapshots the wave packet route and, hence, the dynamics of the proton transfer. The glyoxalmonoxime molecule contains two chemically nonequivalent oxygen atoms that possess distinct roles in the hydrogen bond, a hydrogen donor and an acceptor. Core ionizations of these form two intersecting core-ionized states, the vibronic coupling between which along the OH stretching mode partially delocalizes the core hole, resulting in a hopping of the core hole from one site to another. This, in turn, affects the dynamics of the proton transfer in the core-ionized state. The quantum dynamical simulations of X-ray photoelectron spectra of glyoxalmonoxime driven by strong IR pulses demonstrate the general applicability of the technique for studies of intramolecular proton transfer in systems with vibronic coupling.

Effects of Different Quantum Coherence on the Pump-Probe Polarization Anisotropy of Photosynthetic Light-Harvesting Complexes: A Computational Study.

PubMed

Bai, Shuming; Song, Kai; Shi, Qiang

2015-05-21

Observations of oscillatory features in the 2D spectra of several photosynthetic complexes have led to diverged opinions on their origins, including electronic coherence, vibrational coherence, and vibronic coherence. In this work, effects of these different types of quantum coherence on ultrafast pump-probe polarization anisotropy are investigated and distinguished. We first simulate the isotropic pump-probe signal and anisotropy decay of the Fenna-Matthews-Olson (FMO) complex using a model with only electronic coherence at low temperature and obtain the same coherence time as in the previous experiment. Then, three model dimer systems with different prespecified quantum coherence are simulated, and the results show that their different spectral characteristics can be used to determine the type of coherence during the spectral process. Finally, we simulate model systems with different electronic-vibrational couplings and reveal the condition in which long time vibronic coherence can be observed in systems like the FMO complex.

High-Resolution Laser Spectroscopy of Free Radicals in Nearly Degenerate Electronic States

NASA Astrophysics Data System (ADS)

Liu, Jinjun

2017-06-01

Rovibronic structure of molecules in orbitally degenerate electronic states including Renner-Teller (RT) and Jahn-Teller (JT) active molecules has been extensively studied. Less is known about rotational structure of polyatomic molecules in nearly degenerate states, especially those with low (e.g., C_s) symmetry that are subject to the pseudo-Jahn-Teller (pJT) effect. In the case of free radicals, the unpaired electron further complicates energy levels by inducing spin-orbit (SO) and spin-rotation (SR) splittings. Asymmetric deuteration or methyl substitution of C_{3v} free radicals such as CH_3O, CaCH_3, and CaOCH_3 lowers the molecular symmetry, lifts the vibronic degeneracy, and reduces the JT effect to the pJT effect. New spectroscopic models are required to reproduce the rovibronic structure and simulate the experimentally obtained spectra of pJT-active free radicals. It has been found that rotational and fine-structure analysis of spectra involving nearly degenerate states may aid in vibronic analysis and interpretation of effective molecular constants. Especially, SO and Coriolis interactions that couple the two states can be determined accurately from fitting the experimental spectra. Coupling between the two electronic states also affects the intensities of rotational and vibronic transitions. The study on free radicals in nearly degenerate states provides a promising avenue of research which may bridge the gap between symmetry-induced degenerate states and the Born-Oppenheimer (BO) limit of unperturbed electronic states.

Theoretical analysis of the unusual temperature dependence of the kinetic isotope effect in quinol oxidation.

PubMed

Ludlow, Michelle K; Soudackov, Alexander V; Hammes-Schiffer, Sharon

2009-05-27

In this paper we present theoretical calculations on model biomimetic systems for quinol oxidation. In these model systems, an excited-state [Ru(bpy)(2)(pbim)](+) complex (bpy = 2,2'-dipyridyl, pbim = 2-(2-pyridyl)benzimidazolate) oxidizes a ubiquinol or plastoquinol analogue in acetonitrile. The charge transfer reaction occurs via a proton-coupled electron transfer (PCET) mechanism, in which an electron is transferred from the quinol to the Ru and a proton is transferred from the quinol to the pbim(-) ligand. The experimentally measured average kinetic isotope effects (KIEs) at 296 K are 1.87 and 3.45 for the ubiquinol and plastoquinol analogues, respectively, and the KIE decreases with temperature for plastoquinol but increases with temperature for ubiquinol. The present calculations provide a possible explanation for the differences in magnitudes and temperature dependences of the KIEs for the two systems and, in particular, an explanation for the unusual inverse temperature dependence of the KIE for the ubiquinol analogue. These calculations are based on a general theoretical formulation for PCET reactions that includes quantum mechanical effects of the electrons and transferring proton, as well as the solvent reorganization and proton donor-acceptor motion. The physical properties of the system that enable the inverse temperature dependence of the KIE are a stiff hydrogen bond, which corresponds to a high-frequency proton donor-acceptor motion, and small inner-sphere and solvent reorganization energies. The inverse temperature dependence of the KIE may be observed if the 0/0 pair of reactant/product vibronic states is in the inverted Marcus region, while the 0/1 pair of reactant/product vibronic states is in the normal Marcus region and is the dominant contributor to the overall rate. In this case, the free energy barrier for the dominant transition is lower for deuterium than for hydrogen because of the smaller splittings between the vibronic energy levels for deuterium, and the KIE increases with increasing temperature. The temperature dependence of the KIE is found to be very sensitive to the interplay among the driving force, the reorganization energy, and the vibronic coupling in this regime.

Proton-coupled electron transfer versus hydrogen atom transfer: generation of charge-localized diabatic states.

PubMed

Sirjoosingh, Andrew; Hammes-Schiffer, Sharon

2011-03-24

The distinction between proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms is important for the characterization of many chemical and biological processes. PCET and HAT mechanisms can be differentiated in terms of electronically nonadiabatic and adiabatic proton transfer, respectively. In this paper, quantitative diagnostics to evaluate the degree of electron-proton nonadiabaticity are presented. Moreover, the connection between the degree of electron-proton nonadiabaticity and the physical characteristics distinguishing PCET from HAT, namely, the extent of electronic charge redistribution, is clarified. In addition, a rigorous diabatization scheme for transforming the adiabatic electronic states into charge-localized diabatic states for PCET reactions is presented. These diabatic states are constructed to ensure that the first-order nonadiabatic couplings with respect to the one-dimensional transferring hydrogen coordinate vanish exactly. Application of these approaches to the phenoxyl-phenol and benzyl-toluene systems characterizes the former as PCET and the latter as HAT. The diabatic states generated for the phenoxyl-phenol system possess physically meaningful, localized electronic charge distributions that are relatively invariant along the hydrogen coordinate. These diabatic electronic states can be combined with the associated proton vibrational states to generate the reactant and product electron-proton vibronic states that form the basis of nonadiabatic PCET theories. Furthermore, these vibronic states and the corresponding vibronic couplings may be used to calculate rate constants and kinetic isotope effects of PCET reactions.

Strong vibronic coupling effects in polarized IR spectra of the hydrogen bond in N-methylthioacetamide crystals

NASA Astrophysics Data System (ADS)

Flakus, Henryk T.; Śmiszek-Lindert, Wioleta; Stadnicka, Katarzyna

2007-06-01

This paper presents the investigation results of the polarized IR spectra of the hydrogen bond in crystals of N-methylthioacetamide. The spectral studies were preceded by the determination of the crystal X-ray structure. The spectra were measured at 283 K and at 77 K by a transmission method, using polarized light. Theoretical analysis of the results concerned the linear dichroic effects, the H/D isotopic and temperature effects, observed in the solid-state IR spectra of the hydrogen and of the deuterium bond at the frequency ranges of the νN-H and the νN-D bands, respectively. The main spectral properties of the crystals can be interpreted satisfactorily in terms of the simple quantitative theory of the IR spectra of the hydrogen bond, i.e., the " strong-coupling" theory on the basis of the hydrogen bond centrosymmetric dimer model. The spectra revealed that the strongest vibrational exciton coupling involved the closely spaced hydrogen bonds, each belonging to a different chain of associated N-methylthioacetamide molecules. The crystal spectral properties, along with an abnormal H/D isotopic effect in the spectra, were found to be strongly influenced by vibronic coupling mechanisms in these dimers. These mechanisms were considered as responsible for the activation in IR of the totally symmetric proton stretching vibrations in the dimers. On analyzing the spectra of isotopically diluted crystalline samples of N-methylthioacetamide, it was proved that a non-random distribution of the protons and deuterons took place in the hydrogen bond lattices. In an individual hydrogen-bonded chain in the crystals distribution of the hydrogen isotope atoms H and D was fully random. The H/D isotopic " self-organization" mechanism, of a vibronic nature, involved a pair of hydrogen bonds from a unit cell, where each hydrogen bond belonged to a different chain of the associated molecules.

Semiclassical Path Integral Calculation of Nonlinear Optical Spectroscopy.

PubMed

Provazza, Justin; Segatta, Francesco; Garavelli, Marco; Coker, David F

2018-02-13

Computation of nonlinear optical response functions allows for an in-depth connection between theory and experiment. Experimentally recorded spectra provide a high density of information, but to objectively disentangle overlapping signals and to reach a detailed and reliable understanding of the system dynamics, measurements must be integrated with theoretical approaches. Here, we present a new, highly accurate and efficient trajectory-based semiclassical path integral method for computing higher order nonlinear optical response functions for non-Markovian open quantum systems. The approach is, in principle, applicable to general Hamiltonians and does not require any restrictions on the form of the intrasystem or system-bath couplings. This method is systematically improvable and is shown to be valid in parameter regimes where perturbation theory-based methods qualitatively breakdown. As a test of the methodology presented here, we study a system-bath model for a coupled dimer for which we compare against numerically exact results and standard approximate perturbation theory-based calculations. Additionally, we study a monomer with discrete vibronic states that serves as the starting point for future investigation of vibronic signatures in nonlinear electronic spectroscopy.

Nonadiabatic dynamics of photo-induced proton-coupled electron transfer reactions via ring-polymer surface hopping

NASA Astrophysics Data System (ADS)

Shakib, Farnaz; Huo, Pengfei

Photo-induced proton-coupled electron transfer reactions (PCET) are at the heart of energy conversion reactions in photocatalysis. Here, we apply the recently developed ring-polymer surface-hopping (RPSH) approach to simulate the nonadiabatic dynamics of photo-induced PCET. The RPSH method incorporates ring-polymer (RP) quantization of the proton into the fewest-switches surface-hopping (FSSH) approach. Using two diabatic electronic states, corresponding to the electron donor and acceptor states, we model photo-induced PCET with the proton described by a classical isomorphism RP. From the RPSH method, we obtain numerical results that are comparable to those obtained when the proton is treated quantum mechanically. This accuracy stems from incorporating exact quantum statistics, such as proton tunnelling, into approximate quantum dynamics. Additionally, RPSH offers the numerical accuracy along with the computational efficiency. Namely, compared to the FSSH approach in vibronic representation, there is no need to calculate a massive number of vibronic states explicitly. This approach opens up the possibility to accurately and efficiently simulate photo-induced PCET with multiple transferring protons or electrons.

Towards quantification of vibronic coupling in photosynthetic antenna complexes

NASA Astrophysics Data System (ADS)

Singh, V. P.; Westberg, M.; Wang, C.; Dahlberg, P. D.; Gellen, T.; Gardiner, A. T.; Cogdell, R. J.; Engel, G. S.

2015-06-01

Photosynthetic antenna complexes harvest sunlight and efficiently transport energy to the reaction center where charge separation powers biochemical energy storage. The discovery of existence of long lived quantum coherence during energy transfer has sparked the discussion on the role of quantum coherence on the energy transfer efficiency. Early works assigned observed coherences to electronic states, and theoretical studies showed that electronic coherences could affect energy transfer efficiency—by either enhancing or suppressing transfer. However, the nature of coherences has been fiercely debated as coherences only report the energy gap between the states that generate coherence signals. Recent works have suggested that either the coherences observed in photosynthetic antenna complexes arise from vibrational wave packets on the ground state or, alternatively, coherences arise from mixed electronic and vibrational states. Understanding origin of coherences is important for designing molecules for efficient light harvesting. Here, we give a direct experimental observation from a mutant of LH2, which does not have B800 chromophores, to distinguish between electronic, vibrational, and vibronic coherence. We also present a minimal theoretical model to characterize the coherences both in the two limiting cases of purely vibrational and purely electronic coherence as well as in the intermediate, vibronic regime.

Vibronic Structure of the tilde{X} ^2A_2' State of NO_3

NASA Astrophysics Data System (ADS)

Fukushima, Masaru

2015-06-01

We have measured dispersed fluorescence ( DF ) spectra from the single vibronic levels ( SVL's ) of the tilde{B} ^2E' state of jet cooled 14NO_3 and 15NO_3, and found a new vibronic band around the ν_1 fundamental This new band has two characteristics; (1) inverse isotope shift, and (2) unexpectedly strong intensity, i.e. comparable with that of the ν_1 fundamental. We concluded on the basis of the isotope effect that the terminated ( lower ) vibrational level of the new vibronic band should have vibrationally a_1' symmetry, and assigned to the third over-tone of the ν_4 asymmetric (e') mode, 3 ν_4 (a_1'). We also assigned a weaker band at about 160 cm-1 above the new band to one terminated to 3 ν_4 (a_2'). The 3 ν_4 (a_1') and (a_2') levels are ones with l = ±3. Hirota proposed new vibronic coupling mechanism which suggests that degenerate vibrational modes can induce electronic orbital angular momentum ( L ) even in non-degenerate electronic states. %It is thus thought the surprisingly wide splitting of 3 ν_4, a_1' and a_2', is resulted from vibronic coupling, and the explanation we proposed is as follows. We interpret this as a sort of break-down of the Born-Oppenheimer approximation, and think that ± l induces ∓barΛ, where barΛ expresses the pseudo-L; for the present system, one of the components of the third over-tone level, | Λ = 0; v_4 = 3, l = +3 rangle, can have contributions of | barΛ = -1; v_4 = 3, l = +2 rangle and | -2; 3, +1 rangle. Under this interpretation, it is expected that there is sixth-order vibronic coupling, (q_+^3Q_-^3 + q_-^3Q_+^3), between | 0; 3, +3 rangle and | 0; 3, -3 rangle. The sixth-order coupling is weaker than the Renner-Teller term ( the fourth-order term, (q_+^2Q_-^2 + q_-^2Q_+^2) ), but stronger than the eighth-order term, (q_+^4Q_-^4 + q_-^4Q_+^4). It is well known in linear molecules that the former shows huge separation, comparable with vibrational frequency, among the vibronic levels of Π electronic states, and the latter shows considerable splitting, ˜10 cm-1, at Δ electronic states. Consequently, the ˜160 cm-1 splitting at v_4 = 3 is attributed to the sixth-order interaction. The relatively strong intensity for the band to 3 ν_4 (a_1') can be interpreted as a part of the huge 0-0 band intensity, because the 3 ν_4 (a_1') level, | 0; 3, ±3 rangle, can connect with the vibrationless level, | 0; 0, 0 rangle. 3 ν_4 (a_1') has two-fold intensity because of the vibrational wavefunction, | 0; 3, +3 rangle + | 0; 3, -3 rangle, while negligible intensity is expected for 3 ν_4 (a_2') with | 0; 3, +3 rangle - | 0; 3, -3 rangle due to the cancellation. To confirm these interpretations, experiments on rotationally resolved spectra are underway. M. Fukushima and T. Ishiwata, paper WJ03, ISMS2013, and paper MI17, ISMS2014. E. Hirota, J. Mol. Spectrosc., in press.

Observation of a quadrupole interaction for cubic imperfections exhibiting a dynamic Jahn-Teller effect.

NASA Technical Reports Server (NTRS)

Herrington, J. R.; Estle, T. L.; Boatner, L. A.

1972-01-01

The observation and interpretation of weak EPR transitions, identified as 'forbidden' transitions, establish the existence of a new type of quadrupole interaction for cubic-symmetry imperfections. This interaction is simply a consequence of the ground-vibronic-state degeneracy. The signs as well as the magnitudes of the quadrupole-coupling coefficients are determined experimentally. These data agree well with the predictions of crystal field theory modified to account for a weak-to-moderate vibronic interaction (i.e., a dynamic Jahn-Teller effect).

ExoMol molecular line lists - XIII. The spectrum of CaO

NASA Astrophysics Data System (ADS)

Yurchenko, Sergei N.; Blissett, Audra; Asari, Usama; Vasilios, Marcus; Hill, Christian; Tennyson, Jonathan

2016-03-01

An accurate line list for calcium oxide is presented covering transitions between all bound ro-vibronic levels from the five lowest electronic states X 1Σ+, A' 1Π, A 1Σ+, a 3Π, and b 3Σ+. The ro-vibronic energies and corresponding wavefunctions were obtained by solving the fully coupled Schrödinger equation. Ab initio potential energy, spin-orbit, and electronic angular momentum curves were refined by fitting to the experimental frequencies and experimentally derived energies available in the literature. Using our refined model we could (1) reassign the vibronic states for a large portion of the experimentally derived energies (van Groenendael A., Tudorie M., Focsa C., Pinchemel B., Bernath P. F., 2005, J. Mol. Spectrosc., 234, 255), (2) extended this list of energies to J = 61-118 and (3) suggest a new description of the resonances from the A 1Σ+-X 1Σ+ system. We used high level ab initio electric dipole moments reported previously (Khalil H., Brites V., Le Quere F., Leonard C., 2011, Chem. Phys., 386, 50) to compute the Einstein A coefficients. Our work is the first fully coupled description of this system. Our line list is the most complete catalogue of spectroscopic transitions available for 40Ca16O and is applicable for temperatures up to at least 5000 K. CaO has yet to be observed astronomically but its transitions are characterized by being particularly strong which should facilitate its detection. The CaO line list is made available in an electronic form as supplementary data to this article and at www.exomol.com.

Evidence for a vibrational phase-dependent isotope effect on the photochemistry of vision.

PubMed

Schnedermann, C; Yang, X; Liebel, M; Spillane, K M; Lugtenburg, J; Fernández, I; Valentini, A; Schapiro, I; Olivucci, M; Kukura, P; Mathies, R A

2018-04-01

Vibronic coupling is key to efficient energy flow in molecular systems and a critical component of most mechanisms invoking quantum effects in biological processes. Despite increasing evidence for coherent coupling of electronic states being mediated by vibrational motion, it is not clear how and to what degree properties associated with vibrational coherence such as phase and coupling of atomic motion can impact the efficiency of light-induced processes under natural, incoherent illumination. Here, we show that deuteration of the H 11 -C 11 =C 12 -H 12 double-bond of the 11-cis retinal chromophore in the visual pigment rhodopsin significantly and unexpectedly alters the photoisomerization yield while inducing smaller changes in the ultrafast isomerization dynamics assignable to known isotope effects. Combination of these results with non-adiabatic molecular dynamics simulations reveals a vibrational phase-dependent isotope effect that we suggest is an intrinsic attribute of vibronically coherent photochemical processes.

Vibronic coupling and selectivity of vibrational excitation in the negative ion resonances of ozone

NASA Astrophysics Data System (ADS)

Allan, Michael; Popovic̀, Duška B.

1997-04-01

A recent experimental paper reported two shape resonances in electron impact on ozone, A 1 and B 2, both causing vibrational excitation with a distinct pattern of selectivity. The present Letter attempts to rationalize this selectivity using approximate potential curves, calculated for the A 1 and B 2 resonances by adding the SCF energy of neutral ozone to electron attachment energies calculated from ab initio virtual orbital energies using the Koopmans' theorem and an empirical scaling relation. The slopes of the curves explain the efficient excitation of the symmetric stretch by both resonances and the lack of the bending excitation by the B 2 resonance. The A 1 and B 2 resonances are strongly coupled by the b 2 antisymmetric stretch vibration, causing a double minimum on the lower surface. Nonadiabatic effects caused by the strong vibronic coupling explain the observed excitation of the antisymmetric stretch vibration.

Energy spectra of vibron and cluster models in molecular and nuclear systems

NASA Astrophysics Data System (ADS)

Jalili Majarshin, A.; Sabri, H.; Jafarizadeh, M. A.

2018-03-01

The relation of the algebraic cluster model, i.e., of the vibron model and its extension, to the collective structure, is discussed. In the first section of the paper, we study the energy spectra of vibron model, for diatomic molecule then we derive the rotation-vibration spectrum of 2α, 3α and 4α configuration in the low-lying spectrum of 8Be, 12C and 16O nuclei. All vibrational and rotational states with ground and excited A, E and F states appear to have been observed, moreover the transitional descriptions of the vibron model and α-cluster model were considered by using an infinite-dimensional algebraic method based on the affine \\widehat{SU(1,1)} Lie algebra. The calculated energy spectra are compared with experimental data. Applications to the rotation-vibration spectrum for the diatomic molecule and many-body nuclear clusters indicate that there are solvable models and they can be approximated very well using the transitional theory.

Interference between Coulombic and CT-mediated couplings in molecular aggregates: H- to J-aggregate transformation in perylene-based π-stacks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hestand, Nicholas J.; Spano, Frank C.

2015-12-28

The spectroscopic differences between J and H-aggregates are traditionally attributed to the spatial dependence of the Coulombic coupling, as originally proposed by Kasha. However, in tightly packed molecular aggregates wave functions on neighboring molecules overlap, leading to an additional charge transfer (CT) mediated exciton coupling with a vastly different spatial dependence. The latter is governed by the nodal patterns of the molecular LUMOs and HOMOs from which the electron (t{sub e}) and hole (t{sub h}) transfer integrals derive. The sign of the CT-mediated coupling depends on the sign of the product t{sub e}t{sub h} and is therefore highly sensitive tomore » small (sub-Angstrom) transverse displacements or slips. Given that Coulombic and CT-mediated couplings exist simultaneously in tightly packed molecular systems, the interference between the two must be considered when defining J and H-aggregates. Generally, such π-stacked aggregates do not abide by the traditional classification scheme of Kasha: for example, even when the Coulomb coupling is strong the presence of a similarly strong but destructively interfering CT-mediated coupling results in “null-aggregates” which spectroscopically resemble uncoupled molecules. Based on a Frenkel/CT Holstein Hamiltonian that takes into account both sources of electronic coupling as well as intramolecular vibrations, vibronic spectral signatures are developed for integrated Frenkel/CT systems in both the perturbative and resonance regimes. In the perturbative regime, the sign of the lowest exciton band curvature, which rigorously defines J and H-aggregation, is directly tracked by the ratio of the first two vibronic peak intensities. Even in the resonance regime, the vibronic ratio remains a useful tool to evaluate the J or H nature of the system. The theory developed is applied to the reversible H to J-aggregate transformations recently observed in several perylene bisimide systems.« less

Nodeless vibrational amplitudes and quantum nonadiabatic dynamics in the nested funnel for a pseudo Jahn-Teller molecule or homodimer

NASA Astrophysics Data System (ADS)

Peters, William K.; Tiwari, Vivek; Jonas, David M.

2017-11-01

The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer. For parameters modeling a free-base naphthalocyanine, the nonadiabatic couplings are deeply quantum mechanical and depend on wavepacket width; scalar couplings are as important as the derivative couplings that are usually interpreted to depend on vibrational velocity in semiclassical curve crossing or surface hopping theories. A colored visualization scheme that fully characterizes the non-adiabatic states using the exact factorization is developed. The nonadiabatic states in this nested funnel have nodeless vibrational factors with strongly avoided zeroes in their vibrational probability densities. Vibronic dynamics are visualized through the vibrational coordinate dependent density of the time-dependent dipole moment in free induction decay. Vibrational motion is amplified by the nonadiabatic couplings, with asymmetric and anisotropic motions that depend upon the excitation polarization in the molecular frame and can be reversed by a change in polarization. This generates a vibrational quantum beat anisotropy in excess of 2/5. The amplitude of vibrational motion can be larger than that on the uncoupled potentials, and the electronic population transfer is maximized within one vibrational period. Most of these dynamics are missed by the adiabatic approximation, and some electronic and vibrational motions are completely suppressed by the Condon approximation of a coordinate-independent transition dipole between adiabatic states. For all initial conditions investigated, the initial nonadiabatic electronic motion is driven towards the lower adiabatic state, and criteria for this directed motion are discussed.

Nodeless vibrational amplitudes and quantum nonadiabatic dynamics in the nested funnel for a pseudo Jahn-Teller molecule or homodimer.

PubMed

Peters, William K; Tiwari, Vivek; Jonas, David M

2017-11-21

The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer. For parameters modeling a free-base naphthalocyanine, the nonadiabatic couplings are deeply quantum mechanical and depend on wavepacket width; scalar couplings are as important as the derivative couplings that are usually interpreted to depend on vibrational velocity in semiclassical curve crossing or surface hopping theories. A colored visualization scheme that fully characterizes the non-adiabatic states using the exact factorization is developed. The nonadiabatic states in this nested funnel have nodeless vibrational factors with strongly avoided zeroes in their vibrational probability densities. Vibronic dynamics are visualized through the vibrational coordinate dependent density of the time-dependent dipole moment in free induction decay. Vibrational motion is amplified by the nonadiabatic couplings, with asymmetric and anisotropic motions that depend upon the excitation polarization in the molecular frame and can be reversed by a change in polarization. This generates a vibrational quantum beat anisotropy in excess of 2/5. The amplitude of vibrational motion can be larger than that on the uncoupled potentials, and the electronic population transfer is maximized within one vibrational period. Most of these dynamics are missed by the adiabatic approximation, and some electronic and vibrational motions are completely suppressed by the Condon approximation of a coordinate-independent transition dipole between adiabatic states. For all initial conditions investigated, the initial nonadiabatic electronic motion is driven towards the lower adiabatic state, and criteria for this directed motion are discussed.

Optical Properties of Vibronically Coupled Cy3 Dimers on DNA Scaffolds.

PubMed

Cunningham, Paul D; Kim, Young C; Díaz, Sebastián A; Buckhout-White, Susan; Mathur, Divita; Medintz, Igor L; Melinger, Joseph S

2018-05-17

We examine the effect of electronic coupling on the optical properties of Cy3 dimers attached to DNA duplexes as a function of base pair (bp) separation using steady-state and time-resolved spectroscopy. For close Cy3-Cy3 separations, 0 and 1 bp between dyes, intermediate to strong electronic coupling is revealed by modulation of the absorption and fluorescence properties including spectral band shape, peak wavelength, and excited-state lifetime. Using a vibronic exciton model, we estimate coupling strengths of 150 and 266 cm -1 for the 1 and 0 bp separations, respectively, which are comparable to those found in natural light-harvesting complexes. For the strongest electronic coupling (0 bp separation), we observe that the absorption band shape is strongly affected by the base pairs that surround the dyes, where more strongly hydrogen-bonded G-C pairs produce a red-shifted absorption spectrum consistent with a J-type dimer. This effect is studied theoretically using molecular dynamics simulation, which predicts an in-line dye configuration that is consistent with the experimental J-type spectrum. When the Cy3 dimers are in a standard aqueous buffer, the presence of relatively strong electronic coupling is accompanied by decreased fluorescence lifetime, suggesting that it promotes nonradiative relaxation in cyanine dyes. However, we show that the use of a viscous solvent can suppress this nonradiative recombination and thereby restore the dimer fluorescent emission. Ultrafast transient absorption measurements of Cy3 dimers in both standard aqueous buffer and viscous glycerol buffer suggest that sufficiently strong electronic coupling increases the probability of excited-state relaxation through a dark state that is related to Cy3 torsional motion.

The ÖX˜ absorption of vinoxy radical revisited: Normal and Herzberg-Teller bands observed via cavity ringdown spectroscopy

NASA Astrophysics Data System (ADS)

Thomas, Phillip S.; Chhantyal-Pun, Rabi; Kline, Neal D.; Miller, Terry A.

2010-03-01

The ÖX˜ electronic absorption spectrum of vinoxy radical has been investigated using room temperature cavity ringdown spectroscopy. Analysis of the observed bands on the basis of computed vibrational frequencies and rotational envelopes reveals that two distinct types of features are present with comparable intensities. The first type corresponds to "normal" allowed electronic transitions to the origin and symmetric vibrations in the à state. The second type is interpreted in terms of excitations to asymmetric à state vibrations, which are only vibronically allowed by Herzberg-Teller coupling to the B˜ state. Results of electronic structure calculations indicate that the magnitude of the Herzberg-Teller coupling is appropriate to produce vibronically induced transitions with intensities comparable to those of the normal bands.

Toward a general mixed quantum/classical method for the calculation of the vibronic ECD of a flexible dye molecule with different stable conformers: Revisiting the case of 2,2,2-trifluoro-anthrylethanol.

PubMed

Cerezo, Javier; Aranda, Daniel; Avila Ferrer, Francisco J; Prampolini, Giacomo; Mazzeo, Giuseppe; Longhi, Giovanna; Abbate, Sergio; Santoro, Fabrizio

2018-06-01

We extend a recently proposed mixed quantum/classical method for computing the vibronic electronic circular dichroism (ECD) spectrum of molecules with different conformers, to cases where more than one hindered rotation is present. The method generalizes the standard procedure, based on the simple Boltzmann average of the vibronic spectra of the stable conformers, and includes the contribution of structures that sample all the accessible conformational space. It is applied to the simulation of the ECD spectrum of (S)-2,2,2-trifluoroanthrylethanol, a molecule with easily interconvertible conformers, whose spectrum exhibits a pattern of alternating positive and negative vibronic peaks. Results are in very good agreement with experiment and show that spectra averaged over all the sampled conformational space can deviate significantly from the simple average of the contributions of the stable conformers. The present mixed quantum/classical method is able to capture the effect of the nonlinear dependence of the rotatory strength on the molecular structure and of the anharmonic couplings among the modes responsible for molecular flexibility. Despite its computational cost, the procedure is still affordable and promises to be useful in all cases where the ECD shape arises from a subtle balance between vibronic effects and conformational variety. © 2018 Wiley Periodicals, Inc.

Combining the ensemble and Franck-Condon approaches for calculating spectral shapes of molecules in solution

NASA Astrophysics Data System (ADS)

Zuehlsdorff, T. J.; Isborn, C. M.

2018-01-01

The correct treatment of vibronic effects is vital for the modeling of absorption spectra of many solvated dyes. Vibronic spectra for small dyes in solution can be easily computed within the Franck-Condon approximation using an implicit solvent model. However, implicit solvent models neglect specific solute-solvent interactions on the electronic excited state. On the other hand, a straightforward way to account for solute-solvent interactions and temperature-dependent broadening is by computing vertical excitation energies obtained from an ensemble of solute-solvent conformations. Ensemble approaches usually do not account for vibronic transitions and thus often produce spectral shapes in poor agreement with experiment. We address these shortcomings by combining zero-temperature vibronic fine structure with vertical excitations computed for a room-temperature ensemble of solute-solvent configurations. In this combined approach, all temperature-dependent broadening is treated classically through the sampling of configurations and quantum mechanical vibronic contributions are included as a zero-temperature correction to each vertical transition. In our calculation of the vertical excitations, significant regions of the solvent environment are treated fully quantum mechanically to account for solute-solvent polarization and charge-transfer. For the Franck-Condon calculations, a small amount of frozen explicit solvent is considered in order to capture solvent effects on the vibronic shape function. We test the proposed method by comparing calculated and experimental absorption spectra of Nile red and the green fluorescent protein chromophore in polar and non-polar solvents. For systems with strong solute-solvent interactions, the combined approach yields significant improvements over the ensemble approach. For systems with weak to moderate solute-solvent interactions, both the high-energy vibronic tail and the width of the spectra are in excellent agreement with experiments.

The E(2) symmetry and quantum phase transition in the two-dimensional limit of the vibron model

NASA Astrophysics Data System (ADS)

Zhang, Yu; Pan, Feng; Liu, Yu-Xin; Draayer, J. P.

2010-11-01

We study in detail the relation between the two-dimensional Euclidean dynamical E(2) symmetry and the quantum phase transition in the two-dimensional limit of the vibron model, called the U(3) vibron model. Both geometric and algebraic descriptions of the U(3) vibron model show that structures of low-lying states at the critical point of the model with a quartic potential as its classical limit can be approximately described by the E(2) symmetry. We also fit the finite-size scaling exponent of the energy levels and E1 transition rates in the F(2) model, which is exactly the E(2) model but with truncation in its Hilbert subspace, as well as those at the critical point in the U(3) vibron model. The N-scaling power law around the critical point shows that the E(2) symmetry is well preserved even for cases with finite number of bosons. In addition, two kinds of experimentally accessible effective order parameters, such as the energy ratios E_{2_1}/E_{1_1}, E_{3_1}/E_{1_1} and E1 transition ratios \\frac{B(E1;2_1\\rightarrow 1_1)}{B(E1;1_1\\rightarrow 0_1)}, \\frac{B(E1;0_2\\rightarrow 1_1)}{B(E1;1_1\\rightarrow 0_1)}, are proposed to identify the second-order phase transition in such systems. Possible empirical examples exhibiting approximate E(2) symmetry are also presented.

Ab initio study of dynamical E × e Jahn-Teller and spin-orbit coupling effects in the transition-metal trifluorides TiF3, CrF3, and NiF3

NASA Astrophysics Data System (ADS)

Mondal, Padmabati; Opalka, Daniel; Poluyanov, Leonid V.; Domcke, Wolfgang

2012-02-01

Multiconfiguration ab initio methods have been employed to study the effects of Jahn-Teller (JT) and spin-orbit (SO) coupling in the transition-metal trifluorides TiF3, CrF3, and NiF3, which possess spatially doubly degenerate excited states (ME) of even spin multiplicities (M = 2 or 4). The ground states of TiF3, CrF3, and NiF3 are nondegenerate and exhibit minima of D3h symmetry. Potential-energy surfaces of spatially degenerate excited states have been calculated using the state-averaged complete-active-space self-consistent-field method. SO coupling is described by the matrix elements of the Breit-Pauli operator. Linear and higher order JT coupling constants for the JT-active bending and stretching modes as well as SO-coupling constants have been determined. Vibronic spectra of JT-active excited electronic states have been calculated, using JT Hamiltonians for trigonal systems with inclusion of SO coupling. The effect of higher order (up to sixth order) JT couplings on the vibronic spectra has been investigated for selected electronic states and vibrational modes with particularly strong JT couplings. While the weak SO couplings in TiF3 and CrF3 are almost completely quenched by the strong JT couplings, the stronger SO coupling in NiF3 is only partially quenched by JT coupling.

Understanding the electron-phonon interaction in polar crystals: Perspective presented by the vibronic theory

NASA Astrophysics Data System (ADS)

Pishtshev, A.; Kristoffel, N.

2017-05-01

We outline our novel results relating to the physics of the electron-TO-phonon (el-TO-ph) interaction in a polar crystal. We explained why the el-TO-ph interaction becomes effectively strong in a ferroelectric, and showed how the electron density redistribution establishes favorable conditions for soft-behavior of the long-wavelength branch of the active TO vibration. In the context of the vibronic theory it has been demonstrated that at the macroscopic level the interaction of electrons with the polar zone-centre TO phonons can be associated with the internal long-range dipole forces. Also we elucidated a methodological issue of how local field effects are incorporated within the vibronic theory. These result provided not only substantial support for the vibronic mechanism of ferroelectricity but also presented direct evidence of equivalence between vibronic and the other lattice dynamics models. The corresponding comparison allowed us to introduce the original parametrization for constants of the vibronic interaction in terms of key material constants. The applicability of the suggested formula has been tested for a wide class of polar materials.

Tracking the coherent generation of polaron pairs in conjugated polymers

NASA Astrophysics Data System (ADS)

de Sio, Antonietta; Troiani, Filippo; Maiuri, Margherita; Réhault, Julien; Sommer, Ephraim; Lim, James; Huelga, Susana F.; Plenio, Martin B.; Rozzi, Carlo Andrea; Cerullo, Giulio; Molinari, Elisa; Lienau, Christoph

2016-12-01

The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials.

Ultrafast dynamics of multi-exciton state coupled to coherent vibration in zinc chlorin aggregates for artificial photosynthesis.

PubMed

Shi, Tongchao; Liu, Zhengzheng; Miyatake, Tomohiro; Tamiaki, Hitoshi; Kobayashi, Takayoshi; Zhang, Zeyu; Du, Juan; Leng, Yuxin

2017-11-27

Ultrafast vibronic dynamics induced by the interaction of the Frenkel exciton with the coherent molecular vibrations in a layer-structured zinc chlorin aggregates prepared for artificial photosynthesis have been studied by 7.1 fs real-time vibrational spectroscopy with multi-spectrum detection. The fast decay of 100 ± 5fs is ascribed to the relaxation from the higher multi-exciton state (MES) to the one-exciton state, and the slow one of 863 ± 70fs is assigned to the relaxation from Q-exciton state to the dark nonfluorescent charge-transfer (CT) state, respectively. In addition, the wavelength dependences of the exciton-vibration coupling strength are found to follow the zeroth derivative of the transient absorption spectra of the exciton. It could be explained in term of the transition dipole moment modulated by dynamic intensity borrowing between the B transition and the Q transition through the vibronic interactions.

Experimental investigation of the Jahn-Teller effect in the ground and excited electronic states of the tropyl radical. Part II. Vibrational analysis of the A 2E"3-X 2E"2 electronic transition.

PubMed

Sioutis, Ilias; Stakhursky, Vadim L; Tarczay, György; Miller, Terry A

2008-02-28

Laser-induced fluorescence (LIF) and laser-excited dispersed fluorescence (LEDF) spectra of the cycloheptatrienyl (tropyl) radical C7H7 have been observed under supersonic jet-cooling conditions. Assignment of the LIF excitation spectrum yields detailed information about the A-state vibronic structure. The LEDF emission was collected by pumping different vibronic bands of the A 2E"3<--X 2E"2 electronic spectrum. Analysis of the LEDF spectra yields valuable information about the vibronic levels of the X 2E"2 state. The X- and A-state vibronic structures characterize the Jahn-Teller distortion of the respective potential energy surfaces. A thorough analysis reveals observable Jahn-Teller activity in three of the four e'3 modes for the X 2E"2 state and two of the three e'1 modes for the A 2E"3 state and provides values for their deperturbed vibrational frequencies as well as linear Jahn-Teller coupling constants. The molecular parameters characterizing the Jahn-Teller interaction in the X and A states of C7H7 are compared to theoretical results and to those previously obtained for C5H5 and C6H6+.

Mixed-Valence Molecular Unit for Quantum Cellular Automata: Beyond the Born-Oppenheimer Paradigm through the Symmetry-Assisted Vibronic Approach.

PubMed

Clemente-Juan, Juan Modesto; Palii, Andrew; Coronado, Eugenio; Tsukerblat, Boris

2016-08-09

In this article, we focus on the electron-vibrational problem of the tetrameric mixed-valence (MV) complexes proposed for implementation as four-dot molecular quantum cellular automata (mQCA).1 Although the adiabatic approximation explored in ref 2 is an appropriate tool for the qualitative analysis of the basic characteristics of mQCA, like vibronic trapping of the electrons encoding binary information and cell-cell response, it loses its accuracy providing moderate vibronic coupling and fails in the description of the discrete pattern of the vibronic levels. Therefore, a precise solution of the quantum-mechanical vibronic problem is of primary importance for the evaluation of the shapes of the electron transfer optical absorption bands and quantitative analysis of the main parameters of tetrameric quantum cells. Here, we go beyond the Born-Oppenheimer paradigm and present a solution of the quantum-mechanical pseudo Jahn-Teller (JT) vibronic problem in bielectronic MV species (exemplified by the tetra-ruthenium complexes) based on the recently developed symmetry-assisted approach.3,4 The mathematical approach to the vibronic eigenproblem takes into consideration the point symmetry basis, and therefore, the total matrix of the JT Hamiltonian is blocked to the maximum extent. The submatrices correspond to the irreducible representations (irreps) of the point group. With this tool, we also extend the theory of the mQCA cell beyond the limit of prevailing Coulomb repulsion in the electronic pair (adopted in ref 2), and therefore, the general pseudo-JT problems for spin-singlet ((1)B1g, 2(1)A1g, (1)B2g, (1)Eu) ⊗ (b1g + eu) and spin-triplet states ((3)A2g, (3)B1g, 2(3)Eu) ⊗ (b1g + eu) in a square-planar bielectronic system are solved. The obtained symmetry-adapted electron-vibrational functions are employed for the calculation of the profiles (shape functions) of the charge transfer absorption bands in the tetrameric MV complexes and for the discussion of the magnetic properties.

Comparative study of inelastic squared form factors of the vibronic states of B 1Σu+ , C 1Πu , and E F 1Σg+ for molecular hydrogen: Inelastic x-ray and electron scattering

NASA Astrophysics Data System (ADS)

Xu, Long-Quan; Kang, Xu; Peng, Yi-Geng; Xu, Xin; Liu, Ya-Wei; Wu, Yong; Yang, Ke; Hiraoka, Nozomu; Tsuei, Ku-Ding; Wang, Jian-Guo; Zhu, Lin-Fan

2018-03-01

A joint experimental and theoretical investigation of the valence-shell excitations of hydrogen has been performed by the high-resolution inelastic x-ray scattering and electron scattering as well as the multireference single- and double-excitation configuration-interaction method. Momentum-transfer-dependent inelastic squared form factors for the vibronic series belonging to the B 1Σu+ ,C 1Πu , and E F 1Σg+ electronic states of molecular hydrogen have been derived from the inelastic x-ray scattering method at an impact photon energy around 10 keV, and the electron energy-loss spectra measured at an incident electron energy of 1500 eV. It is found that both the present and the previous calculations cannot satisfactorily reproduce the inelastic squared form-factor profiles for the higher vibronic transitions of the B 1Σu+ state of molecular hydrogen, which may be due to the electronic-vibrational coupling for the higher vibronic states. For the C 1Πu state and some vibronic excitations of E F 1Σg+ state, the present experimental results are in good agreement with the present and previous calculations, while the slight differences between the inelastic x-ray scattering and electron energy-loss spectroscopy results in the larger squared momentum-transfer region may be attributed to the increasing role of the higher-order Born terms in the electron-scattering process.

Electron–vibration coupling induced renormalization in the photoemission spectrum of diamondoids

DOE PAGES

Gali, Adam; Demján, Tamás; Vörös, Márton; ...

2016-04-22

The development of theories and methods devoted to the accurate calculation of the electronic quasi-particle states and levels of molecules, clusters and solids is of prime importance to interpret the experimental data. These quantum systems are often modelled by using the Born–Oppenheimer approximation where the coupling between the electrons and vibrational modes is not fully taken into account, and the electrons are treated as pure quasi-particles. Here, we show that in small diamond cages, called diamondoids, the electron–vibration coupling leads to the breakdown of the electron quasi-particle picture. More importantly, we demonstrate that the strong electron–vibration coupling is essential tomore » properly describe the overall lineshape of the experimental photoemission spectrum. This cannot be obtained by methods within Born–Oppenheimer approximation. Furthermore, we deduce a link between the vibronic states found by our many-body perturbation theory approach and the well-known Jahn–Teller effect.« less

Electron–vibration coupling induced renormalization in the photoemission spectrum of diamondoids

PubMed Central

Gali, Adam; Demján, Tamás; Vörös, Márton; Thiering, Gergő; Cannuccia, Elena; Marini, Andrea

2016-01-01

The development of theories and methods devoted to the accurate calculation of the electronic quasi-particle states and levels of molecules, clusters and solids is of prime importance to interpret the experimental data. These quantum systems are often modelled by using the Born–Oppenheimer approximation where the coupling between the electrons and vibrational modes is not fully taken into account, and the electrons are treated as pure quasi-particles. Here, we show that in small diamond cages, called diamondoids, the electron–vibration coupling leads to the breakdown of the electron quasi-particle picture. More importantly, we demonstrate that the strong electron–vibration coupling is essential to properly describe the overall lineshape of the experimental photoemission spectrum. This cannot be obtained by methods within Born–Oppenheimer approximation. Moreover, we deduce a link between the vibronic states found by our many-body perturbation theory approach and the well-known Jahn–Teller effect. PMID:27103340

Anharmonicity and hydrogen bonding in electrooptic sucrose crystal

NASA Astrophysics Data System (ADS)

Szostak, M. M.; Giermańska, J.

1990-03-01

The polarized absorption spectra of the sucrose crystal in the 5300 - 7300 cm -1 region have been measured. The assignments of all the eight OH stretching overtones are proposed and their mechanical anharmonicities are estimated. The discrepancies from the oriented gas model (OGM) in the observed relative band intensities, especially of the -CH vibrations, are assumed to be connected with vibronic couplings enhanced by the helical arrangement of molecules joined by hydrogen bondings. It seems that this kind of interactions might be important for the second harmonic generation (SHG) by the sucrose crystal.

Vibronic coupling in the excited-states of carotenoids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miki, Takeshi; Buckup, Tiago; Krause, Marie S.

2016-01-01

The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S 2to the optically dark state S 1.

Vibronic coupling in the excited-states of carotenoids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miki, Takeshi; Buckup, Tiago; Krause, Marie S.

The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S 2to the optically dark state S 1.

Carotenoid-to-bacteriochlorophyll energy transfer through vibronic coupling in LH2 from Phaeosprillum molischianum.

PubMed

Thyrhaug, Erling; Lincoln, Craig N; Branchi, Federico; Cerullo, Giulio; Perlík, Václav; Šanda, František; Lokstein, Heiko; Hauer, Jürgen

2018-03-01

The peripheral light-harvesting antenna complex (LH2) of purple photosynthetic bacteria is an ideal testing ground for models of structure-function relationships due to its well-determined molecular structure and ultrafast energy deactivation. It has been the target for numerous studies in both theory and ultrafast spectroscopy; nevertheless, certain aspects of the convoluted relaxation network of LH2 lack a satisfactory explanation by conventional theories. For example, the initial carotenoid-to-bacteriochlorophyll energy transfer step necessary on visible light excitation was long considered to follow the Förster mechanism, even though transfer times as short as 40 femtoseconds (fs) have been observed. Such transfer times are hard to accommodate by Förster theory, as the moderate coupling strengths found in LH2 suggest much slower transfer within this framework. In this study, we investigate LH2 from Phaeospirillum (Ph.) molischianum in two types of transient absorption experiments-with narrowband pump and white-light probe resulting in 100 fs time resolution, and with degenerate broadband 10 fs pump and probe pulses. With regard to the split Q x band in this system, we show that vibronically mediated transfer explains both the ultrafast carotenoid-to-B850 transfer, and the almost complete lack of transfer to B800. These results are beyond Förster theory, which predicts an almost equal partition between the two channels.

Photodissociation of phenol via nonadiabatic tunneling: Comparison of two ab initio based potential energy surfaces

NASA Astrophysics Data System (ADS)

Xie, Changjian; Guo, Hua

2017-09-01

The nonadiabatic tunneling-facilitated photodissociation of phenol is investigated using a reduced-dimensional quantum model on two ab initio-based coupled potential energy surfaces (PESs). Although dynamics occurs largely on the lower adiabat, the proximity to a conical intersection between the S1 and S2 states requires the inclusion of both the geometric phase (GP) and diagonal Born-Oppenheimer correction (DBOC). The lifetime of the lowest-lying vibronic state is computed using the diabatic and various adiabatic models. The GP and DBOC terms are found to be essential on one set of PESs, but have a small impact on the other.

Femtosecond dynamics and laser control of charge transport in trans-polyacetylene.

PubMed

Franco, Ignacio; Shapiro, Moshe; Brumer, Paul

2008-06-28

The induction of dc electronic transport in rigid and flexible trans-polyacetylene oligomers according to the omega versus 2omega coherent control scenario is investigated using a quantum-classical mean field approximation. The approach involves running a large ensemble of mixed quantum-classical trajectories under the influence of omega+2omega laser fields and choosing the initial conditions by sampling the ground-state Wigner distribution function for the nuclei. The vibronic couplings are shown to change the mean single-particle spectrum, introduce ultrafast decoherence, and enhance intramolecular vibrational and electronic relaxation. Nevertheless, even in the presence of significant couplings, limited coherent control of the electronic dynamics is still viable, the most promising route involving the use of femtosecond pulses with a duration that is comparable to the electronic dephasing time. The simulations offer a realistic description of the behavior of a simple coherent control scenario in a complex system and provide a detailed account of the femtosecond photoinduced vibronic dynamics of a conjugated polymer.

A new symmetrical quasi-classical model for electronically non-adiabatic processes: Application to the case of weak non-adiabatic coupling

DOE PAGES

Cotton, Stephen J.; Miller, William H.

2016-10-14

Previous work has shown how a symmetrical quasi-classical (SQC) windowing procedure can be used to quantize the initial and final electronic degrees of freedom in the Meyer-Miller (MM) classical vibronic (i.e, nuclear + electronic) Hamiltonian, and that the approach provides a very good description of electronically non-adiabatic processes within a standard classical molecular dynamics framework for a number of benchmark problems. This study explores application of the SQC/MM approach to the case of very weak non-adiabatic coupling between the electronic states, showing (as anticipated) how the standard SQC/MM approach used to date fails in this limit, and then devises amore » new SQC windowing scheme to deal with it. Finally, application of this new SQC model to a variety of realistic benchmark systems shows that the new model not only treats the weak coupling case extremely well, but it is also seen to describe the “normal” regime (of electronic transition probabilities ≳ 0.1) even more accurately than the previous “standard” model.« less

A new symmetrical quasi-classical model for electronically non-adiabatic processes: Application to the case of weak non-adiabatic coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cotton, Stephen J.; Miller, William H.

Previous work has shown how a symmetrical quasi-classical (SQC) windowing procedure can be used to quantize the initial and final electronic degrees of freedom in the Meyer-Miller (MM) classical vibronic (i.e, nuclear + electronic) Hamiltonian, and that the approach provides a very good description of electronically non-adiabatic processes within a standard classical molecular dynamics framework for a number of benchmark problems. This study explores application of the SQC/MM approach to the case of very weak non-adiabatic coupling between the electronic states, showing (as anticipated) how the standard SQC/MM approach used to date fails in this limit, and then devises amore » new SQC windowing scheme to deal with it. Finally, application of this new SQC model to a variety of realistic benchmark systems shows that the new model not only treats the weak coupling case extremely well, but it is also seen to describe the “normal” regime (of electronic transition probabilities ≳ 0.1) even more accurately than the previous “standard” model.« less

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer

NASA Astrophysics Data System (ADS)

Tiwari, Vivek; Peters, William K.; Jonas, David M.

2017-10-01

Non-adiabatic vibrational-electronic resonance in the excited electronic states of natural photosynthetic antennas drastically alters the adiabatic framework, in which electronic energy transfer has been conventionally studied, and suggests the possibility of exploiting non-adiabatic dynamics for directed energy transfer. Here, a generalized dimer model incorporates asymmetries between pigments, coupling to the environment, and the doubly excited state relevant for nonlinear spectroscopy. For this generalized dimer model, the vibrational tuning vector that drives energy transfer is derived and connected to decoherence between singly excited states. A correlation vector is connected to decoherence between the ground state and the doubly excited state. Optical decoherence between the ground and singly excited states involves linear combinations of the correlation and tuning vectors. Excitonic coupling modifies the tuning vector. The correlation and tuning vectors are not always orthogonal, and both can be asymmetric under pigment exchange, which affects energy transfer. For equal pigment vibrational frequencies, the nonadiabatic tuning vector becomes an anti-correlated delocalized linear combination of intramolecular vibrations of the two pigments, and the nonadiabatic energy transfer dynamics become separable. With exchange symmetry, the correlation and tuning vectors become delocalized intramolecular vibrations that are symmetric and antisymmetric under pigment exchange. Diabatic criteria for vibrational-excitonic resonance demonstrate that anti-correlated vibrations increase the range and speed of vibronically resonant energy transfer (the Golden Rule rate is a factor of 2 faster). A partial trace analysis shows that vibronic decoherence for a vibrational-excitonic resonance between two excitons is slower than their purely excitonic decoherence.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer.

PubMed

Tiwari, Vivek; Peters, William K; Jonas, David M

2017-10-21

Non-adiabatic vibrational-electronic resonance in the excited electronic states of natural photosynthetic antennas drastically alters the adiabatic framework, in which electronic energy transfer has been conventionally studied, and suggests the possibility of exploiting non-adiabatic dynamics for directed energy transfer. Here, a generalized dimer model incorporates asymmetries between pigments, coupling to the environment, and the doubly excited state relevant for nonlinear spectroscopy. For this generalized dimer model, the vibrational tuning vector that drives energy transfer is derived and connected to decoherence between singly excited states. A correlation vector is connected to decoherence between the ground state and the doubly excited state. Optical decoherence between the ground and singly excited states involves linear combinations of the correlation and tuning vectors. Excitonic coupling modifies the tuning vector. The correlation and tuning vectors are not always orthogonal, and both can be asymmetric under pigment exchange, which affects energy transfer. For equal pigment vibrational frequencies, the nonadiabatic tuning vector becomes an anti-correlated delocalized linear combination of intramolecular vibrations of the two pigments, and the nonadiabatic energy transfer dynamics become separable. With exchange symmetry, the correlation and tuning vectors become delocalized intramolecular vibrations that are symmetric and antisymmetric under pigment exchange. Diabatic criteria for vibrational-excitonic resonance demonstrate that anti-correlated vibrations increase the range and speed of vibronically resonant energy transfer (the Golden Rule rate is a factor of 2 faster). A partial trace analysis shows that vibronic decoherence for a vibrational-excitonic resonance between two excitons is slower than their purely excitonic decoherence.

Influences of Quantum Mechanically Mixed Electronic and Vibrational Pigment States in 2D Electronic Spectra of Photosynthetic Systems: Strong Electronic Coupling Cases

DOE PAGES

Fujihashi, Yuta; Fleming, Graham R.; Ishizaki, Akihito

2015-09-07

In 2D electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and several theoretical studies have suggested that the beats are produced by quantum mechanically mixed electronic and vibrational states. Concerning the electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D electronic spectra of a weakly coupled dimer with the Franck-Condon active vibrational modes in the resonant condition. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures.more » However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment electronic coupling. In this paper, we explore the impact of the fluctuations on electronic-vibrational quantum mixtures in a strongly coupled dimer with an off-resonant vibrational mode. Toward this end, we calculate energy transfer dynamics and 2D electronic spectra of a model dimer that corresponds to the most strongly coupled bacteriochlorophyll molecules in the Fenna-Matthews-Olson complex in a numerically accurate manner. The quantum mixtures are found to be robust under the exposure of protein-induced fluctuations at cryogenic temperatures, irrespective of the resonance. At 300 K, however, the quantum mixing is disturbed more strongly by the fluctuations, and therefore, the beats in the 2D spectra become obscure even in a strongly coupled dimer with a resonant vibrational mode. Further, the overall behaviors of the energy transfer dynamics are demonstrated to be dominated by the environment and coupling between the 0 0 vibronic transitions as long as the Huang-Rhys factor of the vibrational mode is small. Finally, the electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics despite contributing to the enhancement of long-lived quantum beating in the 2D spectra.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gali, Adam; Demján, Tamás; Vörös, Márton

The development of theories and methods devoted to the accurate calculation of the electronic quasi-particle states and levels of molecules, clusters and solids is of prime importance to interpret the experimental data. These quantum systems are often modelled by using the Born–Oppenheimer approximation where the coupling between the electrons and vibrational modes is not fully taken into account, and the electrons are treated as pure quasi-particles. Here, we show that in small diamond cages, called diamondoids, the electron–vibration coupling leads to the breakdown of the electron quasi-particle picture. More importantly, we demonstrate that the strong electron–vibration coupling is essential tomore » properly describe the overall lineshape of the experimental photoemission spectrum. This cannot be obtained by methods within Born–Oppenheimer approximation. Furthermore, we deduce a link between the vibronic states found by our many-body perturbation theory approach and the well-known Jahn–Teller effect.« less

Local protein solvation drives direct down-conversion in phycobiliprotein PC645 via incoherent vibronic transport

PubMed Central

Blau, Samuel M.; Bennett, Doran I. G.; Kreisbeck, Christoph; Scholes, Gregory D.; Aspuru-Guzik, Alán

2018-01-01

The mechanisms controlling excitation energy transport (EET) in light-harvesting complexes remain controversial. Following the observation of long-lived beats in 2D electronic spectroscopy of PC645, vibronic coherence, the delocalization of excited states between pigments supported by a resonant vibration, has been proposed to enable direct excitation transport from the highest-energy to the lowest-energy pigments, bypassing a collection of intermediate states. Here, we instead show that for phycobiliprotein PC645 an incoherent vibronic transport mechanism is at play. We quantify the solvation dynamics of individual pigments using ab initio quantum mechanics/molecular mechanics (QM/MM) nuclear dynamics. Our atomistic spectral densities reproduce experimental observations ranging from absorption and fluorescence spectra to the timescales and selectivity of down-conversion observed in transient absorption measurements. We construct a general model for vibronic dimers and establish the parameter regimes of coherent and incoherent vibronic transport. We demonstrate that direct down-conversion in PC645 proceeds incoherently, enhanced by large reorganization energies and a broad collection of high-frequency vibrations. We suggest that a similar incoherent mechanism is appropriate across phycobiliproteins and represents a potential design principle for nanoscale control of EET. PMID:29588417

Vibronic spectra of Cu(2+) in ZnTe

NASA Technical Reports Server (NTRS)

Volz, M. P.; Su, C.-H.; Lehoczky, S. L.; Szofran, F. R.

1992-01-01

Infrared-absorption spectra of substitutional Cu(2+) ions in ZnTe have been measured at 4.6 K. Several distinct absorption peaks are observed between 800 and 2000/cm. Absorption peaks at 1002 and 1069/cm are identified as zero-phonon lines arising from 2T2-2E transitions. Between 1069 and 2000/cm, several sets of sharp absorption lines are seen to recur regularly at an interval of 210/cm, corresponding to the LO phonon energy. Within each set distinct vibronic sidebands that cannot be identified with critical-point energies of TA, LA, TO or LO phonon modes are observed. A dynamic Jahn-Teller effect, involving coupling between a single-phonon mode and the electronic states of the 2E level, is proposed to account for the observed spectra.

Excited electronic states of the methyl radical. Ab initio molecular orbital study of geometries, excitation energies and vibronic spectra

NASA Astrophysics Data System (ADS)

Mebel, Alexander M.; Lin, Sheng-Hsien

1997-03-01

The geometries, vibrational frequencies and vertical and adiabatic excitation energies of the excited valence and Rydberg 3s, 3p, 3d, and 4s electronic states of CH 3 have been studied using ab initio molecular orbital multiconfigurational SCF (CASSCF), internally contracted multireference configuration interaction (MRCI) and equation-of-motion coupled cluster (EOM-CCSD) methods. The vibronic spectra are determined through the calculation of Franck-Condon factors. Close agreement between theory and experiment has been found for the excitation energies, vibrational frequencies and vibronic spectra. The adiabatic excitation energies of the Rydberg 3s B˜ 2A' 1 and 3p 2 2A″ 2 states are calculated to be 46435 and 60065 cm -1 compared to the experimental values of 46300 and 59972 cm -1, respectively. The valence 2A″ excited state of CH 3 has been found to have a pyramidal geometry within C s symmetry and to be adiabatically by 97 kcal/mol higher in energy than the ground state. The 2A″ state is predicted to be stable by 9 and 13 kcal/mol with respect to H 2 and H elimination.

Intensity enhancement and selective detection of proximate solvent molecules by molecular near-field effect in resonance hyper-Raman scattering

NASA Astrophysics Data System (ADS)

Shimada, Rintaro; Kano, Hideaki; Hamaguchi, Hiro-o.

2008-07-01

A new molecular phenomenon associated with resonance hyper-Raman (HR) scattering in solution has been discovered. Resonance HR spectra of all-trans-β-carotene and all-trans-lycopene in various solvents exhibited several extra bands that were not assignable to the solute but were unequivocally assigned to the solvents. Neat solvents did not show detectable HR signals under the same experimental conditions. Similar experiments with all-trans-retinal did not exhibit such enhancement either. All-trans-β-carotene and all-trans-lycopene have thus been shown to induce enhanced HR scattering of solvent molecules through a novel molecular effect that is not associated with all-trans-retinal. We call this new effect the "molecular near-field effect." In order to explain this newly found effect, an extended vibronic theory of resonance HR scattering is developed where the vibronic interaction including the proximate solvent molecule (intermolecular vibronic coupling) is explicitly introduced in the solute hyperpolarizability tensor. The potential of "molecular near-field HR spectroscopy," which selectively detects molecules existing in the close vicinity of a HR probe in complex chemical or biological systems, is discussed.

Vibronic Coupling Analysis of the Ligand-Centered Phosphorescence of Gas-Phase Gd(III) and Lu(III) 9-Oxophenalen-1-one Complexes.

PubMed

Chmela, Jiří; Greisch, Jean-François; Harding, Michael E; Klopper, Wim; Kappes, Manfred M; Schooss, Detlef

2018-03-08

The gas-phase laser-induced photoluminescence of cationic mononuclear gadolinium and lutetium complexes involving two 9-oxophenalen-1-one ligands is reported. Performing measurements at a temperature of 83 K enables us to resolve vibronic transitions. Via comparison to Franck-Condon computations, the main vibrational contributions to the ligand-centered phosphorescence are determined to involve rocking, wagging, and stretching of the 9-oxophenalen-1-one-lanthanoid coordination in the low-energy range, intraligand bending, and stretching in the medium- to high-energy range, rocking of the carbonyl and methine groups, and C-H stretching beyond. Whereas Franck-Condon calculations based on density-functional harmonic frequency computations reproduce the main features of the vibrationally resolved emission spectra, the absolute transition energies as determined by density functional theory are off by several thousand wavenumbers. This discrepancy is found to remain at higher computational levels. The relative energy of the Gd(III) and Lu(III) emission bands is only reproduced at the coupled-cluster singles and doubles level and beyond.

EPR/ENDOR and Theoretical Study of the Jahn-Teller-Active [HIPTN3N]MoVL Complexes (L = N-, NH).

PubMed

Sharma, Ajay; Roemelt, Michael; Reithofer, Michael; Schrock, Richard R; Hoffman, Brian M; Neese, Frank

2017-06-19

The molybdenum trisamidoamine (TAA) complex [Mo] {[3,5-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 3 NCH 2 CH 2 N]Mo} carries out catalytic reduction of N 2 to ammonia (NH 3 ) by protons and electrons at room temperature. A key intermediate in the proposed [Mo] nitrogen reduction cycle is nitridomolybdenum(VI), [Mo(VI)]N. The addition of [e - /H + ] to [Mo(VI)]N to generate [Mo(V)]NH might, in principle, follow one of three possible pathways: direct proton-coupled electron transfer; H + first and then e - ; e - and then H + . In this study, the paramagnetic Mo(V) intermediate {[Mo]N} - and the [Mo]NH transfer product were generated by irradiating the diamagnetic [Mo]N and {[Mo]NH} + Mo(VI) complexes, respectively, with γ-rays at 77 K, and their electronic and geometric structures were characterized by electron paramagnetic resonance and electron nuclear double resonance spectroscopies, combined with quantum-chemical computations. In combination with previous X-ray studies, this creates the rare situation in which each one of the four possible states of [e - /H + ] delivery has been characterized. Because of the degeneracy of the electronic ground states of both {[Mo(V)]N} - and [Mo(V)]NH, only multireference-based methods such as the complete active-space self-consistent field (CASSCF) and related methods provide a qualitatively correct description of the electronic ground state and vibronic coupling. The molecular g values of {[Mo]N} - and [Mo]NH exhibit large deviations from the free-electron value g e . Their actual values reflect the relative strengths of vibronic and spin-orbit coupling. In the course of the computational treatment, the utility and limitations of a formal two-state model that describes this competition between couplings are illustrated, and the implications of our results for the chemical reactivity of these states are discussed.

Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes.

PubMed

Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Weinstein, Julia A

2015-04-21

The Born-Oppenheimer approximation refers to the assumption that the nuclear and electronic wave functions describing a molecular system evolve and can be determined independently. It is now well-known that this approximation often breaks down and that nuclear-electronic (vibronic) coupling contributes greatly to the ultrafast photophysics and photochemistry observed in many systems ranging from simple molecules to biological organisms. In order to probe vibronic coupling in a time-dependent manner, one must use spectroscopic tools capable of correlating the motions of electrons and nuclei on an ultrafast time scale. Recent developments in nonlinear multidimensional electronic and vibrational spectroscopies allow monitoring both electronic and structural factors with unprecedented time and spatial resolution. In this Account, we present recent studies from our group that make use of different variants of frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy, a pulse sequence combining electronic and vibrational excitations in the form of a UV-visible pump, a narrowband (12 cm(-1)) IR pump, and a broadband (400 cm(-1)) IR probe. In the first example, T-2DIR is used to directly compare vibrational dynamics in the ground and relaxed electronic excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine) and Ru(4,4'-diethylester-2,2'-bipyridine)2(NCS)2, prototypical charge transfer complexes used in photocatalytic CO2 reduction and electron injection in dye-sensitized solar cells. The experiments show that intramolecular vibrational redistribution (IVR) and vibrational energy transfer (VET) are up to an order of magnitude faster in the triplet charge transfer excited state than in the ground state. These results show the influence of electronic arrangement on vibrational coupling patterns, with direct implications for vibronic coupling mechanisms in charge transfer excited states. In the second example, we show unambiguously that electronic and vibrational movement are coupled in a donor-bridge-acceptor complex based on a Pt(II) trans-acetylide design motif. Time-resolved IR (TRIR) spectroscopy reveals that the rate of electron transfer (ET) is highly dependent on the amount of excess energy localized on the bridge following electronic excitation. Using an adaptation of T-2DIR, we are able to selectively perturb bridge-localized vibrational modes during charge separation, resulting in the donor-acceptor charge separation pathway being completely switched off, with all excess energy redirected toward the formation of a long-lived intraligand triplet state. A series of control experiments reveal that this effect is mode specific: it is only when the high-frequency bridging C≡C stretching mode is pumped that radical changes in photoproduct yields are observed. These experiments therefore suggest that one may perturb electronic movement by stimulating structural motion along the reaction coordinate using IR light. These studies add to a growing body of evidence suggesting that controlling the pathways and efficiency of charge transfer may be achieved through synthetic and perturbative approaches aiming to modulate vibronic coupling. Achieving such control would represent a breakthrough for charge transfer-based applications such as solar energy conversion and molecular electronics.

Is back-electron transfer process in Betaine-30 coherent?

NASA Astrophysics Data System (ADS)

Rafiq, Shahnawaz; Scholes, Gregory D.

2017-09-01

The possible role of coherent vibrational motion in ultrafast photo-induced electron transfer remains unclear despite considerable experimental and theoretical advances. We revisited this problem by tracking the back-electron transfer (bET) process in Betaine-30 with broadband pump-probe spectroscopy. Dephasing time constant of certain high-frequency vibrations as a function of solvent shows a trend similar to the ET rates. In the purview of Bixon-Jortner model, high-frequency quantum vibrations bridge the reactant-product energy gap by providing activationless vibronic channels. Such interaction reduces the effective coupling significantly and thereby the coherence effects are eliminated due to energy gap fluctuations, making the back-electron transfer incoherent.

Vibronic dephasing model for coherent-to-incoherent crossover in DNA

NASA Astrophysics Data System (ADS)

Karasch, Patrick; Ryndyk, Dmitry A.; Frauenheim, Thomas

2018-05-01

In this paper, we investigate the interplay between coherent and incoherent charge transport in cytosine-guanine (GC-) rich DNA molecules. Our objective is to introduce a physically grounded approach to dephasing in large molecules and to understand the length-dependent charge transport characteristics, and especially the crossover from the coherent tunneling to incoherent hopping regime at different temperatures. Therefore, we apply the vibronic dephasing model and compare the results to the Büttiker probe model which is commonly used to describe decoherence effects in charge transport. Using the full ladder model and simplified one-dimensional model of DNA, we consider molecular junctions with alternating and stacked GC sequences and compare our results to recent experimental measurements.

Temperature-dependent conformations of exciton-coupled Cy3 dimers in double-stranded DNA

NASA Astrophysics Data System (ADS)

Kringle, Loni; Sawaya, Nicolas P. D.; Widom, Julia; Adams, Carson; Raymer, Michael G.; Aspuru-Guzik, Alán; Marcus, Andrew H.

2018-02-01

Understanding the properties of electronically interacting molecular chromophores, which involve internally coupled electronic-vibrational motions, is important to the spectroscopy of many biologically relevant systems. Here we apply linear absorption, circular dichroism, and two-dimensional fluorescence spectroscopy to study the polarized collective excitations of excitonically coupled cyanine dimers (Cy3)2 that are rigidly positioned within the opposing sugar-phosphate backbones of the double-stranded region of a double-stranded (ds)-single-stranded (ss) DNA fork construct. We show that the exciton-coupling strength of the (Cy3)2-DNA construct can be systematically varied with temperature below the ds-ss DNA denaturation transition. We interpret spectroscopic measurements in terms of the Holstein vibronic dimer model, from which we obtain information about the local conformation of the (Cy3)2 dimer, as well as the degree of static disorder experienced by the Cy3 monomer and the (Cy3)2 dimer probe locally within their respective DNA duplex environments. The properties of the (Cy3)2-DNA construct we determine suggest that it may be employed as a useful model system to test fundamental concepts of protein-DNA interactions and the role of electronic-vibrational coherence in electronic energy migration within exciton-coupled bio-molecular arrays.

Direct observation of slow intersystem crossing in an aromatic ketone, fluorenone.

PubMed

Soep, Benoît; Mestdagh, Jean-Michel; Briant, Marc; Gaveau, Marc-André; Poisson, Lionel

2016-08-17

Direct measurements of Single vibronic Level InterSystem Crossing (SLISC) have been performed on the fluorenone molecule in the gas phase, by time resolved photoelectron and photoion spectroscopy. Vibronic transitions above the S1 nπ* origin were excited in the 432-420 nm region and the decay of S1 and growth of T1(3)ππ* could be observed within a 10 ns time domain. The ionization potential is measured as 8.33 ± 0.04 eV. The energy of the first excited triplet state of fluorenone, T1 has been characterized directly at 18 640 ± 250 cm(-1). The internal conversion of S1 to S0 is found to amount to ∼15% of the population decay, thus ISC is the dominant electronic relaxation process. ISC, although favored by the S1(1)nπ*-T1(3)ππ* coupling scheme, is 3 orders of magnitude less efficient than in the similar molecule benzophenone. Thus, the planarity of the fluorenone molecule disfavors the exploration of the configuration space where surface crossings would create high ISC probability, which occurs in benzophenone through surface crossings. The time evolution of S1 fluorenone is well accounted for by the statistical decay of individual levels into a quasi-continuum of T1 vibronic levels.

Vibronic effects in the 1.4-eV optical center in diamond

NASA Astrophysics Data System (ADS)

Iakoubovskii, Konstantin; Davies, Gordon

2004-12-01

We report optical absorption and luminescence measurements on the 1.4-eV center in diamond. We show that the zero-phonon lines have a temperature-dependent Ni-isotope shift, that the isotopic shifts induced by carbon and nickel are opposite in sign, and that a local vibronic mode is present in the absorption spectrum but not in luminescence. The microscopic properties of the center are successfully analyzed with the Ludwig-Woodbury theory (LWT), revealing that the Ni+ ion in the 1.4-eV center only weakly interacts with the diamond lattice. The importance of vibronic effects in the LWT analysis is experimentally demonstrated. It is believed that similar effects can account for the discrepancies previously encountered in modeling other 3d9 impurities in semiconductors.

Long-lived coherence in carotenoids

NASA Astrophysics Data System (ADS)

Davis, J. A.; Cannon, E.; Van Dao, L.; Hannaford, P.; Quiney, H. M.; Nugent, K. A.

2010-08-01

We use two-colour vibronic coherence spectroscopy to observe long-lived vibrational coherences in the ground electronic state of carotenoid molecules, with decoherence times in excess of 1 ps. Lycopene and spheroidene were studied isolated in solution, and within the LH2 light-harvesting complex extracted from purple bacteria. The vibrational coherence time is shown to increase significantly for the carotenoid in the complex, providing further support to previous assertions that long-lived electronic coherences in light-harvesting complexes are facilitated by in-phase motion of the chromophores and surrounding proteins. Using this technique, we are also able to follow the evolution of excited state coherences and find that for carotenoids in the light-harvesting complex the langS2|S0rang superposition remains coherent for more than 70 fs. In addition to the implications of this long electronic decoherence time, the extended coherence allows us to observe the evolution of the excited state wavepacket. These experiments reveal an enhancement of the vibronic coupling to the first vibrational level of the C-C stretching mode and/or methyl-rocking mode in the ground electronic state 70 fs after the initial excitation. These observations open the door to future experiments and modelling that may be able to resolve the relaxation dynamics of carotenoids in solution and in natural light-harvesting systems.

The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine.

PubMed

Trachsel, Maria A; Wiedmer, Timo; Blaser, Susan; Frey, Hans-Martin; Li, Quansong; Ruiz-Barragan, Sergi; Blancafort, Lluís; Leutwyler, Samuel

2016-10-07

We have investigated the S 0 → S 1 UV vibronic spectrum and time-resolved S 1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm -1 about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon 1 ππ ∗ excitation predicted by the calculations. The methyl torsion and ν 1 ' (butterfly) vibrations are strongly coupled, in the S 1 state. The S 0 → S 1 vibronic spectrum breaks off at a vibrational excess energy E exc ∼ 500 cm -1 , indicating that a barrier in front of the ethylene-type S 1 ⇝S 0 conical intersection is exceeded, which is calculated to lie at E exc = 366 cm -1 . The S 1 ⇝S 0 internal conversion rate constant increases from k IC = 2 ⋅ 10 9 s -1 near the S 1 (v = 0) level to 1 ⋅ 10 11 s -1 at E exc = 516 cm -1 . The 1 ππ ∗ state of 1MCyt also relaxes into the lower-lying triplet T 1 ( 3 ππ ∗ ) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm -1 . The ISC rate constant is 10-100 times lower than k IC ; it increases from k ISC = 2 ⋅ 10 8 s -1 near S 1 (v = 0) to k ISC = 2 ⋅ 10 9 s -1 at E exc = 516 cm -1 . The T 1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm -1 . The T 2 ( 3 nπ ∗ ) state lies >1500 cm -1 above S 1 (v = 0), so S 1 ⇝T 2 ISC cannot occur, despite the large SOC parameter of 10.6 cm -1 . An upper limit to the adiabatic ionization energy of 1MCyt is determined as 8.41 ± 0.02 eV. Compared to cytosine, methyl substitution at N1 lowers the adiabatic ionization energy by ≥0.32 eV and leads to a much higher density of vibronic bands in the S 0 → S 1 spectrum. The effect of methylation on the radiationless decay to S 0 and ISC to T 1 is small, as shown by the similar break-off of the spectrum and the similar computed mechanisms.

The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

NASA Astrophysics Data System (ADS)

Trachsel, Maria A.; Wiedmer, Timo; Blaser, Susan; Frey, Hans-Martin; Li, Quansong; Ruiz-Barragan, Sergi; Blancafort, Lluís; Leutwyler, Samuel

2016-10-01

We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm-1 about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion and ν1 ' (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ˜ 500 cm-1, indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm-1. The S1⇝S0 internal conversion rate constant increases from kIC = 2 ṡ 109 s-1 near the S1(v = 0) level to 1 ṡ 1011 s-1 at Eexc = 516 cm-1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm-1. The ISC rate constant is 10-100 times lower than kIC; it increases from kISC = 2 ṡ 108 s-1 near S1(v = 0) to kISC = 2 ṡ 109 s-1 at Eexc = 516 cm-1. The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm-1. The T2 (3nπ∗) state lies >1500 cm-1 above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm-1. An upper limit to the adiabatic ionization energy of 1MCyt is determined as 8.41 ± 0.02 eV. Compared to cytosine, methyl substitution at N1 lowers the adiabatic ionization energy by ≥0.32 eV and leads to a much higher density of vibronic bands in the S0 → S1 spectrum. The effect of methylation on the radiationless decay to S0 and ISC to T1 is small, as shown by the similar break-off of the spectrum and the similar computed mechanisms.

Proton-Coupled Electron Transfer in a Strongly Coupled Photosystem II-Inspired Chromophore–Imidazole–Phenol Complex: Stepwise Oxidation and Concerted Reduction

DOE PAGES

Manbeck, Gerald F.; Fujita, Etsuko; Concepcion, Javier J.

2016-08-18

Proton-coupled electron-transfer (PCET) reactions were studied in acetonitrile for a Photosystem II (PSII) inspired [Ru(bpy) 2(phen-imidazole-Ph(OH)( tBu) 2)] 2+, in which Ru(III) generated by a flash-quench sequence oxidizes the appended phenol and the proton is transferred to the hydrogen bonded imidazole base. In contrast to related systems, the donor and acceptor are strongly coupled, as indicated by the shift in the Ru III/IIcouple upon phenol oxidation, and intramolecular oxidation of the phenol by Ru(III) is energetically favorable by both stepwise or concerted pathways. The phenol oxidation occurs via a stepwise ET-PT mechanism with k ET = 2.7 × 10 7more » s ₋1 and a kinetic isotope effect (KIE) of 0.99 ± 0.03. The electron transfer reaction was characterized as adiabatic with λ DA = 1.16 eV and 280 < H DA < 540 cm ₋1 consistent with strong electronic coupling and slow solvent dynamics. Reduction of the phenoxyl radical by the quencher radical was examined as the analogue of the redox reaction between the PSII tyrosyl radical and the oxygen evolving complex (OEC). In our PSII-inspired complex, the recombination reaction activation energy is < 2 kcal mol ₋1. In conclusion, the reaction is nonadiabatic (V PCET ~ 22 cm ₋1 (H) and 49 cm ₋1 (D)), concerted, and exhibits an unexpected inverse KIE of 0.55 that is attributed to greater overlap of the reactant vibronic ground state with the OD vibronic states of the proton acceptor due to the smaller quantum spacing of the deuterium vibrational levels.« less

Dissociation kinetics of metal clusters on multiple electronic states including electronic level statistics into the vibronic soup

NASA Astrophysics Data System (ADS)

Shvartsburg, Alexandre A.; Siu, K. W. Michael

2001-06-01

Modeling the delayed dissociation of clusters had been over the last decade a frontline development area in chemical physics. It is of fundamental interest how statistical kinetics methods previously validated for regular molecules and atomic nuclei may apply to clusters, as this would help to understand the transferability of statistical models for disintegration of complex systems across various classes of physical objects. From a practical perspective, accurate simulation of unimolecular decomposition is critical for the extraction of true thermochemical values from measurements on the decay of energized clusters. Metal clusters are particularly challenging because of the multitude of low-lying electronic states that are coupled to vibrations. This has previously been accounted for assuming the average electronic structure of a conducting cluster approximated by the levels of electron in a cavity. While this provides a reasonable time-averaged description, it ignores the distribution of instantaneous electronic structures in a "boiling" cluster around that average. Here we set up a new treatment that incorporates the statistical distribution of electronic levels around the average picture using random matrix theory. This approach faithfully reflects the completely chaotic "vibronic soup" nature of hot metal clusters. We found that the consideration of electronic level statistics significantly promotes electronic excitation and thus increases the magnitude of its effect. As this excitation always depresses the decay rates, the inclusion of level statistics results in slower dissociation of metal clusters.

Iron monocyanide (FeCN): Spin-orbit and vibronic interactions in low-lying electronic states

NASA Astrophysics Data System (ADS)

Jerosimić, Stanka V.; Milovanović, Milan Z.

2018-04-01

The spin-orbit eigenvalues of low-energy quartet and sextet spatially degenerate electronic states of FeCN are reported, together with the combined effect of vibronic and spin-orbit interaction in the lowest-lying 14Δ and 16Δ states of FeCN, by using perturbational and variational method. Spin-orbit constants (ASO) have been calculated in the basis of: (a) two components of each degenerate state, (b) four components of 14Δ and 14Π (16Δ and 16Π) states, and (c) ten components of 16Δ, 16Π, 16Σ+, 14Δ, 14Π, and 14Σ+ states. The present calculations predict the values of ASO= -77 cm-1 for 16Δ and ASO= -108 cm-1 for 14Δ state in the lowest-energy spin-orbit manifolds of each state. The major perturbing state for the 14Δ state is the 14Π state (16Π for the sextet 16Δ). As expected, based on extremely small splitting and shallowness of the bending potential energy curves for the lowest-lying 4,6Δ states, the present study indicate that the vibronic coupling does not create significant splitting of the bending levels, but the influence of anharmonicity in the bending mode is more pronounced. However, the spin-orbit fine structure dominantly influences the spectra of this species.

Computational Spectroscopy of Polycyclic Aromatic Hydrocarbons In Support of Laboratory Astrophysics

NASA Technical Reports Server (NTRS)

Tan, Xiaofeng; Salama, Farid

2006-01-01

Polycyclic aromatic hydrocarbons (PAHs) are strong candidates for the molecular carriers of the unidentified infrared bands (UIR) and the diffuse interstellar bands (DIBs). In order to test the PAH hypothesis, we have systematically measured the vibronic spectra of a number of jet-cooled neutral and ionized PAHs in the near ultraviolet (UV) to visible spectral ranges using the cavity ring-down spectroscopy. To support this experimental effort, we have carried out theoretical studies of the spectra obtained in our measurements. Ab initio and (time-dependent) density.functiona1 theory calculations are performed to obtain the geometries, energetics, vibrational frequencies, transition dipole moments, and normal coordinates of these PAH molecules. Franck-Condon (FC) calculations and/or vibronic calculations are then performed using the calculated normal coordinates and vibrational frequencies to simulate the vibronic spectra. It is found that vibronic interactions in these conjugated pi electron systems are often strong enough to cause significant deviations from the Born-Oppenheimer (BO) approximation. For vibronic transitions that are well described by the BO approximation, the vibronic band profiles are simulated by calculating the rotational structure of the vibronic transitions. Vibronic oscillator strength factors are calculated in the frame of the FC approximation from the electronic transition dipole moments and the FC factors. This computational effort together with our experimental measurements provides, for the first time, powerful tools for comparison with space-based data and, hence, a powerful approach to understand the spectroscopy of interstellar PAH analogs and the nature of the UIR and DIBs.

The Phenalenyl Free Radical - a Jahn-Teller D3H PAH

NASA Astrophysics Data System (ADS)

O'Connor, G. D.; Troy, T. P.; Roberts, D. A.; Chalyavi, N.; Fückel, B.; Crossley, M. J.; Nauta, K.; Schmidt, T. W.; Stanton, J. F.

2012-06-01

After benzene and naphthalene, the smallest polycyclic aromatic hydrocarbon bearing six-membered rings is the threefold-symmetric phenalenyl radical. Despite the fact that it is so fundamental, its electronic spectroscopy has not been rigorously scrutinized, in spite of growing interest in graphene fragments for molecular electronic applications. Here we used complementary laser spectroscopic techniques to probe the jet-cooled phenalenyl radical in vacuo. Its spectrum reveals the interplay between four electronic states that exhibit Jahn-Teller and pseudo-Jahn-Teller (Herzberg-Teller) vibronic coupling. The coupling mechanism has been elucidated by the application of various ab initio quantum-chemical techniques.

Two orders of magnitude reduction in silicon membrane thermal conductivity by resonance hybridizations

NASA Astrophysics Data System (ADS)

Honarvar, Hossein; Hussein, Mahmoud I.

2018-05-01

The thermal conductivity of a freestanding single-crystal silicon membrane may be reduced significantly by attaching nanoscale pillars on one or both surfaces. Atomic resonances of the nanopillars form vibrons that intrinsically couple with the base membrane phonons causing mode hybridization and flattening at each coupling location in the phonon band structure. This in turn causes group velocity reductions of existing phonons, in addition to introducing new modes that get excited but are localized and do not transport energy. The nanopillars also reduce the phonon lifetimes at and around the hybridization zones. These three effects, which in principle may be tuned to take place across silicon's full spectrum, lead to a lowering of the in-plane thermal conductivity in the base membrane. Using equilibrium molecular dynamics simulations, and utilizing the concept of vibrons compensation, we report a staggering two orders of magnitude reduction in the thermal conductivity at room temperature by this mechanism. Specifically, a reduction of a factor of 130 is demonstrated for a roughly 10-nm-thick pillared membrane compared to a corresponding unpillared membrane. This amounts to a record reduction of a factor of 481 compared to bulk crystalline silicon and nearly a factor of 2 compared to bulk amorphous silicon. These results are obtained while providing a path for preserving performance with upscaling.

Towards a global model of spin-orbit coupling in the halocarbenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nyambo, Silver; Karshenas, Cyrus; Reid, Scott A., E-mail: scott.reid@marquette.edu, E-mail: dawesr@mst.edu

We report a global analysis of spin-orbit coupling in the mono-halocarbenes, CH(D)X, where X = Cl, Br, and I. These are model systems for examining carbene singlet-triplet energy gaps and spin-orbit coupling. Over the past decade, rich data sets collected using single vibronic level emission spectroscopy and stimulated emission pumping spectroscopy have yielded much information on the ground vibrational level structure and clearly demonstrated the presence of perturbations involving the low-lying triplet state. To model these interactions globally, we compare two approaches. First, we employ a diabatic treatment of the spin-orbit coupling, where the coupling matrix elements are written inmore » terms of a purely electronic spin-orbit matrix element which is independent of nuclear coordinates, and an integral representing the overlap of the singlet and triplet vibrational wavefunctions. In this way, the structures, harmonic frequencies, and normal mode displacements from ab initio calculations were used to calculate the vibrational overlaps of the singlet and triplet state levels, including the full effects of Duschinsky mixing. These calculations have allowed many new assignments to be made, particularly for CHI, and provided spin-orbit coupling parameters and values for the singlet-triplet gaps. In a second approach, we have computed and fit full geometry dependent spin-orbit coupling surfaces and used them to compute matrix elements without the product form approximation. Those matrix elements were used in similar fits varying the anharmonic constants and singlet-triplet gap to reproduce the experimental levels. The derived spin-orbit parameters for carbenes CHX (X = Cl, Br, and I) show an excellent linear correlation with the atomic spin-orbit constant of the corresponding halogen, indicating that the spin-orbit coupling in the carbenes is consistently around 14% of the atomic value.« less

Origin of long-lived oscillations in 2D-spectra of a quantum vibronic model: Electronic versus vibrational coherence

NASA Astrophysics Data System (ADS)

Plenio, M. B.; Almeida, J.; Huelga, S. F.

2013-12-01

We demonstrate that the coupling of excitonic and vibrational motion in biological complexes can provide mechanisms to explain the long-lived oscillations that have been obtained in nonlinear spectroscopic signals of different photosynthetic pigment protein complexes and we discuss the contributions of excitonic versus purely vibrational components to these oscillatory features. Considering a dimer model coupled to a structured spectral density we exemplify the fundamental aspects of the electron-phonon dynamics, and by analyzing separately the different contributions to the nonlinear signal, we show that for realistic parameter regimes purely electronic coherence is of the same order as purely vibrational coherence in the electronic ground state. Moreover, we demonstrate how the latter relies upon the excitonic interaction to manifest. These results link recently proposed microscopic, non-equilibrium mechanisms to support long lived coherence at ambient temperatures with actual experimental observations of oscillatory behaviour using 2D photon echo techniques to corroborate the fundamental importance of the interplay of electronic and vibrational degrees of freedom in the dynamics of light harvesting aggregates.

Molecular electronics: some views on transport junctions and beyond.

PubMed

Joachim, Christian; Ratner, Mark A

2005-06-21

The field of molecular electronics comprises a fundamental set of issues concerning the electronic response of molecules as parts of a mesoscopic structure and a technology-facing area of science. We will overview some important aspects of these subfields. The most advanced ideas in the field involve the use of molecules as individual logic or memory units and are broadly based on using the quantum state space of the molecule. Current work in molecular electronics usually addresses molecular junction transport, where the molecule acts as a barrier for incoming electrons: This is the fundamental Landauer idea of "conduction as scattering" generalized to molecular junction structures. Another point of view in terms of superexchange as a guiding mechanism for coherent electron transfer through the molecular bridge is discussed. Molecules generally exhibit relatively strong vibronic coupling. The last section of this overview focuses on vibronic effects, including inelastic electron tunneling spectroscopy, hysteresis in junction charge transport, and negative differential resistance in molecular transport junctions.

Molecular electronics: Some views on transport junctions and beyond

PubMed Central

Joachim, Christian; Ratner, Mark A.

2005-01-01

The field of molecular electronics comprises a fundamental set of issues concerning the electronic response of molecules as parts of a mesoscopic structure and a technology-facing area of science. We will overview some important aspects of these subfields. The most advanced ideas in the field involve the use of molecules as individual logic or memory units and are broadly based on using the quantum state space of the molecule. Current work in molecular electronics usually addresses molecular junction transport, where the molecule acts as a barrier for incoming electrons: This is the fundamental Landauer idea of “conduction as scattering” generalized to molecular junction structures. Another point of view in terms of superexchange as a guiding mechanism for coherent electron transfer through the molecular bridge is discussed. Molecules generally exhibit relatively strong vibronic coupling. The last section of this overview focuses on vibronic effects, including inelastic electron tunneling spectroscopy, hysteresis in junction charge transport, and negative differential resistance in molecular transport junctions. PMID:15956192

Jet-Cooled Laser-Induced Fluorescence Spectroscopy of T-Butoxy

NASA Astrophysics Data System (ADS)

Reilly, Neil J.; Cheng, Lan; Stanton, John F.; Miller, Terry A.; Liu, Jinjun

2015-06-01

The vibrational structures of the tilde A ^2A_1 and tilde X ^2E states of t-butoxy were obtained in jet-cooled laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectroscopic measurements. The observed transitions are assigned based on vibrational frequencies calculated using Complete Active Space Self-Consistent Field (CASSCF) method and the predicted Franck-Condon factors. The spin-orbit (SO) splitting was measured to be 35(5) cm-1 for the lowest vibrational level of the ground (tilde X ^2E) state and increases with increasing vibrational quantum number of the CO stretch mode. Vibronic analysis of the DF spectra suggests that Jahn-Teller (JT)-active modes of the ground-state t-butoxy radical are similar to those of methoxy and would be the same if methyl groups were replaced by hydrogen atoms. Coupled-cluster calculations show that electron delocalization, introduced by the substitution of hydrogens with methyl groups, reduces the electronic contribution of the SO splittings by only around ten percent, and a calculation on the vibronic levels based on quasidiabatic model Hamiltonian clearly attributes the relatively small SO splitting of the tilde X ^2E state of t-butoxy mainly to stronger reduction of orbital angular momentum by the JT-active modes when compared to methoxy. The rotational and fine structure of the LIF transition to the first CO stretch overtone level of the tilde A^2A_1 state has been simulated using a spectroscopic model first proposed for methoxy, yielding an accurate determination of the rotational constants of both tilde A and tilde X states.

Widely tunable 1.94-μm Tm:BaY2F8 laser

NASA Astrophysics Data System (ADS)

Galzerano, Gianluca; Cornacchia, Francesco; Parisi, Daniela; Toncelli, Alessandra; Tonelli, Mauro; Laporta, Paolo

2005-04-01

A novel BaY2F8 crystal doped with thulium ions is grown and extensively investigated. Owing to the large number of vibronic levels and to a favorable electron-phonon coupling, extremely wide absorption and emission bands around 1.9 μm are observed. A room-temperature Tm:BaY2F8 laser tunable over a 210-nm interval, from 1849 to 2059 nm, is demonstrated.

The best of both Reps—Diabatized Gaussians on adiabatic surfaces

NASA Astrophysics Data System (ADS)

Meek, Garrett A.; Levine, Benjamin G.

2016-11-01

When simulating nonadiabatic molecular dynamics, choosing an electronic representation requires consideration of well-known trade-offs. The uniqueness and spatially local couplings of the adiabatic representation come at the expense of an electronic wave function that changes discontinuously with nuclear motion and associated singularities in the nonadiabatic coupling matrix elements. The quasi-diabatic representation offers a smoothly varying wave function and finite couplings, but identification of a globally well-behaved quasi-diabatic representation is a system-specific challenge. In this work, we introduce the diabatized Gaussians on adiabatic surfaces (DGAS) approximation, a variant of the ab initio multiple spawning (AIMS) method that preserves the advantages of both electronic representations while avoiding their respective pitfalls. The DGAS wave function is expanded in a basis of vibronic functions that are continuous in both electronic and nuclear coordinates, but potentially discontinuous in time. Because the time-dependent Schrödinger equation contains only first-order derivatives with respect to time, singularities in the second-derivative nonadiabatic coupling terms (i.e., diagonal Born-Oppenheimer correction; DBOC) at conical intersections are rigorously absent, though singular time-derivative couplings remain. Interpolation of the electronic wave function allows the accurate prediction of population transfer probabilities even in the presence of the remaining singularities. We compare DGAS calculations of the dynamics of photoexcited ethene to AIMS calculations performed in the adiabatic representation, including the DBOC. The 28 fs excited state lifetime observed in DGAS simulations is considerably shorter than the 50 fs lifetime observed in the adiabatic simulations. The slower decay in the adiabatic representation is attributable to the large, repulsive DBOC in the neighborhood of conical intersections. These repulsive DBOC terms are artifacts of the discontinuities in the individual adiabatic vibronic basis functions and therefore cannot reflect the behavior of the exact molecular wave function, which must be continuous.

Nonadiabatic quantum dynamics and laser control of Br2 in solid argon.

PubMed

Accardi, A; Borowski, A; Kühn, O

2009-07-02

A five-dimensional reaction surface-vibronic coupling model is introduced to describe the B- to C-state predissociation dynamics of Br(2) occupying a double substitutional lattice site in a face-centered cubic argon crystal at low temperatures. The quantum dynamics driven by a Franck-Condon vertical excitation is investigated, revealing the role of matrix cage compression for efficient nonadiabatic transitions. Vibrational preexcitation of the Br(2) bond in the electronic ground state can be used to access a different regime of predissociation which does not require substantial matrix compression because the Franck-Condon window shifts into the energetic range of the B-C level crossing. Using optimal control theory, it is shown how vibrational preexcitation can be achieved via a pump-dump-type mechanism involving the repulsive C state.

LO-TO splittings, effective charges and interactions in electro-optic meta-nitroaniline crystal as studied by polarized IR reflection and transmission spectra

NASA Astrophysics Data System (ADS)

Szostak, M. M.; Le Calvé, N.; Romain, F.; Pasquier, B.

1994-10-01

The polarized IR reflection spectra of the meta-nitroaniline ( m-NA) single crystal along the a, b and c crystallographic axes as well as the b and c polarized transmission spectra have been measured in the 100-400 cm -1 region. The LO-TO splitting values have been calculated from the reflection spectra by fitting them with the four parameter dielectric function. The dipole moment derivatives, relevant to dynamic effective charges, of the vibrations have also been calculated and used to check the applicability of the oriented gas model (OGM) to reflection spectra. The discrepancies from the OGM have been discussed in terms of vibronic couplings, weak hydrogen bondings (HB) and intramolecular charge transfer.

Vibron Solitons and Soliton-Induced Infrared Spectra of Crystalline Acetanilide

NASA Astrophysics Data System (ADS)

Takeno, S.

1986-01-01

Red-shifted infrared spectra at low temperatures of amide I (C=O stretching) vibrations of crystalline acetanilide measured by Careri et al. are shown to be due to vibron solitons, which are nonlinearity-induced localized modes of vibrons arising from their nonlinear interactions with optic-type phonons. A nonlinear eigenvalue equation giving the eigenfrequency of stationary solitons is solved approximately by introducing lattice Green's functions, and the obtained result is in good agreement with the experimental result. Inclusion of interactions with acoustic phonons yields the Debye-Waller factor in the zero-phonon line spectrum of vibron solitons, in a manner analogous to the case of impurity-induced localized harmonic phonon modes in alkali halides.

An experimental and theoretical study of the A˜ 2A″Π -X˜ 2A' band system of the jet-cooled HBBr/DBBr free radical

NASA Astrophysics Data System (ADS)

Gharaibeh, Mohammed; Clouthier, Dennis J.; Tarroni, Riccardo

2016-06-01

The electronic spectra of the HBBr and DBBr free radicals have been studied in depth. These species were prepared in a pulsed electric discharge jet using a precursor mixture of BBr3 vapor and H2 or D2 in high pressure argon. Transitions to the electronic excited state of the jet-cooled radicals were probed with laser-induced fluorescence and the ground state energy levels were measured from the single vibronic level emission spectra. HBBr has an extensive band system in the red which involves a linear-bent transition between the two Renner-Teller components of what would be a 2Π state at linearity. We have used high level ab initio theory to calculate potential energy surfaces for the bent 2A' ground state and the linear A˜ 2A″Π excited state and we have determined the ro-vibronic energy levels variationally, including spin orbit effects. The correspondence between the computed and experimentally observed transition frequencies, upper state level symmetries, and H and B isotope shifts was used to make reliable assignments. We have shown that the ground state barriers to linearity, which range from 10 000 cm-1 in HBF to 2700 cm-1 in BH2, are inversely related to the energy of the first excited 2Σ (2A') electronic state. This suggests that a vibronic coupling mechanism is responsible for the nonlinear equilibrium geometries of the ground states of the HBX free radicals.

Tuning of quantum entanglement in molecular quantum cellular automata based on mixed-valence tetrameric units.

PubMed

Palii, Andrew; Tsukerblat, Boris

2016-10-25

In this article we consider two coupled tetrameric mixed-valence (MV) units accommodating electron pairs, which play the role of cells in molecular quantum cellular automata. It is supposed that the Coulombic interaction between instantly localized electrons within the cell markedly inhibits the transfer processes between the redox centers. Under this condition, as well as due to the vibronic localization of the electron pair, the cell can encode binary information, which is controlled by neighboring cells. We show that under certain conditions the two low-lying vibronic spin levels of the cell (ground and first excited states) can be regarded as originating from an effective spin-spin interaction. This is shown to depend on the internal parameters of the cell as well as on the induced polarization. Within this simplified two-level picture we evaluate the quantum entanglement in the system represented by the two electrons in the cell and show how the entanglement within the cell and concurrence can be controlled via polarization of the neighboring cells and temperature.

Spectroscopy Identification of Benzyl-Type Radicals Generated by Corona Discharge of Precursors of Mixed Substituents

NASA Astrophysics Data System (ADS)

Yoon, Young Wook; Huh, Chang Soon; Lee, Sang Kuk

2012-06-01

We generated vibronically excited but jet-cooled benzyl-type radicals from corona discharge of precursor of mixed substituents using a technique of corona excited supersonic expansion coupled with a pinhole-type glass nozzle, from which the visible vibronic emission spectra were recorded with a long-path monochromator. The spectra exhibit the intensity variation of each species with discharging voltage, indicating the radical species generated in corona discharge is highly sensitive to excitation. From the analysis of the spectra, we found the Cl substituent is replaced in preference to the F substituent by the hydrogen atoms liberated from the dissociation of the C-H bond of the methyl group of the precursor, from which we proposed the possible mechanism for the elimination reaction of substituent in terms of the bond dissociation energy. Additionally, we obtained an accurate electronic energy in the D_1 → D_0 transition and the vibrational mode frequencies of newly detected benzyl-type radicals in the ground electronic state by comparison with those of ab initio calculations and the known spectroscopic data of precursors for the first time.

Luminescence of the (O2(a(1)Δ(g)))2 collisional complex in the temperature range of 90-315 K: Experiment and theory.

PubMed

Zagidullin, M V; Pershin, A A; Azyazov, V N; Mebel, A M

2015-12-28

Experimental and theoretical studies of collision induced emission of singlet oxygen molecules O2(a(1)Δg) in the visible range have been performed. The rate constants, half-widths, and position of peaks for the emission bands of the (O2(a(1)Δg))2 collisional complex centered around 634 nm (2) and 703 nm (3) have been measured in the temperature range of 90-315 K using a flow-tube apparatus that utilized a gas-liquid chemical singlet oxygen generator. The absolute values of the spontaneous emission rate constants k2 and k3 are found to be similar, with the k3/k2 ratio monotonically decreasing from 1.1 at 300 K to 0.96 at 90 K. k2 slowly decreases with decreasing temperature but a sharp increase in its values is measured below 100 K. The experimental results were rationalized in terms of ab initio calculations of the ground and excited potential energy and transition dipole moment surfaces of singlet electronic states of the (O2)2 dimole, which were utilized to compute rate constants k2 and k3 within a statistical model. The best theoretical results reproduced experimental rate constants with the accuracy of under 40% and correctly described the observed temperature dependence. The main contribution to emission process (2), which does not involve vibrational excitation of O2 molecules at the ground electronic level, comes from the spin- and symmetry-allowed 1(1)Ag←(1)B3u transition in the rectangular H configuration of the dimole. Alternatively, emission process (3), in which one of the monomers becomes vibrationally excited in the ground electronic state, is found to be predominantly due to the vibronically allowed 1(1)Ag←2(1)Ag transition induced by the asymmetric O-O stretch vibration in the collisional complex. The strong vibronic coupling between nearly degenerate excited singlet states of the dimole makes the intensities of vibronically and symmetry-allowed transitions comparable and hence the rate constants k2 and k3 close to one another.

Non-Condon nonequilibrium Fermi’s golden rule rates from the linearized semiclassical method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xiang; Geva, Eitan

2016-08-14

The nonequilibrium Fermi’s golden rule describes the transition between a photoexcited bright donor electronic state and a dark acceptor electronic state, when the nuclear degrees of freedom start out in a nonequilibrium state. In a previous paper [X. Sun and E. Geva, J. Chem. Theory Comput. 12, 2926 (2016)], we proposed a new expression for the nonequilibrium Fermi’s golden rule within the framework of the linearized semiclassical approximation and based on the Condon approximation, according to which the electronic coupling between donor and acceptor is assumed constant. In this paper we propose a more general expression, which is applicable tomore » the case of non-Condon electronic coupling. We test the accuracy of the new non-Condon nonequilibrium Fermi’s golden rule linearized semiclassical expression on a model where the donor and acceptor potential energy surfaces are parabolic and identical except for shifts in the equilibrium energy and geometry, and the coupling between them is linear in the nuclear coordinates. Since non-Condon effects may or may not give rise to conical intersections, both possibilities are examined by considering the following: (1) A modified Garg-Onuchic-Ambegaokar model for charge transfer in the condensed phase, where the donor-acceptor coupling is linear in the primary-mode coordinate, and for which non-Condon effects do not give rise to a conical intersection; (2) the linear vibronic coupling model for electronic transitions in gas phase molecules, where non-Condon effects give rise to conical intersections. We also present a comprehensive comparison between the linearized semiclassical expression and a progression of more approximate expressions, in both normal and inverted regions, and over a wide range of initial nonequilibrium states, temperatures, and frictions.« less

Vibronic transitions of trivalent Er and Ce in BaY2F8 single crystals

NASA Astrophysics Data System (ADS)

Baraldi, A.; Capelletti, R.; Mazzera, M.; Ponzoni, A.; Sani, E.; Tonelli, M.

2003-01-01

High resolution (0.02 cm(-1)) Fourier transform spectroscopy was applied in the 9-300 K and 100-24,000 cm(-1) ranges, respectively, to detect in Er3+ and Ce3+ doped Bay(2)F(8) single crystals (1) the narrow line spectra due to the intraconfigurational 4f-->4f transitions of the rare earths (RE) and (2) the possible vibronic tails accompanying the zero-phonon lines. The F-2(5/2) --> F-2(7/2) transition was monitored for the Ce3+-doping and the crystal field splitting of the initial and final manifold was determined. Weak vibronic spectra accompanying six among the nine investigated 4f-->4f transitions of Er3+ and the F-2(5/2) --> F-2(7/2) transition of Ce3+ were detected. The vibronic spectra amplitude was found to scale with the RE contents. On the basis of the IR- and Raman-active vibrational modes, either measured or quoted in the literature, most of the vibronic lines could be successfully assigned to the lattice modes. Violations of the selection rules were envisaged and discussed.

Effect of friction on electron transfer: The two reaction coordinate case

NASA Astrophysics Data System (ADS)

Onuchic, José Nelson

1987-04-01

Electron transfer is a very important reaction in many biological processes such as photosynthesis and oxidative phosphorylation. In many of these reactions, most of the interesting dynamics can be included by using two reaction coordinates: one fast (local high frequency vibration modes) and one slow (outersphere modes such as solvent polarization). We report a model to describe this problem, which uses path integral techniques to calculate electron transfer rates, and also to obtain the Fokker-Planck equations associated with this model. Different limiting cases lead to qualitatively different results such as exponential or nonexponential time decay for the donor survival probability. Conditions for the validity of the adiabatic or the nonadiabatic limits will be discussed. Application of this model to real systems is proposed, in particular for a porphyrin rigidly linked to a quinone, which is a very interesting model compound for primary events of photosynthesis. This model can also be used for other multicoordinate biological reactions such as ligand binding to heme proteins. Also, in the concluding part of Sec. III, we discuss the important limit where the fast vibronic mode is much faster than all the other nuclear modes coupled to the problem. In this limit the fast mode ``renormalizes'' the electronic matrix element, and this considerably simplifies the treatment of the problem, reducing it to coupling only to the slow modes.

Non-Condon equilibrium Fermi’s golden rule electronic transition rate constants via the linearized semiclassical method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xiang; Geva, Eitan

2016-06-28

In this paper, we test the accuracy of the linearized semiclassical (LSC) expression for the equilibrium Fermi’s golden rule rate constant for electronic transitions in the presence of non-Condon effects. We do so by performing a comparison with the exact quantum-mechanical result for a model where the donor and acceptor potential energy surfaces are parabolic and identical except for shifts in the equilibrium energy and geometry, and the coupling between them is linear in the nuclear coordinates. Since non-Condon effects may or may not give rise to conical intersections, both possibilities are examined by considering: (1) A modified Garg-Onuchic-Ambegaokar modelmore » for charge transfer in the condensed phase, where the donor-acceptor coupling is linear in the primary mode coordinate, and for which non-Condon effects do not give rise to a conical intersection; (2) the linear vibronic coupling model for electronic transitions in gas phase molecules, where non-Condon effects give rise to conical intersections. We also present a comprehensive comparison between the linearized semiclassical expression and a progression of more approximate expressions. The comparison is performed over a wide range of frictions and temperatures for model (1) and over a wide range of temperatures for model (2). The linearized semiclassical method is found to reproduce the exact quantum-mechanical result remarkably well for both models over the entire range of parameters under consideration. In contrast, more approximate expressions are observed to deviate considerably from the exact result in some regions of parameter space.« less

High resolution Fourier transform spectroscopy and crystal-field analysis in Tm,Ho:BaY2F8

NASA Astrophysics Data System (ADS)

Baraldi, A.; Capelletti, R.; Mazzera, M.; Riolo, P.; Amoretti, G.; Magnani, N.; Sani, E.; Toncelli, A.; Tonelli, M.

2005-01-01

A Tm3+- Ho3+ -codoped single crystal of monoclinic BaY2F8 has been characterized by means of high resolution FTIR spectroscopy in the wave number range 2000-24000 cm-1 and in the temperature range 9-300 K. The energy level schemes of the two lanthanide ions as determined by the optical absorption spectra is presented, analyzed, and fitted within a single ion Hamiltonian model. The very small energy separation (about 0.6-1.6 cm-1) measured between the first and second sublevels of the ground state manifolds for both the ions is in line with the theoretical predictions. The impurity-phonon coupling is put into evidence by the thermally induced line shift and broadening, and by the detection of vibronic replicas of a few lines.

Solvatochromism of 9,10-phenanthrenequinone: An electronic and resonance Raman spectroscopic study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ravi Kumar, Venkatraman; Rajkumar, Nagappan; Umapathy, Siva, E-mail: umapathy@ipc.iisc.ernet.in

2015-01-14

Solvent effects play a vital role in various chemical, physical, and biological processes. To gain a fundamental understanding of the solute-solvent interactions and their implications on the energy level re-ordering and structure, UV-VIS absorption, resonance Raman spectroscopic, and density functional theory calculation studies on 9,10-phenanthrenequinone (PQ) in different solvents of diverse solvent polarity has been carried out. The solvatochromic analysis of the absorption spectra of PQ in protic dipolar solvents suggests that the longest (1n-π{sup 1}*; S{sub 1} state) and the shorter (1π-π{sup 1}*; S{sub 2} state) wavelength band undergoes a hypsochromic and bathochromic shift due to intermolecular hydrogen bondmore » weakening and strengthening, respectively. It also indicates that hydrogen bonding plays a major role in the differential solvation of the S{sub 2} state relative to the ground state. Raman excitation profiles of PQ (400–1800 cm{sup −1}) in various solvents followed their corresponding absorption spectra therefore the enhancements on resonant excitation are from single-state rather than mixed states. The hyperchromism of the longer wavelength band is attributed to intensity borrowing from the nearby allowed electronic transition through vibronic coupling. Computational calculation with C{sub 2ν} symmetry constraint on the S{sub 2} state resulted in an imaginary frequency along the low-frequency out-of-plane torsional modes involving the C=O site and therefore, we hypothesize that this mode could be involved in the vibronic coupling.« less

Influence of intra-pigment vibrations on dynamics of photosynthetic exciton.

PubMed

Sato, Yoshihiro; Doolittle, Brian

2014-11-14

We have numerically investigated the effect of an underdamped intra-pigment vibrational mode on an exciton's quantum coherence and energy transfer efficiency. Our model describes a bacteriochlorophyll a pigment-protein dimer under the conditions at which photosynthetic energy transfer occurs. The dimer is modeled using a theoretical treatment of a vibronic exciton, and its dynamics are numerically analyzed using a non-Markovian and non-perturbative method. We examined the system's response to various values of the Huang-Rhys factor, site energy difference, reorganization energy, and reorganization energy difference. We found that the inclusion of the intra-pigment vibronic mode allows for long-lived oscillatory quantum coherences to occur. This excitonic coherence is robust against static site-energy disorder. The vibrational mode also promotes exciton transfer along the site-energy landscape thus improving the overall energy transfer efficiency.

Vibronic relaxation dynamics of o-dichlorobenzene in its lowest excited singlet state

NASA Astrophysics Data System (ADS)

Liu, Benkang; Zhao, Haiyan; Lin, Xiang; Li, Xinxin; Gao, Mengmeng; Wang, Li; Wang, Wei

2018-01-01

Vibronic dynamics of o-dichlorobenzene in its lowest excited singlet state, S1, is investigated in real time by using femtosecond pump-probe method, combined with time-of-flight mass spectroscopy and photoelectron velocity mapping technique. Relaxation processes for the excitation in the range of 276-252 nm can be fitted by single exponential decay model, while in the case of wavelength shorter than 252 nm two-exponential decay model must be adopted for simulating transient profiles. Lifetime constants of the vibrationally excited S1 states change from 651 ± 10 ps for 276 nm excitation to 61 ± 1 ps for 242 nm excitation. Both the internal conversion from the S1 to the highly vibrationally excited ground state S0 and the intersystem crossing from the S1 to the triplet state are supposed to play important roles in de-excitation processes. Exponential fitting of the de-excitation rates on the excitation energy implies such de-excitation process starts from the highly vibrationally excited S0 state, which is validated, by probing the relaxation following photoexcitation at 281 nm, below the S1 origin. Time-dependent photoelectron kinetic energy distributions have been obtained experimentally. As the excitation wavelength changes from 276 nm to 242 nm, different cationic vibronic vibrations can be populated, determined by the Franck-Condon factors between the large geometry distorted excited singlet states and final cationic states.

Jet-resolved vibronic structure in the higher excited states of N2O - Ultraviolet three-photon absorption spectroscopy from 80,000 to 90,000/cm

NASA Technical Reports Server (NTRS)

Patsilinakou, E.; Wiedmann, R. T.; Fotakis, C.; Grant, E. R.

1989-01-01

Ionization-detected UV multiphoton absorption spectroscopy of the excited states of N2O is presented, showing Rydberg structure within 20,000/cm of the first ionization threshold. Despite evidence for strong Rydberg-continuum coupling in the form of broadened bands and Fano line-shapes, the Rydberg structure persists, with atomic-like quantum defects and vibration structure well-matched with that of the ion. In the most clearly resolved spectrum, corresponding to the 3p(delta)1Pi state, Renner-Teller and Herzberg-Teller coupling of electronic and vibrational angular momentum are revealed. It is suggested that these mixings are properties of the N2O(+)Pi ion core.

Selective excitation of exciton transitions in PTCDA crystals and films

NASA Astrophysics Data System (ADS)

Gangilenka, V. R.; Titova, L. V.; Smith, L. M.; Wagner, H. P.; Desilva, L. A. A.; Gisslén, L.; Scholz, R.

2010-04-01

Photoluminescence excitation studies on 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) single crystals and polycrystalline PTCDA films are compared to the calculated excitonic dispersion deduced from an exciton model including the coupling between Frenkel and charge transfer (CT) excitons along the stacking direction. For excitation energies below the 0-0 Frenkel exciton absorption band at 5 K these measurements enable the selective excitation of several CT states. The CT2 state involving stacked PTCDA molecules reveals two excitation resonances originating from different vibronic sublevels. Moreover, the fundamental transition of the CT1 exciton state delocalized over both basis molecules in the crystal unit cell has been identified from the corresponding excitation resonance. From the excitation energy dependence the fundamental transition energies of the CT2 and CT1 excitons have been deduced to occur at 1.95 and 1.98 eV, respectively. When the excitation energy exceeds ˜2.08eV , we observe a strong emission channel which is related to the indirect minimum of the lowest dispersion branch dominated by Frenkel excitons. Photoluminescence excitation spectroscopy measurements on polycrystalline PTCDA films reveal a strong CT2 signal intensity which is attributed to an increased density of defect-related CT2 states that are preferentially formed by slightly deformed or compressed stacked PTCDA molecules in the vicinity of defects or at grain boundaries. Temperature-dependent PL measurements in polycrystalline PTCDA films between 10 and 300 K at an excitation of 1.88 eV further allow a detailed investigation of the CT2 transition and its vibronic subband.

Vibronic Origin for the Diffuse Band Spectrum

NASA Astrophysics Data System (ADS)

Duley, W. W.

1983-09-01

The two arguments outlined by Nuth and Donn (1983) against an interpretation of the diffuse band spectrum between 677 and 536 nm as vibronic systems associated with forbidden origins at 14321, 15153, and 15343 cm-1 (Duley, 1982) are controverted. It is concluded that the vibronic analysis presented by Duley, 1983 for the diffuse band spectrum is in keeping with current spectroscopic practice. The identification of a forbidden origin for 19 of these bands at 14321 cm-1 strongly suggests the involvement of Cr3+ ions in MgO solids in the production of these features.

Jet-cooled laser-induced fluorescence spectroscopy of cyclohexoxy: rotational and fine structure of molecules in nearly degenerate electronic States.

PubMed

Liu, Jinjun; Miller, Terry A

2014-12-26

The rotational structure of the previously observed B̃(2)A' ← X̃(2)A″ and B̃(2)A' ← Ã(2)A' laser-induced fluorescence spectra of jet-cooled cyclohexoxy radical (c-C6H11O) [ Zu, L.; Liu, J.; Tarczay, G.; Dupré, P; Miller, T. A. Jet-cooled laser spectroscopy of the cyclohexoxy radical. J. Chem. Phys. 2004 , 120 , 10579 ] has been analyzed and simulated using a spectroscopic model that includes the coupling between the nearly degenerate X̃ and à states separated by ΔE. The rotational and fine structure of these two states is reproduced by a 2-fold model using one set of molecular constants including rotational constants, spin-rotation constants (ε's), the Coriolis constant (Aζt), the quenched spin-orbit constant (aζed), and the vibronic energy separation between the two states (ΔE0). The energy level structure of both states can also be reproduced using an isolated-state asymmetric top model with rotational constants and effective spin-rotation constants (ε's) and without involving Coriolis and spin-orbit constants. However, the spin-orbit interaction introduces transitions that have no intensity using the isolated-state model but appear in the observed spectra. The line intensities are well simulated using the 2-fold model with an out-of-plane (b-) transition dipole moment for the B̃ ← X̃ transitions and in-plane (a and c) transition dipole moment for the B̃ ← à transitions, requiring the symmetry for the X̃ (Ã) state to be A″ (A'), which is consistent with a previous determination and opposite to that of isopropoxy, the smallest secondary alkoxy radical. The experimentally determined Ã-X̃ separation and the energy level ordering of these two states with different (A' and A″) symmetries are consistent with quantum chemical calculations. The 2-fold model also enables the independent determination of the two contributions to the Ã-X̃ separation: the relativistic spin-orbit interaction (magnetic effect) and the nonrelativistic vibronic separation between the lowest vibrational energy levels of these two states due to both electrostatic interaction (Coulombic effect) and difference in zero-point energies (kinetic effect).

A reinterpretation of the electronic spectrum of pyrrole: A quantum dynamics study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neville, S. P.; Worth, G. A., E-mail: g.a.worth@bham.ac.uk

The first band in the electronic spectrum of pyrrole is calculated from wavepacket propagations performed using the MCTDH method. To do so, two model Hamiltonians are constructed to describe seven low-lying excited electronic states of pyrrole. These Hamiltonians are based on the vibronic coupling model, and are parameterised via fitting to extensive CASPT2 and EOM-CCSD calculations. A detailed analysis of the structure of pyrrole's electronic spectrum in the range 5.5 to 6.5 eV is made. The role of intensity borrowing from transitions to ππ{sup *} states by lower-lying 3s and 3p Rydberg states is assessed, and reassignments of much ofmore » the spectrum are subsequently made which indicate that most of the states in the spectrum are predominantly Rydberg in character. The resulting conclusions drawn serve to highlight the limitations of assignments based on the matching of calculated vertical excitation energies and the positions of peak maxima observed in electronic spectra.« less

Ro-vibronic transition intensities for triatomic molecules from the exact kinetic energy operator; electronic spectrum for the C̃ 1B2 ← X̃ 1A1 transition in SO2.

PubMed

Zak, Emil J; Tennyson, Jonathan

2017-09-07

A procedure for calculating ro-vibronic transition intensities for triatomic molecules within the Born-Oppenheimer approximation is reported. Ro-vibrational energy levels and wavefunctions are obtained with the DVR3D suite, which solves the nuclear motion problem with an exact kinetic energy operator. Absolute transition intensities are calculated both with the Franck-Condon approximation and with a full transition dipole moment surface. The theoretical scheme is tested on C̃  1 B 2  ← X̃  1 A 1 ro-vibronic transitions of SO 2 . Ab initio potential energy and dipole moment surfaces are generated for this purpose. The calculated ro-vibronic transition intensities and cross sections are compared with the available experimental and theoretical data.

Quasi-classical approaches to vibronic spectra revisited

NASA Astrophysics Data System (ADS)

Karsten, Sven; Ivanov, Sergei D.; Bokarev, Sergey I.; Kühn, Oliver

2018-03-01

The framework to approach quasi-classical dynamics in the electronic ground state is well established and is based on the Kubo-transformed time correlation function (TCF), being the most classical-like quantum TCF. Here we discuss whether the choice of the Kubo-transformed TCF as a starting point for simulating vibronic spectra is as unambiguous as it is for vibrational ones. Employing imaginary-time path integral techniques in combination with the interaction representation allowed us to formulate a method for simulating vibronic spectra in the adiabatic regime that takes nuclear quantum effects and dynamics on multiple potential energy surfaces into account. Further, a generalized quantum TCF is proposed that contains many well-established TCFs, including the Kubo one, as particular cases. Importantly, it also provides a framework to construct new quantum TCFs. Applying the developed methodology to the generalized TCF leads to a plethora of simulation protocols, which are based on the well-known TCFs as well as on new ones. Their performance is investigated on 1D anharmonic model systems at finite temperatures. It is shown that the protocols based on the new TCFs may lead to superior results with respect to those based on the common ones. The strategies to find the optimal approach are discussed.

Importance of Vibronic Effects in the UV-Vis Spectrum of the 7,7,8,8-Tetracyanoquinodimethane Anion.

PubMed

Tapavicza, Enrico; Furche, Filipp; Sundholm, Dage

2016-10-11

We present a computational method for simulating vibronic absorption spectra in the ultraviolet-visible (UV-vis) range and apply it to the 7,7,8,8-tetracyanoquinodimethane anion (TCNQ - ), which has been used as a ligand in black absorbers. Gaussian broadening of vertical electronic excitation energies of TCNQ - from linear-response time-dependent density functional theory produces only one band, which is qualitatively incorrect. Thus, the harmonic vibrational modes of the two lowest doublet states were computed, and the vibronic UV-vis spectrum was simulated using the displaced harmonic oscillator approximation, the frequency-shifted harmonic oscillator approximation, and the full Duschinsky formalism. An efficient real-time generating function method was implemented to avoid the exponential complexity of conventional Franck-Condon approaches to vibronic spectra. The obtained UV-vis spectra for TCNQ - agree well with experiment; the Duschinsky rotation is found to have only a minor effect on the spectrum. Born-Oppenheimer molecular dynamics simulations combined with calculations of the electronic excitation energies for a large number of molecular structures were also used for simulating the UV-vis spectrum. The Born-Oppenheimer molecular dynamics simulations yield a broadening of the energetically lowest peak in the absorption spectrum, but additional vibrational bands present in the experimental and simulated quantum harmonic oscillator spectra are not observed in the molecular dynamics simulations. Our results underline the importance of vibronic effects for the UV-vis spectrum of TCNQ - , and they establish an efficient method for obtaining vibronic spectra using a combination of linear-response time-dependent density functional theory and a real-time generating function approach.

Vibronic Analysis for widetilde{B} - widetilde{X} Transition of Isopropoxy Radical

NASA Astrophysics Data System (ADS)

Chhantyal-Pun, Rabi; Miller, Terry A.

2013-06-01

Alkoxy radicals are important intermediates in combustion and atmospheric chemistry. Alkoxy radicals are also of significant spectroscopic interest for the study of Jahn Teller and pseudo Jahn Teller effects, involving the widetilde{X} and widetilde{A} states. The Jahn Teller effect has been studied in methoxy. Substitution of one or two hydrogens by methyl groups transforms the interaction to a pseudo Jahn Teller effect in ethoxy and isopropoxy. Previously, moderate resolution scans have been obtained for widetilde{B} - widetilde{X} and widetilde{B} - widetilde{A} transition systems, the latter observable at higher temperature. These measurements have shown that the widetilde{X} and widetilde{A} states of isopropoxy are separated by only 60.7(7) cm^{-1} which indicates a strong pseudo Jahn Teller effect in the widetilde{X} state. Such pseduo Jahn Teller coupling should also introduce additional bands into the widetilde{B} - widetilde{X} spectrum and a number of weaker transitions have been observed which may be caused by such effects. In this talk we present a vibronic analysis for the widetilde{B} - widetilde{X} transition based on the experimental results and also the results from recent quantum chemistry calculations.

Extended quantum jump description of vibronic two-dimensional spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Albert, Julian; Falge, Mirjam; Keß, Martin

2015-06-07

We calculate two-dimensional (2D) vibronic spectra for a model system involving two electronic molecular states. The influence of a bath is simulated using a quantum-jump approach. We use a method introduced by Makarov and Metiu [J. Chem. Phys. 111, 10126 (1999)] which includes an explicit treatment of dephasing. In this way it is possible to characterize the influence of dissipation and dephasing on the 2D-spectra, using a wave function based method. The latter scales with the number of stochastic runs and the number of system eigenstates included in the expansion of the wave-packets to be propagated with the stochastic methodmore » and provides an efficient method for the calculation of the 2D-spectra.« less

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope

PubMed Central

Nazin, G. V.; Wu, S. W.; Ho, W.

2005-01-01

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends. PMID:15956189

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope.

PubMed

Nazin, G V; Wu, S W; Ho, W

2005-06-21

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.

From transistor to trapped-ion computers for quantum chemistry.

PubMed

Yung, M-H; Casanova, J; Mezzacapo, A; McClean, J; Lamata, L; Aspuru-Guzik, A; Solano, E

2014-01-07

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology.

From transistor to trapped-ion computers for quantum chemistry

PubMed Central

Yung, M.-H.; Casanova, J.; Mezzacapo, A.; McClean, J.; Lamata, L.; Aspuru-Guzik, A.; Solano, E.

2014-01-01

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology. PMID:24395054

Design of UV laser pulses for the preparation of matrix isolated homonuclear diatomic molecules in selective vibrational superposition states.

PubMed

Korolkov, M V; Manz, J

2007-05-07

The preparation of matrix isolated homonuclear diatomic molecules in a vibrational superposition state c0Phie=1,v=0+cjPhie=1,v=j, with large (|c0|2 approximately 1) plus small contributions (|cj|2<1) of the ground v=0 and specific v=j low excited vibrational eigenstates, respectively, in the electronic ground (e=1) state, and without any net population transfer to electronic excited (e>1) states, is an important challenge; it serves as a prerequisite for coherent spin control. For this purpose, the authors investigate two scenarios of laser pulse control, involving sequential or intrapulse pump- and dump-type transitions via excited vibronic states Phiex,k with a dominant singlet or triplet character. The mechanisms are demonstrated by means of quantum simulations for representative nuclear wave packets on coupled potential energy surfaces, using as an example a one-dimensional model for Cl2 in an Ar matrix. A simple three-state model (including Phi1,0, Phi1,j and Phiex,k) allows illuminating analyses and efficient determinations of the parameters of the laser pulses based on the values of the transition energies and dipole couplings of the transient state which are derived from the absorption spectra.

A Direct Mechanism of Ultrafast Intramolecular Singlet Fission in Pentacene Dimers

DOE PAGES

Fuemmeler, Eric G.; Sanders, Samuel N.; Pun, Andrew B.; ...

2016-05-05

Interest in materials that undergo singlet fission (SF) has been catalyzed by the potential to exceed the Shockley–Queisser limit of solar power conversion efficiency. In conventional materials, the mechanism of SF is an intermolecular process (xSF), which is mediated by charge transfer (CT) states and depends sensitively on crystal packing or molecular collisions. In contrast, recently reported covalently coupled pentacenes yield ~2 triplets per photon absorbed in individual molecules: the hallmark of intramolecular singlet fission (iSF). But, the mechanism of iSF is unclear. Here, using multireference electronic structure calculations and transient absorption spectroscopy, we establish that iSF can occur viamore » a direct coupling mechanism that is independent of CT states. Moreover, we show that a near-degeneracy in electronic state energies induced by vibronic coupling to intramolecular modes of the covalent dimer allows for strong mixing between the correlated triplet pair state and the local excitonic state, despite weak direct coupling.« less

Quantum coherence effects in natural light-induced processes: cis-trans photoisomerization of model retinal under incoherent excitation.

PubMed

Tscherbul, Timur V; Brumer, Paul

2015-12-14

We present a theoretical study of quantum coherence effects in the primary cis-trans photoisomerization of retinal in rhodopsin induced by incoherent solar light. Using the partial secular Bloch-Redfield quantum master equation approach based on a two-state two-mode linear vibronic coupling model of the retinal chromophore [S. Hahn and G. Stock, J. Phys. Chem. B, 2000, 104, 1146-1149], we show that a sudden turn-on of incoherent pumping can generate substantial Fano coherences among the excited states of retinal. These coherences are the most pronounced in the regime where the matrix elements of the transition dipole moment between the ground and excited eigenstates are parallel to one another. We show that even when the transition dipole moments are perpendicular (implying the absence of light-induced Fano coherence) a small amount of excited-state coherence is still generated due to the coupling to intramolecular vibrational modes and the protein environment, causing depopulation of the excited eigenstates. The overall effect of the coherences on the steady-state population and on the photoproduct quantum yield is shown to be small; however we observe a significant transient effect on the formation of the trans photoproduct, enhancing the photoreaction quantum yield by ∼11% at 200 fs. These calculations suggest that coupling to intramolecular vibrational modes and the protein environment play an important role in photoreaction dynamics, suppressing oscillations in the quantum yield associated with Fano interference.

Luminescence of the (O{sub 2}(a{sup 1}Δ{sub g})){sub 2} collisional complex in the temperature range of 90-315 K: Experiment and theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zagidullin, M. V., E-mail: marsel@fian.smr.ru; Pershin, A. A., E-mail: anchizh93@gmail.com; Azyazov, V. N., E-mail: azyazov@ssau.ru

Experimental and theoretical studies of collision induced emission of singlet oxygen molecules O{sub 2}(a{sup 1}Δ{sub g}) in the visible range have been performed. The rate constants, half-widths, and position of peaks for the emission bands of the (O{sub 2}(a{sup 1}Δ{sub g})){sub 2} collisional complex centered around 634 nm (2) and 703 nm (3) have been measured in the temperature range of 90–315 K using a flow-tube apparatus that utilized a gas-liquid chemical singlet oxygen generator. The absolute values of the spontaneous emission rate constants k{sub 2} and k{sub 3} are found to be similar, with the k{sub 3}/k{sub 2} ratiomore » monotonically decreasing from 1.1 at 300 K to 0.96 at 90 K. k{sub 2} slowly decreases with decreasing temperature but a sharp increase in its values is measured below 100 K. The experimental results were rationalized in terms of ab initio calculations of the ground and excited potential energy and transition dipole moment surfaces of singlet electronic states of the (O{sub 2}){sub 2} dimole, which were utilized to compute rate constants k{sub 2} and k{sub 3} within a statistical model. The best theoretical results reproduced experimental rate constants with the accuracy of under 40% and correctly described the observed temperature dependence. The main contribution to emission process (2), which does not involve vibrational excitation of O{sub 2} molecules at the ground electronic level, comes from the spin- and symmetry-allowed 1{sup 1}A{sub g}←{sup 1}B{sub 3u} transition in the rectangular H configuration of the dimole. Alternatively, emission process (3), in which one of the monomers becomes vibrationally excited in the ground electronic state, is found to be predominantly due to the vibronically allowed 1{sup 1}A{sub g}←2{sup 1}A{sub g} transition induced by the asymmetric O–O stretch vibration in the collisional complex. The strong vibronic coupling between nearly degenerate excited singlet states of the dimole makes the intensities of vibronically and symmetry-allowed transitions comparable and hence the rate constants k{sub 2} and k{sub 3} close to one another.« less

Rotational Parameters from Vibronic Eigenfunctions of Jahn-Teller Active Molecules

NASA Astrophysics Data System (ADS)

Garner, Scott M.; Miller, Terry A.

2017-06-01

The structure in rotational spectra of many free radical molecules is complicated by Jahn-Teller distortions. Understanding the magnitudes of these distortions is vital to determining the equilibrium geometric structure and details of potential energy surfaces predicted from electronic structure calculations. For example, in the recently studied {\\widetilde{A}^2E^{''} } state of the NO_3 radical, the magnitudes of distortions are yet to be well understood as results from experimental spectroscopic studies of its vibrational and rotational structure disagree with results from electronic structure calculations of the potential energy surface. By fitting either vibrationally resolved spectra or vibronic levels determined by a calculated potential energy surface, we obtain vibronic eigenfunctions for the system as linear combinations of basis functions from products of harmonic oscillators and the degenerate components of the electronic state. Using these vibronic eigenfunctions we are able to predict parameters in the rotational Hamiltonian such as the Watson Jahn-Teller distortion term, h_1, and compare with the results from the analysis of rotational experiments.

A unifying model for non-adiabatic coupling at metallic surfaces beyond the local harmonic approximation: From vibrational relaxation to scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Tremblay, Jean Christophe

2013-06-01

A model for treating excitation and relaxation of adsorbates at metallic surfaces induced by non-adiabatic coupling is developed. The derivation is based on the concept of resonant electron transfer, where the adsorbate serves as a molecular bridge for the inelastic transition between an electron source and a sink. In this picture, energy relaxation and scanning tunneling microscopy (STM) at metallic surfaces are treated on an equal footing as a quasi-thermal process. The model goes beyond the local harmonic approximation and allows for an unbiased description of floppy systems with multiple potential wells. Further, the limitation of the product ansatz for the vibronic wave function to include the position-dependence of the non-adiabatic couplings is avoided by explicitly enforcing detailed balance. The theory is applied to the excitation of hydrogen on palladium, which has multiple local potential minima connected by low energy barriers. The main aspects investigated are the lifetimes of adsorbate vibrations in different adsorption sites, as well as the dependence of the excitation, response, and transfer rates on an applied potential bias. The excitation and relaxation simulations reveal intricate population dynamics that depart significantly from the simplistic tunneling model in a truncated harmonic potential. In particular, the population decay from an initially occupied local minimum induced by the contact with an STM tip is found to be better described by a double exponential. The two rates are interpreted as a response to the system perturbation and a transfer rate following the perturbation. The transfer rate is found to obey a power law, as was the case in previous experimental and theoretical work.

High-resolution threshold photoionization of N2O

NASA Technical Reports Server (NTRS)

Wiedmann, R. T.; Grant, E. R.; Tonkyn, R. G.; White, M. G.

1991-01-01

Pulsed field ionization (PFI) has been used in conjunction with a coherent VUV source to obtain high-resolution threshold photoelectron spectra for the (000), (010), (020), and (100) vibrational states of the N2O(+) cation. Simulations for the rotational profiles of each vibronic level were obtained by fitting the Buckingham-Orr-Sichel equations using accurate spectroscopic constants for the ground states of the neutral and the ion. The relative branch intensities are interpreted in terms of the partial waves of the outgoing photoelectron to which the ionic core is coupled and in terms of the angular momentum transferred to the core.

Synthesis of Five‐Porphyrin Nanorings by Using Ferrocene and Corannulene Templates

PubMed Central

Liu, Pengpeng; Hisamune, Yutaka; Peeks, Martin D.; Odell, Barbara; Gong, Juliane Q.; Herz, Laura M.

2016-01-01

Abstract The smallest and most strained member of a family of π‐conjugated cyclic porphyrin oligomers was synthesized by using pentapyridyl templates based on ferrocene and corannulene. Both templates are effective for directing the synthesis of the butadiyne‐linked cyclic pentamer, despite the fact that the radii of their N5 donor sets are too small by 0.5 Å and 0.9 Å, respectively (from DFT calculations). The five‐porphyrin nanoring exhibits a structured absorption spectrum and its fluorescence extends to 1200 nm, reflecting strong π conjugation and Herzberg–Teller vibronic coupling. PMID:27213825

Diabatic Definition of Geometric Phase Effects.

PubMed

Izmaylov, Artur F; Li, Jiaru; Joubert-Doriol, Loïc

2016-11-08

Electronic wave functions in the adiabatic representation acquire nontrivial geometric phases (GPs) when corresponding potential energy surfaces undergo conical intersection (CI). These GPs have profound effects on the nuclear quantum dynamics and cannot be eliminated in the adiabatic representation without changing the physics of the system. To define dynamical effects arising from the GP presence, the nuclear quantum dynamics of the CI containing system is compared with that of the system with artificially removed GP. We explore a new construction of the system with removed GP via a modification of the diabatic representation for the original CI containing system. Using an absolute value function of diabatic couplings, we remove the GP while preserving adiabatic potential energy surfaces and CI. We assess GP effects in dynamics of a two-dimensional linear vibronic coupling model both for ground and excited state dynamics. Results are compared with those obtained with a conventional removal of the GP by ignoring double-valued boundary conditions of the real electronic wave functions. Interestingly, GP effects appear similar in two approaches only for the low energy dynamics. In contrast with the conventional approach, the new approach does not have substantial GP effects in the ultrafast excited state dynamics.

Vibrational quenching of excitonic splittings in H-bonded molecular dimers: The electronic Davydov splittings cannot match experiment

NASA Astrophysics Data System (ADS)

Ottiger, Philipp; Leutwyler, Samuel; Köppel, Horst

2012-05-01

The S1/S2 state exciton splittings of symmetric doubly hydrogen-bonded gas-phase dimers provide spectroscopic benchmarks for the excited-state electronic couplings between UV chromophores. These have important implications for electronic energy transfer in multichromophoric systems ranging from photosynthetic light-harvesting antennae to photosynthetic reaction centers, conjugated polymers, molecular crystals, and nucleic acids. We provide laser spectroscopic data on the S1/S2 excitonic splitting Δexp of the doubly H-bonded o-cyanophenol (oCP) dimer and compare to the splittings of the dimers of (2-aminopyridine)2, [(2AP)2], (2-pyridone)2, [(2PY)2], (benzoic acid)2, [(BZA)2], and (benzonitrile)2, [(BN)2]. The experimental S1/S2 excitonic splittings are Δexp = 16.4 cm-1 for (oCP)2, 11.5 cm-1 for (2AP)2, 43.5 cm-1 for (2PY)2, and <1 cm-1 for (BZA)2. In contrast, the vertical S1/S2 energy gaps Δcalc calculated by the approximate second-order coupled cluster (CC2) method for the same dimers are 10-40 times larger than the Δexp values. The qualitative failure of this and other ab initio methods to reproduce the exciton splitting Δexp arises from the Born-Oppenheimer (BO) approximation, which implicitly assumes the strong-coupling case and cannot be employed to evaluate excitonic splittings of systems that are in the weak-coupling limit. Given typical H-bond distances and oscillator strengths, the majority of H-bonded dimers lie in the weak-coupling limit. In this case, the monomer electronic-vibrational coupling upon electronic excitation must be accounted for; the excitonic splittings arise between the vibronic (and not the electronic) transitions. The discrepancy between the BO-based splittings Δcalc and the much smaller experimental Δexp values is resolved by taking into account the quenching of the BO splitting by the intramolecular vibronic coupling in the monomer S1 ← S0 excitation. The vibrational quenching factors Γ for the five dimers (oCP)2, (2AP)2, (2AP)2, (BN)2, and (BZA)2 lie in the range Γ = 0.03-0.2. The quenched excitonic splittings Γ.Δcalc are found to be in very good agreement with the observed splittings Δexp. The vibrational quenching approach predicts reliable Δexp values for the investigated dimers, confirms the importance of vibrational quenching of the electronic Davydov splittings, and provides a sound basis for predicting realistic exciton splittings in multichromophoric systems.

Selective two-photon excitation of a vibronic state by correlated photons.

PubMed

Oka, Hisaki

2011-03-28

We theoretically investigate the two-photon excitation of a molecular vibronic state by correlated photons with energy anticorrelation. A Morse oscillator having three sets of vibronic states is used, as an example, to evaluate the selectivity and efficiency of two-photon excitation. We show that a vibrational mode can be selectively excited with high efficiency by the correlated photons, without phase manipulation or pulse-shaping techniques. This can be achieved by controlling the quantum correlation so that the photon pair concurrently has two pulse widths, namely, a temporally narrow width and a spectrally narrow width. Though this concurrence is seemingly contradictory, we can create such a photon pair by tailoring the quantum correlation between two photons.

Real-time observation of multi-mode vibronic coherence in pentafluoropyridine

NASA Astrophysics Data System (ADS)

Kus, J. A.; Hüter, O.; Temps, F.

2017-07-01

The ultrafast dynamics of pentafluoropyridine in the 1 1B2 (ππ*) electronic state excited at λpump = 255 nm is investigated by femtosecond time-resolved time-of-flight mass spectrometry and photoelectron imaging spectroscopy. A pronounced, long-lived, and complex periodic modulation of the transient ion yield signal with contributions by four distinct frequency components, 72 cm-1, 144 cm-1, 251 cm-1, and 281 cm-1, is observed for up to 9 ps. The recorded photoelectron images display a spectral band from the excited 1 1B2 (ππ*) state only in the oscillation maxima; the signal is strongly reduced in the oscillation minima. Supported by electronic structure calculations at the RI-SCS-CC2 and XMCQDPT2 levels of theory, the oscillating components of the signal are identified as frequencies of b1 symmetry coupling modes in a vibronic coherence of the 1 1B2 (ππ*) and 1 1A2 (πσ*) electronic states. The optical excitation initiates regular and periodic wavepacket motion along those out-of-plane modes. In the distorted molecular structure, the initially excited state acquires substantial πσ* character that modulates the transition dipole moment for ionization and results in the observed oscillations.

Spectroscopic Identification of Isomeric Trimethylbenzyl Radicals Generated in Corona Discharge of Tetramethylbenzene

NASA Astrophysics Data System (ADS)

Yoon, Young Wook; Lee, Sang Kuk; Lee, Gi Woo

2011-06-01

The visible vibronic emission spectra were recorded from the corona discharge of precursor tetramethylbenzene with a large amount of inert carrier gas helium using a pinhole-type glass nozzle coupled with corona excited supersonic expansion (CESE) well developed in this laboratory. The spectra showed a series of vibronic bands in the D_1 → D_0 electronic transition of jet-cooled benzyl-type radicals formed from the precursor in a corona excitation. The analysis confirmed that two isomeric radicals, 2,3,4- and 2,3,6-trimethylbenzyl radicals and three isomeric radicals, 3,4,5-, 2,3,5- and 2,4,6-trimethylbenzyl radicals were produced, respectively, from 1,2,3,4- and 1,2,3,5-tetramethylbenzenes as a result of removal of a hydrogen atom from the methyl group at different substitution position. For each isomeric trimethylbenzyl radical generated in the corona discharge of precursor, the electronic transition and a few vibrational mode frequencies were determined in the ground electronic state by comparing with those from both ab initio calculations and the known vibrational data of the precursor. The substitution effect that states the shift of electronic transition depends on the nature, the number, and the position of substituents on the ring has been qualitatively proved for the case of benzyl-type radicals.

To Be or Not to Be Symmetric: That is the Question for Potentially Active Vibronic Modes

ERIC Educational Resources Information Center

Tyler, Sarah F.; Judkins, Eileen C.; Morozov, Dmitry; Borca, Carlos H.; Slipchenko, Lyudmila V.; McMillin, David R.

2017-01-01

Electronic spectra often exhibit vibronic structure when vibrational and electronic transitions occur in concert. Theory reveals (1) that orbital symmetry considerations determine specific roles played by the nuclear degrees of freedom and (2) that the vibrational excitation is often highly regiospecific, that is, attributable to an identifiable…

Vibronic Boson Sampling: Generalized Gaussian Boson Sampling for Molecular Vibronic Spectra at Finite Temperature.

PubMed

Huh, Joonsuk; Yung, Man-Hong

2017-08-07

Molecular vibroic spectroscopy, where the transitions involve non-trivial Bosonic correlation due to the Duschinsky Rotation, is strongly believed to be in a similar complexity class as Boson Sampling. At finite temperature, the problem is represented as a Boson Sampling experiment with correlated Gaussian input states. This molecular problem with temperature effect is intimately related to the various versions of Boson Sampling sharing the similar computational complexity. Here we provide a full description to this relation in the context of Gaussian Boson Sampling. We find a hierarchical structure, which illustrates the relationship among various Boson Sampling schemes. Specifically, we show that every instance of Gaussian Boson Sampling with an initial correlation can be simulated by an instance of Gaussian Boson Sampling without initial correlation, with only a polynomial overhead. Since every Gaussian state is associated with a thermal state, our result implies that every sampling problem in molecular vibronic transitions, at any temperature, can be simulated by Gaussian Boson Sampling associated with a product of vacuum modes. We refer such a generalized Gaussian Boson Sampling motivated by the molecular sampling problem as Vibronic Boson Sampling.

Raman spectroscopy and melting of nitrogen between 290 and 900 K and 2. 3 and 18 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zinn, A.S.; Schiferl, D.; Nicol, M.F.

1987-07-15

Raman spectroscopy was used to study the melting of nitrogen from 290 to 900 K at pressures from 2.3 to 18 GPa. This work, which extends the melting by a factor of 9 over previously published results was made possible by new developments in high-temperature diamond-anvil cells. The ..beta../delta phase boundary was also determined, and the ..beta..--delta--fluid triple point was found to be at 578 +- 10 K and 9.9 +- 0.5 GPa. The Raman frequencies of the vibron in fluid N/sub 2/ and the ..nu../sub 2/ vibron in delta-N/sub 2/ were found to have the same pressure dependence andmore » be independent of temperature to a good approximation. A temperature-independent pressure scale, useful to at least 900 K is approximated by P/GPa = 0.4242 ..nu../cm/sup -1/ -987.8, where ..nu.. is the frequency of either the ..nu../sub 2/ vibron in delta-N/sub 2/ or the vibron in fluid-N/sub 2/.« less

The origin of unequal bond lengths in the C 1B 2 state of SO 2: Signatures of high-lying potential energy surface crossings in the low-lying vibrational structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, G. Barratt; Jiang, Jun; Field, Robert W.

Here the C 1B 2 state of SO 2 has a double-minimum potential in the antisymmetric stretch coordinate, such that the minimum energy geometry has nonequivalent SO bond lengths. The asymmetry in the potential energy surface is expressed as a staggering in the energy levels of the v' 3 progression. We have recently made the first observation of low-lying levels with odd quanta of v' 3, which allows us--in the current work--to characterize the origins of the level staggering. Our work demonstrates the usefulness of low-lying vibrational level structure, where the character of the wavefunctions can be relatively easily understood,more » to extract information about dynamically important potential energy surface crossings that occur at much higher energy. The measured staggering pattern is consistent with a vibronic coupling model for the double-minimum, which involves direct coupling to the bound 2 1A 1 state and indirect coupling with the repulsive 3 1A 1 state. The degree of staggering in the v' 3 levels increases with quanta of bending excitation, which is consistent with the approach along the C state potential energy surface to a conical intersection with the 2 1A 1 surface at a bond angle of ~145°.« less

The origin of unequal bond lengths in the C 1B 2 state of SO 2: Signatures of high-lying potential energy surface crossings in the low-lying vibrational structure

DOE PAGES

Park, G. Barratt; Jiang, Jun; Field, Robert W.

2016-04-14

Here the C 1B 2 state of SO 2 has a double-minimum potential in the antisymmetric stretch coordinate, such that the minimum energy geometry has nonequivalent SO bond lengths. The asymmetry in the potential energy surface is expressed as a staggering in the energy levels of the v' 3 progression. We have recently made the first observation of low-lying levels with odd quanta of v' 3, which allows us--in the current work--to characterize the origins of the level staggering. Our work demonstrates the usefulness of low-lying vibrational level structure, where the character of the wavefunctions can be relatively easily understood,more » to extract information about dynamically important potential energy surface crossings that occur at much higher energy. The measured staggering pattern is consistent with a vibronic coupling model for the double-minimum, which involves direct coupling to the bound 2 1A 1 state and indirect coupling with the repulsive 3 1A 1 state. The degree of staggering in the v' 3 levels increases with quanta of bending excitation, which is consistent with the approach along the C state potential energy surface to a conical intersection with the 2 1A 1 surface at a bond angle of ~145°.« less

Fluorescence spectroscopy and amplified spontaneous emission (ASE) of phenylimidazoles: predicted vibronic coupling along the excited-state intramolecular proton transfer in 2-(2'-hydroxyphenyl)imidazoles.

PubMed

del Valle, Juan Carlos; Claramunt, R M; Catalán, J

2008-06-26

Methylation at the 1N position of 2-phenylimidazole provides the shortest wavelength for a liquid-state laser dye reported to date; that is, the 1-methyl-2-phenylimidazole molecule in cyclohexane solution yields amplified spontaneous emission (ASE) with a peak wavelength at 314.5 nm and a constant laser gain value of 5 cm(-1) from 310 to 317 nm. Methyl substitution in this case favors the appearance of laser action (owing to a torsion-vibrational mechanism) in cyclohexane as compared with the nonmethylated species which does not exhibit ASE in this solvent. The 2-(2'-hydroxyphenyl)imidazole molecules give rise to ASE with high gain values (ca. 9 cm(-1)) at 450 and 466 nm. The mechanism of population inversion is understood in terms of a vibronic coupling between the hydroxyl stretching motion and the torsional vibration of the phenyl and imidazole rings. The proton-transfer spectroscopy of 2-(2'-hydroxyphenyl)imidazoles is studied in dioxane, cyclohexane, dimethyl sulfoxide, methanol, and water. The greater the acidity of the solvent the greater the disruption of the intramolecular hydrogen bond; solvent acidity is the main parameter which favors formation of the open-form species in the ground electronic state. Methyl substitution at the 1N position favors formation of the open species for 2-hydroxyphenylimidazoles in the ground electronic state, which decreases their own capacity to undergo ASE. Low-temperature absorption spectroscopy confirms aggregation processes for 2-(2'-hydroxyphenyl)imidazoles in solution. In accordance with X-ray analyses in the solid phase, these molecules form associations through intermolecular chains of the type N-H...O or O-H...N.

Applied quantum chemistry: Spectroscopic detection and characterization of the F{sub 2}BS and Cl{sub 2}BS free radicals in the gas phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Bing; Clouthier, Dennis J., E-mail: dclaser@uky.edu; Sheridan, Phillip M.

2015-03-28

In this and previous work [D. J. Clouthier, J. Chem. Phys. 141, 244309 (2014)], the spectroscopic signatures of the X{sub 2}BY (X = H, halogen, Y = O, S) free radicals have been predicted using high level ab initio theory. The theoretical results have been used to calculate the electronic absorption and single vibronic level (SVL) emission spectra of the radicals under typical jet-cooled conditions. Using these diagnostic predictions, the previously unknown F{sub 2}BS and Cl{sub 2}BS free radicals have been identified and characterized. The radicals were prepared in a free jet expansion by subjecting precursor mixtures of BF{sub 3}more » or BCl{sub 3} and CS{sub 2} vapor to an electric discharge at the exit of a pulsed molecular beam valve. The B{sup ~2}A{sub 1}–X{sup ~} {sup 2}B{sub 2} laser-induced fluorescence spectra were found within 150 cm{sup −1} of their theoretically predicted positions with vibronic structure consistent with our Franck-Condon simulations. The B{sup ~2}A{sub 1} state emits down to the ground state and to the low-lying A{sup ~2}B{sub 1} excited state and the correspondence between the observed and theoretically derived SVL emission Franck-Condon profiles was used to positively identify the radicals and make assignments. Excited state Coriolis coupling effects complicate the emission spectra of both radicals. In addition, a forbidden component of the electronically allowed B{sup ~}–X{sup ~} band system of Cl{sub 2}BS is evident, as signaled by the activity in the b{sub 2} modes in the spectrum. Symmetry arguments indicate that this component gains intensity due to a vibronic interaction of the B{sup ~2}A{sub 1} state with a nearby electronic state of {sup 2}B{sub 2} symmetry.« less

Optical spectra obtained from amorphous films of rubrene: Evidence for predominance of twisted isomer

NASA Astrophysics Data System (ADS)

Kytka, M.; Gisslen, L.; Gerlach, A.; Heinemeyer, U.; Kováč, J.; Scholz, R.; Schreiber, F.

2009-06-01

In order to investigate the optical properties of rubrene we study the vibronic progression of the first absorption band (lowest π →π∗ transition). We analyze the dielectric function ɛ2 of rubrene in solution and thin films using the displaced harmonic oscillator model and derive all relevant parameters of the vibronic progression. The findings are supplemented by density functional calculations using B3LYP hybrid functionals. Our theoretical results for the molecule in two different conformations, i.e., with a twisted or planar tetracene backbone, are in very good agreement with the experimental data obtained for rubrene in solution and thin films. Moreover, a simulation based on the monomer spectrum and the calculated transition energies of the two conformations indicates that the thin film spectrum of rubrene is dominated by the twisted isomer.

Optical spectra obtained from amorphous films of rubrene: Evidence for predominance of twisted isomer.

PubMed

Kytka, M; Gisslen, L; Gerlach, A; Heinemeyer, U; Kovác, J; Scholz, R; Schreiber, F

2009-06-07

In order to investigate the optical properties of rubrene we study the vibronic progression of the first absorption band (lowest pi-->pi( *) transition). We analyze the dielectric function epsilon(2) of rubrene in solution and thin films using the displaced harmonic oscillator model and derive all relevant parameters of the vibronic progression. The findings are supplemented by density functional calculations using B3LYP hybrid functionals. Our theoretical results for the molecule in two different conformations, i.e., with a twisted or planar tetracene backbone, are in very good agreement with the experimental data obtained for rubrene in solution and thin films. Moreover, a simulation based on the monomer spectrum and the calculated transition energies of the two conformations indicates that the thin film spectrum of rubrene is dominated by the twisted isomer.

A quantum dynamics study of the benzopyran ring opening guided by laser pulses

NASA Astrophysics Data System (ADS)

Saab, Mohamad; Doriol, Loïc Joubert; Lasorne, Benjamin; Guérin, Stéphane; Gatti, Fabien

2014-10-01

The ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection, has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use a six-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of the vibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of strategies that could help experimentalists to control the photoreactivity vs. photostability ratio (selectivity). In this work we present: (i) a pump-dump technique used to control the photostability, (ii) a two-step strategy to enhance the reactivity of the system: first, a pure vibrational excitation in the electronic ground state that prepares the system and, second, an ultraviolet excitation that brings the system to the first adiabatic electronic state; (iii) finally the effect of a non-resonant pulse (Stark effect) on the dynamics.

Magnetic susceptibility and spin-lattice interactions in U1-xPuxO2 single crystals

NASA Astrophysics Data System (ADS)

Kolberg, D.; Wastin, F.; Rebizant, J.; Boulet, P.; Lander, G. H.; Schoenes, J.

2002-12-01

Single crystals of mixed uranium-plutonium dioxides have been grown by means of a chemical vapor transport reaction and characterized by x-ray diffraction on bulk and powdered single crystals. Magnetization and susceptibility data were taken using a commercial superconducting quantum interference device. Characteristic ordering temperatures have been determined as well as paramagnetic Curie temperatures and effective magnetic moments. Departures of the reciprocal susceptibility as a function of temperature from linearity have been treated in detail based on a model of vibronic interactions introduced to explain the gross features of susceptibility measurements on thorium-diluted UO2 [Sasaki and Obata, J. Phys. Soc. Jpn. 28, 1157 (1970)]. The influence of spin-lattice interactions causes a certain shape of the observed 1/χ vs T curves from which we are able to suggest different mechanisms for the interactions as a function of the constituent’s concentrations. From our susceptibility measurements characteristic parameters have been calculated using a model of tetragonal vibrational modes of the oxygen cage surrounding each uranium ion. These include specific coupling parameters G, mode characteristic temperatures Tω, and molecular-field constants λ.

Dispersed fluorescence spectroscopy of the SiCN A ˜ 2 Δ - X ˜ 2 Π system: Observation of some vibrational levels with chaotic characteristics

NASA Astrophysics Data System (ADS)

Fukushima, Masaru; Ishiwata, Takashi

2016-12-01

The laser induced fluorescence (LIF) spectrum of the A ˜ 2Δ - X ˜ 2Π transition was obtained for SiCN generated by laser ablation under supersonic free jet expansion. The vibrational structures of the dispersed fluorescence (DF) spectra from single vibronic levels (SVL's) were analyzed with consideration of the Renner-Teller (R-T) interaction. Analysis of the pure bending (ν2) structure by a perturbation approach including R-T, anharmonicity, spin-orbit (SO), and Herzberg-Teller (H-T) interactions indicated considerably different spin splitting for the μ and κ levels of the X ˜ 2Π state of SiCN, in contrast to identical spin splitting for general species derived from the perturbation approach, where μ and κ specify the lower and upper levels, respectively, separated by R-T. Further analysis of the vibrational structure including R-T, anharmonicity, SO, H-T, Fermi, and Sears interactions was carried out via a direct diagonalization procedure, where Sears resonance is a second-order interaction combined from SO and H-T interactions with Δ K = ± 1, ΔΣ = ∓1, and Δ P = 0, and where P is a quantum number, P = K + Σ. The later numerical analysis reproduced the observed structure, not only the pure ν2 structure but also the combination structure of the ν2 and the Si-CN stretching (ν3) modes. As an example, the analysis demonstrates Sears resonance between vibronic levels, (0110) κ Σ(+) and ( 0 2 0 0 ) μ Π /1 2 , with Δ K = ± 1 and Δ P = 0. On the basis of coefficients of their eigen vectors derived from the numerical analysis, it is interpreted as an almost one-to-one mixing between the two levels. The mixing coefficients of the two vibronic levels agree with those obtained from computational studies. The numerical analysis also indicates that some of the vibronic levels show chaotic characteristics in view of the two-dimensional harmonic oscillator (2D-HO) basis which is used as the basis function in the present numerical analysis; i.e., the eigen vectors for some of the observed levels have several components of the basis, and we have not been able to give precise vibronic assignments for the levels, but just vibronically labeled, referring the largest component in their vectors. (To emphasize this situation, we do not use the word "assignment," but prefer to use "label" as the meaning of just "label," but not "assign," throughout this paper.) The latter shows that the vibronic labels of the levels are meaningless, and the P quantum number and the order of their eigen states in the P matrix block derived in the numerical analysis only characterize the vibronic levels. Comparing the constants obtained for all of the interactions with those of species showing Sears resonance and studied previously, it is found that none of them are strong, but are moderate. It is thus concluded that the chaotic appearance is not derived by any strong interaction, but is induced by complex and accidental proximities of the vibronic levels caused by the moderate interactions.

Vibrational and Nonadiabatic Coherence in 2D Electronic Spectroscopy, the Jahn-Teller Effect, and Energy Transfer

NASA Astrophysics Data System (ADS)

Jonas, David M.

2018-04-01

Femtosecond two-dimensional (2D) Fourier transform spectroscopy generates and probes several types of coherence that characterize the couplings between vibrational and electronic motions. These couplings have been studied in molecules with Jahn-Teller conical intersections, pseudo-Jahn-Teller funnels, dimers, molecular aggregates, photosynthetic light harvesting complexes, and photosynthetic reaction centers. All have closely related Hamiltonians and at least two types of vibrations, including one that is decoupled from the electronic dynamics and one that is nonadiabatically coupled. Polarized pulse sequences can often be used to distinguish these types of vibrations. Electronic coherences are rapidly obscured by inhomogeneous dephasing. The longest-lived coherences in these systems arise from delocalized vibrations on the ground electronic state that are enhanced by a nonadiabatic Raman excitation process. These characterize the initial excited-state dynamics. 2D oscillation maps are beginning to isolate the medium lifetime vibronic coherences that report on subsequent stages of the excited-state dynamics.

Organic Microcrystal Vibronic Lasers with Full-Spectrum Tunable Output beyond the Franck-Condon Principle.

PubMed

Dong, Haiyun; Zhang, Chunhuan; Liu, Yuan; Yan, Yongli; Hu, Fengqin; Zhao, Yong Sheng

2018-03-12

The very broad emission bands of organic semiconductor materials are, in theory, suitable for achieving versatile solid-state lasers; however, most of organic materials only lase at short wavelength corresponding to the 0-1 transition governed by the Franck-Condon (FC) principle. A strategy is developed to overcome the limit of FC principle for tailoring the output of microlasers over a wide range based on the controlled vibronic emission of organic materials at microcrystal state. For the first time, the output wavelength of organic lasers is tailored across all vibronic (0-1, 0-2, 0-3, and even 0-4) bands spanning the entire emission spectrum. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ab initio study of energy transfer rates and impact sensitivities of crystalline explosives.

PubMed

Bernstein, Jonathan

2018-02-28

Impact sensitivities of various crystalline explosives were predicted by means of plane wave-density functional theory calculations. Crystal structures and complete vibrational spectra of TATB, PETN, FOX7, TEX, 14DNI, and β-HMX molecular crystals were calculated. A correlation between the phonon-vibron coupling (which is proportionally related to the energy transfer rate between the phonon manifold and the intramolecular vibrational modes) and impact sensitivities of secondary explosives was found. We propose a method, based on ab initio calculations, for the evaluation of impact sensitivities, which consequently can assist in screening candidates for chemical synthesis of high energetic materials.

Resonant stimulation of Raman scattering from single-crystal thiophene/phenylene co-oligomers

NASA Astrophysics Data System (ADS)

Yanagi, Hisao; Marutani, Yusuke; Matsuoka, Naoki; Hiramatsu, Toru; Ishizumi, Atsushi; Sasaki, Fumio; Hotta, Shu

2013-12-01

Amplified Raman scattering was observed from single crystals of thiophene/phenylene co-oligomers (TPCOs). Under ns-pulsed excitation, the TPCO crystals exhibited amplified spontaneous emission (ASE) at resonant absorption wavelengths. With increasing excitation wavelength to the 0-0 absorption edge, the stimulated resonant Raman peaks appeared both in the 0-1 and 0-2 ASE band regions. When the excitation wavelength coincided with the 0-1 ASE band energy, the Raman peaks selectively appeared in the 0-2 ASE band. Such unusual enhancement of the 0-2 Raman scattering was ascribed to resonant stimulation via vibronic coupling with electronic transitions in the uniaxially oriented TPCO molecules.

Ab initio study of energy transfer rates and impact sensitivities of crystalline explosives

NASA Astrophysics Data System (ADS)

Bernstein, Jonathan

2018-02-01

Impact sensitivities of various crystalline explosives were predicted by means of plane wave-density functional theory calculations. Crystal structures and complete vibrational spectra of TATB, PETN, FOX7, TEX, 14DNI, and β-HMX molecular crystals were calculated. A correlation between the phonon-vibron coupling (which is proportionally related to the energy transfer rate between the phonon manifold and the intramolecular vibrational modes) and impact sensitivities of secondary explosives was found. We propose a method, based on ab initio calculations, for the evaluation of impact sensitivities, which consequently can assist in screening candidates for chemical synthesis of high energetic materials.

Assigning the low lying vibronic states of CH3O and CD3O

NASA Astrophysics Data System (ADS)

Johnson, Britta A.; Sibert, Edwin L.

2017-05-01

The assignment of lines in vibrational spectra in strongly mixing systems is considered. Several low lying vibrational states of the ground electronic X˜ 2E state of the CH3O and CD3O radicals are assigned. Jahn-Teller, spin-orbit, and Fermi couplings mix the normal mode states. The mixing complicates the assignment of the infrared spectra using a zero-order normal mode representation. Alternative zero-order representations, which include specific Jahn-Teller couplings, are explored. These representations allow for definitive assignments. In many instances it is possible to plot the wavefunctions on which the assignments are based. The plots, which are shown in the adiabatic representation, allow one to visualize the effects of various higher order couplings. The plots also enable one to visualize the conical seam and its effect on the wavefunctions. The first and the second order Jahn-Teller couplings in the rocking motion dominate the spectral features in CH3O, while first order and modulated first order couplings dominate the spectral features in CD3O. The methods described here are general and can be applied to other Jahn-Teller systems.

The shape of the electronic circular dichroism spectrum of (2,6-dimethylphenyl)(phenyl)methanol: interplay between conformational equilibria and vibronic effects.

PubMed

Padula, Daniele; Cerezo, Javier; Pescitelli, Gennaro; Santoro, Fabrizio

2017-12-13

Comparison between chiroptical spectra and theoretical predictions is the method of choice for the assignment of the absolute configuration of chiral compounds in solution. Here we report the case of an apparently simple biarylcarbinol, whose electronic circular dichroism (ECD) in the 1 L b region exhibits a peculiar alternation of negative and positive bands. Adopting Density Functional Theory, and describing solvent effects with implicit methods, we found three stable conformers in ethanol, each of them with two close lying states corresponding to similar local 1 L b excitations on the two phenyls. We computed the corresponding vibronic ECD spectra in harmonic approximation, including Duschinsky mixings as well as both Franck Condon (FC) and Herzberg Teller (HT) effects. Exploiting a recently developed mixed quantum/classical method, we further investigated the contribution of the vibronic spectra of out-of-equilibrium structures along the interconversion path connecting the different conformers. In this way, we achieved a reasonable agreement with experiment and attributed the alternating signs of the bands to the existence of different conformers. The remaining discrepancies with experiment indicate that specific solute-solvent interactions modulate the relative conformers' stabilities, calling for new methods able to combine Molecular Dynamics explorations and vibronic calculations. Moreover, the poor performance of HT approaches and the existence of two closely-lying states suggest the necessity of an improved fully-nonadiabatic vibronic approach. These findings demonstrate that even for such a simple system as the biarylcarbinol investigated here, a full reproduction of the fine details of the ECD spectrum requires the development of new improved methods.

Understanding Molecular Conduction: Old Wine in a New Bottle?

NASA Astrophysics Data System (ADS)

Ghosh, Avik

2007-03-01

Molecules provide an opportunity to test our understanding of fundamental non-equilibrium transport processes, as well as explore new device possibilities. We have developed a unified approach to nanoscale conduction, coupling bandstructure and electrostatics of the channel and contacts with a quantum kinetic theory of current flow. This allows us to describe molecular conduction at various levels of detail, -- from quantum corrected compact models, to semi-empirical models for quick physical insights, and `first-principles' calculations of current-voltage (I-V) characteristics with no adjustable parameters. Using this suite of tools, we can quantitatively explain various experimental I-Vs, including complex reconstructed silicon substrates. We find that conduction in most molecules is contact dominated, and limited by fundamental electrostatic and thermodynamic restrictions quite analogous to those faced by the silicon industry, barring a few interesting exceptions. The distinction between molecular and silicon electronics must therefore be probed at a more fundamental level. Ultra-short molecules are unique in that they possess large Coulomb energies as well as anomalous vibronic couplings with current flow -- in other words, strong non-equilibrium electron-electron and electron-phonon correlations. These effects yield prominent experimental signatures, but require a completely different modeling approach -- in fact, popular approaches to include correlation typically do not work for non-equilibrium. Molecules exhibit rich physics, including the ability to function both as weakly interacting current conduits (quantum wires) as well as strongly correlated charge storage centers (quantum dots). Theoretical treatment of the intermediate coupling regime is particularly challenging, with a large `fine structure constant' for transport that negates orthodox theories of Coulomb Blockade and phonon-assisted tunneling. It is in this regime that the scientific and technological merits of molecular conductors may need to be explored. For instance, the tunable quantum coupling of current flow in silicon transistors with engineered molecular scatterers could lead to devices that operate on completely novel principles.

Vibrational relaxation and internal conversion in the overlapped optically-allowed 1Bu+ and optically-forbidden 1Bu- or 3Ag- vibronic levels of carotenoids: Effects of diabatic mixing as determined by Kerr-gate fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Kakitani, Yoshinori; Miki, Takeshi; Koyama, Yasushi; Nagae, Hiroyoshi; Nakamura, Ryosuke; Kanematsu, Yasuo

2009-07-01

The time constants of the vibrational relaxation, υ = 2 → υ = 1 and υ = 1 → υ = 0, in the 1Bu+ manifold and those of internal conversion from the 1Bu+(0) level, which is isoenergetic (so-called 'diabatic') with the 1Bu- vibronic levels in neurosporene and spheroidene and with the 3Ag- vibronic levels in lycopene and anhydrorhodovibrin, were determined by Kerr-gate fluorescence spectroscopy. The time constants of the vibrational relaxation were in the ˜1:2 ratio, and those of internal conversion agreed with the lifetimes of the diabatic counterparts, i.e., the 1Bu- and 3Ag- electronic states, respectively.

Chromophore-Dependent Intramolecular Exciton-Vibrational Coupling in the FMO Complex: Quantification and Importance for Exciton Dynamics.

PubMed

Padula, Daniele; Lee, Myeong H; Claridge, Kirsten; Troisi, Alessandro

2017-11-02

In this paper, we adopt an approach suitable for monitoring the time evolution of the intramolecular contribution to the spectral density of a set of identical chromophores embedded in their respective environments. We apply the proposed method to the Fenna-Matthews-Olson (FMO) complex, with the objective to quantify the differences among site-dependent spectral densities and the impact of such differences on the exciton dynamics of the system. Our approach takes advantage of the vertical gradient approximation to reduce the computational demands of the normal modes analysis. We show that the region of the spectral density that is believed to strongly influence the exciton dynamics changes significantly in the timescale of tens of nanoseconds. We then studied the impact of the intramolecular vibrations on the exciton dynamics by considering a model of FMO in a vibronic basis and neglecting the interaction with the environment to isolate the role of the intramolecular exciton-vibration coupling. In agreement with the assumptions in the literature, we demonstrate that high frequency modes at energy much larger than the excitonic energy splitting have negligible influence on exciton dynamics despite the large exciton-vibration coupling. We also find that the impact of including the site-dependent spectral densities on exciton dynamics is not very significant, indicating that it may be acceptable to apply the same spectral density on all sites. However, care needs to be taken for the description of the exciton-vibrational coupling in the low frequency part of intramolecular modes because exciton dynamics is more susceptible to low frequency modes despite their small Huang-Rhys factors.

Theoretical Studies of Relaxation and Optical Properties of Polymers

NASA Astrophysics Data System (ADS)

Jin, Bih-Yaw

1993-01-01

This thesis is composed of two parts. In the part one, the empirical correlation between the logarithm of tunneling splittings and the temperature at which the spin-lattice relaxation time is minimum for methyl groups in different molecular crystals is explained successfully by taking multiphonon processes into account. We show that one phonon transitions dominate in the low barrier limit. However, in the intermediate barrier range and high barrier limit, it is necessary to include multiphonon processes. We also show that the empirical correlation depends only logarithmically on the details of the phonon bath. In the part two, we have investigated the optical and relaxation properties of conjugated polymers. The connection between the vibronic picture of Raman scattering and the third order perturbation approach in solid state physics is clarified in chapter 2. Starting from the Kramers -Heissenberg-Dirac formula for Raman scattering, we derive expressions for the Condon and Herzberg-Teller terms from a simple two-level system to a two-band system, i.e. polyacetylene, by using traditional vibronic picture. Both the Condon and Herzberg-Teller terms contribute to two-band processes, while three-band processes consist only of Herzberg-Teller terms in the solid state limit. Close to resonance the Condon term dominates and converges to the usual solid state result. In the off-resonance region the Herzberg -Teller term is comparable to Condon term for both small molecule and solid state system. In chapter 3, we will concentrate on the lattice relaxation of the lowest optically allowed 1B_ {u} state, especially, the effect of electron correlation on the excited state geometric relaxation for finite polyenes. We have examined the competition between electron-electron interaction and electron-phonon coupling on the formation of localized lattice distortion in the 1B_{u} state for finite polyene with chain length up to 30 double bonds. The chain length dependence of the lattice relaxation in 1B _{u} state has been studied thoroughly within singly excited configuration interaction for short range Hubbard, extended Hubbard model and long-range Pariser -Parr-Pople model. We have found that local distortion is not favored until a critical chain length is reached. Beyond this critical length, which is a function of electron-electron interaction and electron-phonon coupling strength, a self -trapped exciton is formed rather than the separated soliton -antisoliton configuration as expected in the independent electron theory. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).

Wave function continuity and the diagonal Born-Oppenheimer correction at conical intersections

NASA Astrophysics Data System (ADS)

Meek, Garrett A.; Levine, Benjamin G.

2016-05-01

We demonstrate that though exact in principle, the expansion of the total molecular wave function as a sum over adiabatic Born-Oppenheimer (BO) vibronic states makes inclusion of the second-derivative nonadiabatic energy term near conical intersections practically problematic. In order to construct a well-behaved molecular wave function that has density at a conical intersection, the individual BO vibronic states in the summation must be discontinuous. When the second-derivative nonadiabatic terms are added to the Hamiltonian, singularities in the diagonal BO corrections (DBOCs) of the individual BO states arise from these discontinuities. In contrast to the well-known singularities in the first-derivative couplings at conical intersections, these singularities are non-integrable, resulting in undefined DBOC matrix elements. Though these singularities suggest that the exact molecular wave function may not have density at the conical intersection point, there is no physical basis for this constraint. Instead, the singularities are artifacts of the chosen basis of discontinuous functions. We also demonstrate that continuity of the total molecular wave function does not require continuity of the individual adiabatic nuclear wave functions. We classify nonadiabatic molecular dynamics methods according to the constraints placed on wave function continuity and analyze their formal properties. Based on our analysis, it is recommended that the DBOC be neglected when employing mixed quantum-classical methods and certain approximate quantum dynamical methods in the adiabatic representation.

Wave function continuity and the diagonal Born-Oppenheimer correction at conical intersections.

PubMed

Meek, Garrett A; Levine, Benjamin G

2016-05-14

We demonstrate that though exact in principle, the expansion of the total molecular wave function as a sum over adiabatic Born-Oppenheimer (BO) vibronic states makes inclusion of the second-derivative nonadiabatic energy term near conical intersections practically problematic. In order to construct a well-behaved molecular wave function that has density at a conical intersection, the individual BO vibronic states in the summation must be discontinuous. When the second-derivative nonadiabatic terms are added to the Hamiltonian, singularities in the diagonal BO corrections (DBOCs) of the individual BO states arise from these discontinuities. In contrast to the well-known singularities in the first-derivative couplings at conical intersections, these singularities are non-integrable, resulting in undefined DBOC matrix elements. Though these singularities suggest that the exact molecular wave function may not have density at the conical intersection point, there is no physical basis for this constraint. Instead, the singularities are artifacts of the chosen basis of discontinuous functions. We also demonstrate that continuity of the total molecular wave function does not require continuity of the individual adiabatic nuclear wave functions. We classify nonadiabatic molecular dynamics methods according to the constraints placed on wave function continuity and analyze their formal properties. Based on our analysis, it is recommended that the DBOC be neglected when employing mixed quantum-classical methods and certain approximate quantum dynamical methods in the adiabatic representation.

Analysis of the vibronic structure of the trans-stilbene fluorescence and excitation spectra: the S0 and S1 PES along the Ce[double bond, length as m-dash]Ce and Ce-Cph torsions.

PubMed

Orlandi, Giorgio; Garavelli, Marco; Zerbetto, Francesco

2017-09-20

We analyze the highly resolved vibronic structure of the low energy (≤200 cm -1 ) region of the fluorescence and fluorescence excitation spectra of trans-stilbene in supersonic beams. In this spectral region the vibronic structure is associated mainly with vibrational levels of the C e -C e torsion (τ) and the a u combination of the two C e -C ph bond twisting (ϕ). We base this analysis on the well-established S 0 (τ, ϕ) two-dimensional potential energy surface (PES) and on a newly refined S 1 (τ, ϕ) PES. We obtain vibrational eigenvalues and eigenvectors of the anharmonic S 0 (τ, ϕ) and S 1 (τ, ϕ) PES using a numerical procedure based on the Meyer's flexible model [R. Meyer, J. Mol. Spectrosc., 1979, 76, 266]. Then we derive Franck-Condon factors and therefore intensities of the relevant vibronic bands for the S 0 → S 1 excitation and S 1 → S 0 fluorescence spectra. Furthermore, we assess the role of the b g combination of the two C e -C ph bond twisting (ν 48 ) in the structure of the S 1 → S 0 fluorescence spectra. By the use of these results we are able to assign most of the low energy vibrational levels of the S 0 → S 1 excitation spectra and of the fluorescence spectra of the emission from several low energy S 1 vibronic levels. The good agreement between the observed and the computed vibrational structure of the S 0 → S 1 and S 1 → S 0 spectra suggests that the proposed picture of the E 1 (τ, ϕ) and E 0 (τ, ϕ) PES, in particular along the coordinate τ governing trans-cis photo-isomerization in S 1 , is accurate. In S 0 , the barriers for the C e [double bond, length as m-dash]C e torsion and for the a u type C e -C ph bond twisting are 16 080 cm -1 and 3125 cm -1 , respectively, while in S 1 , where the bond orders of the C e [double bond, length as m-dash]C e and C e -C ph bonds are reversed, the two barriers become 1350 cm -1 and 8780 cm -1 , respectively.

On the adiabatic representation of Meyer-Miller electronic-nuclear dynamics

NASA Astrophysics Data System (ADS)

Cotton, Stephen J.; Liang, Ruibin; Miller, William H.

2017-08-01

The Meyer-Miller (MM) classical vibronic (electronic + nuclear) Hamiltonian for electronically non-adiabatic dynamics—as used, for example, with the recently developed symmetrical quasiclassical (SQC) windowing model—can be written in either a diabatic or an adiabatic representation of the electronic degrees of freedom, the two being a canonical transformation of each other, thus giving the same dynamics. Although most recent applications of this SQC/MM approach have been carried out in the diabatic representation—because most of the benchmark model problems that have exact quantum results available for comparison are typically defined in a diabatic representation—it will typically be much more convenient to work in the adiabatic representation, e.g., when using Born-Oppenheimer potential energy surfaces (PESs) and derivative couplings that come from electronic structure calculations. The canonical equations of motion (EOMs) (i.e., Hamilton's equations) that come from the adiabatic MM Hamiltonian, however, in addition to the common first-derivative couplings, also involve second-derivative non-adiabatic coupling terms (as does the quantum Schrödinger equation), and the latter are considerably more difficult to calculate. This paper thus revisits the adiabatic version of the MM Hamiltonian and describes a modification of the classical adiabatic EOMs that are entirely equivalent to Hamilton's equations but that do not involve the second-derivative couplings. The second-derivative coupling terms have not been neglected; they simply do not appear in these modified adiabatic EOMs. This means that SQC/MM calculations can be carried out in the adiabatic representation, without approximation, needing only the PESs and the first-derivative coupling elements. The results of example SQC/MM calculations are presented, which illustrate this point, and also the fact that simply neglecting the second-derivative couplings in Hamilton's equations (and presumably also in the Schrödinger equation) can cause very significant errors.

Coherent fifth-order visible-infrared spectroscopies: ultrafast nonequilibrium vibrational dynamics in solution.

PubMed

Lynch, Michael S; Slenkamp, Karla M; Cheng, Mark; Khalil, Munira

2012-07-05

Obtaining a detailed description of photochemical reactions in solution requires measuring time-evolving structural dynamics of transient chemical species on ultrafast time scales. Time-resolved vibrational spectroscopies are sensitive probes of molecular structure and dynamics in solution. In this work, we develop doubly resonant fifth-order nonlinear visible-infrared spectroscopies to probe nonequilibrium vibrational dynamics among coupled high-frequency vibrations during an ultrafast charge transfer process using a heterodyne detection scheme. The method enables the simultaneous collection of third- and fifth-order signals, which respectively measure vibrational dynamics occurring on electronic ground and excited states on a femtosecond time scale. Our data collection and analysis strategy allows transient dispersed vibrational echo (t-DVE) and dispersed pump-probe (t-DPP) spectra to be extracted as a function of electronic and vibrational population periods with high signal-to-noise ratio (S/N > 25). We discuss how fifth-order experiments can measure (i) time-dependent anharmonic vibrational couplings, (ii) nonequilibrium frequency-frequency correlation functions, (iii) incoherent and coherent vibrational relaxation and transfer dynamics, and (iv) coherent vibrational and electronic (vibronic) coupling as a function of a photochemical reaction.

Excited state absorption spectra of dissolved and aggregated distyrylbenzene: A TD-DFT state and vibronic analysis

NASA Astrophysics Data System (ADS)

Oliveira, Eliezer Fernando; Shi, Junqing; Lavarda, Francisco Carlos; Lüer, Larry; Milián-Medina, Begoña; Gierschner, Johannes

2017-07-01

A time-dependent density functional theory study is performed to reveal the excited state absorption (ESA) features of distyrylbenzene (DSB), a prototype π-conjugated organic oligomer. Starting with a didactic insight to ESA based on simple molecular orbital and configuration considerations, the performance of various density functional theory functionals is tested to reveal the full vibronic ESA features of DSB at short and long probe delay times.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. II. 1D spectra for a dimer.

PubMed

Tiwari, Vivek; Jonas, David M

2018-02-28

Vibrational-electronic resonance in photosynthetic pigment-protein complexes invalidates Förster's adiabatic framework for interpreting spectra and energy transfer, thus complicating determination of how the surrounding protein affects pigment properties. This paper considers the combined effects of vibrational-electronic resonance and inhomogeneous variations in the electronic excitation energies of pigments at different sites on absorption, emission, circular dichroism, and hole-burning spectra for a non-degenerate homodimer. The non-degenerate homodimer has identical pigments in different sites that generate differences in electronic energies, with parameters loosely based on bacteriochlorophyll a pigments in the Fenna-Matthews-Olson antenna protein. To explain the intensity borrowing, the excited state vibrational-electronic eigenvectors are discussed in terms of the vibrational basis localized on the individual pigments, as well as the correlated/anti-correlated vibrational basis delocalized over both pigments. Compared to those in the isolated pigment, vibrational satellites for the correlated vibration have the same frequency and precisely a factor of 2 intensity reduction through vibrational delocalization in both absorption and emission. Vibrational satellites for anti-correlated vibrations have their relaxed emission intensity reduced by over a factor 2 through vibrational and excitonic delocalization. In absorption, anti-correlated vibrational satellites borrow excitonic intensity but can be broadened away by the combination of vibronic resonance and site inhomogeneity; in parallel, their vibronically resonant excitonic partners are also broadened away. These considerations are consistent with photosynthetic antenna hole-burning spectra, where sharp vibrational and excitonic satellites are absent. Vibrational-excitonic resonance barely alters the inhomogeneously broadened linear absorption, emission, and circular dichroism spectra from those for a purely electronic excitonic coupling model. Energy transfer can leave excess energy behind as vibration on the electronic ground state of the donor, allowing vibrational relaxation on the donor's ground electronic state to make energy transfer permanent by removing excess energy from the excited electronic state of the dimer.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. II. 1D spectra for a dimer

NASA Astrophysics Data System (ADS)

Tiwari, Vivek; Jonas, David M.

2018-02-01

Vibrational-electronic resonance in photosynthetic pigment-protein complexes invalidates Förster's adiabatic framework for interpreting spectra and energy transfer, thus complicating determination of how the surrounding protein affects pigment properties. This paper considers the combined effects of vibrational-electronic resonance and inhomogeneous variations in the electronic excitation energies of pigments at different sites on absorption, emission, circular dichroism, and hole-burning spectra for a non-degenerate homodimer. The non-degenerate homodimer has identical pigments in different sites that generate differences in electronic energies, with parameters loosely based on bacteriochlorophyll a pigments in the Fenna-Matthews-Olson antenna protein. To explain the intensity borrowing, the excited state vibrational-electronic eigenvectors are discussed in terms of the vibrational basis localized on the individual pigments, as well as the correlated/anti-correlated vibrational basis delocalized over both pigments. Compared to those in the isolated pigment, vibrational satellites for the correlated vibration have the same frequency and precisely a factor of 2 intensity reduction through vibrational delocalization in both absorption and emission. Vibrational satellites for anti-correlated vibrations have their relaxed emission intensity reduced by over a factor 2 through vibrational and excitonic delocalization. In absorption, anti-correlated vibrational satellites borrow excitonic intensity but can be broadened away by the combination of vibronic resonance and site inhomogeneity; in parallel, their vibronically resonant excitonic partners are also broadened away. These considerations are consistent with photosynthetic antenna hole-burning spectra, where sharp vibrational and excitonic satellites are absent. Vibrational-excitonic resonance barely alters the inhomogeneously broadened linear absorption, emission, and circular dichroism spectra from those for a purely electronic excitonic coupling model. Energy transfer can leave excess energy behind as vibration on the electronic ground state of the donor, allowing vibrational relaxation on the donor's ground electronic state to make energy transfer permanent by removing excess energy from the excited electronic state of the dimer.

Analysis of Rotationally Resolved Spectra to Non-Degenerate (a''_1) Upper-State Vibronic Levels in the tilde{A} ^2E''-tilde{X}^2A^'_2 Electronic Transition of NO_3

NASA Astrophysics Data System (ADS)

Roudjane, Mourad; Codd, Terrance Joseph; Chen, Ming-Wei; Tran, Henry; Melnik, Dmitry G.; Miller, Terry A.; Stanton, John F.

2015-06-01

The vibronic structure of the tilde{A}-tilde{X} electronic spectrum of NO_3 has been observed using both room-temperature and jet-cooled samples. A recent analysis of this structure is consistent with the Jahn-Teller effect (JTE) in the e^' ν_3 vibrational mode (N-O stretch) being quite strong while the JTE in the e^' ν_4 mode (O-N-O) bend) is rather weak. Electronic structure calculations qualitatively predict these results but the calculated magnitude of the JTE is quantitatively inconsistent with the spectral analysis. Rotationally resolved spectra have been obtained for over a dozen vibronic bands of the tilde{A}-tilde{X} electronic transition in NO_3. An analysis of these spectra should provide considerably more experimental information about the JTE in the tilde{A} state of NO_3 as the rotational structure should be quite sensitive to the geometric distortion of the molecule due to the JTE. This talk will focus upon the parallel bands, which terminate on tilde{A} state levels of a''_1 vibronic symmetry, which were the subject of a preliminary analysis reported at this meeting in 2014. We have now recorded the rotational structure of over a half-dozen parallel bands and have completed analysis on the 3^1_0 and 3^1_0 4^1_0 transitions with several other bands being reasonably well understood. Two general conclusions emerge from this work. (i) All the spectral bands show evidence of perturbations which can reasonably be assumed to result from interactions of the observed tilde{A} state levels with high vibrational levels of the tilde{X} state. The perturbations range from severe in some bands to quite modest in others. (ii) Analyses of observed spectra, insofar as the perturbations permit, have all been performed with an oblate symmetric top model including only additional spin-rotation effects. This result is, of course, consistent with an effective, undistorted geometry for NO_3 of D3h symmetry on the rotational timescale.

Hyperfine interaction constants of 14NO2 in 14 500-16 800 cm-1 energy region

NASA Astrophysics Data System (ADS)

Tada, Kohei; Hirata, Michihiro; Kasahara, Shunji

2017-10-01

We observed hyperfine-resolved high-resolution fluorescence excitation spectra of k = 0, N = 1 ← 0 transitions in 82 vibronic bands of the à 2B2 ← X ˜ 2A1 system of 14NO2 in the 14 500-16 800 cm-1 region by crossing a jet-cooled molecular beam and a single-mode dye laser beam at right angles. We determined hyperfine interaction constants of the lower and upper states for all the observed vibronic bands based on the analysis of the hyperfine structures of k = 0, N = 1 ← 0 transitions. Most of the determined Fermi contact interaction constants were found to be distributed in 0.0013-0.0038 cm-1, which are intermediate in magnitude between those in lower and higher energy region reported by other groups. A sharp decreasing of the Fermi contact interaction constant was found in 16 200-16 600 cm-1, and it may be caused by the interaction with the dark C ˜ 2A2 state. The hyperfine interaction constants are powerful clues to obtain reliable vibronic assignment. We tentatively assigned vibronic bands located at 14 836 cm-1, 15 586 cm-1, and 16 322 cm-1 as the transitions to the intrinsic (0,7,0), (0,8,0), and (0,9,0) vibrational levels of the à 2B2 state, respectively.

Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups.

PubMed

Nieto-Pescador, Jesus; Abraham, Baxter; Li, Jingjing; Batarseh, Alberto; Bartynski, Robert A; Galoppini, Elena; Gundlach, Lars

2016-01-14

Heterogeneous electron transfer (HET) between photoexcited molecules and colloidal TiO 2 has been investigated for a set of Zn-porphyrin chromophores attached to the semiconductor via linkers that allow to change level alignment by 200 meV by reorientation of the dipole moment. These unique dye molecules have been studied by femtosecond transient absorption spectroscopy in solution and adsorbed on the TiO 2 colloidal film in vacuum. In solution energy transfer from the excited chromophore to the dipole group has been identified as a slow relaxation pathway competing with S 2 -S 1 internal conversion. On the film heterogeneous electron transfer occurred in 80 fs, much faster compared to all intramolecular pathways. Despite a difference of 200 meV in level alignment of the excited state with respect to the semiconductor conduction band, identical electron transfer times were measured for different linkers. The measurements are compared to a quantum-mechanical model that accounts for electronic-vibronic coupling and finite band width for the acceptor states. We conclude that HET occurs into a distribution of transition states that differs from regular surface states or bridge mediated states.

Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission

NASA Astrophysics Data System (ADS)

Stern, Hannah L.; Cheminal, Alexandre; Yost, Shane R.; Broch, Katharina; Bayliss, Sam L.; Chen, Kai; Tabachnyk, Maxim; Thorley, Karl; Greenham, Neil; Hodgkiss, Justin M.; Anthony, John; Head-Gordon, Martin; Musser, Andrew J.; Rao, Akshay; Friend, Richard H.

2017-12-01

Singlet exciton fission (SF), the conversion of one spin-singlet exciton (S1) into two spin-triplet excitons (T1), could provide a means to overcome the Shockley-Queisser limit in photovoltaics. SF as measured by the decay of S1 has been shown to occur efficiently and independently of temperature, even when the energy of S1 is as much as 200 meV less than that of 2T1. Here we study films of triisopropylsilyltetracene using transient optical spectroscopy and show that the triplet pair state (TT), which has been proposed to mediate singlet fission, forms on ultrafast timescales (in 300 fs) and that its formation is mediated by the strong coupling of electronic and vibrational degrees of freedom. This is followed by a slower loss of singlet character as the excitation evolves to become only TT. We observe the TT to be thermally dissociated on 10-100 ns timescales to form free triplets. This provides a model for 'temperature-independent' efficient TT formation and thermally activated TT separation.

An algebraic cluster model based on the harmonic oscillator basis

NASA Technical Reports Server (NTRS)

Levai, Geza; Cseh, J.

1995-01-01

We discuss the semimicroscopic algebraic cluster model introduced recently, in which the internal structure of the nuclear clusters is described by the harmonic oscillator shell model, while their relative motion is accounted for by the Vibron model. The algebraic formulation of the model makes extensive use of techniques associated with harmonic oscillators and their symmetry group, SU(3). The model is applied to some cluster systems and is found to reproduce important characteristics of nuclei in the sd-shell region. An approximate SU(3) dynamical symmetry is also found to hold for the C-12 + C-12 system.

Acoustic Properties of Crystals with Jahn-Teller Impurities: Elastic Moduli and Relaxation Time. Application to SrF2:Cr2+

NASA Astrophysics Data System (ADS)

Averkiev, Nikita S.; Bersuker, Isaac B.; Gudkov, Vladimir V.; Zhevstovskikh, Irina V.; Sarychev, Maksim N.; Zherlitsyn, Sergei; Yasin, Shadi; Shakurov, Gilman S.; Ulanov, Vladimir A.; Surikov, Vladimir T.

2017-11-01

A new approach to evaluate the relaxation contribution to the total elastic moduli for crystals with Jahn-Teller (JT) impurities is worked out and applied to the analysis of the experimentally measured ultrasound velocity and attenuation in SrF2:Cr2+. Distinguished from previous work, the background adiabatic contribution to the moduli, important for revealing the impurity relaxation contribution, is taken into account. The temperature dependence of the relaxation time for transitions between the equivalent configurations of the JT centers has been obtained, and the activation energy for the latter in SrF2:Cr2+, as well as the linear vibronic coupling constant have been evaluated.

Vacuum ultraviolet spectroscopy of the lowest-lying electronic state in subcritical and supercritical water

NASA Astrophysics Data System (ADS)

Marin, Timothy W.; Janik, Ireneusz; Bartels, David M.; Chipman, Daniel M.

2017-05-01

The nature and extent of hydrogen bonding in water has been scrutinized for decades, including how it manifests in optical properties. Here we report vacuum ultraviolet absorption spectra for the lowest-lying electronic state of subcritical and supercritical water. For subcritical water, the spectrum redshifts considerably with increasing temperature, demonstrating the gradual breakdown of the hydrogen-bond network. Tuning the density at 381 °C gives insight into the extent of hydrogen bonding in supercritical water. The known gas-phase spectrum, including its vibronic structure, is duplicated in the low-density limit. With increasing density, the spectrum blueshifts and the vibronic structure is quenched as the water monomer becomes electronically perturbed. Fits to the supercritical water spectra demonstrate consistency with dimer/trimer fractions calculated from the water virial equation of state and equilibrium constants. Using the known water dimer interaction potential, we estimate the critical distance between molecules (ca. 4.5 Å) needed to explain the vibronic structure quenching.

Vacuum ultraviolet spectroscopy of the lowest-lying electronic state in subcritical and supercritical water

DOE PAGES

Marin, Timothy W.; Janik, Ireneusz; Bartels, David M.; ...

2017-05-17

The nature and extent of hydrogen bonding in water has been scrutinized for decades, including how it manifests in optical properties. Here we report vacuum ultraviolet absorption spectra for the lowest-lying electronic state of subcritical and supercritical water. For subcritical water, the spectrum redshifts considerably with increasing temperature, demonstrating the gradual breakdown of the hydrogen-bond network. Tuning the density at 381°C gives insight into the extent of hydrogen bonding in supercritical water. The known gas-phase spectrum, including its vibronic structure, is duplicated in the low-density limit. With increasing density, the spectrum blueshifts and the vibronic structure is quenched as themore » water monomer becomes electronically perturbed. Fits to the supercritical water spectra demonstrate consistency with dimer/trimer fractions calculated from the water virial equation of state and equilibrium constants. As a result, using the known water dimer interaction potential, we estimate the critical distance between molecules (ca. 4.5 Å) needed to explain the vibronic structure quenching.« less

Experimental and Computational Investigations of the Threshold Photoelectron Spectrum of the HCCN Radical

NASA Astrophysics Data System (ADS)

Gans, B.; Falvo, Cyril; Coudert, L. H.; Garcia, Gustavo A.; Küger, J.; Loison, J.-C.

2017-06-01

The HCCN radical, already detected in the interstellar medium, is also important for nitrile chemistry in Titan's atmosphere. Quite recently the photoionization spectrum of the radical has been recorded using mass selected threshold photoelectron (TPE) spectroscopy and this provided us with the first spectroscopic information about the HCCN} cation. Modeling such a spectrum requires accounting for the non-rigidity of HCCN and for the Renner-Teller effect in HCCN+. In its ^3A'' electronic ground state, HCCN is a non-rigid molecule as the potential for the \\angle{HCC} bending angle is very shallow. Vibronic couplings with the same bending angle leads, in the ^2Π electronic ground state of HCCN+, to a strong Renner-Teller effect giving rise to a bent ^2A' and a quasi-linear ^2A'' state. In this paper the photoionization spectrum of the HCCN radical is simulated. The model developped treats the \\angle{HCC} bending angle as a large amplitude coordinate in both the radical and the cation and accounts for the overall rotation and the Renner-Teller couplings. Gaussian quadrature are used to calculate matrix elements of the three potential energy functions retrieved through ab initio calculations and rovibrational operators going to infinity for the linear configuration are treated rigorously. The HCCN TPE spectrum is computed with the above model calculating all rotational components and choosing the appropriate lineshape. This synthetic spectrum will be shown in the paper and compared with the experimental one.^b Guélin and Cernicharo, A&A 244 (1991) L21 Loison et al., Icarus 247 (2015) 218 Garcia, Krüger, Gans, Falvo, Coudert, and Loison, J. Chem. Phys. (2017) submitted Koput, J. Phys. Chem. A 106 (2002) 6183 Zhao, Zhang, and Sun, J. Phys. Chem. A 112 (2008) 12125

Nonadiabatic excited-state molecular dynamics modeling of photoinduced dynamics in conjugated molecules.

PubMed

Nelson, Tammie; Fernandez-Alberti, Sebastian; Chernyak, Vladimir; Roitberg, Adrian E; Tretiak, Sergei

2011-05-12

Nonadiabatic dynamics generally defines the entire evolution of electronic excitations in optically active molecular materials. It is commonly associated with a number of fundamental and complex processes such as intraband relaxation, energy transfer, and light harvesting influenced by the spatial evolution of excitations and transformation of photoexcitation energy into electrical energy via charge separation (e.g., charge injection at interfaces). To treat ultrafast excited-state dynamics and exciton/charge transport we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework incorporating quantum transitions. Our calculations rely on the use of the Collective Electronic Oscillator (CEO) package accounting for many-body effects and actual potential energy surfaces of the excited states combined with Tully's fewest switches algorithm for surface hopping for probing nonadiabatic processes. This method is applied to model the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene, PPV). Our analysis shows intricate details of photoinduced vibronic relaxation and identifies specific slow and fast nuclear motions that are strongly coupled to the electronic degrees of freedom, namely, torsion and bond length alternation, respectively. Nonadiabatic relaxation of the highly excited mA(g) state is predicted to occur on a femtosecond time scale at room temperature and on a picosecond time scale at low temperature.

Note: Observation of a new electronically excited state of cobalt monoxide

NASA Astrophysics Data System (ADS)

Zang, Jianzheng; Zhang, Qun; Qin, Chengbing; Gu, Zhong; Bai, Xilin; Chen, Yang

2012-11-01

The laser-induced fluorescence excitation spectra of jet-cooled CoO molecules have been recorded in the energy region of 21 800—25 000 cm-1. Apart from the seven vibronic bands assigned to the known G4Φ9/2(υ') - X4Δ7/2(υ″ = 0) progression [M. Barnes, D. J. Clouthier, P. G. Hajigeorgiou, G. Huang, C. T. Kingston, A. J. Merer, G. F. Metha, J. R. D. Peers, and S. J. Rixon, J. Mol. Spectrosc. 186, 374 (1997), 10.1006/jmsp.1997.7456], we observed a new band system assignable to the [22.95]4Δ7/2(υ' = 0 - 4) - X4Δ7/2(υ″ = 0) progression. Extensive perturbations among these vibronic bands have been revealed by means of reduced energy plots. The new electronically excited 4Δ state has been determined to be most likely of an electronic configuration (2pπ)3(4sσ)2(3dδ)3(3dπ)3 based on the charge-transferred promotion model.

Mesoepitaxy: A Universal Route to Oriented Materials

DTIC Science & Technology

1993-06-14

naphthoic acid) (VecuaZ, Hoechst-Celanese], a perfluorinated copolymer of ethylene and propylene (FEP TI00, Du Pont], poly(butylene terephthalate) (PBT...189 meV). In ferences are evident in the vibronic character of the ab- addition, the zero-phonon emission line, now at 2.09 eV, sorption and emission...the ab- sorption spectra is disorder-induced localization. To model the photoluminescence spectrum, we con- Qualitatively, the disordered -,r-electron

Enhanced vibronic interaction caused by local lattice symmetry lowering in the (Fe, Mg)As2 ternary system

NASA Astrophysics Data System (ADS)

Pishtshev, A.; Rubin, P.

2018-04-01

By means of periodic density functional theory (DFT) electronic structure calculations, we investigate iron-site doping effects in a structural model of bulk FeAs2. Simulations performed within the projector augmented-wave method-Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) functional scheme reveal that the impacts of the two stoichiometric substitutions Fe → Mg and Fe → Ni are radically different with respect to the structural and electronic behavior of the dopants. In particular, unlike the Ni dopant, the Mg dopant incorporated in FeAs2 occupies a noncentral equilibrium position characterized by an off-center displacement from the reference higher-symmetry position. Analysis of the respective electron and vibrational factors allows us to explain this result in terms of the local pseudo Jahn-Teller effect (pJTE). On the basis of DFT calculations, we deduce which electron orbitals and lattice vibrational modes are appropriate for promoting the local instability at the origin of the pJTE. Quantitative evaluations of the pJTE parameters performed within the polyatomic formalism of an effective tight-binding model show that it is just the enhanced vibronic interaction in the Mg-[FeAs6] cluster that is responsible for the local lattice symmetry breaking.

Hot Band Analysis and Kinetics Measurements for Ethynyl Radical, C_2H, in the 1.49 μm Region

NASA Astrophysics Data System (ADS)

Le, Anh T.; Hall, Gregory; Sears, Trevor

2017-06-01

Ethynyl, C_2H, is an important intermediate in combustion processes and has been widely observed in interstellar space. Spectroscopically, it is of particular interest because it possesses three low-lying electronic surfaces: a ground ^2Σ^+state, and a low-lying ^2Π excited electronic state, which splits due to the Renner-Teller effect. Vibronic coupling among these states leads to a complicated, mixed-character, energy level structure. We have previously reported work on three bands originating from the ˜{X}(0,0,0) ^2Σ ground state to excited vibronic states: two ^2Σ - ^2 Σ transitions at 6696 and 7088 \\wn and a ^2Π - ^2Σ transition at 7108 \\wn. In this work, the radicals were formed in a hot, non-thermal, population distribution by u.v. pulsed laser photolysis of a precursor. Kinetic measurements of the time-evolution of the ground state populations following collisional relaxation and reactive loss were also made, using some of the stronger rotational lines observed. Time-dependent signals in mixtures containing a variable concentration of precursor in argon suggested that vibronically hot C_2H radicals were less reactive than the relaxed, thermalized, radical. Two additional hot bands originating in states ˜{X}(0,1^1,0) ^2Π and ˜{X}(0,2^0,0) ^2Σ, have now been identified in the same spectral region. In a new series of experiments, we have measured the kinetics of formation and decay of representative levels involving all the assigned transitions, i.e. originating in ˜{X}(0,v_2,0), with v_2 =0 ,1, and 2, in various concentrations of mixtures of precursor, inert gas and hydrogen. The new spectra also show greatly improved signal-to-noise ratio in comparison to our previous work, due to the use of a transient FM detection scheme, and additional spectral assignments seem likely. Both kinetics and spectroscopic results will be described in the talk. Acknowledgments: Work at Brookhaven National Laboratory was carried out under Contract No. DE-SC0012704 with the U.S. Department of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences and Biosciences within the Office of Basic Energy Sciences. A. T. Le, G. E. Hall, T. J. Sears, J. Chem. Phys. 145 074306, 2016

The Spectroscopy and Photophysics of Aniline, 2-AMINOPYRIDINE, and 3-AMINOPYRIDINE

NASA Astrophysics Data System (ADS)

Kim, Byungjoo

1995-01-01

Two-photon ionization photoelectron spectroscopic techniques have been employed in concert with a picosecond laser system and molecular beam machine to study the vibrational structure of molecular ions and the intramolecular dynamics of optically prepared intermediate states. From photoelectron spectra of 2-aminopyridine via various S_1 vibronic resonances, the frequencies of several vibrations in the ionic state are assigned. The ionization potential of the molecule is found to be 8.099 +/- 0.003 eV. Using two-color ionization techniques, the electronic overlap effects in the photoionization of excited molecules have been studied, on the example of 2-aminopyridine, 3-aminopyridine, and aniline. The molecules are excited to their S_1 states, and ionized by a 200 nm laser pulse within 50 ps. The spectra of the aminopyridines show a striking absence of transitions to excited electronic states of the ions, indicating small electronic overlap factors in the ionization transitions and very little configuration interaction in the S _1 states. The spectra of aniline show the vibrationally resolved first excited electronic state band of the ion, which is very weak compared to the ground electronic state band, indicating a small amount of orbital mixing in the S_1 state. The vibrational peaks in the band were assigned by comparison of the spectra via two different vibronic resonances. The observations demonstrate that electronic overlap effects play a very general role in the ionization of polyatomic molecules in electronically excited states, and that orbital mixing patterns of the excited electronic states may become observable by projecting molecular electronic wavefunctions onto the ion states. In the time-delayed experiments for these molecules, all spectra reveal only one product of the nonradiative relaxation process. Careful considerations of electronic and vibrational overlap propensity rules for the ionization step lead to the conclusion that the dominant nonradiative decay mechanism in these molecules is the intersystem crossing to excited vibrational states of the T_1 state. This technique has been applied to study the predissociation process of CS_2 in the S_3 vibronic levels near 200 nm. The spectra show extensive vibrational structure, with unusual activity in the antisymmetric vibrations, indicating the possibility of level mixing in the intermediate state by the IVR couplings.

Communication: Transient anion states of phenol…(H2O)n (n = 1, 2) complexes: Search for microsolvation signatures

NASA Astrophysics Data System (ADS)

de Oliveira, Eliane M.; Freitas, Thiago C.; Coutinho, Kaline; do N. Varella, Márcio T.; Canuto, Sylvio; Lima, Marco A. P.; Bettega, Márcio H. F.

2014-08-01

We report on the shape resonance spectra of phenol-water clusters, as obtained from elastic electron scattering calculations. Our results, along with virtual orbital analysis, indicate that the well-known indirect mechanism for hydrogen elimination in the gas phase is significantly impacted on by microsolvation, due to the competition between vibronic couplings on the solute and solvent molecules. This fact suggests how relevant the solvation effects could be for the electron-driven damage of biomolecules and the biomass delignification [E. M. de Oliveira et al., Phys. Rev. A 86, 020701(R) (2012)]. We also discuss microsolvation signatures in the differential cross sections that could help to identify the solvated complexes and access the composition of gaseous admixtures of these species.

Symmetry breaking in the planar configurations of disilicon tetrahalides: Pseudo-Jahn-Teller effect parameters, hardness and electronegativity.

PubMed

Kouchakzadeh, Ghazaleh; Nori-Shargh, Davood

2015-11-21

CCSD(T), MP2, LC-BLYP, LC-ωPBE and B3LYP methods with the Def2-TZVPP basis set and natural bond orbital (NBO) interpretations were performed to investigate the correlations between the Pseudo-Jahn-Teller Effect (PJTE) parameters [i.e. vibronic coupling constant values (F), energy gaps between reference states (Δ) and the primary force constant (K0)], structural and configurational properties, global hardness, global electronegativity, natural bond orders, stabilization energies associated with electron delocalizations and natural atomic charges of disilicon tetrafluoride (1), disilicon tetrachloride (2), disilicon tetrabromide (3) and disilicon tetraiodide (4). All levels of theory showed the trans-bent (C2h) configurations as the energy minimum structures of compounds 1-4, and the flap angles between the X2Si planes and the Si=Si bonds in the distorted (C2h) configurations decrease from compound 1 to compound 4. The negative curvatures of the ground state electronic configurations and the positive curvatures of the excited states of the adiabatic potential energy surfaces (APESs) which resulted from the mixing of the ground Ag and excited B2g states are due to the PJTE (i.e. PJT(Ag + B2g) ⊗ b2g problem). Contrary to the usual expectation, with the decrease of the energy gaps between reference states (Δ), the PJTE stabilization energy, E(PJT), decreases from compound 1 to compound 4. The canonical molecular orbital (CMO) analysis revealed that the contributions of the ψ(HOMO)(b3u) and ψL(UMO)(b1u) molecular orbitals in the vibronic coupling constant (F) decrease from compound 1 to compound 4. This fact clearly justifies the decrease of the vibronic coupling constant (F) and the primary force constant (the force constant without the PJTE) values on going from compound 1 to compound 4, leading to the decrease of the negative curvatures of the ground state electronic configuration curves of their corresponding APESs. The results obtained showed that the stabilization energies associated with the mixing of the distorted donor π(Si-Si)(b(u)) bonding and acceptor σ(Si-Si)*(b(u)) antibonding orbitals along the b2g bending distortions decrease from compound 1 to compound 4. This fact reasonably explains the increase of the Si-Si natural bond orders (nbo) on going from compound 1 to compound 4. With the increase of the Si-Si natural bond orders, the corresponding E(PJT) decreases from compound 1 to compound 4. Importantly, the variations of the global hardness (η) differences (Δ[η(C2h) - η(D2h)]) do not correlate with the trend observed for their corresponding total energy differences, justifying that the configurational properties of compounds 1-4 do not obey the maximum hardness principle. Interestingly, the trans-bent (C2h) configurations of compounds 1-4 are more electronegative than their corresponding planar (D2h) forms and the variations of their global electronegativity (χ) differences (Δ[χ(C2h) - χ(D2h)]) succeed in accounting for the decrease of the E(PJT) stabilization energies for the D2h → C2h conversion processes on going from compound 1 to compound 4.

Near UV bands of jet-cooled CaO

NASA Astrophysics Data System (ADS)

Stewart, Jacob T.; Sullivan, Michael N.; Heaven, Michael C.

2016-04-01

The electronic spectrum of CaO has been recorded for the 29,800-33,150 cm-1 energy range. Jet cooling was used to obtain relatively uncongested spectra. Rotationally resolved bands have been assigned to the C1Σ+-X1Σ+ and F1∏-X transitions. These data extend the range of vibronic levels characterized for the upper states. Three additional vibronic states were observed as a short progression. One of these levels, which are of 0+ symmetry, interacts strongly with the C1Σ+, v‧ = 7 level. Possible assignments for the perturbing state are considered.

The influence of the nature of a substituent on the parameters of the intra- and intermolecular interactions in molecules of cross-conjugated ketones

NASA Astrophysics Data System (ADS)

Kompaneets, V. V.; Vasilieva, I. A.

2017-08-01

We have quantitatively analyzed the vibronic parameters of two cross-conjugated δ-dimethylaminoketones. The presence of the -N(CH3)2, C=O, and -NO2 groups in the benzene ring has been shown to affect the manifestation of the vibronic parameters of characteristic bands that describe the state (vibrations, types of deformation upon excitation) of polyene systems with aromatic rings. Data on the influence of the nature of the substituent on the parameters of intra- and intermolecular interactions in the examined compounds have been presented.

FAR-INFRARED SPECTROSCOPY OF CATIONIC POLYCYCLIC AROMATIC HYDROCARBONS: ZERO KINETIC ENERGY PHOTOELECTRON SPECTROSCOPY OF PENTACENE VAPORIZED FROM LASER DESORPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Jie; Han Fangyuan; Pei Linsen

2010-05-20

The distinctive set of infrared (IR) emission bands at 3.3, 6.2, 7.7, 8.6, and 11.3 {mu}m are ubiquitously seen in a wide variety of astrophysical environments. They are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules. However, not a single PAH species has yet been identified in space, as the mid-IR vibrational bands are mostly representative of functional groups and thus do not allow one to fingerprint individual PAH molecules. In contrast, the far-IR (FIR) bands are sensitive to the skeletal characteristics of a molecule, hence they are important for chemical identification of unknown species. With an aim to offermore » laboratory astrophysical data for the Herschel Space Observatory, Stratospheric Observatory for Infrared Astronomy, and similar future space missions, in this work we report neutral and cation FIR spectroscopy of pentacene (C{sub 22}H{sub 14}), a five-ring PAH molecule. We report three IR active modes of cationic pentacene at 53.3, 84.8, and 266 {mu}m that may be detectable by space missions such as the SAFARI instrument on board SPICA. In the experiment, pentacene is vaporized from a laser desorption source and cooled by a supersonic argon beam. We have obtained results from two-color resonantly enhanced multiphoton ionization and two-color zero kinetic energy photoelectron (ZEKE) spectroscopy. Several skeletal vibrational modes of the first electronically excited state of the neutral species and those of the cation are assigned, with the aid of ab initio and density functional calculations. Although ZEKE is governed by the Franck-Condon principle different from direct IR absorption or emission, vibronic coupling in the long ribbon-like molecule results in the observation of a few IR active modes. Within the experimental resolution of {approx}7 cm{sup -1}, the frequency values from our calculation agree with the experiment for the cation, but differ for the electronically excited intermediate state. Consequently, modeling of the intensity distribution is difficult and may require explicit inclusion of vibronic interactions.« less

Optical and tunneling microscopy and spectroscopy at the ultimate spatial limit

NASA Astrophysics Data System (ADS)

Chen, Chi

2009-12-01

The combination of optical detection system with a scanning tunneling microscope (STM) leads to the possibility of resolving radiative transition probability with the ultrahigh spatial resolution of STM in real space. This opens an innovative approach toward revealing the correlation between molecular structure, electronic characteristics, and optical properties. This thesis describes a series of experiments that manifests this correlation, including atomic silver chains and single porphine molecules. In atomic silver chains, the number and positions of the emission maxima in the photon images match the nodes in the dI/d V images of "particle-in-a-box" states. This surprising correlation between the emission maxima and nodes in the density of states is a manifestation of Fermi's golden rule in real space for radiative transitions, which provides an understanding of the mechanism of STM induced light emission. From single porphine molecules, orthogonal spatial contrast of two types of vibronic coupling is resolved by both photon spectroscopy and vibronic-mode-selected photon images. Intramolecular transitions from the two orthogonal LUMOs individually couple to different molecular normal modes. This is the first demonstration of the photon emission probability of a single molecule and its direct correlations with the molecular orbitals. This also provides the first real space experimental evidence to separate the tangled effects of molecular conformations and nano-environments on the inhomogeneity of molecular emission. DSB molecules are found to have two conformational isomers and one of them shows surface chirality. All these conformers and enantiomers can be switched to each other by electron injection. Different DSB conformers present distinct manipulation dynamics, which demonstrate how different conformations and their preferred adsorption geometries can have pronounced influence on the molecular mechanics on the surface. Overall, this thesis studies the very fundamental nature of single molecules and artificial nanostructures by integrating all kinds of important functions of STM: topography, spectroscopy, manipulation, and photon emission. Detailed correlations between the emission patterns and orbital structures are revealed by the ultimate spatial resolution of our "STM photon microscopy".

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seyler, Kyle L.; Zhong, Ding; Klein, Dahlia R.

Bulk chromium tri-iodide (CrI 3) has long been known as a layered van der Waals ferromagnet. However, its monolayer form was only recently isolated and confirmed to be a truly two-dimensional (2D) ferromagnet, providing a new platform for investigating light–matter interactions and magneto-optical phenomena in the atomically thin limit. Here in this paper, we report spontaneous circularly polarized photoluminescence in monolayer CrI 3 under linearly polarized excitation, with helicity determined by the monolayer magnetization direction. In contrast, the bilayer CrI 3 photoluminescence exhibits vanishing circular polarization, supporting the recently uncovered anomalous antiferromagnetic interlayer coupling in CrI 3 bilayers. Distinct frommore » the Wannier–Mott excitons that dominate the optical response in well-known 2D van der Waals semiconductors, our absorption and layer-dependent photoluminescence measurements reveal the importance of ligand-field and charge-transfer transitions to the optoelectronic response of atomically thin CrI 3. We attribute the photoluminescence to a parity-forbidden d–d transition characteristic of Cr 3+ complexes, which displays broad linewidth due to strong vibronic coupling and thickness-independent peak energy due to its localized molecular orbital nature.« less

Franck-Condon Simulations including Anharmonicity of the Ã(1)A''-X̃(1)A' Absorption and Single Vibronic Level Emission Spectra of HSiCl and DSiCl.

PubMed

Mok, Daniel W K; Lee, Edmond P F; Chau, Foo-Tim; Dyke, John M

2009-03-10

RCCSD(T) and/or CASSCF/MRCI calculations have been carried out on the X̃(1)A' and Ã(1)A'' states of HSiCl employing basis sets of up to the aug-cc-pV5Z quality. Contributions from core correlation and extrapolation to the complete basis set limit were included in determining the computed equilibrium geometrical parameters and relative electronic energy of these two states of HSiCl. Franck-Condon factors which include allowance for anharmonicity and Duschinsky rotation between these two states of HSiCl and DSiCl were calculated employing RCCSD(T) and CASSCF/MRCI potential energy functions, and were used to simulate the Ã(1)A'' ← X̃(1)A' absorption and Ã(1)A'' → X̃(1)A' single vibronic level (SVL) emission spectra of HSiCl and DSiCl. Simulated absorption and experimental LIF spectra, and simulated and observed Ã(1)A''(0,0,0) → X̃(1)A' SVL emission spectra, of HSiCl and DSiCl are in very good agreement. However, agreement between simulated and observed Ã(1)A''(0,1,0) → X̃(1)A' and Ã(1)A''(0,2,1) → X̃(1)A' SVL emission spectra of DSiCl is not as good. Preliminary calculations on low-lying excited states of HSiCl suggest that vibronic interaction between low-lying vibrational levels of the Ã(1)A'' state and highly excited vibrational levels of the ã(3)A'' is possible. Such vibronic interaction may change the character of the low-lying vibrational levels of the Ã(1)A'' state, which would lead to perturbation in the SVL emission spectra from these vibrational levels.

a Zero-Order Picture of the Infrared Spectrum for the Methoxy Radical: Assignment of States

NASA Astrophysics Data System (ADS)

Johnson, Britta; Sibert, Edwin

2016-06-01

The ground tilde{X}^2E vibrations of the methoxy radical have intrigued both experimentalists and theorists alike due to the presence of a conical intersection at the C3v molecular geometry. This conical intersection causes methoxy's vibrational spectrum to be strongly influenced by Jahn-Teller vibronic coupling which leads to large amplitude vibrations and extensive mixing of the two lowest electronic states. This coupling combined with spin-orbit and Fermi couplings greatly complicates the assignments of states. Using the potential force field and calculated spectra of Nagesh and Sibert1,2, we assign quantum numbers to the infrared spectrum. When the zero-order states are the diabatic normal mode states, there is sufficient mode mixing that the normal mode quantum numbers are poor labels for the final states. We define a series of zero-order Hamiltonians which include additional coupling elements beyond the normal mode picture but still allow for the assignment of Jahn-Teller quantum numbers. In methoxy, the two lowest frequency e} modes, the bend (q_5) and the rock (q_6), are the modes with the strongest Jahn-Teller coupling. In general, a zero-order Hamiltonian which includes first-order Jahn-Teller coupling in q_6 is sufficient for most states of interest. Working in a representation which includes first-order Jahn-Teller coupling in q_6, we identify states in which additional coupling elements must be included; these couplings include first-order Jahn-Teller coupling in q_5, higher order Jahn-Teller coupling in q_5 and q_6, and, in the dueterated case, Jahn-Teller coupling which is modulated by the corresponding a modes. [^1] Nagesh, J.; Sibert, E. L. J. Phys. Chem. A 2012, 116, 3846-3855. Lee, Y.F.; Chou, W.T.; Johnson, B.A.; Tabor, D.P. ; Sibert, E.L.; Lee, Y.P. J. Mol. Spectrosc. 2015, 310, 57-67. Barckholtz, T. A.; Miller, T. A. Int. Revs. in Phys. Chem. 1998, 17, 435-524.

Spectroscopic identification of dichlorobenzyl radicals: Jet-cooled 2,3-dichlorobenzyl radical

NASA Astrophysics Data System (ADS)

Chae, Sang Youl; Yoon, Young Wook; Lee, Sang Kuk

2015-07-01

The vibronically excited but jet-cooled 2,3-dichlorobenzyl radical was generated from the corona discharge of precursor 2,3-dichlorotoluene seeded in a large amount of carrier gas He using a pinhole-type glass nozzle. From an analysis of the visible vibronic emission spectrum observed, we obtained the electronic energy of the D1 → D0 transition and vibrational mode frequencies in the D0 state of the 2,3-dichlorobenzyl radical by comparing the observation with the results of ab initio calculations. In addition, we discussed substituent effect of Cls on electronic transition energy in terms of substituent orientation for the first time.

Efficient, diode-pumped Tm3+:BaY2F8 vibronic laser

NASA Astrophysics Data System (ADS)

Cornacchia, F.; Parisi, D.; Bernardini, C.; Toncelli, A.; Tonelli, M.

2004-05-01

In this work we report the spectroscopy and laser results of several Thulium doped BaY2F8 single crystals grown using the Czochralski technique. The doping concentration is between 2at.% and 18at.%. We performed room temperature laser experiments pumping the samples with a laser diode at 789 nm obtaining 61% as maximum optical-to-optical efficiency with a maximum output power of 290 mW and a minimum lasing threshold of 26 mW. The lasing wavelength changed with the dopant concentration from 1927 nm up to 2030 nm and the nature of the transition changed from purely electronic to vibronic, accordingly.

Observation of direct infrared multiphoton pumping of the triplet manifold of biacetyl

NASA Astrophysics Data System (ADS)

Tsao, Jeffrey Y.; Black, Jerry G.; Yablonovitch, Eli; Burak, Itamar

1980-09-01

Direct collisionless multiphoton (MP) excitation of the triplet vibronic manifold of biacetyl is reported. Following a dye laser pulse which prepares some of the biacetyl molecules in the triplet metastable state, the system is irradiated by an intense 20 ns 9.6μ CO2 pulse. The CO2 radiation induces fast quenching of the phosphorescence emission from the 3Au excited molecules. It also induces an emission signal in the fluorescence spectral region of biacetyl. This signal is related to an inverse electronic relaxation (IER) from excited triplet vibronic levels into isoenergetic singlet 1Au vibronic levels. Analysis of the induced luminescence signals provides information on the collisionless MP prompted vibrational distribution. Excitation with 10.6μ CO2 pulses leads to the simultaneous MP pumping of both the ground and triplet manifolds. The generation of blue emission signals in this experiment bears a close resemblance to recent observations of prompt visible emission due to MP pumping of ground state molecules. General expressions for the emission intensities are derived with special emphasis on the specific features of MP vibrational distributions. The detectability of MP induced emission signals is discussed.

The polarization anisotropy of vibrational quantum beats in resonant pump-probe experiments: Diagrammatic calculations for square symmetric molecules.

PubMed

Farrow, Darcie A; Smith, Eric R; Qian, Wei; Jonas, David M

2008-11-07

By analogy to the Raman depolarization ratio, vibrational quantum beats in pump-probe experiments depend on the relative pump and probe laser beam polarizations in a way that reflects vibrational symmetry. The polarization signatures differ from those in spontaneous Raman scattering because the order of field-matter interactions is different. Since pump-probe experiments are sensitive to vibrations on excited electronic states, the polarization anisotropy of vibrational quantum beats can also reflect electronic relaxation processes. Diagrammatic treatments, which expand use of the symmetry of the two-photon tensor to treat signal pathways with vibrational and vibronic coherences, are applied to find the polarization anisotropy of vibrational and vibronic quantum beats in pump-probe experiments for different stages of electronic relaxation in square symmetric molecules. Asymmetric vibrational quantum beats can be distinguished from asymmetric vibronic quantum beats by a pi phase jump near the center of the electronic spectrum and their disappearance in the impulsive limit. Beyond identification of vibrational symmetry, the vibrational quantum beat anisotropy can be used to determine if components of a doubly degenerate electronic state are unrelaxed, dephased, population exchanged, or completely equilibrated.

Nuclear Dynamics at Molecule–Metal Interfaces: A Pseudoparticle Perspective

DOE PAGES

Galperin, Michael; Nitzan, Abraham

2015-11-20

We discuss nuclear dynamics at molecule-metal interfaces including nonequilibrium molecular junctions. Starting from the many-body states (pseudoparticle) formulation of the molecule-metal system in the molecular vibronic basis, we introduce gradient expansion to reduce the adiabatic nuclear dynamics (that is, nuclear dynamics on a single molecular potential surface) into its semiclassical form while maintaining the effect of the nonadiabatic electronic transitions between different molecular charge states. Finally, this yields a set of equations for the nuclear dynamics in the presence of these nonadiabatic transitions, which reproduce the surface-hopping formulation in the limit of small metal-molecule coupling (where broadening of the molecularmore » energy levels can be disregarded) and Ehrenfest dynamics (motion on the potential of mean force) when information on the different charging states is traced out.« less

The generation of O(1S) from the dissociative recombination of O2(+)

NASA Technical Reports Server (NTRS)

Guberman, Steven L.; Giusti-Suzor, Annick

1991-01-01

The multichannel quantum defect theory (MQDT) method and large scale wave functions are applied to the calculation of the cross sections and rates for dissociative recombination of O2(+) along the 1Sigma-u(+) dissociative potential. Indirect dissociative recombination is accounted for by simultaneously including both the vibronic and electronic coupling to the intermediate Rydberg resonances. An enhanced MQDT approach involving a second-order K matrix is described. Cross sections and rates for the lowest three vibrational levels of the ion are reported. The shapes of the cross sections are discussed in terms of Fano's profile index. It is found that, for each of the three ion vibrational levels, the intermediate Rydberg resonances reduce the dissociative recombination rate below the direct recombination rate. Just above threshold, resonances with centers below threshold play an important role.

Interplay of localized pyrene chromophores and π-conjugation in novel poly(2,7-pyrene) ladder polymers

NASA Astrophysics Data System (ADS)

Rudnick, Alexander; Kass, Kim-Julia; Preis, Eduard; Scherf, Ullrich; Bässler, Heinz; Köhler, Anna

2017-05-01

We present a detailed spectroscopic study, along with the synthesis, of conjugated, ladder-type 2,7-linked poly(pyrene)s. We observe a delocalization of the first singlet excited state along the polymer backbone, i.e., across the 2,7 linkage in the pyrene moiety, in contrast to earlier studies on conjugated 2,7-linked poly(pyrene)s without ladder structure. The electronic signature of the pyrene unit is, however, manifested in an increased lifetime and reduced oscillator strength as well as a modified vibronic progression in absorption of the singlet state compared to a ladder-type poly(para-phenylene) (MeLPPP). Furthermore, the reduced oscillator strength and increased lifetime slow down Förster-type energy transfer in films, where this transfer occurs to sites with increasing inter-chain coupling of H-type nature.

Predicting Keto-Enol Equilibrium from Combining UV/Visible Absorption Spectroscopy with Quantum Chemical Calculations of Vibronic Structures for Many Excited States. A Case Study on Salicylideneanilines.

PubMed

Zutterman, Freddy; Louant, Orian; Mercier, Gabriel; Leyssens, Tom; Champagne, Benoît

2018-06-21

Salicylideneanilines are characterized by a tautomer equilibrium, between an enol and a keto form of different colors, at the origin of their remarkable thermochromic, solvatochromic, and photochromic properties. The enol form is usually the most stable but appropriate choice of substituents and conditions (solvent, crystal, host compound) can displace the equilibrium toward the keto form so that there is a need for fast prediction of the keto:enol abundance ratio. Here we demonstrate the reliability of a combined theoretical-experimental method, based on comparing simulated and measured UV/visible absorption spectra, to determine this keto/enol ratio. The calculations of the excitation energies, oscillator strengths, and vibronic structures of both enol and keto forms are performed for all excited states absorbing in the relevant (visible and near-UV) wavelength range at the time-dependent density functional theory level by accounting for solvent effects using the polarizable continuum model. This approach is illustrated for two salicylideneaniline derivatives, which are present, in solution, under the form of keto-enol mixtures. The results are compared to those of chemometric analysis as well as ab initio predictions of the reaction free enthalpies.

Franck-Condon simulation of the single-vibronic-level emission spectra of HPCl/DPCl and the chemiluminescence spectrum of HPCl, including anharmonicity.

PubMed

Chau, Foo-Tim; Mok, Daniel K W; Lee, Edmond P F; Dyke, John M

2004-07-22

Restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] potential energy functions (PEFs) were calculated for the X (2)A" and A (2)A' states of HPCl employing the augmented correlation-consistent polarized-valence-quadruple-zeta (aug-cc-pVQZ) basis set. Further geometry optimization calculations were carried out on both electronic states of HPCl at the RCCSD(T) level with all electron and quasirelativistic effective core potential basis sets of better than the aug-cc-pVQZ quality, and also including some core electrons, in order to obtain more reliable geometrical parameters and relative electronic energy of the two states. Anharmonic vibrational wave functions of the two states of HPCl and DPCl, and Franck-Condon (FC) factors of the A (2)A'-X (2)A" transition were computed employing the RCCSD(T)/aug-cc-pVQZ PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the single-vibronic-level (SVL) emission spectra of HPCl and DPCl reported by Brandon et al. [J. Chem. Phys. 119, 2037 (2003)] and the chemiluminescence spectrum reported by Bramwell et al. [Chem. Phys. Lett. 331, 483 (2000)]. Comparison between simulated and observed SVL emission spectra gives the experimentally derived equilibrium geometry of the A (2)A' state of HPCl of r(e)(PCl) = 2.0035 +/- 0.0015 A, theta(e) = 116.08 +/- 0.60 degrees, and r(e)(HP) = 1.4063+/-0.0015 A via the iterative Franck-Condon analysis procedure. Comparison between simulated and observed chemiluminescence spectra confirms that the vibrational population distribution of the A (2)A' state of HPCl is non-Boltzmann, as proposed by Baraille et al. [Chem. Phys. 289, 263 (2003)].

Spectroscopic properties of the S1 state of linear carotenoids after excess energy excitation

NASA Astrophysics Data System (ADS)

Kuznetsova, Valentyna; Southall, June; Cogdell, Richard J.; Fuciman, Marcel; Polívka, Tomáš

2017-09-01

Properties of the S1 state of neurosporene, spheroidene and lycopene were studied after excess energy excitation in the S2 state. Excitation of carotenoids into higher vibronic levels of the S2 state generates excess vibrational energy in the S1 state. The vibrationally hot S1 state relaxes faster when carotenoid is excited into the S2 state with excess energy, but the S1 lifetime remains constant regardless of which vibronic level of the S2 state is excited. The S∗ signal depends on excitation energy only for spheroidene, which is likely due to asymmetry of the molecule, facilitating conformations responsible for the S∗ signal.

Spectroscopic evidence of jet-cooled p-methyl-α-methylbenzyl radical

NASA Astrophysics Data System (ADS)

Chae, Sang Youl; Yoon, Young Wook; Lim, Manho; Lee, Sang Kuk

2015-08-01

We report spectroscopic evidence of the jet-cooled p-methyl-α-methylbenzyl radical in corona discharge. The visible vibronic emission spectra were recorded from the corona discharge of three precursors, p-xylene, p-ethyltoluene, and p-isopropyltoluene seeded in a large amount of carrier gas helium using a pinhole-type glass nozzle. From the analysis of the vibronic spectra observed from each precursor and the bond dissociation energies of precursor molecules, we are able to confirm the formation of the jet-cooled p-methyl-α-methylbenzyl radical in corona discharge, and determine the energy of the D1 → D0 transition and a few vibrational mode frequencies in the D0 state.

Spectroscopic evidence of α,α-dichlorobenzyl radical produced by corona discharge of benzotrichloride

NASA Astrophysics Data System (ADS)

Yoon, Young Wook; Chae, Sang Youl; Lim, Manho; Lee, Sang Kuk

2015-08-01

We report spectroscopic observations of the α,α-dichlorobenzyl radical obtained by corona excited supersonic jet expansion using a pinhole-type glass nozzle. Vibronically excited but jet-cooled radicals were generated by corona discharge of the precursor benzotrichloride with a large amount of helium carrier gas, from which the visible vibronic emission spectrum was recorded using a long path monochromator. From an analysis of the spectrum observed, the electronic energy of the D1 → D0 transition and a few vibrational mode frequencies in the ground electronic state were obtained for the α,α-dichlorobenzyl radical by comparing observed frequencies with those obtained by ab initio calculation.

Vibronic singlet and triplet steady-state interplay emissions in phenazine-based 1,2,3-triazole films

NASA Astrophysics Data System (ADS)

Costa, Bárbara B. A.; Souza, Paula D. C.; Gontijo, Rafael N.; Jardim, Guilherme A. M.; Moreira, Roberto L.; da Silva, Eufrânio N.; Cury, Luiz A.

2018-03-01

Photoluminescence and phosphorescence emissions of solid-state phenazine films were investigated in steady-state experimental conditions. Important discrepancies were observed for blended films where a host optically inert matrix was introduced to disperse the probe molecules. A vibronic spin-orbit phosphorescent emission clearly appeared, while for the films solely composed by the probe molecules, the phosphorescence broadened and presented a structureless shape, shifted to longer wavelengths. Further Arrhenius behavior analysis on the photoluminescent and phosphorescent emissions on temperature, corroborated the direct and reverse intersystem crossing interplay between singlet and triplet states. Molecular aggregation is responsible for the deterioration of non-blended triazole films phosphorescence.

Anion photoelectron spectroscopy of radicals and clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Travis, Taylor R.

1999-12-01

Anion photoelectron spectroscopy is used to study free radicals and clusters. The low-lying 2Σ and 2π states of C 2nH (n = 1--4) have been studied. The anion photoelectron spectra yielded electron affinities, term values, and vibrational frequencies for these combustion and astrophysically relevant species. Photoelectron angular distributions allowed the author to correctly assign the electronic symmetry of the ground and first excited states and to assess the degree of vibronic coupling in C 2H and C 4H. Other radicals studied include NCN and I 3. The author was able to observe the low-lying singlet and triplet states of NCNmore » for the first time. Measurement of the electron affinity of I 3 revealed that it has a bound ground state and attachment of an argon atom to this moiety enabled him to resolve the symmetric stretching progression.« less

Quantifying the effects of higher order coupling terms on fits using a second order Jahn-Teller Hamiltonian

NASA Astrophysics Data System (ADS)

Tran, Henry K.; Stanton, John F.; Miller, Terry A.

2018-01-01

The limitations associated with the common practice of fitting a quadratic Hamiltonian to vibronic levels of a Jahn-Teller system have been explored quantitatively. Satisfactory results for the prototypical X∼2E‧ state of Li3 are obtained from fits to both experimental spectral data and to an "artificial" spectrum calculated by a quartic Hamiltonian which accurately reproduces the adiabatic potential obtained from state-of-the-art quantum chemistry calculations. However the values of the Jahn-Teller parameters, stabilization energy, and pseudo-rotation barrier obtained from the quadratic fit differ markedly from those associated with the ab initio potential. Nonetheless the RMS deviations of the fits are not strikingly different. Guidelines are suggested for comparing parameters obtained from fits to experiment to those obtained by direct calculation, but a principal conclusion of this work is that such comparisons must be done with a high degree of caution.

Influence of nuclear exchange on nonadiabatic electron processes in H(+)+H2 collisions.

PubMed

Errea, L F; Illescas, Clara; Macías, A; Méndez, L; Pons, B; Rabadán, I; Riera, A

2010-12-28

H(+)+H(2) collisions are studied by means of a semiclassical approach that explicitly accounts for nuclear rearrangement channels in nonadiabatic electron processes. A set of classical trajectories is used to describe the nuclear motion, while the electronic degrees of freedom are treated quantum mechanically in terms of a three-state expansion of the collision wavefunction. We describe electron capture and vibrational excitation, which can also involve nuclear exchange and dissociation, in the E = 2-1000 eV impact energy range. We compare dynamical results obtained with two parametrizations of the potential energy surface of H(3)(+) ground electronic state. Total cross sections for E > 10 eV agree with previous results using a vibronic close-coupling expansion, and with experimental data for E < 10 eV. Additionally, some prototypical features of both nuclear and electron dynamics at low E are discussed.

Cr/sup 3 +/-doped colquiriite solid state laser material

DOEpatents

Payne, S.A.; Chase, L.L.; Newkirk, H.W.; Krupke, W.F.

1988-03-31

Chromium doped colquiriite, LiCaAlF/sub 6/:Cr/sup 3 +/, is useful as a tunable laser crystal that has a high intrinsic slope efficiency, comparable to or exceeding that of alexandrite, the current leading performer of vibronic sideband Cr/sup 3 +/ lasers. The laser output is tunable from at least 720 nm to 840 nm with a measured slope efficiency of about 60% in a Kr laser pumped laser configuration. The intrinsic slope efficiency (in the limit of large output coupling) may approach the quantum defect limited value of 83%. The high slope efficiency implies that excited state absorption (ESA) is negligible. The potential for efficiency and the tuning range of this material satisfy the requirements for a pump laser for a high density storage medium incorporating Nd/sup 3 +/ or Tm/sup 3 +/ for use in a multimegajoule single shot fusion research facility. 4 figs.

Cr.sup.3+ -doped colquiriite solid state laser material

DOEpatents

Payne, Stephen A.; Chase, Lloyd L.; Newkirk, Herbert W.; Krupke, William F.

1989-01-01

Chromium doped colquiriite, LiCaAlF.sub.6 :Cr.sup.3+, is useful as a tunable laser crystal that has a high intrinsic slope efficiency, comparable to or exceeding that of alexandrite, the current leading performer of vibronic sideband Cr.sup.3+ lasers. The laser output is tunable from at least 720 nm to 840 nm with a measured slop efficiency of about 60% in a Kr laser pumped laser configuration. The intrinsic slope efficiency (in the limit of large output coupling) may approach the quantum defect limited value of 83%. The high slope efficiency implies that excited state absorption (ESA) is negligible. The potential for efficiency and the tuning range of this material satisfy the requirements for a pump laser for a high density storage medium incorporating Nd.sup.3+ or Tm.sup.3+ for use in a multimegajoule single shot fusion research facility.

Photovoltaic concepts inspired by coherence effects in photosynthetic systems

NASA Astrophysics Data System (ADS)

Brédas, Jean-Luc; Sargent, Edward H.; Scholes, Gregory D.

2017-01-01

The past decade has seen rapid advances in our understanding of how coherent and vibronic phenomena in biological photosynthetic systems aid in the efficient transport of energy from light-harvesting antennas to photosynthetic reaction centres. Such coherence effects suggest strategies to increase transport lengths even in the presence of structural disorder. Here we explore how these principles could be exploited in making improved solar cells. We investigate in depth the case of organic materials, systems in which energy and charge transport stand to be improved by overcoming challenges that arise from the effects of static and dynamic disorder -- structural and energetic -- and from inherently strong electron-vibration couplings. We discuss how solar-cell device architectures can evolve to use coherence-exploiting materials, and we speculate as to the prospects for a coherent energy conversion system. We conclude with a survey of the impacts of coherence and bioinspiration on diverse solar-energy harvesting solutions, including artificial photosynthetic systems.

Observing interactions between DNA bases using ion dip spectroscopy.

NASA Astrophysics Data System (ADS)

Vries Mattanjah, De

2002-03-01

We investigate biomolecular building blocks and their clusters with each other and with water on a single molecular level. The motivation is the need to distinguish between intrinsic molecular properties and those that result from the biological environment. This is achieved by a combination of laser desorption and jet cooling, applied to aromatic amino acids, small peptides containing those, purine bases and nucleosides. This approach is coupled with a number of gas phase laser spectroscopic techniques. We will present results for DNA bases guanine, adenine, cytosine, and their derivatives, for which we obtained tautomer selected vibronic spectra. Capitalizing on these results we use these bases as chromophores to study interactions in single base pairs, obtained by formation of clusters of laser desorbed bases in a supersonic beam. For analysis we employ both UV/UV and IR/UV ion-dip spectroscopy, the results of which we compare with ab initio calculations.

Infrared Spectroscopy of the Tropyl Radical in Helium Droplets

DOE PAGES

Kaufmann, Matin; Leicht, Daniel; Havenith, Martina; ...

2016-08-16

Here, the infrared spectrum of themore » $$\\tilde{X}$$ 2E 2" tropyl radical has been recorded in the range of the CH-stretch vibrational modes using the helium droplet isolation technique. Two bands are observed at 3053 and 3058 cm –1. The electronic degeneracy of the ground state results in a Jahn–Teller interaction for two of the CH-stretch modes, i.e., first-order interaction for E 3' symmetry modes and second-order interaction for E 2' symmetry modes. The experimentally observed bands are assigned to the E 1' and E 3' CH-stretch modes. The E 1' mode is infrared-active, whereas the E 3' mode is inactive in the absence of the Jahn–Teller interaction. The transition to the upper component of the Jahn–Teller split E 3' mode gains intensity via vibronic coupling, giving rise to the second experimentally observed band.« less

An alternative laser driven photodissociation mechanism of pyrrole via πσ*1∕S0 conical intersection.

PubMed

Nandipati, K R; Lan, Z; Singh, H; Mahapatra, S

2017-06-07

A first principles quantum dynamics study of N-H photodissociation of pyrrole on the S 0 - 1 πσ * (A21) coupled electronic states is carried out with the aid of an optimally designed UV-laser pulse. A new photodissociation path, as compared to the conventional barrier crossing on the πσ*1 state, opens up upon electronic transitions under the influence of pump-dump laser pulses, which efficiently populate both the dissociation channels. The interplay of electronic transitions due both to vibronic coupling and the laser pulse is observed in the control mechanism and discussed in detail. The proposed control mechanism seems to be robust, and not discussed in the literature so far, and is expected to trigger future experiments on the πσ*1 photochemistry of molecules of chemical and biological importance. The design of the optimal pulses and their application to enhance the overall dissociation probability is carried out within the framework of optimal control theory. The quantum dynamics of the system in the presence of pulse is treated by solving the time-dependent Schrödinger equation in the semi-classical dipole approximation.

An alternative laser driven photodissociation mechanism of pyrrole via πσ*1∕S0 conical intersection

PubMed Central

Nandipati, K. R.; Lan, Z.; Singh, H.; Mahapatra, S.

2017-01-01

A first principles quantum dynamics study of N–H photodissociation of pyrrole on the S0−1πσ*(A21) coupled electronic states is carried out with the aid of an optimally designed UV-laser pulse. A new photodissociation path, as compared to the conventional barrier crossing on the πσ*1 state, opens up upon electronic transitions under the influence of pump-dump laser pulses, which efficiently populate both the dissociation channels. The interplay of electronic transitions due both to vibronic coupling and the laser pulse is observed in the control mechanism and discussed in detail. The proposed control mechanism seems to be robust, and not discussed in the literature so far, and is expected to trigger future experiments on the πσ*1 photochemistry of molecules of chemical and biological importance. The design of the optimal pulses and their application to enhance the overall dissociation probability is carried out within the framework of optimal control theory. The quantum dynamics of the system in the presence of pulse is treated by solving the time-dependent Schrödinger equation in the semi-classical dipole approximation. PMID:28595406

Ligand-field helical luminescence in a 2D ferromagnetic insulator

DOE PAGES

Seyler, Kyle L.; Zhong, Ding; Klein, Dahlia R.; ...

2017-12-04

Bulk chromium tri-iodide (CrI 3) has long been known as a layered van der Waals ferromagnet. However, its monolayer form was only recently isolated and confirmed to be a truly two-dimensional (2D) ferromagnet, providing a new platform for investigating light–matter interactions and magneto-optical phenomena in the atomically thin limit. Here in this paper, we report spontaneous circularly polarized photoluminescence in monolayer CrI 3 under linearly polarized excitation, with helicity determined by the monolayer magnetization direction. In contrast, the bilayer CrI 3 photoluminescence exhibits vanishing circular polarization, supporting the recently uncovered anomalous antiferromagnetic interlayer coupling in CrI 3 bilayers. Distinct frommore » the Wannier–Mott excitons that dominate the optical response in well-known 2D van der Waals semiconductors, our absorption and layer-dependent photoluminescence measurements reveal the importance of ligand-field and charge-transfer transitions to the optoelectronic response of atomically thin CrI 3. We attribute the photoluminescence to a parity-forbidden d–d transition characteristic of Cr 3+ complexes, which displays broad linewidth due to strong vibronic coupling and thickness-independent peak energy due to its localized molecular orbital nature.« less

An alternative laser driven photodissociation mechanism of pyrrole via π*1σ/S0 conical intersection

NASA Astrophysics Data System (ADS)

Nandipati, K. R.; Lan, Z.; Singh, H.; Mahapatra, S.

2017-06-01

A first principles quantum dynamics study of N-H photodissociation of pyrrole on the S0-1π σ*(A12) coupled electronic states is carried out with the aid of an optimally designed UV-laser pulse. A new photodissociation path, as compared to the conventional barrier crossing on the π*1σ state, opens up upon electronic transitions under the influence of pump-dump laser pulses, which efficiently populate both the dissociation channels. The interplay of electronic transitions due both to vibronic coupling and the laser pulse is observed in the control mechanism and discussed in detail. The proposed control mechanism seems to be robust, and not discussed in the literature so far, and is expected to trigger future experiments on the π*1σ photochemistry of molecules of chemical and biological importance. The design of the optimal pulses and their application to enhance the overall dissociation probability is carried out within the framework of optimal control theory. The quantum dynamics of the system in the presence of pulse is treated by solving the time-dependent Schrödinger equation in the semi-classical dipole approximation.

Femtosecond dynamics of correlated many-body states in C60 fullerenes

NASA Astrophysics Data System (ADS)

Usenko, Sergey; Schüler, Michael; Azima, Armin; Jakob, Markus; Lazzarino, Leslie L.; Pavlyukh, Yaroslav; Przystawik, Andreas; Drescher, Markus; Laarmann, Tim; Berakdar, Jamal

2016-11-01

Fullerene complexes may play a key role in the design of future molecular electronics and nanostructured devices with potential applications in light harvesting using organic solar cells. Charge and energy flow in these systems is mediated by many-body effects. We studied the structure and dynamics of laser-induced multi-electron excitations in isolated C60 by two-photon photoionization as a function of excitation wavelength using a tunable fs UV laser and developed a corresponding theoretical framework on the basis of ab initio calculations. The measured resonance line width gives direct information on the excited state lifetime. From the spectral deconvolution we derive a lower limit for purely electronic relaxation on the order of {τ }{el}={10}-3+5 fs. Energy dissipation towards nuclear degrees of freedom is studied with time-resolved techniques. The evaluation of the nonlinear autocorrelation trace gives a characteristic time constant of {τ }{vib}=400+/- 100 fs for the exponential decay. In line with the experiment, the observed transient dynamics is explained theoretically by nonadiabatic (vibronic) couplings involving the correlated electronic, the nuclear degrees of freedom (accounting for the Herzberg-Teller coupling), and their interplay.

Theoretical study on the photoabsorption in the Herzberg I band system of the O 2 molecule

NASA Astrophysics Data System (ADS)

Takegami, Ryuta; Yabushita, Satoshi

2005-01-01

The Herzberg I band system of the oxygen molecule is electric-dipole forbidden and its absorption strength has been explained by intensity borrowing models which include the spin-orbit (SO) and L-uncoupling (RO) interactions as perturbations. We employed three different levels of theoretical models to evaluate these two interactions, and obtained the rotational and vibronic absorption strengths using the ab initio method. The first model calculates the transition moments induced by the SO interaction variationally with the SO configuration interaction method (SOCI), and uses the first-order perturbation theory for the RO interaction, and is called SOCI. The second is based on the first-order perturbation theory for both the SO and RO interactions, and is called Pert(Full). The last is a limited version of Pert(Full), in that the first-order perturbation wavefunction for the initial and final state is represented by only one dominant basis, namely the 1 3Π g and B3Σu- state, respectively, as originally used by England et al. [Can. J. Phys. 74 (1996) 185], and is called Pert(England). The vibronic oscillator strengths calculated by these three models were in good agreement with the experimental values. As for the integrated rotational linestrengths, the SOCI and Pert(Full) models reproduced the experimental results very well, however the Pert(England) model did not give satisfactory results. Since the Pert(England) model takes only the 1 3Π g and B3Σu- states into consideration, it cannot contain the complicated configuration interactions with highly excited states induced by the SO and RO interaction, which plays an important role for calculating the delicate integrated rotational linestrength. This result suggests that the configuration interaction with highly excited states due to some perturbations cannot be neglected in the case of very weak absorption band systems.

Analysis of geometric phase effects in the quantum-classical Liouville formalism.

PubMed

Ryabinkin, Ilya G; Hsieh, Chang-Yu; Kapral, Raymond; Izmaylov, Artur F

2014-02-28

We analyze two approaches to the quantum-classical Liouville (QCL) formalism that differ in the order of two operations: Wigner transformation and projection onto adiabatic electronic states. The analysis is carried out on a two-dimensional linear vibronic model where geometric phase (GP) effects arising from a conical intersection profoundly affect nuclear dynamics. We find that the Wigner-then-Adiabatic (WA) QCL approach captures GP effects, whereas the Adiabatic-then-Wigner (AW) QCL approach does not. Moreover, the Wigner transform in AW-QCL leads to an ill-defined Fourier transform of double-valued functions. The double-valued character of these functions stems from the nontrivial GP of adiabatic electronic states in the presence of a conical intersection. In contrast, WA-QCL avoids this issue by starting with the Wigner transform of single-valued quantities of the full problem. As a consequence, GP effects in WA-QCL can be associated with a dynamical term in the corresponding equation of motion. Since the WA-QCL approach uses solely the adiabatic potentials and non-adiabatic derivative couplings as an input, our results indicate that WA-QCL can capture GP effects in two-state crossing problems using first-principles electronic structure calculations without prior diabatization or introduction of explicit phase factors.

Analysis of geometric phase effects in the quantum-classical Liouville formalism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryabinkin, Ilya G.; Izmaylov, Artur F.; Chemical Physics Theory Group, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6

2014-02-28

We analyze two approaches to the quantum-classical Liouville (QCL) formalism that differ in the order of two operations: Wigner transformation and projection onto adiabatic electronic states. The analysis is carried out on a two-dimensional linear vibronic model where geometric phase (GP) effects arising from a conical intersection profoundly affect nuclear dynamics. We find that the Wigner-then-Adiabatic (WA) QCL approach captures GP effects, whereas the Adiabatic-then-Wigner (AW) QCL approach does not. Moreover, the Wigner transform in AW-QCL leads to an ill-defined Fourier transform of double-valued functions. The double-valued character of these functions stems from the nontrivial GP of adiabatic electronic statesmore » in the presence of a conical intersection. In contrast, WA-QCL avoids this issue by starting with the Wigner transform of single-valued quantities of the full problem. As a consequence, GP effects in WA-QCL can be associated with a dynamical term in the corresponding equation of motion. Since the WA-QCL approach uses solely the adiabatic potentials and non-adiabatic derivative couplings as an input, our results indicate that WA-QCL can capture GP effects in two-state crossing problems using first-principles electronic structure calculations without prior diabatization or introduction of explicit phase factors.« less

Resonant two-photon ionization and laser induced fluorescence spectroscopy of jet-cooled adenine

NASA Astrophysics Data System (ADS)

Kim, Nam Joon; Jeong, Gawoon; Kim, Yung Sam; Sung, Jiha; Keun Kim, Seong; Park, Young Dong

2000-12-01

Electronic spectra of the jet-cooled DNA base adenine were obtained by the resonant two-photon ionization (R2PI) and the laser induced fluorescence (LIF) techniques. The 0-0 band to the lowest electronically excited state was found to be located at 35 503 cm-1. Well-resolved vibronic structures were observed up to 1100 cm-1 above the 0-0 level, followed by a slow rise of broad structureless absorption. The lowest electronic state was proposed to be of nπ* character, which lies ˜600 cm-1 below the onset of the ππ* state. The broad absorption was attributed to the extensive vibronic mixing between the nπ* state and the high-lying ππ* state.

Confirmed assignments of isomeric dimethylbenzyl radicals generated by corona discharge.

PubMed

Yoon, Young Wook; Lee, Sang Kuk

2011-12-07

The controversial vibronic assignments of isomeric dimethylbenzyl radicals were clearly resolved by using different precursors. By employing corresponding dimethylbenzyl chlorides as precursors, we identified the origins of the vibronic bands of the dimethylbenzyl radicals generated by corona discharge of 1,2,4-trimethylbenzene. From the analysis of the spectra observed from the dimethylbenzyl chlorides in a corona excited supersonic expansion, we revised previous assignments of the 3,4-, 2,4-, and 2,5-dimethylbenzyl radicals. Spectroscopic data of electronic transition and vibrational mode frequencies in the ground electronic state of each isomer were accurately determined by comparing them with those obtained by an ab initio calculation and with the known vibrational data of 1,2,4-trimethylbenzene. © 2011 American Institute of Physics

Spectroscopic studies of nanomaterials with a liquid-helium-free high-stability cryogenic scanning tunneling microscope

NASA Astrophysics Data System (ADS)

Kislitsyn, Dmitry Anatolevich

This dissertation presents results of a project bringing Scanning Tunneling Microscope (STM) into a regime of unlimited operational time at cryogenic conditions. Freedom from liquid helium consumption was achieved and technical characteristics of the instrument are reported, including record low noise for a scanning probe instrument coupled to a close-cycle cryostat, which allows for atomically resolved imaging, and record low thermal drift. Subsequent studies showed that the new STM opened new prospects in nanoscience research by enabling Scanning Tunneling Spectroscopic (STS) spatial mapping to reveal details of the electronic structure in real space for molecules and low-dimensional nanomaterials, for which this depth of investigation was previously prohibitively expensive. Quantum-confined electronic states were studied in single-walled carbon nanotubes (SWCNTs) deposited on the Au(111) surface. Localization on the nanometer-scale was discovered to produce a local vibronic manifold resulting from the localization-enhanced electron-vibrational coupling. STS showed the vibrational overtones, identified as D-band Kekule vibrational modes and K-point transverse out-of plane phonons. This study experimentally connected the properties of well-defined localized electronic states to the properties of associated vibronic states. Electronic structures of alkyl-substituted oligothiophenes with different backbone lengths were studied and correlated with torsional conformations assumed on the Au(111) surface. The molecules adopted distinct planar conformations with alkyl ligands forming cis- or trans-mutual orientations and at higher coverage self-assembled into ordered structures, binding to each other via interdigitated alkyl ligands. STS maps visualized, in real space, particle-in-a-box-like molecular orbitals. Shorter quaterthiophenes have substantially varying orbital energies because of local variations in surface reactivity. Different conformers of longer oligothiophenes with significant geometrical distortions of the oligothiophene backbones surprisingly exhibited similar electronic structures, indicating insensitivity of interaction with the surface to molecular conformation. Electronic states for annealed ligand-free lead sulfide nanocrystals were investigated, as well as hydrogen-passivated silicon nanocrystals, supported on the Au(111) surface. Delocalized quantum-confined states and localized defect-related states were identified, for the first time, via STS spatial mapping. Physical mechanisms, involving surface reconstruction or single-atom defects, were proposed for surface state formation to explain the observed spatial behavior of the electronic density of states. This dissertation includes previously published co-authored material.

Analog of small Holstein polaron in hydrogen-bonded amide systems

NASA Astrophysics Data System (ADS)

Alexander, D. M.

1985-01-01

A class of amide-I (C = O stretch) related excitations and their contribution to the spectral function for infrared absorption is determined by use of the Davydov Hamiltonian. The treatment is a fully quantum, finite-temperature one. A consistent picture and a quantitative fit to the absorption data for crystalline acetanilide confirms that the model adequately explains the anomalous behavior cited by Careri et al. The localized excitation responsible for this behavior is the vibronic analog of the small Holstein polaron. The possible extension to other modes and biological relevance is examined.

Distinct properties of the triplet pair state from singlet fission

DOE PAGES

Trinh, M. Tuan; Pinkard, Andrew; Pun, Andrew B.; ...

2017-07-14

Singlet fission, the conversion of a singlet exciton (S 1) to two triplets (2 × T 1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1(TT). Despite extensive research, the nature of the 1(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of themore » S 1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1(TT)→S n and S 1→S n' transitions; S n and S n' likely come from the antisymmetric and symmetric linear combinations, respectively, of the S 2 state localized on each pentacene unit in the dimer molecule. The 1(TT)→S n transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1(TT) state also shows chemical reactivity that is distinctively different from that of an individual T 1 state. Using an electron-accepting iron oxide molecular cluster [Fe 8O 4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T 1 in pentacene but not from the tightly bound 1(TT) state. Thus, reducing intertriplet electronic coupling in 1(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.« less

Distinct properties of the triplet pair state from singlet fission.

PubMed

Trinh, M Tuan; Pinkard, Andrew; Pun, Andrew B; Sanders, Samuel N; Kumarasamy, Elango; Sfeir, Matthew Y; Campos, Luis M; Roy, Xavier; Zhu, X-Y

2017-07-01

Singlet fission, the conversion of a singlet exciton (S 1 ) to two triplets (2 × T 1 ), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1 (TT). Despite extensive research, the nature of the 1 (TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1 (TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of the S 1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1 (TT)→S n and S 1 →S n' transitions; S n and S n' likely come from the antisymmetric and symmetric linear combinations, respectively, of the S 2 state localized on each pentacene unit in the dimer molecule. The 1 (TT)→S n transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1 (TT) state also shows chemical reactivity that is distinctively different from that of an individual T 1 state. Using an electron-accepting iron oxide molecular cluster [Fe 8 O 4 ] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T 1 in pentacene but not from the tightly bound 1 (TT) state. Thus, reducing intertriplet electronic coupling in 1 (TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trinh, M. Tuan; Pinkard, Andrew; Pun, Andrew B.

Singlet fission, the conversion of a singlet exciton (S 1) to two triplets (2 × T 1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1(TT). Despite extensive research, the nature of the 1(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of themore » S 1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1(TT)→S n and S 1→S n' transitions; S n and S n' likely come from the antisymmetric and symmetric linear combinations, respectively, of the S 2 state localized on each pentacene unit in the dimer molecule. The 1(TT)→S n transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1(TT) state also shows chemical reactivity that is distinctively different from that of an individual T 1 state. Using an electron-accepting iron oxide molecular cluster [Fe 8O 4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T 1 in pentacene but not from the tightly bound 1(TT) state. Thus, reducing intertriplet electronic coupling in 1(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.« less

Distinct properties of the triplet pair state from singlet fission

PubMed Central

Trinh, M. Tuan; Pinkard, Andrew; Pun, Andrew B.; Sanders, Samuel N.; Kumarasamy, Elango; Sfeir, Matthew Y.; Campos, Luis M.; Roy, Xavier; Zhu, X.-Y.

2017-01-01

Singlet fission, the conversion of a singlet exciton (S1) to two triplets (2 × T1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1(TT). Despite extensive research, the nature of the 1(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of the S1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1(TT)→Sn and S1→Sn′ transitions; Sn and Sn′ likely come from the antisymmetric and symmetric linear combinations, respectively, of the S2 state localized on each pentacene unit in the dimer molecule. The 1(TT)→Sn transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1(TT) state also shows chemical reactivity that is distinctively different from that of an individual T1 state. Using an electron-accepting iron oxide molecular cluster [Fe8O4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T1 in pentacene but not from the tightly bound 1(TT) state. Thus, reducing intertriplet electronic coupling in 1(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission. PMID:28740866

Spectroscopic study on deuterated benzenes. III. Vibronic structure and dynamics in the S1 state

NASA Astrophysics Data System (ADS)

Kunishige, Sachi; Katori, Toshiharu; Kawabata, Megumi; Yamanaka, Takaya; Baba, Masaaki

2015-12-01

We observed the fluorescence excitation spectra and mass-selected resonance enhanced multiphoton ionization (REMPI) excitation spectra for the 6 01 , 6 01 10 1 , and 6 01 10 2 bands of the S1←S0 transition of jet-cooled deuterated benzene and assigned the vibronic bands of C6D6 and C6HD5. The 60 1 10 n (n = 0, 1, 2) and 00 0 transition energies were found to be dependent only on the number of D atoms (ND), which was reflected by the zero-point energy of each H/D isotopomer. In some isotopomers some bands, such as those of out-of-plane vibrations mixed with 611n, make the spectra complex. These included the 611021n level or combination bands with ν12 which are allowed because of reduced molecular symmetry. From the lifetime measurements of each vibronic band, some enhancement of the nonradiative intramolecular vibrational redistribution (IVR) process was observed. It was also found that the threshold excess energy of "channel three" was higher than the 6112 levels, which were similar for all the H/D isotopomers. We suggest that the channel three nonradiative process could be caused mainly by in-plane processes such as IVR and internal conversion at the high vibrational levels in the S1 state of benzene, although the out-of-plane vibrations might contribute to some degree.

Coupled potential energy surface for the F(2P)+CH4→HF+CH3 entrance channel and quantum dynamics of the CH4·F- photodetachment.

PubMed

Westermann, Till; Eisfeld, Wolfgang; Manthe, Uwe

2013-07-07

An approach to construct vibronically and spin-orbit coupled diabatic potential energy surfaces (PESs) which describe all three relevant electronic states in the entrance channels of the X(P) + CH4 →HX + CH3 reactions (with X=F((2)P), Cl((2)P), or O((3)P)) is introduced. The diabatization relies on the permutational symmetry present in the methane molecule and results in diabatic states which transform as the three p orbitals of the X atom. Spin-orbit coupling is easily and accurately included using the atomic spin-orbit coupling matrix of the isolated X atom. The method is applied to the F + CH4 system obtaining an accurate PES for the entrance channel based on ab initio multi-reference configuration interaction (MRCI) calculations. Comparing the resulting PESs with spin-orbit MRCI calculations, excellent agreement is found for the excited electronic states at all relevant geometries. The photodetachment spectrum of CH4·F(-) is investigated via full-dimensional (12D) quantum dynamics calculations on the coupled PESs using the multi-layer multi-configurational time-dependent Hartree approach. Extending previous work [J. Palma and U. Manthe, J. Chem. Phys. 137, 044306 (2012)], which was restricted to the dynamics on a single adiabatic PES, the contributions of the electronically excited states to the photodetachment spectrum are calculated and compared to experiment. Considering different experimental setups, good agreement between experiment and theory is found. Addressing questions raised in the previous work, the present dynamical calculations show that the main contribution to the second peak in the photodetachment spectrum results from electron detachment into the electronically excited states of the CH4F complex.

Presence and absence of electronic mixing in shorter-chain and longer-chain carotenoids: Assignment of the symmetries of 1Bu- and 3Ag- states located just below the 1Bu+ state

NASA Astrophysics Data System (ADS)

Sutresno, Adita; Kakitani, Yoshinori; Zuo, Ping; Li, Chunyong; Koyama, Yasushi; Nagae, Hiroyoshi

2007-10-01

In spheroidene (having the number of conjugated double bonds n = 10), stimulated emission was observed from the mixed vibronic levels of 1Bu+(0)+1Bu-(2) and 1Bu+(1)+1Bu-(3), whereas in lycopene, anhydrorhodovibrin and spirilloxanthin ( n = 11-13), stimulated emission, from the pure vibronic levels of 1Bu+(0) and 1Bu+(1). Thus, the 1Bu+ state can mix with the 1Bu- state but not with the 3Ag- state, both being located just below the 1Bu+ state. The presence and absence of the mixing of the neighboring diabatic states support the symmetries of the next low-lying 1Bu- and 3Ag- states.

Study of polarized IR spectra of the hydrogen bond system in crystals of styrylacetic acid

NASA Astrophysics Data System (ADS)

Flakus, Henryk T.; Jabłońska, Magdalena; Jones, Peter G.

2006-10-01

We have investigated the polarized IR spectra of the hydrogen bond system in crystals of trans-styrylacetic acid C 6H 5sbnd CH dbnd CH sbnd CH 2sbnd COOH, and also in crystals of the following three deuterium isotopomers of the compound: C 6H 5sbnd CH dbnd CH sbnd CH 2sbnd COOD, C 6H 5sbnd CH dbnd CH sbnd CD 2sbnd COOH and C 6H 5sbnd CH dbnd CH sbnd CD 2sbnd COOD. The spectra were measured at room temperature and at 77 K by a transmission method. The spectral studies were preceded by determination of the X-ray crystal structure. Theoretical analysis of the results concerned linear dichroic effects, the H/D isotopic and temperature effects, observed in the solid-state IR spectra of the hydrogen and of the deuterium bond, at the frequency ranges of the νO sbnd H and the νO sbnd D bands, respectively. Basic spectral properties of the crystals can be interpreted satisfactorily in terms of the " strong-coupling" theory, when based on a hydrogen bond dimer model. This model sufficiently explained not only a two-branch structure of the νO sbnd H and the νO sbnd D bands, and temperature-induced evolution of the crystalline spectra, but also the linear dichroic effects observed in the band frequency ranges. A vibronic mechanism was analyzed, responsible for promotion of the symmetry-forbidden transition in the IR for the totally symmetric proton stretching vibrations in centrosymmetric hydrogen bond dimers. It was found to be of minor importance, when compared with analogous spectral properties of arylcarboxylic acid, or of cinnamic acid crystals. These effects were ascribed to a substantial weakening of electronic couplings between the hydrogen bonds of the associated carboxyl groups and the styryl radicals, associated with the separation of these groups in styrylacetic acid molecules by methylene groups in the molecules.

Molecular near-field antenna effect in resonance hyper-Raman scattering: Intermolecular vibronic intensity borrowing of solvent from solute through dipole-dipole and dipole-quadrupole interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shimada, Rintaro; Hamaguchi, Hiro-o, E-mail: hhama@nctu.edu.tw

2014-05-28

We quantitatively interpret the recently discovered intriguing phenomenon related to resonance Hyper-Raman (HR) scattering. In resonance HR spectra of all-trans-β-carotene (β-carotene) in solution, vibrations of proximate solvent molecules are observed concomitantly with the solute β-carotene HR bands. It has been shown that these solvent bands are subject to marked intensity enhancements by more than 5 orders of magnitude under the presence of β-carotene. We have called this phenomenon the molecular-near field effect. Resonance HR spectra of β-carotene in benzene, deuterated benzene, cyclohexane, and deuterated cyclohexane have been measured precisely for a quantitative analysis of this effect. The assignments of themore » observed peaks are made by referring to the infrared, Raman, and HR spectra of neat solvents. It has been revealed that infrared active and some Raman active vibrations are active in the HR molecular near-field effect. The observed spectra in the form of difference spectra (between benzene/deuterated benzene and cyclohexane/deuterated cyclohexane) are quantitatively analyzed on the basis of the extended vibronic theory of resonance HR scattering. The theory incorporates the coupling of excited electronic states of β-carotene with the vibrations of a proximate solvent molecule through solute–solvent dipole–dipole and dipole–quadrupole interactions. It is shown that the infrared active modes arise from the dipole–dipole interaction, whereas Raman active modes from the dipole–quadrupole interaction. It is also shown that vibrations that give strongly polarized Raman bands are weak in the HR molecular near-field effect. The observed solvent HR spectra are simulated with the help of quantum chemical calculations for various orientations and distances of a solvent molecule with respect to the solute. The observed spectra are best simulated with random orientations of the solvent molecule at an intermolecular distance of 10 Å.« less

Confirmed Assignments of Isomeric Dimethylbenzyl Radicals Generated by Corona Discharge

NASA Astrophysics Data System (ADS)

Yoon, Young Wook; Lee, Sang Kuk

2012-06-01

Polymethylbenzyl radicals, multi-methyl-substituted benzyl radicals, have been believed to be an ideal model for understanding the torsional effect of methyl group and substitution effect on electronic transition. These radicals are mainly generated from polymethylbenzenes by electric discharge for spectroscopic observation. However, the existence of several methyl groups on the benzene ring may produce several isomeric polymethylbenzyl radicals by removing one of the C-H bonds of each methyl group at different substitution position, which makes the assignment of spectrum ambiguous. In this work, the controversial vibronic assignments of isomeric dimethylbenzyl radicals were clearly resolved by using different precursors. By using corresponding dimethylbenzyl chlorides as precursors, we identified the origins of the vibronic bands of the dimethylbenzyl radicals generated by corona discharge of precursors 1,2,3- and 1,2,4-trimethylbenzenes. From the analysis of the spectra observed from the dimethylbenzyl chlorides in a corona excited supersonic expansion using a pinhole-type glass nozzle, we revised previous assignments of the 2,6- and 2,3-dimethylbenzyl radicals as well as the 3,4-, 2,4-, and 2,5-dimethylbenzyl radicals. In addition, spectroscopic data of electronic transition and vibrational mode frequencies in the ground electronic state of each isomer were accurately determined by comparing them with those obtained by an ab initio calculation and with the known vibrational data of precursors.

Nonadiabatic coupling reduces the activation energy in thermally activated delayed fluorescence.

PubMed

Gibson, J; Penfold, T J

2017-03-22

The temperature dependent rate of a thermally activated process is given by the Arrhenius equation. The exponential decrease in the rate with activation energy, which this imposes, strongly promotes processes with small activation barriers. This criterion is one of the most challenging during the design of thermally activated delayed fluorescence (TADF) emitters used in organic light emitting diodes. The small activation energy is usually achieved with donor-acceptor charge transfer complexes. However, this sacrifices the radiative rate and is therefore incommensurate with the high luminescence quantum yields required for applications. Herein we demonstrate that the spin-vibronic mechanism, operative for efficient TADF, overcomes this limitation. Nonadiabatic coupling between the lowest two triplet states give rise to a strong enhancement of the rate of reserve intersystem crossing via a second order mechanism and promotes population transfer between the T 1 to T 2 states. Consequently the rISC mechanism is actually operative between initial and final state exhibiting an energy gap that is smaller than between the T 1 and S 1 states. This contributes to the small activation energies for molecules exhibiting a large optical gap, identifies limitations of the present design procedures and provides a basis from which to construct TADF molecules with simultaneous high radiative and rISC rates.

The study for the incipient solvation process of NaCl in water: the observation of the NaCl-(H2O)n (n = 1, 2, and 3) complexes using Fourier-transform microwave spectroscopy.

PubMed

Mizoguchi, Asao; Ohshima, Yasuhiro; Endo, Yasuki

2011-08-14

Pure rotational spectra of the sodium chloride-water complexes, NaCl-(H(2)O)(n) (n = 1, 2, and 3), in the vibronic ground state have been observed by a Fourier- transform microwave spectrometer coupled with a laser ablation source. The (37)Cl-isotopic species and a few deuterated species have also been observed. From the analyses of the spectra, the rotational constants, the centrifugal distortion constants, and the nuclear quadrupole coupling constants of the Na and Cl nuclei were determined precisely for all the species. The molecular structures of NaCl-(H(2)O)(n) were determined using the rotational constants and the molecular symmetry. The charge distributions around Na and Cl nuclei in NaCl are dramatically changed by the complex formation with H(2)O. Prominent dependences of the bond lengths r(Na-Cl) on the number of H(2)O were also observed. By a comparison with results of theoretical studies, it is shown that the structure of NaCl-(H(2)O)(3) is approaching to that of the contact ion-pair, which is considered to be an intermediate species in the incipient solvation process.

Quantum coherence selective 2D Raman–2D electronic spectroscopy

PubMed Central

Spencer, Austin P.; Hutson, William O.; Harel, Elad

2017-01-01

Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational–vibrational, electronic–vibrational and electronic–electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment–protein complexes. PMID:28281541

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born–Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersionmore » of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.« less

High-resolution threshold photoionization of N sub 2 O

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiedmann, R.T.; Grant, E.R.; Tonkyn, R.G.

1991-07-15

Pulsed field ionization (PFI) has been used in conjunction with a coherent vuv source to obtain high-resolution threshold photoelectron spectra for the (000), (010), (020), and (100) vibrational states of the N{sub 2}O{sup +} cation. Simulations for the rotational profiles of each vibronic level were obtained by fitting the Buckingham--Orr--Sichel equations (A. D. Buckingham, B. J. Orr, and J. M. Sichel, Philos. Trans. R. Soc. London, Ser. A {bold 268}, 147 (1970)) using accurate spectroscopic constants for the ground states of the neutral and the ion. The relative branch intensities are interpreted in terms of the partial waves of themore » outgoing photoelectron to which the ionic core is coupled and in terms of the angular momentum transferred to the core. The PFI technique also allows us to report an improved value for the ionization potential of N{sub 2}O of 103 963{plus minus}5 cm{sup {minus}1}.« less

Electronic relaxation effects in condensed polyacenes: A high-resolution photoemission study

NASA Astrophysics Data System (ADS)

Rocco, M. L. M.; Haeming, M.; Batchelor, D. R.; Fink, R.; Schöll, A.; Umbach, E.

2008-08-01

We present a high-resolution photoelectron spectroscopy investigation of condensed films of benzene, naphthalene, anthracene, tetracene, and pentacene. High spectroscopic resolution and a systematic variation of the molecular size allow a detailed analysis of the fine structures. The line shapes of the C 1s main lines are analyzed with respect to the different contributions of inhomogeneous broadening, vibronic coupling, and chemical shifts. The shake-up satellite spectra reveal trends, which give insight into the charge redistribution within the molecule upon photoexcitation. In particular, the shake-up between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) increases in intensity and moves closer toward the C 1s main line if the size of the aromatic system is increased. An explanation is given on the basis of the delocalization of the aromatic system and its capability in screening the photogenerated core hole. A comparison of the HOMO-LUMO shake-up position to the optical band gap gives additional insight into the reorganization of the electronic system upon photoexcitation.

Electron-flux infrared response to varying π-bond topology in charged aromatic monomers

PubMed Central

Álvaro Galué, Héctor; Oomens, Jos; Buma, Wybren Jan; Redlich, Britta

2016-01-01

The interaction of delocalized π-electrons with molecular vibrations is key to charge transport processes in π-conjugated organic materials based on aromatic monomers. Yet the role that specific aromatic motifs play on charge transfer is poorly understood. Here we show that the molecular edge topology in charged catacondensed aromatic hydrocarbons influences the Herzberg-Teller coupling of π-electrons with molecular vibrations. To this end, we probe the radical cations of picene and pentacene with benchmark armchair- and zigzag-edges using infrared multiple-photon dissociation action spectroscopy and interpret the recorded spectra via quantum-chemical calculations. We demonstrate that infrared bands preserve information on the dipolar π-electron-flux mode enhancement, which is governed by the dynamical evolution of vibronically mixed and correlated one-electron configuration states. Our results reveal that in picene a stronger charge π-flux is generated than in pentacene, which could justify the differences of electronic properties of armchair- versus zigzag-type families of technologically relevant organic molecules. PMID:27577323

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

DOE PAGES

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert; ...

2017-05-24

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born–Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersionmore » of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.« less

Infrared spectroscopy of the ν1 + ν4 and 3ν4 bands of the nitrate radical

NASA Astrophysics Data System (ADS)

Kawaguchi, Kentarou; Fujimori, Ryuji; Ishiwata, Takashi

2018-05-01

High-resolution Fourier transform infrared spectra of the ν1 + ν4 and 3ν4 bands of 14NO3 were observed in the 1414 and 1174 cm-1 regions, respectively, and the corresponding ones of 15NO3 in the 1407 and 1159 cm-1 regions, respectively, and analyzed as E‧-A2‧ bands. The rotational constants of the upper states of 14NO3 are determined to be 0.457584 and 0.46089 cm-1 for ν1 + ν4 and 3ν4, respectively, consistent with the vibrational assignment. Effective Coriolis coupling constants of the ground electronic state are partly explained by vibronic interaction from the B2E‧ state, and a large change (37% decrease) in the value of the ν1 + ν4 state compared with that of the ν4 state is attributed to a mixing with the ν3 + ν4 state (1492 cm-1) through vibrational anharmonicity.

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

NASA Astrophysics Data System (ADS)

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert; van Driel, Tim B.; Chollet, Matthieu; Glownia, James M.; Song, Sanghoon; Zhu, Diling; Pace, Elisabetta; Matar, Samir F.; Nielsen, Martin M.; Benfatto, Maurizio; Gaffney, Kelly J.; Collet, Eric; Cammarata, Marco

2017-05-01

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born-Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersion of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.

Multicomponent Time-Dependent Density Functional Theory: Proton and Electron Excitation Energies.

PubMed

Yang, Yang; Culpitt, Tanner; Hammes-Schiffer, Sharon

2018-04-05

The quantum mechanical treatment of both electrons and protons in the calculation of excited state properties is critical for describing nonadiabatic processes such as photoinduced proton-coupled electron transfer. Multicomponent density functional theory enables the consistent quantum mechanical treatment of more than one type of particle and has been implemented previously for studying ground state molecular properties within the nuclear-electronic orbital (NEO) framework, where all electrons and specified protons are treated quantum mechanically. To enable the study of excited state molecular properties, herein the linear response multicomponent time-dependent density functional theory (TDDFT) is derived and implemented within the NEO framework. Initial applications to FHF - and HCN illustrate that NEO-TDDFT provides accurate proton and electron excitation energies within a single calculation. As its computational cost is similar to that of conventional electronic TDDFT, the NEO-TDDFT approach is promising for diverse applications, particularly nonadiabatic proton transfer reactions, which may exhibit mixed electron-proton vibronic excitations.

Statistical quasi-particle theory for open quantum systems

NASA Astrophysics Data System (ADS)

Zhang, Hou-Dao; Xu, Rui-Xue; Zheng, Xiao; Yan, YiJing

2018-04-01

This paper presents a comprehensive account on the recently developed dissipaton-equation-of-motion (DEOM) theory. This is a statistical quasi-particle theory for quantum dissipative dynamics. It accurately describes the influence of bulk environments, with a few number of quasi-particles, the dissipatons. The novel dissipaton algebra is then followed, which readily bridges the Schrödinger equation to the DEOM theory. As a fundamental theory of quantum mechanics in open systems, DEOM characterizes both the stationary and dynamic properties of system-and-bath interferences. It treats not only the quantum dissipative systems of primary interest, but also the hybrid environment dynamics that could be experimentally measurable. Examples are the linear or nonlinear Fano interferences and the Herzberg-Teller vibronic couplings in optical spectroscopies. This review covers the DEOM construction, the underlying dissipaton algebra and theorems, the physical meanings of dynamical variables, the possible identifications of dissipatons, and some recent advancements in efficient DEOM evaluations on various problems. The relations of the present theory to other nonperturbative methods are also critically presented.

Application of artificial neural networks and genetic algorithms to modeling molecular electronic spectra in solution

NASA Astrophysics Data System (ADS)

Lilichenko, Mark; Kelley, Anne Myers

2001-04-01

A novel approach is presented for finding the vibrational frequencies, Franck-Condon factors, and vibronic linewidths that best reproduce typical, poorly resolved electronic absorption (or fluorescence) spectra of molecules in condensed phases. While calculation of the theoretical spectrum from the molecular parameters is straightforward within the harmonic oscillator approximation for the vibrations, "inversion" of an experimental spectrum to deduce these parameters is not. Standard nonlinear least-squares fitting methods such as Levenberg-Marquardt are highly susceptible to becoming trapped in local minima in the error function unless very good initial guesses for the molecular parameters are made. Here we employ a genetic algorithm to force a broad search through parameter space and couple it with the Levenberg-Marquardt method to speed convergence to each local minimum. In addition, a neural network trained on a large set of synthetic spectra is used to provide an initial guess for the fitting parameters and to narrow the range searched by the genetic algorithm. The combined algorithm provides excellent fits to a variety of single-mode absorption spectra with experimentally negligible errors in the parameters. It converges more rapidly than the genetic algorithm alone and more reliably than the Levenberg-Marquardt method alone, and is robust in the presence of spectral noise. Extensions to multimode systems, and/or to include other spectroscopic data such as resonance Raman intensities, are straightforward.

Analysis of the chemiluminescence from electronically excited lead oxide generated in a flow tube reactor

NASA Astrophysics Data System (ADS)

Dorko, E. A.; Glessner, J. W.; Ritchey, C. M.; Rutger, L. L.; Pow, J. J.; Brasure, L. D.; Duray, J. P.; Snyder, S. R.

1986-03-01

The chemiluminescence from electronically excited lead oxide formed during the reaction between lead vapor and either 3Σ O 2 or 1Δ O 2 has been studied. The reactions were accomplished in a flow tube reactor. A microwave discharge was used to generate 1Δ O 2. The vibronic spectrum was analyzed and the band head assignments were used in a linear least-squares calculation to obtain the vibronic molecular constants for the X, a, b, A, B, C, C', D, and E electronic states of lead oxide. Based on these and other molecular constants, Franck-Condon factors were calculated for the transitions to the ground state and also for the A-a and D-a transitions. Evidence was presented to support a kinetic analysis of the mechanism leading to chemiluminescence under the experimental conditions encountered in the flow tube reactor. Mechanisms presented earlier were verified by the present data.

Norbornane: An investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories

NASA Astrophysics Data System (ADS)

Knippenberg, S.; Nixon, K. L.; Brunger, M. J.; Maddern, T.; Campbell, L.; Trout, N.; Wang, F.; Newell, W. R.; Deleuze, M. S.; Francois, J.-P.; Winkler, D. A.

2004-12-01

We report on the results of an exhaustive study of the valence electronic structure of norbornane (C7H12), up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-ζ quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented (e,2e) ionization spectra, except for the band associated with the 1a2-1 one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at ˜25 eV characterized by a momentum distribution of "s-type" symmetry, which Green's function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at ˜26 eV.

Electron-nuclear corellations for photoinduced dynamics in molecular dimers

NASA Astrophysics Data System (ADS)

Kilin, Dmitri S.; Pereversev, Yuryi V.; Prezhdo, Oleg V.

2003-03-01

Ultrafast photoinduced dynamics of electronic excitation in molecular dimers is drastically affected by dynamic reorganization of of inter- and intra- molecular nuclear configuration modelled by quantized nuclear degree of freedom [1]. The dynamics of the electronic population and nuclear coherence is analyzed with help of both numerical solution of the chain of coupled differential equations for mean coordinate, population inversion, electronic-vibrational correlation etc.[2] and by propagating the Gaussian wavepackets in relevant adiabatic potentials. Intriguing results were obtained in the approximation of small energy difference and small change of nuclear equilibrium configuration for excited electronic states. In the limiting case of resonance between electronic states energy difference and frequency of the nuclear mode these results have been justified by comparison to exactly solvable Jaynes-Cummings model. It has been found that the photoinduced processes in dimer are arranged according to their time scales:(i) fast scale of nuclear motion,(ii) intermediate scale of dynamical redistribution of electronic population between excited states as well as growth and dynamics of electronic -nuclear correlation,(iii) slow scale of electronic population approaching to the quasiequilibrium distribution, decay of electronic-nuclear correlation, and diminishing the amplitude of mean coordinate oscillations, accompanied by essential growth of the nuclear coordinate dispersion associated with the overall nuclear wavepacket width. Demonstrated quantum-relaxational features of photoinduced vibronic dinamical processess in molecular dimers are obtained by simple method, applicable to large biological systems with many degrees of freedom. [1] J. A. Cina, D. S. Kilin, T. S. Humble, J. Chem. Phys. (2003) in press. [2] O. V. Prezhdo, J. Chem. Phys. 117, 2995 (2002).

Molecular Chirality: Enantiomer Differentiation by High-Resolution Spectroscopy

NASA Astrophysics Data System (ADS)

Hirota, Eizi

2014-06-01

I have demonstrated that triple resonance performed on a three-rotational-level system of a chiral molecule of C1 symmetry exhibits signals opposite in phase for different enantiomers, thereby making enantiomer differentiation possible by microwave spectroscopy This prediction was realized by Patterson et al. on 1,2-propanediol and 1,3-butanediol. We thus now add a powerful method: microwave spectroscopy to the study of chiral molecules, for which hitherto only the measurement of optical rotation has been employed. Although microwave spectroscopy is applied to molecules in the gaseous phase, it is unprecedentedly superior to the traditional method: polarimeter in resolution, accuracy, sensitivity, and so on, and I anticipate a new fascinating research area to be opened in the field of molecular chirality. More versatile and efficient systems should be invented and developed for microwave spectroscopy, in order to cope well with new applications expected for this method For C2 and Cn (n ≥ 3)chiral molecules, the three-rotational-level systems treated above for C1 molecules are no more available within one vibronic state. It should, however, be pointed out that, if we take into account an excited vibronic state in addition to the ground state, for example, we may encounter many three-level systems. Namely, either one rotational transition in the ground state is combined with two vibronic transitions, or such a rotational transition in an excited state may be connected through two vibronic transitions to a rotational level in the ground state manifold. The racemization obviously plays a crucial role in the study of molecular chirality. However, like many other terms employed in chemistry, this important process has been "defined" only in a vague way, in other words, it includes many kinds of processes, which are not well classified on a molecular basis. I shall mention an attempt to obviate these shortcomings in the definition of racemization and also to clarify the implicit assumptions made in Hund's paradox. E. Hirota, 3rd Molecular Science Symposium, Nagoya, September 2009, E. Hirota, Proc. Jpn. Acad. Ser. B, 88, 120 (2012). D. Patterson, M. Schnell and J. M. Doyle, Nature 497, 475 (2013), D. Patterson and J. M. Doyle, Phys. Rev. Lett. 111, 023008 (2013). F. Hund, Z. Phys. 43, 805 (1927).

Strong and Long Makes Short: Strong-Pump Strong-Probe Spectroscopy.

PubMed

Gelin, Maxim F; Egorova, Dassia; Domcke, Wolfgang

2011-01-20

We propose a new time-domain spectroscopic technique that is based on strong pump and probe pulses. The strong-pump strong-probe (SPSP) technique provides temporal resolution that is not limited by the durations of the pump and probe pulses. By numerically exact simulations of SPSP signals for a multilevel vibronic model, we show that the SPSP signals exhibit electronic and vibrational beatings on time scales which are significantly shorter than the pulse durations. This suggests the possible application of SPSP spectroscopy for the real-time investigation of molecular processes that cannot be temporally resolved by pump-probe spectroscopy with weak pump and probe pulses.

Theoretical modeling of UV-Vis absorption and emission spectra in liquid state systems including vibrational and conformational effects: explicit treatment of the vibronic transitions.

PubMed

D'Abramo, Marco; Aschi, Massimiliano; Amadei, Andrea

2014-04-28

Here, we extend a recently introduced theoretical-computational procedure [M. D'Alessandro, M. Aschi, C. Mazzuca, A. Palleschi, and A. Amadei, J. Chem. Phys. 139, 114102 (2013)] to include quantum vibrational transitions in modelling electronic spectra of atomic molecular systems in condensed phase. The method is based on the combination of Molecular Dynamics simulations and quantum chemical calculations within the Perturbed Matrix Method approach. The main aim of the presented approach is to reproduce as much as possible the spectral line shape which results from a subtle combination of environmental and intrinsic (chromophore) mechanical-dynamical features. As a case study, we were able to model the low energy UV-vis transitions of pyrene in liquid acetonitrile in good agreement with the experimental data.

Two-dimensional vibrational-electronic spectroscopy

NASA Astrophysics Data System (ADS)

Courtney, Trevor L.; Fox, Zachary W.; Slenkamp, Karla M.; Khalil, Munira

2015-10-01

Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE) to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (νCN) and either a ligand-to-metal charge transfer transition ([FeIII(CN)6]3- dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN)5FeIICNRuIII(NH3)5]- dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific νCN modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a wide range of complex molecular, material, and biological systems.

Two-dimensional vibrational-electronic spectroscopy.

PubMed

Courtney, Trevor L; Fox, Zachary W; Slenkamp, Karla M; Khalil, Munira

2015-10-21

Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE) to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (νCN) and either a ligand-to-metal charge transfer transition ([Fe(III)(CN)6](3-) dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN)5Fe(II)CNRu(III)(NH3)5](-) dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific νCN modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a wide range of complex molecular, material, and biological systems.

Communication: Coherences observed in vivo in photosynthetic bacteria using two-dimensional electronic spectroscopy

NASA Astrophysics Data System (ADS)

Dahlberg, Peter D.; Norris, Graham J.; Wang, Cheng; Viswanathan, Subha; Singh, Ved P.; Engel, Gregory S.

2015-09-01

Energy transfer through large disordered antenna networks in photosynthetic organisms can occur with a quantum efficiency of nearly 100%. This energy transfer is facilitated by the electronic structure of the photosynthetic antennae as well as interactions between electronic states and the surrounding environment. Coherences in time-domain spectroscopy provide a fine probe of how a system interacts with its surroundings. In two-dimensional electronic spectroscopy, coherences can appear on both the ground and excited state surfaces revealing detailed information regarding electronic structure, system-bath coupling, energy transfer, and energetic coupling in complex chemical systems. Numerous studies have revealed coherences in isolated photosynthetic pigment-protein complexes, but these coherences have not been observed in vivo due to the small amplitude of these signals and the intense scatter from whole cells. Here, we present data acquired using ultrafast video-acquisition gradient-assisted photon echo spectroscopy to observe quantum beating signals from coherences in vivo. Experiments were conducted on isolated light harvesting complex II (LH2) from Rhodobacter sphaeroides, whole cells of R. sphaeroides, and whole cells of R. sphaeroides grown in 30% deuterated media. A vibronic coherence was observed following laser excitation at ambient temperature between the B850 and the B850∗ states of LH2 in each of the 3 samples with a lifetime of ˜40-60 fs.

Photoabsorption and photodissociation studies of dimethyl sulphoxide (DMSO) in the 35,000-80,000 cm-1 region using synchrotron radiation

NASA Astrophysics Data System (ADS)

Mandal, Anuvab; Singh, Param Jeet; Shastri, Aparna; Sunanda, K.; Jagatap, B. N.

2015-05-01

Photoabsorption and photodissociation studies of dimethyl sulphoxide and its deuterated isotopologue (DMSO-h6 and DMSO-d6) are performed using synchrotron radiation in the 35,000-80,000 cm-1 region. In the photoabsorption spectrum, Rydberg series converging to the first three ionization potentials of DMSO at 9.1, 10.1 and 12.3 eV corresponding to removal of an electron from the highest three occupied molecular orbitals (14a‧, 7a″ and 13a‧) are observed. Based on a quantum defect analysis, Rydberg series assignments are extended to higher members as compared to earlier works and a few ambiguities in earlier assignments are clarified. Analysis is aided by quantum chemical calculations using the DFT and TDDFT methodologies. Vibronic structures observed in the spectrum of DMSO-h6 in the regions 7.7-8.1 eV and 8.1-8.8 eV are attributed to the transitions 7a″→4p at 7.862 eV and 14a‧→6s/4d at 8.182 eV, respectively. Photoabsorption spectra of DMSO-h6 and -d6 recorded using a broad band incident radiation show prominent peaks, which are identified and assigned to electronic and vibronic transitions of the SO radical. This provides a direct confirmation of the fact that DMSO preferentially dissociates into CH3 and SO upon UV-VUV excitation, as proposed in earlier photodissociation studies. An extended vibronic band system associated with the e1Π-X3Σ- transition of the SO radical is identified and assigned. The complete VUV photoabsorption spectrum of DMSO-d6 is also reported here for the first time.

Simulation of the single-vibronic-level emission spectrum of HPS.

PubMed

Mok, Daniel K W; Lee, Edmond P F; Chau, Foo-tim; Dyke, John M

2014-05-21

We have computed the potential energy surfaces of the X¹A' and ùA" states of HPS using the explicitly correlated multi-reference configuration interaction (MRCI-F12) method, and Franck-Condon factors between the two states, which include anharmonicity and Duschinsky rotation, with the aim of testing the assignment of the recently reported single-vibronic-level (SVL) emission spectrum of HPS [R. Grimminger, D. J. Clouthier, R. Tarroni, Z. Wang, and T. J. Sears, J. Chem. Phys. 139, 174306 (2013)]. These are the highest level calculations on these states yet reported. It is concluded that our spectral simulation supports the assignments of the molecular carrier, the electronic states involved and the vibrational structure of the experimental laser induced fluorescence, and SVL emission spectra proposed by Grimminger et al. [J. Chem. Phys. 139, 174306 (2013)]. However, there remain questions unanswered regarding the relative electronic energies of the two states and the geometry of the excited state of HPS.

Near-field scanning magneto-optical spectroscopy of Wigner molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mintairov, A. M., E-mail: amintair@nd.edu; Rouvimov, S.; Ioffe Physical-Technical Institute of the Russian Academy of Sciences, Saint Petersburg, 194021

We study the emission spectra of single self-organized InP/GaInP QDs (size 100-220 nm) using high-spatial-resolution, low-temperature (5 K) near-field scanning optical microscope (NSOM) operating at magnetic field strength B=0-10 T. The dots contain up to twenty electrons and represent natural Wigner molecules (WM). We observed vibronic-type shake-up structure in single electron QDs manifesting formation of two electron (2e) WM in photo-excited state. We found that relative intensities of the shake-up components described well by vibronic Frank-Condon factors giving for dots having parabolic confinement energy ħω{sub 0}=1.2-4 meV molecule bond lengths 40-140 nm. We used measurements of magnetic-field-induced shifts to distinguishmore » emission of 2e-WM and singly charged exciton (trion). We also observed magnetic-field-induced molecular-droplet transition for two electron dot, emitting through doubly charge exciton (tetron) at zero magnetic field.« less

A new basis set for molecular bending degrees of freedom.

PubMed

Jutier, Laurent

2010-07-21

We present a new basis set as an alternative to Legendre polynomials for the variational treatment of bending vibrational degrees of freedom in order to highly reduce the number of basis functions. This basis set is inspired from the harmonic oscillator eigenfunctions but is defined for a bending angle in the range theta in [0:pi]. The aim is to bring the basis functions closer to the final (ro)vibronic wave functions nature. Our methodology is extended to complicated potential energy surfaces, such as quasilinearity or multiequilibrium geometries, by using several free parameters in the basis functions. These parameters allow several density maxima, linear or not, around which the basis functions will be mainly located. Divergences at linearity in integral computations are resolved as generalized Legendre polynomials. All integral computations required for the evaluation of molecular Hamiltonian matrix elements are given for both discrete variable representation and finite basis representation. Convergence tests for the low energy vibronic states of HCCH(++), HCCH(+), and HCCS are presented.

Ultraviolet photodissociation action spectroscopy of the N-pyridinium cation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Christopher S., E-mail: csh297@uowmail.edu.au; Trevitt, Adam J., E-mail: adamt@uow.edu.au; Blanksby, Stephen J.

2015-01-07

The S{sub 1}←S{sub 0} electronic transition of the N-pyridinium ion (C{sub 5}H{sub 5}NH{sup +}) is investigated using ultraviolet photodissociation (PD) spectroscopy of the bare ion and also the N{sub 2}-tagged complex. Gas-phase N-pyridinium ions photodissociate by the loss of molecular hydrogen (H{sub 2}) in the photon energy range 37 000–45 000 cm{sup −1} with structurally diagnostic ion-molecule reactions identifying the 2-pyridinylium ion as the exclusive co-product. The photodissociation action spectra reveal vibronic details that, with the aid of electronic structure calculations, support the proposal that dissociation occurs through an intramolecular rearrangement on the ground electronic state following internal conversion. Quantum chemical calculationsmore » are used to analyze the measured spectra. Most of the vibronic features are attributed to progressions of totally symmetric ring deformation modes and out-of-plane modes active in the isomerization of the planar excited state towards the non-planar excited state global minimum.« less

Intense Vibronic Modulation of the Chiral Photoelectron Angular Distribution Generated by Photoionization of Limonene Enantiomers with Circularly Polarized Synchrotron Radiation.

PubMed

Rafiee Fanood, Mohammad M; Ganjitabar, Hassan; Garcia, Gustavo A; Nahon, Laurent; Turchini, Stefano; Powis, Ivan

2018-04-17

Photoionization of the chiral monoterpene limonene has been investigated using polarized synchrotron radiation between the adiabatic ionization threshold, 8.505 and 23.5 eV. A rich vibrational structure is seen in the threshold photoelectron spectrum and is interpreted using a variety of computational methods. The corresponding photoelectron circular dichroism-measured in the photoelectron angular distribution as a forward-backward asymmetry with respect to the photon direction-was found to be strongly dependent on the vibronic structure appearing in the photoelectron spectra, with the observed asymmetry even switching direction in between the major vibrational peaks. This effect can be ultimately attributed to the sensitivity of this dichroism to small phase shifts between adjacent partial waves of the outgoing photoelectron. These observations have implications for potential applications of this chiroptical technique, where the enantioselective analysis of monoterpene components is of particular interest. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Full Quantum Dynamics Simulation of a Realistic Molecular System Using the Adaptive Time-Dependent Density Matrix Renormalization Group Method.

PubMed

Yao, Yao; Sun, Ke-Wei; Luo, Zhen; Ma, Haibo

2018-01-18

The accurate theoretical interpretation of ultrafast time-resolved spectroscopy experiments relies on full quantum dynamics simulations for the investigated system, which is nevertheless computationally prohibitive for realistic molecular systems with a large number of electronic and/or vibrational degrees of freedom. In this work, we propose a unitary transformation approach for realistic vibronic Hamiltonians, which can be coped with using the adaptive time-dependent density matrix renormalization group (t-DMRG) method to efficiently evolve the nonadiabatic dynamics of a large molecular system. We demonstrate the accuracy and efficiency of this approach with an example of simulating the exciton dissociation process within an oligothiophene/fullerene heterojunction, indicating that t-DMRG can be a promising method for full quantum dynamics simulation in large chemical systems. Moreover, it is also shown that the proper vibronic features in the ultrafast electronic process can be obtained by simulating the two-dimensional (2D) electronic spectrum by virtue of the high computational efficiency of the t-DMRG method.

A multi-plate velocity-map imaging design for high-resolution photoelectron spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kregel, Steven J.; Thurston, Glen K.; Zhou, Jia

A velocity map imaging (VMI) setup consisting of multiple electrodes with three adjustable voltage parameters, designed for slow electron velocity map imaging applications, is presented. The motivations for this design are discussed in terms of parameters that influence the VMI resolution and functionality. Particularly, this VMI has two tunable potentials used to adjust for optimal focus, yielding good VMI focus across a relatively large energy range. It also allows for larger interaction volumes without significant sacrifice to the resolution via a smaller electric gradient at the interaction region. All the electrodes in this VMI have the same dimensions for practicalitymore » and flexibility, allowing for relatively easy modifications to suit different experimental needs. We have coupled this VMI to a cryogenic ion trap mass spectrometer that has a flexible source design. The performance is demonstrated with the photoelectron spectra of S- and CS 2 -. The latter has a long vibrational progression in the ground state, and the temperature dependence of the vibronic features is probed by changing the temperature of the ion trap.« less

Resonant inelastic x-ray scattering and photoemission measurement of O2: Direct evidence for dependence of Rydberg-valence mixing on vibrational states in O 1s → Rydberg states

NASA Astrophysics Data System (ADS)

Gejo, T.; Oura, M.; Tokushima, T.; Horikawa, Y.; Arai, H.; Shin, S.; Kimberg, V.; Kosugi, N.

2017-07-01

High-resolution resonant inelastic x-ray scattering (RIXS) and low-energy photoemission spectra of oxygen molecules have been measured for investigating the electronic structure of Rydberg states in the O 1s → σ* energy region. The electronic characteristics of each Rydberg state have been successfully observed, and new assignments are made for several states. The RIXS spectra clearly show that vibrational excitation is very sensitive to the electronic characteristics because of Rydberg-valence mixing and vibronic coupling in O2. This observation constitutes direct experimental evidence that the Rydberg-valence mixing characteristic depends on the vibrational excitation near the avoided crossing of potential surfaces. We also measured the photoemission spectra of metastable oxygen atoms (O*) from O2 excited to 1s → Rydberg states. The broadening of the 4p Rydberg states of O* has been found with isotropic behavior, implying that excited oxygen molecules undergo dissociation with a lifetime of the order of 10 fs in 1s → Rydberg states.

Triazatruxene: A Rigid Central Donor Unit for a D-A3 Thermally Activated Delayed Fluorescence Material Exhibiting Sub-Microsecond Reverse Intersystem Crossing and Unity Quantum Yield via Multiple Singlet-Triplet State Pairs.

PubMed

Dos Santos, Paloma L; Ward, Jonathan S; Congrave, Daniel G; Batsanov, Andrei S; Eng, Julien; Stacey, Jessica E; Penfold, Thomas J; Monkman, Andrew P; Bryce, Martin R

2018-06-01

By inverting the common structural motif of thermally activated delayed fluorescence materials to a rigid donor core and multiple peripheral acceptors, reverse intersystem crossing (rISC) rates are demonstrated in an organic material that enables utilization of triplet excited states at faster rates than Ir-based phosphorescent materials. A combination of the inverted structure and multiple donor-acceptor interactions yields up to 30 vibronically coupled singlet and triplet states within 0.2 eV that are involved in rISC. This gives a significant enhancement to the rISC rate, leading to delayed fluorescence decay times as low as 103.9 ns. This new material also has an emission quantum yield ≈1 and a very small singlet-triplet gap. This work shows that it is possible to achieve both high photoluminescence quantum yield and fast rISC in the same molecule. Green organic light-emitting diode devices with external quantum efficiency >30% are demonstrated at 76 cd m -2 .

A multi-plate velocity-map imaging design for high-resolution photoelectron spectroscopy

DOE PAGES

Kregel, Steven J.; Thurston, Glen K.; Zhou, Jia; ...

2017-09-01

A velocity map imaging (VMI) setup consisting of multiple electrodes with three adjustable voltage parameters, designed for slow electron velocity map imaging applications, is presented. The motivations for this design are discussed in terms of parameters that influence the VMI resolution and functionality. Particularly, this VMI has two tunable potentials used to adjust for optimal focus, yielding good VMI focus across a relatively large energy range. It also allows for larger interaction volumes without significant sacrifice to the resolution via a smaller electric gradient at the interaction region. All the electrodes in this VMI have the same dimensions for practicalitymore » and flexibility, allowing for relatively easy modifications to suit different experimental needs. We have coupled this VMI to a cryogenic ion trap mass spectrometer that has a flexible source design. The performance is demonstrated with the photoelectron spectra of S- and CS 2 -. The latter has a long vibrational progression in the ground state, and the temperature dependence of the vibronic features is probed by changing the temperature of the ion trap.« less

Andrew Liehr and the structure of Jahn-Teller surfaces

NASA Astrophysics Data System (ADS)

Chibotaru, Liviu F.; Iwahara, Naoya

2017-05-01

The present article is an attempt to draw attention to a seminal work by Andrew Liehr “Topological aspects of conformational stability problem” [1, 2] issued more than half century ago. The importance of this work stems from two aspects of static Jahn-Teller and pseudo-Jahn-Teller problems fully developed by the author. First, the work of Liehr offers an almost complete overview of adiabatic potential energy surfaces for most known Jahn-Teller problems including linear, quadratic and higher-order vibronic couplings. Second, and most importantly, it identifies the factors defining the structure of Jahn-Teller surfaces. Among them, one should specially mention the minimax principle stating that the distorted Jahn-Teller systems tend to preserve the highest symmetry consistent with the loss of their orbital degeneracy. We believe that the present short reminiscence not only will introduce a key Jahn-Teller scientist to the young members of the community but also will serve as a vivid example of how a complete understanding of a complex problem, which the Jahn-Teller effect certainly was in the beginning of 1960s, can be achieved.

Experimental and ab initio characterization of HC3N+ vibronic structure. II. High-resolution VUV PFI-ZEKE spectroscopy.

PubMed

Gans, Bérenger; Lamarre, Nicolas; Broquier, Michel; Liévin, Jacques; Boyé-Péronne, Séverine

2016-12-21

Vacuum-ultraviolet pulsed-field-ionization zero-kinetic-energy photoelectron spectra of X + Π2←XΣ+1 and B + Π2←XΣ+1 transitions of the HC 3 14 N and HC 3 15 N isotopologues of cyanoacetylene have been recorded. The resolution of the photoelectron spectra allowed us to resolve the vibrational structures and the spin-orbit splittings in the cation. Accurate values of the adiabatic ionization potentials of the two isotopologues (E I /hc(HC 3 14 N)=93 909(2) cm -1 and E I /hc(HC 3 15 N)=93 912(2) cm -1 ), the vibrational frequencies of the ν 2 , ν 6 , and ν 7 vibrational modes, and the spin-orbit coupling constant (A SO = -44(2) cm -1 ) of the X + Π2 cationic ground state have been derived from the measurements. Using ab initio calculations, the unexpected structure of the B + Π2←XΣ+1 transition is tentatively attributed to a conical intersection between the A + and B + electronic states of the cation.

Tunneling explains efficient electron transport via protein junctions.

PubMed

Fereiro, Jerry A; Yu, Xi; Pecht, Israel; Sheves, Mordechai; Cuevas, Juan Carlos; Cahen, David

2018-05-15

Metalloproteins, proteins containing a transition metal ion cofactor, are electron transfer agents that perform key functions in cells. Inspired by this fact, electron transport across these proteins has been widely studied in solid-state settings, triggering the interest in examining potential use of proteins as building blocks in bioelectronic devices. Here, we report results of low-temperature (10 K) electron transport measurements via monolayer junctions based on the blue copper protein azurin (Az), which strongly suggest quantum tunneling of electrons as the dominant charge transport mechanism. Specifically, we show that, weakening the protein-electrode coupling by introducing a spacer, one can switch the electron transport from off-resonant to resonant tunneling. This is a consequence of reducing the electrode's perturbation of the Cu(II)-localized electronic state, a pattern that has not been observed before in protein-based junctions. Moreover, we identify vibronic features of the Cu(II) coordination sphere in transport characteristics that show directly the active role of the metal ion in resonance tunneling. Our results illustrate how quantum mechanical effects may dominate electron transport via protein-based junctions.

Pulsed Discharge Nozzle Cavity Ring Down Spectroscopy of Cold PAH Ions

NASA Technical Reports Server (NTRS)

Biennier, Ludovic; Salama, Farid; Allamandola, Louis J.; Scherer, James J.; DeVincenzi, Donald (Technical Monitor)

2002-01-01

The gas-phase electronic absorption spectra of the naphthalene (C10H8(+)) and acenaphthene (C12H10(+)) cations have been measured in the visible range in a free 10 jet planar expansion in an attempt to collect data in an astrophysically relevant environment. The direct absorption spectra of two out of four bands measured of the gas-phase cold naphthalene cation along with the gas-phase vibronic absorption spectrum of the cold acenaphthene cation are reported for the first time. The study has been carried out using the ultrasensitive and versatile technique of cavity ringdown spectroscopy (CRDS) coupled to a pulsed discharge slit nozzle (PDN). The new CRDS-PDN set up is described and its characteristics are evaluated. The direct-absorption spectra of the PAH ions are discussed and compared to the gas-phase and solid-phase data available in the literature. The analysis of the results show that cold, free flying PAH ions are generated in the argon discharge primarily through soft Penning ionization. This enables the intrinsic band profiles to be measured, a key requirement for astrophysical applications.

Adenine and 2-aminopurine: Paradigms of modern theoretical photochemistry

PubMed Central

Serrano-Andrés, Luis; Merchán, Manuela; Borin, Antonio C.

2006-01-01

Distinct photophysical behavior of nucleobase adenine and its constitutional isomer, 2-aminopurine, has been studied by using quantum chemical methods, in particular an accurate ab initio multiconfigurational second-order perturbation theory. After light irradiation, the efficient, ultrafast energy dissipation observed for nonfluorescent 9H-adenine is explained here by the nonradiative internal conversion process taking place along a barrierless reaction path from the initially populated 1(ππ* La) excited state toward a low-lying conical intersection (CI) connected with the ground state. In contrast, the strong fluorescence recorded for 2-aminopurine at 4.0 eV with large decay lifetime is interpreted by the presence of a minimum in the 1(ππ* La) hypersurface lying below the lowest CI and the subsequent potential energy barrier required to reach the funnel to the ground state. Secondary deactivation channels were found in the two systems related to additional CIs involving the 1(ππ* Lb) and 1(nπ*) states. Although in 9H-adenine a population switch between both states is proposed, in 7H-adenine this may be perturbed by a relatively larger barrier to access the 1(nπ*) state, and, therefore, the 1(ππ* Lb) state becomes responsible for the weak fluorescence measured in aqueous adenine at ≈4.5 eV. In contrast to previous models that explained fluorescence quenching in adenine, unlike in 2-aminopurine, on the basis of the vibronic coupling of the nearby 1(ππ*) and 1(nπ*) states, the present results indicate that the 1(nπ*) state does not contribute to the leading photophysical event and establish the prevalence of a model based on the CI concept in modern photochemistry. PMID:16731617

Adenine and 2-aminopurine: paradigms of modern theoretical photochemistry.

PubMed

Serrano-Andrés, Luis; Merchán, Manuela; Borin, Antonio C

2006-06-06

Distinct photophysical behavior of nucleobase adenine and its constitutional isomer, 2-aminopurine, has been studied by using quantum chemical methods, in particular an accurate ab initio multiconfigurational second-order perturbation theory. After light irradiation, the efficient, ultrafast energy dissipation observed for nonfluorescent 9H-adenine is explained here by the nonradiative internal conversion process taking place along a barrierless reaction path from the initially populated 1(pipi* La) excited state toward a low-lying conical intersection (CI) connected with the ground state. In contrast, the strong fluorescence recorded for 2-aminopurine at 4.0 eV with large decay lifetime is interpreted by the presence of a minimum in the 1(pipi* La) hypersurface lying below the lowest CI and the subsequent potential energy barrier required to reach the funnel to the ground state. Secondary deactivation channels were found in the two systems related to additional CIs involving the 1(pipi* Lb) and 1(npi*) states. Although in 9H-adenine a population switch between both states is proposed, in 7H-adenine this may be perturbed by a relatively larger barrier to access the 1(npi*) state, and, therefore, the 1(pipi* Lb) state becomes responsible for the weak fluorescence measured in aqueous adenine at approximately 4.5 eV. In contrast to previous models that explained fluorescence quenching in adenine, unlike in 2-aminopurine, on the basis of the vibronic coupling of the nearby 1(pipi*) and 1(npi*) states, the present results indicate that the 1(npi*) state does not contribute to the leading photophysical event and establish the prevalence of a model based on the CI concept in modern photochemistry.

a Study of the Role of Large-Amplitude Motions in Unimolecular Energy Transfer Using Molecular Beam Optothermal Spectroscopy.

NASA Astrophysics Data System (ADS)

Miller, Carl Cameron

1995-01-01

The role of molecular structure in energy transfer reactions in the ground and excited electronic states was explored using optothermal spectroscopy. In the ground state, the relationship between intramolecular van der Waals interactions and vibrational mode coupling was explored in a homologous series of disubstituted ethanes, including Gg^' -2-fluoroethanol, g-1,2-difluoroethane, g-1-chloro-2-fluoroethane, t-1-chloro-2-fluoroethane, and 1,1,2-trifluoroethane. This series of substituted ethanes varies in degree of van der Waals interactions that hinder internal rotation about the C-C bond. High resolution infrared molecular beam spectroscopy was used to determine the extent of vibrational mode coupling. Perturbations in the rotational structure of these molecules provided a measure of vibrational mode coupling. We have observed that the degree of intramolecular interaction, which is dependent on the van der Waals separation of the substituents and the shape of the potential well, correlates with the extent of vibrational mode coupling. The extent of vibrational mode coupling in this series of molecules did not correlate with the density of states available for coupling. Therefore, density of states alone is insufficient to explain the observed trend. In the excited electronic state, optothermal detection has been used to observe non-radiative relaxation channels in aniline, p-bromoaniline and trans-stilbene. p-Bromoaniline has no detectable fluorescence due to a heavy atom effect which increases the rate of intersystem crossing to the triplet state. An optothermal spectrum of p-bromoaniline was observed with the origin at 32625 cm^ {-1}. For trans-stilbene the differences between the laser excitation spectrum and the optothermal spectrum of the S_1 state clearly show the onset of isomerization at ~1250 cm^{-1} above the origin. Absolute quantum yields of fluorescence, Frank-Condon factors, non -radiative rates, and radiative rates have been obtained for a series of vibronic transitions. For low energy vibrational states there is good agreement between the current study and previous work. For vibrational energies above the barrier of isomerization predicted quantum yields do not agree with our experimental results.

Pseudo Jahn-Teller coupling in trioxides XO3(0,1,-1) with 22 and 23 valence electrons

NASA Astrophysics Data System (ADS)

Grein, Friedrich

2013-05-01

D3h and C2v geometries and energies, vertical excitation energies, as well as minimal energy paths as function of the O1(z)-X-O2 angle α were obtained for XO3(0,1,-1) (X = B, Al, Ga; C, Si, Ge; N, P, As; S, Se) molecules and ions with 22 and 23 valence electrons (VE), using density functional theory (DFT), coupled cluster with single and double substitutions with noniterative triple excitations (CCSD(T)), equation of motion (EOM)-CCSD, time-dependent DFT, and multi-reference configuration interaction methods. It is shown that pseudo Jahn-Teller (PJT) coupling increases as the central atom X becomes heavier, due to decreases in excitation energies. As is well known for CO3, the excited 1E' states of the 22 VE systems SiO3, GeO3; NO_3 ^ +, PO3+, AsO3+; BO3-, AlO3-, GaO3- have strong vibronic coupling with the 1A1' ground state via the e' vibrational modes, leading to a C2v minimum around α = 145°. For first and second row X atoms, there is an additional D3h minimum (α = 120°). Interacting excited states have minima around 135°. In the 23 VE systems CO3-, SiO3-; NO3, PO3; SO3+, coupling of the excited 2E' with the 2A2' ground state via the e' mode does not generate a C2v state. Minima of interacting excited states are close to 120°. However, due to very strong PJT coupling, a double-well potential is predicted for GeO3-, AsO3, and SeO3+, with a saddle point at D3h symmetry. Interaction of the b2 highest occupied molecular orbital with the b2 lowest unoccupied molecular orbital, both oxygen lone pair molecular orbitals, is seen as the reason for the C2v stabilization of 22 VE molecules.

Practical Model for First Hyperpolarizability Dispersion Accounting for Both Homogeneous and Inhomogeneous Broadening Effects.

PubMed

Campo, Jochen; Wenseleers, Wim; Hales, Joel M; Makarov, Nikolay S; Perry, Joseph W

2012-08-16

A practical yet accurate dispersion model for the molecular first hyperpolarizability β is presented, incorporating both homogeneous and inhomogeneous line broadening because these affect the β dispersion differently, even if they are indistinguishable in linear absorption. Consequently, combining the absorption spectrum with one free shape-determining parameter Ginhom, the inhomogeneous line width, turns out to be necessary and sufficient to obtain a reliable description of the β dispersion, requiring no information on the homogeneous (including vibronic) and inhomogeneous line broadening mechanisms involved, providing an ideal model for practical use in extrapolating experimental nonlinear optical (NLO) data. The model is applied to the efficient NLO chromophore picolinium quinodimethane, yielding an excellent fit of the two-photon resonant wavelength-dependent data and a dependable static value β0 = 316 × 10(-30) esu. Furthermore, we show that including a second electronic excited state in the model does yield an improved description of the NLO data at shorter wavelengths but has only limited influence on β0.

Photodissociation of water. II. Wave packet calculations for the photofragmentation of H2O and D2O in the B˜ band

NASA Astrophysics Data System (ADS)

van Harrevelt, Rob; van Hemert, Marc C.

2000-04-01

A complete three-dimensional quantum mechanical description of the photodissociation of water in the B˜ band, starting from its rotational ground state, is presented. In order to include B˜-X˜ vibronic coupling and the B˜-Ã Renner-Teller coupling, diabatic electronic states have been constructed from adiabatic electronic states and matrix elements of the electronic angular momentum operators, following the procedure developed by A. J. Dobbyn and P. J. Knowles [Mol. Phys. 91, 1107 (1997)], using the ab initio results discussed in the preceding paper. The dynamics is studied using wave packet methods, and the evolution of the time-dependent wave function is discussed in detail. Results for the H2O and D2O absorption spectra, OH(A)/OH(X) and OD(A)/OD(X) branching ratios, and rovibrational distributions of the OH and OD fragments are presented and compared with available experimental data. The present theoretical results agree at least qualitatively with the experiments. The calculations show that the absorption spectrum and the product state distributions are strongly influenced by long-lived resonances on the adiabatic B˜ state. It is also shown that molecular rotation plays an important role in the photofragmentation process, due to both the Renner-Teller B˜-X˜ mixing, and the strong effect of out-of-plane molecular rotations (K>0) on the dynamics at near linear HOH and HHO geometries.

A Simple and Convenient Method of Multiple Linear Regression to Calculate Iodine Molecular Constants

ERIC Educational Resources Information Center

Cooper, Paul D.

2010-01-01

A new procedure using a student-friendly least-squares multiple linear-regression technique utilizing a function within Microsoft Excel is described that enables students to calculate molecular constants from the vibronic spectrum of iodine. This method is advantageous pedagogically as it calculates molecular constants for ground and excited…

Zooming in on vibronic structure by lowest-value projection reconstructed 4D coherent spectroscopy

NASA Astrophysics Data System (ADS)

Harel, Elad

2018-05-01

A fundamental goal of chemical physics is an understanding of microscopic interactions in liquids at and away from equilibrium. In principle, this microscopic information is accessible by high-order and high-dimensionality nonlinear optical measurements. Unfortunately, the time required to execute such experiments increases exponentially with the dimensionality, while the signal decreases exponentially with the order of the nonlinearity. Recently, we demonstrated a non-uniform acquisition method based on radial sampling of the time-domain signal [W. O. Hutson et al., J. Phys. Chem. Lett. 9, 1034 (2018)]. The four-dimensional spectrum was then reconstructed by filtered back-projection using an inverse Radon transform. Here, we demonstrate an alternative reconstruction method based on the statistical analysis of different back-projected spectra which results in a dramatic increase in sensitivity and at least a 100-fold increase in dynamic range compared to conventional uniform sampling and Fourier reconstruction. These results demonstrate that alternative sampling and reconstruction methods enable applications of increasingly high-order and high-dimensionality methods toward deeper insights into the vibronic structure of liquids.

Two-Dimensional Resonance Raman Signatures of Vibronic Coherence Transfer in Chemical Reactions.

PubMed

Guo, Zhenkun; Molesky, Brian P; Cheshire, Thomas P; Moran, Andrew M

2017-11-02

Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in condensed phase systems. 2DRR spectroscopy is motivated by knowledge of non-equilibrium effects that cannot be detected with traditional resonance Raman spectroscopy. For example, 2DRR spectra may reveal correlated distributions of reactant and product geometries in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this chapter, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide. We show that signatures of "vibronic coherence transfer" in the photodissociation process can be targeted with particular 2DRR pulse sequences. Key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopy techniques are also addressed. Overall, recent experimental developments and applications of the 2DRR method suggest that it will be a valuable tool for elucidating ultrafast chemical reaction mechanisms.

Response functions for dimers and square-symmetric molecules in four-wave-mixing experiments with polarized light

NASA Astrophysics Data System (ADS)

Smith, Eric Ryan; Farrow, Darcie A.; Jonas, David M.

2005-07-01

Four-wave-mixing nonlinear-response functions are given for intermolecular and intramolecular vibrations of a perpendicular dimer and intramolecular vibrations of a square-symmetric molecule containing a doubly degenerate state. A two-dimensional particle-in-a-box model is used to approximate the electronic wave functions and obtain harmonic potentials for nuclear motion. Vibronic interactions due to symmetry-lowering distortions along Jahn-Teller active normal modes are discussed. Electronic dephasing due to nuclear motion along both symmetric and asymmetric normal modes is included in these response functions, but population transfer between states is not. As an illustration, these response functions are used to predict the pump-probe polarization anisotropy in the limit of impulsive excitation.

Laser spectroscopy of a halocarbocation in the gas phase: CH2I+.

PubMed

Tao, Chong; Mukarakate, Calvin; Reid, Scott A

2006-07-26

We report the first gas-phase observation of the electronic spectrum of a simple halocarbocation, CH2I+. The ion was generated rotationally cold (Trot approximately 20 K) using pulsed discharge methods and was detected via laser spectroscopy. The identity of the spectral carrier was confirmed by modeling the rotational contour observed in the excitation spectra and by comparison of ground state vibrational frequencies determined by single vibronic level emission spectroscopy with Density Functional Theory (DFT) predictions. The transition was assigned as 3A1 <-- X1A1. This initial detection of the electronic spectrum of a halocarbocation in the gas phase should open new avenues for study of the structure and reactivity of these important ions.

Two-dimensional vibrational-electronic spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Courtney, Trevor L.; Fox, Zachary W.; Slenkamp, Karla M.

2015-10-21

Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE)more » to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (ν{sub CN}) and either a ligand-to-metal charge transfer transition ([Fe{sup III}(CN){sub 6}]{sup 3−} dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN){sub 5}Fe{sup II}CNRu{sup III}(NH{sub 3}){sub 5}]{sup −} dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific ν{sub CN} modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a wide range of complex molecular, material, and biological systems.« less

The near-infrared spectrum of ethynyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le, Anh T., E-mail: anhle@bnl.gov; Hall, Gregory E., E-mail: gehall@bnl.gov; Sears, Trevor J., E-mail: sears@bnl.gov, E-mail: trevor.sears@stonybrook.edu

2016-08-21

Transient diode laser absorption spectroscopy has been used to measure three strong vibronic bands in the near infrared spectrum of the C{sub 2}H, ethynyl, radical not previously observed in the gas phase. The radical was produced by ultraviolet excimer laser photolysis of either acetylene or (1,1,1)-trifluoropropyne in a slowly flowing sample of the precursor diluted in inert gas, and the spectral resolution was Doppler-limited. The character of the upper states was determined from the rotational and fine structure in the observed spectra and assigned by measurement of ground state rotational combination differences. The upper states include a {sup 2}Σ{sup +}more » state at 6696 cm{sup −1}, a second {sup 2}Σ{sup +} state at 7088 cm{sup −1}, and a {sup 2}Π state at 7110 cm{sup −1}. By comparison with published calculations [R. Tarroni and S. Carter, J. Chem. Phys 119, 12878 (2003); Mol. Phys. 102, 2167 (2004)], the vibronic character of these levels was also assigned. The observed states contain both X{sup 2}Σ{sup +} and A{sup 2}Π electronic characters. Several local rotational level perturbations were observed in the excited states. Kinetic measurements of the time-evolution of the ground state populations following collisional relaxation and reactive loss of the radicals formed in a hot, non-thermal, population distribution were made using some of the strong rotational lines observed. The case of C{sub 2}H may be a good place to investigate the behavior at intermediate pressures of inert colliders, where the competition between relaxation and reaction can be tuned and observed to compare with master equation models, rather than deliberately suppressed to measure thermal rate constants.« less

The near-infrared spectrum of ethynyl radical

DOE PAGES

Le, Anh T.; Hall, Gregory E.; Sears, Trevor J.

2016-08-17

We used transient diode laser absorption spectroscopy to measure three strong vibronic bands in the near infrared spectrum of the C 2H, ethynyl, radical not previously observed in the gas phase. The radical was produced by ultraviolet excimer laser photolysis of either acetylene or (1,1,1)-trifluoropropyne in a slowly flowing sample of the precursor diluted in inert gas, and the spectral resolution was Doppler-limited. The character of the upper states was determined from the rotational and fine structure in the observed spectra and assigned by measurement of ground state rotational combination differences. The upper states include a 2Σ + state atmore » 6696 cm -1, a second 2Σ + state at 7088 cm -1, and a 2Π state at 7110 cm -1. By comparison with published calculations [R. Tarroni and S. Carter, J. Chem. Phys 119, 12878 (2003); Mol. Phys. 102, 2167 (2004)], the vibronic character of these levels was also assigned. Moreover, the observed states contain both X 2Σ + and A 2Π electronic characters. Several local rotational level perturbations were observed in the excited states. Kinetic measurements of the time-evolution of the ground state populations following collisional relaxation and reactive loss of the radicals formed in a hot, non-thermal, population distribution were made using some of the strong rotational lines observed. Finally, the case of C 2H may be a good place to investigate the behavior at intermediate pressures of inert colliders, where the competition between relaxation and reaction can be tuned and observed to compare with master equation models, rather than deliberately suppressed to measure thermal rate constants.« less

Oscillations in two-dimensional photon-echo signals of excitonic and vibronic systems: Stick-spectrum analysis and its computational verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egorova, Dassia

2014-01-21

Stick-spectrum expressions for electronic two-dimensional (2D) photon-echo (PE) signal of a generic multi-level system are presented and employed to interrelate oscillations in individual peaks of 2D PE signal and the underlying properties (eigenstates and coherent dynamics) of excitonic or vibronic systems. When focusing on the identification of the origin of oscillations in the rephasing part of 2D PE it is found, in particular, that multiple frequencies in the evolution of the individual peaks do not necessarily directly reflect the underlying system dynamics. They may originate from the excited-state absorption contribution to the signal, or arise due to multi-level vibrational structuremore » of the electronic ground state, and represent a superposition of system frequencies, while the latter may evolve independently. The analytical stick-spectrum predictions are verified and illustrated by numerical calculations of 2D PE signals of an excitonic trimer and of a displaced harmonic oscillator with unequal vibrational frequencies in the two electronic states. The excitonic trimer is the smallest excitonic oligomer where excited-state absorption may represent a superposition of excited-state coherences and significantly influence the phase of the observed oscillations. The displaced oscillator is used to distinguish between the frequencies of the ground-state and of the excited-state manifolds, and to demonstrate how the location of a cross peak in 2D pattern of the PE signal “predetermines” its oscillatory behavior. Although the considered models are kept as simple as possible for clarity, the stick-spectrum analysis provides a solid general basis for interpretation of oscillatory signatures in electronic 2D PE signals of much more complex systems with multi-level character of the electronic states.« less

A multifrequency virtual spectrometer for complex bio-organic systems: vibronic and environmental effects on the UV/Vis spectrum of chlorophyll a.

PubMed

Barone, Vincenzo; Biczysko, Malgorzata; Borkowska-Panek, Monika; Bloino, Julien

2014-10-20

The subtle interplay of several different effects means that the interpretation and analysis of experimental spectra in terms of structural and dynamic characteristics is a challenging task. In this context, theoretical studies can be helpful, and as such, computational spectroscopy is rapidly evolving from a highly specialized research field toward a versatile and widespread tool. However, in the case of electronic spectra (e.g. UV/Vis, circular dichroism, photoelectron, and X-ray spectra), the most commonly used methods still rely on the computation of vertical excitation energies, which are further convoluted to simulate line shapes. Such treatment completely neglects the influence of nuclear motions, despite the well-recognized notion that a proper account of vibronic effects is often mandatory to correctly interpret experimental findings. Development and validation of improved models rooted into density functional theory (DFT) and its time-dependent extension (TD-DFT) is of course instrumental for the optimal balance between reliability and favorable scaling with the number of electrons. However, the implementation of easy-to-use and effective procedures to simulate vibrationally resolved electronic spectra, and their availability to a wide community of users, is at least equally important for reliable simulations of spectral line shapes for compounds of biological and technological interest. Here, such an approach has been applied to the study of the UV/Vis spectra of chlorophyll a. The results show that properly tailored approaches are feasible for state-of-the-art computational spectroscopy studies, and allow, with affordable computational resources, vibrational and environmental effects on the spectral line shapes to be taken into account for large systems. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vacuum ultraviolet photoabsorption spectroscopy of CH2Cl2 and CD2Cl2 in the energy region 50,000-95,000 cm-1

NASA Astrophysics Data System (ADS)

Mandal, Anuvab; Singh, Param Jeet; Shastri, Aparna; Jagatap, B. N.

2014-12-01

A consolidated study of the VUV absorption spectra of CH2Cl2 and CD2Cl2 in the 50,000-95,000 cm-1 region using synchrotron radiation is presented. Rydberg series and vibronic analysis are carried out and supported by quantum chemical calculations. The broad absorption band of CH2Cl2 in the region 50,000-60,000 cm-1 is attributed to the valence states 11B2, 11B1 and 11A1. Most of the bands in the 60,000-95,000 cm-1 region are fitted to Rydberg series of ns, np and nd type converging to the first four ionization potentials 11.320, 11.357, 12.152 and 12.271 eV of CH2Cl2 arising from excitation of an electron from one of the four outermost Cl non-bonding orbitals (2b1, 3b2, 1a2 and 4a1). Vertical excited states of CH2Cl2 calculated using TDDFT are correlated with experimentally observed electronic states based on the symmetries of the initial and final MOs involved in a transition. A few Rydberg transitions viz. 2b1→5s, 4p, 5p, 6p; 3b2→4p, 5p; 1a2→4p are accompanied by vibronic features. Observed vibronic bands are assigned mainly to the CCl symmetric stretch (ν3‧) mode with smaller contributions from the CH symmetric stretch (ν1‧), CH2 bend (ν2‧) and CH2 wag (ν8‧) modes. Assignments are corroborated by comparison with the VUV absorption spectrum of the deuterated isotopologue CD2Cl2, reported here for the first time. The high underlying intensities seen in several sub-regions are explained by valence or valence-Rydberg mixed type transitions predicted with high oscillator strengths by the TDDFT calculations.

The CaO orange system in meteor spectra

NASA Astrophysics Data System (ADS)

Berezhnoy, A. A.; Borovička, J.; Santos, J.; Rivas-Silva, J. F.; Sandoval, L.; Stolyarov, A. V.; Palma, A.

2018-02-01

The CaO orange band system was simulated in the region 5900-6300 Å and compared with the experimentally observed spectra of Benešov bolide wake. The required vibronic Einstein emission coefficients were estimated by means of the experimental radiative lifetimes under the simplest Franck-Condon approximation. A moderate agreement was achieved, and the largest uncertainties come from modeling shape of FeO orange bands. Using a simple model the CaO column density in the wake of the Benešov bolide at the height of 29 km was estimated as (5 ± 2) × 1014 cm-2 by a comparison of the present CaO spectra with the AlO bands nicely observed at 4600-5200 Å in the same spectrum. The obtained CaO content is in a good agreement with the quenching model developed for the impact-produced cloud, although future theoretical and experimental studies of both CaO and FeO orange systems contribution would be needed to confirm these results.

Ab Initio Determinations of Photoelectron Spectra Including Vibronic Features: An Upper-Level Undergraduate Physical Chemistry Laboratory

ERIC Educational Resources Information Center

Lord, Richard L.; Davis, Lisa; Millam, Evan L.; Brown, Eric; Offerman, Chad; Wray, Paul; Green, Susan M. E.

2008-01-01

We present a first-principles determination of the photoelectron spectra of water and hypochlorous acid as a laboratory exercise accessible to students in an undergraduate physical chemistry course. This paper demonstrates the robustness and user-friendliness of software developed for the Franck-Condon factor calculation. While the calculator is…

Luminescence of 1,4-naphthoquinone and the vitamin K system in Shpolskii matrices at 4 K

NASA Astrophysics Data System (ADS)

Vo-Dinh, Tuan; Wild, Urs P.

This work investigates the high-resolution phosphorescence spectra of 1,4-naphthoquinone and the vitamin K system in Shpolskii solvents at 4 K. The quasi-linear vibronic bands are discussed with regard to spectral assignments and polarization data. The effect of non-totally symmetric vibrations is also discussed.

Developing Potential Energy Curves of Acidic and Basic Amino Acids Using Quantum Computational Techniques

NASA Astrophysics Data System (ADS)

de Guzman, C. P.; Andrianarijaona, M.; Yoshida, Y.; Kim, K.; Andrianarijaona, V. M.

2017-04-01

Proteins are made out of long chains of amino acids and are an integral part of many tasks of a cell. Because the function of a protein is caused by its structure, even minute changes in the molecular geometry of the protein can have large effects on how the protein can be used. This study investigated how manipulations in the structure of acidic and basic amino acids affected their potential energy. Acidic and basic amino acids were chosen because prior studies have suggested that the ionizable side chains of these amino acids can be very influential on a molecule's prefered conformation. Each atom in the molecule was pulled along x, y, and z axis to see how different types of changes affect the potential energy of the whole structure. The results of our calculations, which were done using ORCA, emphasize the vibronic couplings. The aggregated data was used to create a data set of potential energy curves to better understand the quantum dynamic properties of acidic and basic amino acids (preliminary data was presented in http://meetings.aps.org/Meeting/MAR16/Session/M1.273 andhttp://meetings.aps.org/Meeting/FWS16/Session/F2.6).

Spontaneous symmetry breaking and electronic and dielectric properties in commensurate La7 /4Sr1 /4CuO4 and La5 /3Sr1 /3NiO4

NASA Astrophysics Data System (ADS)

Petersen, J.; Bechstedt, F.; Furthmüller, J.; Scolfaro, L. M.

2018-05-01

Complex ordered phases involving spin and charge degrees of freedom in condensed matter, such as layered cuprates and nickelates, are exciting but not well understood solid-state phenomena. The rich underlying physics of the overdoped high-temperature superconductor L a7 /4S r1 /4Cu O4 and colossal dielectric constant insulator L a5 /3S r1 /3Ni O4 is studied from first principles within density functional (perturbation) theory, including an effective Hubbard potential U for the exchange and correlation of d orbitals. Charge density wave (CDW) and spin density wave (SDW) orders are found in both materials, where the stripes are commensurate with the lattice. The SDWs are accompanied by complex antiferromagnetic spin arrangements along the stripes. The first series of conduction bands related to the pseudogap observed in the cuprate are found to be directly related to CDW order, while the colossal dielectric constant in the nickelate is demonstrated to be a result of vibronic coupling with CDW order. Differences between the two oxides are related to how the stripes fill with carriers.

Luminescent spectroscopy and structural properties of Ce3+-doped low-temperature X1-Y2SiO5 material prepared by polymer-assisted sol-gel method

NASA Astrophysics Data System (ADS)

Hamroun, M. S. E.; Guerbous, L.; Bensafi, A.

2016-04-01

Cerium (Ce3+)-doped monoclinic X1-Y2SiO5 (YSO)-type oxyorthosilicates powders were prepared by monomer and polymer-assisted sol-gel method. The present work aims to study the influence of ethylene glycol (EG) monomer, polyethylene glycol (PEG) polymer and polyvinyl alcohol (PVA) polymer, as fuels and nucleating agents for the crystallization, on structural and luminescence properties of the Ce3+ (xCe = 0.01)-doped Y2SiO5. The X-ray diffraction technique, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and steady photoluminescence have been used to characterize the samples. It is found that the types of fuels affect the phase purity and luminescent characteristics of phosphors. All samples exhibit intense violet-blue asymmetric emission band in the range of 370-540 nm with a maximum intensity centered at around 420 nm assigned to the 5d → 4f (2F5/2, 2F7/2) interconfigurational transitions of Ce3+ ion in YSO nanomaterial. Finally, the vibronic coupling parameters are estimated and discussed.

All the nonadiabatic (J=0) bound states of NO{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salzgeber, R.F.; Mandelshtam, V.A.; Schlier, C.

1999-02-01

We calculated all 3170 A{sub 1} and B{sub 2} (J=0) vibronic bound states of the coupled electronic ground ({tilde X}&hthinsp;{sup 2}A{sub 1}) and the first excited ({tilde A}&hthinsp;{sup 2}B{sub 2}) surfaces of NO{sub 2}, using a modification of the {ital ab initio} potentials of Leonardi {ital et al.} [J. Chem. Phys. {bold 105}, 9051 (1996)]. The calculation was performed by harmonic inversion of the Chebyshev correlation function generated from a DVR Hamiltonian in Radau coordinates. The rms error of the eigenenergies is about 2.5 cm{sup {minus}1}, corresponding to a relative error of 10{sup {minus}4} near the dissociation energy. The resultsmore » are compared with the adiabatic and diabatic levels calculated from the same surfaces, with experimental data, and with some approximations for the number of states function N(E). The experimental levels are reproduced fairly well up to an energy of 12&hthinsp;000 cm{sup {minus}1} above the potential minimum while the total number of bound levels agrees to within 2{percent} with that calculated from the phase space volume. {copyright} {ital 1999 American Institute of Physics.}« less

Vibronic transitions in the alkali-metal (Li, Na, K, Rb) - alkaline-earth-metal (Ca, Sr) series: A systematic analysis of de-excitation mechanisms based on the graphical mapping of Frank-Condon integrals

NASA Astrophysics Data System (ADS)

Pototschnig, Johann V.; Meyer, Ralf; Hauser, Andreas W.; Ernst, Wolfgang E.

2017-02-01

Research on ultracold molecules has seen a growing interest recently in the context of high-resolution spectroscopy and quantum computation. After forming weakly bound molecules from atoms in cold collisions, the preparation of molecules in low vibrational levels of the ground state is experimentally challenging, and typically achieved by population transfer using excited electronic states. Accurate potential energy surfaces are needed for a correct description of processes such as the coherent de-excitation from the highest and therefore weakly bound vibrational levels in the electronic ground state via couplings to electronically excited states. This paper is dedicated to the vibrational analysis of potentially relevant electronically excited states in the alkali-metal (Li, Na, K, Rb)- alkaline-earth metal (Ca,Sr) diatomic series. Graphical maps of Frank-Condon overlap integrals are presented for all molecules of the group. By comparison to overlap graphics produced for idealized potential surfaces, we judge the usability of the selected states for future experiments on laser-enhanced molecular formation from mixtures of quantum degenerate gases.

Quantum Nuclear Dynamics Pumped and Probed by Ultrafast Polarization Controlled Steering of a Coherent Electronic State in LiH.

PubMed

Nikodem, Astrid; Levine, R D; Remacle, F

2016-05-19

The quantum wave packet dynamics following a coherent electronic excitation of LiH by an ultrashort, polarized, strong one-cycle infrared optical pulse is computed on several electronic states using a grid method. The coupling to the strong field of the pump and the probe pulses is included in the Hamiltonian used to solve the time-dependent Schrodinger equation. The polarization of the pump pulse allows us to control the localization in time and in space of the nonequilibrium coherent electronic motion and the subsequent nuclear dynamics. We show that transient absorption, resulting from the interaction of the total molecular dipole with the electric fields of the pump and the probe, is a very versatile probe of the different time scales of the vibronic dynamics. It allows probing both the ultrashort, femtosecond time scale of the electronic coherences as well as the longer dozens of femtoseconds time scales of the nuclear motion on the excited electronic states. The ultrafast beatings of the electronic coherences in space and in time are shown to be modulated by the different periods of the nuclear motion.

Neutron generator flux enhancement techniques and construction of a more efficient neutron detector for borehole-logging gamma-ray spectroscopy

NASA Astrophysics Data System (ADS)

Ghias, Asghar

1999-11-01

Neutron activation methods and bore-hole gamma-ray spectrometry have been versatile techniques for real time field evaluation in mineral exploration. The most common neutron generators producing 14 MeV and 2.5 MeV neutrons accelerate deuterium ions into a tritium or deuterium target via the 3H( 2H,n)4He or the 2H(2H,n) 3H reactions. The development and design of bore-hole 2.5 MeV high flux neutron generator coupled with an efficient gamma-ray detector is the primary focus of this work, which is needed by the coal and petroleum industries. A 2.5 MeV neutron generator, which used the D(D,n)T reaction, was constructed similar to a conventional Zetatron 14 MeV generator. The performance of the low energy neutron generator was studied under various operating conditions. In order to enhance the neutron flux of the generator, an r.f. field was applied to the ion source which increased the neutron yield per pulse by about thirty percent. A theoretical study of the r.f enhancement has been made to explain the operation of the r.f. added Zetatron tube. An alternative, method of neutron flux enhancement by use of laser-excitation is discussed and explained theoretically. The laser technique although not experimentally verified, is based on the recent development of vibronic lasers, the neutron flux can be enhanced several orders of magnitude by precise tuning of the wavelength within vibronic band. Activation experiments using a large coal sample (about I ton) were conducted, and studies were made on inter and intrapulse counting, detector gated spectra, and comparison of the spectra using different neutron sources. Preliminary results on coal analysis reveal that lower energy (2.5 MeV) is superior to high energy (14 MeV) neutrons. During the course of this work it became necessary to measure fast neutrons, efficiently and in real time. A new type of detector was consequently developed using SnO2 as sheath material around a BGO detector to measure the capture gamma-rays of oxygen. Using neutron activation studies of coal, the feasibility of applying the technique to aid medical diagnostics is also discussed in this dissertation.

Theory of optical transitions in π-conjugated macrocycles

NASA Astrophysics Data System (ADS)

Marcus, Max; Coonjobeeharry, Jaymee; Barford, William

2016-04-01

We describe a theoretical and computational investigation of the optical properties of π-conjugated macrocycles. Since the low-energy excitations of these systems are Frenkel excitons that couple to high-frequency dispersionless phonons, we employ the quantized Frenkel-Holstein model and solve it via the density matrix renormalization group (DMRG) method. First we consider optical emission from perfectly circular systems. Owing to optical selection rules, such systems radiate via two mechanisms: (i) within the Condon approximation, by thermally induced emission from the optically allowed j = ± 1 states and (ii) beyond the Condon approximation, by emission from the j = 0 state via coupling with a totally non-symmetric phonon (namely, the Herzberg-Teller effect). Using perturbation theory, we derive an expression for the Herzberg-Teller correction and show via DMRG calculations that this expression soon fails as ħ ω/J and the size of the macrocycle increase. Next, we consider the role of broken symmetry caused by torsional disorder. In this case the quantum number j no longer labels eigenstates of angular momentum, but instead labels localized local exciton groundstates (LEGSs) or quasi-extended states (QEESs). As for linear polymers, LEGSs define chromophores, with the higher energy QEESs being extended over numerous LEGSs. Within the Condon approximation (i.e., neglecting the Herzberg-Teller correction) we show that increased disorder increases the emissive optical intensity, because all the LEGSs are optically active. We next consider the combined role of broken symmetry and curvature, by explicitly evaluating the Herzberg-Teller correction in disordered systems via the DMRG method. The Herzberg-Teller correction is most evident in the emission intensity ratio, I00/I01. In the Condon approximation I00/I01 is a constant function of curvature, whereas in practice it vanishes for closed rings and only approaches a constant in the limit of vanishing curvature. We calculate the optical spectra of a model system, cyclo-poly(para-phenylene ethynylene), for different amounts of torsional disorder within and beyond the Condon approximation. We show how broken symmetry and the Herzberg-Teller effect explain the spectral features. The Herzberg-Teller correction to the 0-1 emission vibronic peak is always significant. Finally, we note the qualitative similarities between the optical properties of conformationally disordered linear polymers and macrocycles in the limit of sufficiently large disorder, because in both cases they are determined by the optical properties of curved chromophores.

The effects of Raman scattering accompanied by the soliton excitation occurring in molecular crystals

NASA Astrophysics Data System (ADS)

Pang, X. F.

2001-06-01

A theoretical research is made for the effects of Raman scattering caused by the soliton excitation occurring in the organic molecular crystals, e.g., acetanilide, on the basis of vibration model of amide-I. The energy gap between the soliton state and the vibron state have been found by partial diagonalized method in second quantized representation, which is 18.1-33 cm -1. This result is approximately consistent with the red shift value obtained from the experiments, 16 cm -1. The differential cross-section of the Raman scattering, arising from the soliton excitation, has also been obtained. Finally, we derive some properties of the Raman scattering in such a case. This result establishes spectral signatures of the soliton in the molecular crystals, which may be observed in the experiment.

Zero kinetic energy photoelectron spectroscopy of triphenylene.

PubMed

Harthcock, Colin; Zhang, Jie; Kong, Wei

2014-06-28

We report vibrational information of both the first electronically excited state and the ground cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited electronic state S1 of the neutral molecule is of A1' symmetry and is therefore electric dipole forbidden in the D3h group. Consequently, there are no observable Franck-Condon allowed totally symmetric a1' vibrational bands in the REMPI spectrum. All observed vibrational transitions are due to Herzberg-Teller vibronic coupling to the E' third electronically excited state S3. The assignment of all vibrational bands as e' symmetry is based on comparisons with calculations using the time dependent density functional theory and spectroscopic simulations. When an electron is eliminated, the molecular frame undergoes Jahn-Teller distortion, lowering the point group to C2v and resulting in two nearly degenerate electronic states of A2 and B1 symmetry. Here we follow a crude treatment by assuming that all e' vibrational modes resolve into b2 and a1 modes in the C2v molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic ionization threshold is determined to be 63 365 ± 7 cm(-1). The observed ZEKE spectra contain a consistent pattern, with a cluster of transitions centered near the same vibrational level of the cation as that of the intermediate state, roughly consistent with the propensity rule. However, complete assignment of the detailed vibrational structure due to Jahn-Teller coupling requires much more extensive calculations, which will be performed in the future.

Isotopically selective two-photon ionization of aniline in supersonic beams

NASA Astrophysics Data System (ADS)

Leutwyler, S.; Even, U.

1981-08-01

Tunable laser two-photon ionization of aniline cooled in supersonic expansions combined with TOF mass spectrometry reveal an isotopic shift of the vibronic origin at 2938 Å (ππ ∗; 1B 2← 1A 1 transition). The shift (+4.6 cm -1) is smaller than the rotational bandwidth and would be unobservable by laser-induced fluorescence.

An Experimental and Quantum Chemical Study of the Electronic Spectrum of the HBCl Free Radical

NASA Astrophysics Data System (ADS)

Gharaibeh, Mohammed A.; Nagarajan, Ramya; Clouthier, Dennis J.; Tarroni, Ricardo

2012-06-01

The chloroborane (HBCl) free radical has a complex electronic spectrum in the visible that involves a transition from a bent ground state to a linear excited state, both of which are the Renner-Teller components of what would be a ^2π state at linearity. We have used the synchronous-scan LIF and single vibronic level emission techniques to untangle the many overlapping vibronic bands and assign upper state K quantum numbers for jet-cooled HBCl and DBCl. The radicals were produced in a pulsed electric discharge jet using a precursor mixture of boron trichloride (BCl_3) and hydrogen or deuterium in high-pressure argon. As an important aid to understanding the data, the ground and excited state high level ab initio potential energy surfaces (PES) have been calculated and the vibrational levels obtained variationally. The calculated ground state levels are in excellent agreement with the emission data validating the quality of the PES. Aside from an approximately 100 cm-1 shift in the upper state electronic term value, the calculated excited state vibrational energy levels and isotope shifts match the LIF data very well, allowing the observed bands to be assigned with confidence.

Identification of gram-negative and gram-positive bacteria by fluorescence studies

NASA Astrophysics Data System (ADS)

Demchak, Jonathan; Calabrese, Joseph; Tzolov, Marian

2011-03-01

Several type strains of bacteria including Vibrio fischeri, Azotobacter vinelandii, Enterobacter cloacae, and Corynebacterium xerosis, were cultured in the laboratory following standard diagnostic protocol based on their individual metabolic strategies. The bacterial cultures were not further treated and they were studied in their pristine state (pure culture - axenic). The fluorescent studies were applied using a continuous wave and a pulsed excitation light sources. Emission and excitation spectra were recorded for the continuous wave excitation and they all show similar spectral features with the exception of the gram positive bacteria showing vibronic structures. The vibrational modes involved in these vibronic bands have energy typical for carbon-carbon vibrations. The fluorescence is quenched in addition of water, even a very thin layer, which confirms that the observed spectral features originate from the outer parts of the bacteria. These results allow to conclude that the fluorescence spectroscopy can be used as a method for studying the membranes of the bacteria and eventually to discriminate between gram positive and gram negative bacteria. The pulsed experiments show that the fluorescence lifetime is in the sub-microsecond range. The results indicate that the observed spectra are superposition of the emission with different lifetimes.

Multi-MBar studies of Oxygen and Hydrogen

NASA Astrophysics Data System (ADS)

Dalladay-Simpson, Philip

2013-06-01

The study of simple archetypal molecular systems having an electronic structure heavily altered by ultra-high compression holds the promise of major breakthroughs in our understanding of matter. Among these systems, oxygen and deuterium are of particular interest due to their abundance in the Universe. We have used optical and synchrotron x-ray diffraction techniques to probe O2 and H2 (D2) to above 300 GPa. Our study on dense oxygen more than doubles the pressure range at which it had been investigated before; the picture we observe is quite different from what was experimentally reported and predicted by theory. Our experiments on dense hydrogen (deuterium) reveal the appearance of a new semiconducting phase at above 220 GPa which persists up to 320 GPa - the highest pressure reached in our studies. This phase is characterized by emergence of intense, well defined low frequency Raman bands, together with the unprecedented softening of the vibron, ν1, and appearance of a secondary vibron, ν2 and slowly closing band-gap. Analysis of the Raman spectra suggests a peculiar graphene-like structure consisting of both atomic and molecular layers. For both systems we will discuss the differences in results and interpretations which currently present in the literature.

Algebraic approach to electronic spectroscopy and dynamics.

PubMed

Toutounji, Mohamad

2008-04-28

Lie algebra, Zassenhaus, and parameter differentiation techniques are utilized to break up the exponential of a bilinear Hamiltonian operator into a product of noncommuting exponential operators by the virtue of the theory of Wei and Norman [J. Math. Phys. 4, 575 (1963); Proc. Am. Math. Soc., 15, 327 (1964)]. There are about three different ways to find the Zassenhaus exponents, namely, binomial expansion, Suzuki formula, and q-exponential transformation. A fourth, and most reliable method, is provided. Since linearly displaced and distorted (curvature change upon excitation/emission) Hamiltonian and spin-boson Hamiltonian may be classified as bilinear Hamiltonians, the presented algebraic algorithm (exponential operator disentanglement exploiting six-dimensional Lie algebra case) should be useful in spin-boson problems. The linearly displaced and distorted Hamiltonian exponential is only treated here. While the spin-boson model is used here only as a demonstration of the idea, the herein approach is more general and powerful than the specific example treated. The optical linear dipole moment correlation function is algebraically derived using the above mentioned methods and coherent states. Coherent states are eigenvectors of the bosonic lowering operator a and not of the raising operator a(+). While exp(a(+)) translates coherent states, exp(a(+)a(+)) operation on coherent states has always been a challenge, as a(+) has no eigenvectors. Three approaches, and the results, of that operation are provided. Linear absorption spectra are derived, calculated, and discussed. The linear dipole moment correlation function for the pure quadratic coupling case is expressed in terms of Legendre polynomials to better show the even vibronic transitions in the absorption spectrum. Comparison of the present line shapes to those calculated by other methods is provided. Franck-Condon factors for both linear and quadratic couplings are exactly accounted for by the herein calculated linear absorption spectra. This new methodology should easily pave the way to calculating the four-point correlation function, F(tau(1),tau(2),tau(3),tau(4)), of which the optical nonlinear response function may be procured, as evaluating F(tau(1),tau(2),tau(3),tau(4)) is only evaluating the optical linear dipole moment correlation function iteratively over different time intervals, which should allow calculating various optical nonlinear temporal/spectral signals.

A full-dimensional multilayer multiconfiguration time-dependent Hartree study on the ultraviolet absorption spectrum of formaldehyde oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Qingyong, E-mail: mengqingyong@dicp.ac.cn; Meyer, Hans-Dieter, E-mail: hans-dieter.meyer@pci.uni-heidelberg.de

2014-09-28

Employing the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method in conjunction with the multistate multimode vibronic coupling Hamiltonian (MMVCH) model, we perform a full dimensional (9D) quantum dynamical study on the simplest Criegee intermediate, formaldehyde oxide, in five lower-lying singlet electronic states. The ultraviolet (UV) spectrum is then simulated by a Fourier transform of the auto-correlation function. The MMVCH model is built based on extensive MRCI(8e,8o)/aug-cc-pVTZ calculations. To ensure a fast convergence of the final calculations, a large number of ML-MCTDH test calculations is performed to find an appropriate multilayer separations (ML-trees) of the ML-MCTDH nuclear wave functions, and the dynamicalmore » calculations are carefully checked to ensure that the calculations are well converged. To compare the computational efficiency, standard MCTDH simulations using the same Hamiltonian are also performed. A comparison of the MCTDH and ML-MCTDH calculations shows that even for the present not-too-large system (9D here) the ML-MCTDH calculations can save a considerable amount of computational resources while producing identical spectra as the MCTDH calculations. Furthermore, the present theoretical B{sup ~} {sup 1}A{sup ′}←X{sup ~} {sup 1}A{sup ′} UV spectral band and the corresponding experimental measurements [J. M. Beames, F. Liu, L. Lu, and M. I. Lester, J. Am. Chem. Soc. 134, 20045–20048 (2012); L. Sheps, J. Phys. Chem. Lett. 4, 4201–4205 (2013); W.-L. Ting, Y.-H. Chen, W. Chao, M. C. Smith, and J. J.-M. Lin, Phys. Chem. Chem. Phys. 16, 10438–10443 (2014)] are discussed. To the best of our knowledge, this is the first theoretical UV spectrum simulated for this molecule including nuclear motion beyond an adiabatic harmonic approximation.« less

Dynamic mapping of conical intersection seams: A general method for incorporating the geometric phase in adiabatic dynamics in polyatomic systems

NASA Astrophysics Data System (ADS)

Xie, Changjian; Malbon, Christopher L.; Yarkony, David R.; Guo, Hua

2017-07-01

The incorporation of the geometric phase in single-state adiabatic dynamics near a conical intersection (CI) seam has so far been restricted to molecular systems with high symmetry or simple model Hamiltonians. This is due to the fact that the ab initio determined derivative coupling (DC) in a multi-dimensional space is not curl-free, thus making its line integral path dependent. In a recent work [C. L. Malbon et al., J. Chem. Phys. 145, 234111 (2016)], we proposed a new and general approach based on an ab initio determined diabatic representation consisting of only two electronic states, in which the DC is completely removable, so that its line integral is path independent in the simply connected domains that exclude the CI seam. Then with the CIs included, the line integral of the single-valued DC can be used to construct the complex geometry-dependent phase needed to exactly eliminate the double-valued character of the real-valued adiabatic electronic wavefunction. This geometry-dependent phase gives rise to a vector potential which, when included in the adiabatic representation, rigorously accounts for the geometric phase in a system with an arbitrary locus of the CI seam and an arbitrary number of internal coordinates. In this work, we demonstrate this approach in a three-dimensional treatment of the tunneling facilitated dissociation of the S1 state of phenol, which is affected by a Cs symmetry allowed but otherwise accidental seam of CI. Here, since the space is three-dimensional rather than two-dimensional, the seam is a curve rather than a point. The nodal structure of the ground state vibronic wavefunction is shown to map out the seam of CI.

Sibling rivalry: intrinsic luminescence from two xanthene dye monoanions, resorufin and fluorescein, provides evidence for excited-state proton transfer in the latter.

PubMed

Kjær, Christina; Brøndsted Nielsen, Steen; Stockett, Mark H

2017-09-20

While the emission spectrum of fluorescein monoanions isolated in vacuo displays a broad and featureless band, that of resorufin, also belonging to the xanthene family, has a sharp band maximum, clear vibronic structure, and experiences a small Stokes shift. Excited-state proton transfer in fluorescein can account for the differences.

Jet-Cooled Chlorofluorobenzyl Radicals: Spectroscopy and Mechanism

NASA Astrophysics Data System (ADS)

Yoon, Young; Lee, Sang

2016-06-01

Whereas the benzyl radical, a prototypic aromatic free radical, has been the subject of numerous spectroscopic studies, halo-substituted benzyl radicals have received less attention, due to the difficulties associated with production of radicals from precursors. In particular, chloro-substituted benzyl radicals have been much less studied because of the weak visible emission intensity and weak C-Cl bond dissociation energy. The jet-cooled chlorofluorobenzyl radicals were generated in a technique of corona excited supersonic jet expansion using a pinhole-type glass nozzle for the vibronic assignments and measurements of electronic energies of the D_1 → D_0 transition. The 2,4-,2.5-, and 2.6- chlorofluorobenzyl radicals were generated by corona discharge of corresponding precursors, chlorofluorotoluenes seeded in a large amount of helium carrier gas. The vibronic emission spectra were recorded with a long-path monochromator in the visible region. The emission spectra show the vibronic bands originating from two types of benzyl-type radicals, chlorofluorobenzyl and fluorobenzyl benzyl radicals, in which fluorobenzyl radicals were obtained by displacement of Cl by H produced by dissociation of methyl C-H bond. From the analysis of the spectra observed, we could determine the electronic energies in D_1 → D_0 transition and vibrational mode frequencies at the D_0 state of chlorofluorobenzyl radicals, which show the origin band of the electronic transition to be shifted to red region, comparing with the parental benzyl radical. From the quantitative analysis of the red-shift, it has been found that the additivity rule can be applied to dihalo-substituted benzyl radicals. In this presentation, the dissociation process of precursors in corona discharge is discussed in terms of bond dissociation energy as well as the spectroscopic analysis of the radicals. C. S. Huh, Y. W. Yoon, and S. K. Lee, J. Chem. Phys. 136, 174306 (2012). Y. W. Huh, S. Y. Chae, and S. K. Lee, Chem. Phys. Lett. 608, 6 (2014). Y. W. Yoon, S. Y. Chae, M. Lim, and S. K. Lee, Chem. Phys. Lett. 637, 148 (2015).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogilvie, Jennifer P.

Photosystem II (PSII) is the only known natural enzyme that uses solar energy to split water, making the elucidation of its design principles critical for our fundamental understanding of photosynthesis and for our ability to mimic PSII’s remarkable properties. This report discusses progress towards addressing key open questions about the PSII RC. It describes new spectroscopic methods that were developed to answer these questions, and summarizes the outcomes of applying these methods to study the PSII RC. Using 2D electronic spectroscopy and 2D electronic Stark spectroscopy, models for the PSII RC were tested and refined. Work is ongoing to usemore » the collected data to elucidate the charge separation mechanism in the PSII RC. Coherent dynamics were also observed in the PSII RC for the first time. Through extensive characterization and modeling we have assigned these coherences as vibronic in nature, and believe that they reflect resonances between key vibrational pigment modes and electronic energy gaps that may facilitate charge separation. Work is ongoing to definitively test the functional relevance of electronic-vibrational resonances.« less

Magnetization and heat-capacity measurements on Zn1-xCrxTe

NASA Astrophysics Data System (ADS)

Pekarek, T. M.; Luning, J. E.; Miotkowski, I.; Crooker, B. C.

1994-12-01

We have taken magnetization and calorimetric measurements on Zn1-xCrxTe (x=0.003). The heat-capacity measurements show a Schottky peak indicating an energy-level splitting of 3.1 K between the ground and first excited states. Above 1.5 K we observe additional heat capacity, which indicates the presence of additional low-energy vibronic excitations. The magnetization data reveal a small anisotropy (~7%) with the (111) direction giving the largest value. The magnetization data were fit with a model including a static Jahn-Teller distortion proposed previously in these materials [J. T. Vallin, G. A. Slack, S. Roberts, and A. E. Hughes, Phys. Rev. B 2, 4313 (1970)]. Reasonable agreement was found with the data for a spin-orbit parameter of -59 cm-1 and a Jahn-Teller energy of 320 cm-1.

Quantifying the Performances of DFT for Predicting Vibrationally Resolved Optical Spectra: Asymmetric Fluoroborate Dyes as Working Examples.

PubMed

Bednarska, Joanna; Zaleśny, Robert; Bartkowiak, Wojciech; Ośmiałowski, Borys; Medved', Miroslav; Jacquemin, Denis

2017-09-12

This article aims at a quantitative assessment of the performances of a panel of exchange-correlation functionals, including semilocal (BLYP and PBE), global hybrids (B3LYP, PBE0, M06, BHandHLYP, M06-2X, and M06-HF), and range-separated hybrids (CAM-B3LYP, LC-ωPBE, LC-BLYP, ωB97X, and ωB97X-D), in predicting the vibrationally resolved absorption spectra of BF 2 -carrying compounds. To this end, for 19 difluoroborates as examples, we use, as a metric, the vibrational reorganization energy (λ vib ) that can be determined based on the computationally efficient linear coupling model (a.k.a. vertical gradient method). The reference values of λ vib were determined by employing the CC2 method combined with the cc-pVTZ basis set for a representative subset of molecules. To validate the performances of CC2, comparisons with experimental data have been carried out as well. This study shows that the vibrational reorganization energy, involving Huang-Rhys factors and normal-mode frequencies, can indeed be used to quantify the reliability of functionals in the calculations of the vibrational fine structure of absorption bands, i.e., an accurate prediction of the vibrational reorganization energy leads to absorption band shapes better fitting the selected reference. The CAM-B3LYP, M06-2X, ωB97X-D, ωB97X, and BHandHLYP functionals all deliver vibrational reorganization energies with absolute relative errors smaller than 20% compared to CC2, whereas 10% accuracy can be achieved with the first three functionals. Indeed, the set of examined exchange-correlation functionals can be divided into three groups: (i) BLYP, B3LYP, PBE, PBE0, and M06 yield inaccurate band shapes (λ vib,TDDFT < λ vib,CC2 ), (ii) BHandHLYP, CAM-B3LYP, M06-2X, ωB97X, and ωB97X-D provide accurate band shapes (λ vib,TDDFT ≈ λ vib,CC2 ), and (iii) LC-ωPBE, LC-BLYP, and M06-HF deliver rather poor band topologies (λ vib,TDDFT > λ vib,CC2 ). This study also demonstrates that λ vib can be reliably estimated using the CC2 model and the relatively small cc-pVDZ basis set. Therefore, the linear coupling model combined with the CC2/cc-pVDZ level of theory can be used as a very efficient approach to determine λ vib values that can be used to select the most adequate functional for more accurate vibronic calculations, e.g., including more refined models and environmental effects.

Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters

PubMed Central

Etherington, Marc K.; Franchello, Flavio; Gibson, Jamie; Northey, Thomas; Santos, Jose; Ward, Jonathan S.; Higginbotham, Heather F.; Data, Przemyslaw; Kurowska, Aleksandra; Dos Santos, Paloma Lays; Graves, David R.; Batsanov, Andrei S.; Dias, Fernando B.; Bryce, Martin R.; Penfold, Thomas J.; Monkman, Andrew P.

2017-01-01

Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two regioisomers of bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide, a donor–acceptor–donor (D–A–D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes. PMID:28406153

A tunable emerald laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shand, M.L.; Walling, J.C.

1982-11-01

Emerald is a new broadly wavelength-tunable vibronic laser material with stimulated emission in the red to infrared due to /sup 4/T/sub 2/..-->../sup 4/A transitions of Cr/sup 3 +/. Emerald has gain from 12 050 cm/sup -1/ to 14 000 cm/sup -1/ with high gain from about 12 300 cm/sup -1/ to 13 700 cm/sup -1/. An emerald laser oscillator has been achieved, but has high losses.

Raman spectroscopic studies of hydrogen clathrate hydrates.

PubMed

Strobel, Timothy A; Sloan, E Dendy; Koh, Carolyn A

2009-01-07

Raman spectroscopic measurements of simple hydrogen and tetrahydrofuran+hydrogen sII clathrate hydrates have been performed. Both the roton and vibron bands illuminate interesting quantum dynamics of enclathrated H(2) molecules. The complex vibron region of the Raman spectrum has been interpreted by observing the change in population of these bands with temperature, measuring the absolute H(2) content as a function of pressure, and with D(2) isotopic substitution. Quadruple occupancy of the large sII clathrate cavity shows the highest H(2) vibrational frequency, followed by triple and double occupancies. Singly occupied small cavities display the lowest vibrational frequency. The vibrational frequencies of H(2) within all cavity environments are redshifted from the free gas phase value. At 76 K, the progression from ortho- to para-H(2) occurs over a relatively slow time period (days). The rotational degeneracy of H(2) molecules within the clathrate cavities is lifted, observed directly in splitting of the para-H(2) roton band. Raman spectra from H(2) and D(2) hydrates suggest that the occupancy patterns between the two hydrates are analogous, increasing confidence that D(2) is a suitable substitute for H(2). The measurements suggest that Raman is an effective and convenient method to determine the relative occupancy of hydrogen molecules in different clathrate cavities.

Molecular Line Lists for Scandium and Titanium Hydride Using the DUO Program

NASA Astrophysics Data System (ADS)

Lodi, Lorenzo; Yurchenko, Sergei N.; Tennyson, Jonathan

2015-06-01

Transition-metal-containing (TMC) molecules often have very complex electronic spectra because of their large number of low-lying, interacting electronic states, of the large multi-reference character of the electronic states and of the large magnitude of spin-orbit and relativistic effects. As a result, fully ab initio calculations of line positions and intensities of TMC molecules have an accuracy which is considerably worse than the one usually achievable for molecules made up by main-group atoms only. In this presentation we report on new theoretical line lists for scandium hydride ScH and titanium hydride TiH. Scandium and titanium are the lightest transition metal atoms and by virtue of their small number of valence electrons are amenable to high-level electronic-structure treatments and serve as ideal benchmark systems. We report for both systems energy curves, dipole curves and various coupling curves (including spin-orbit) characterising their electronic spectra up to about 20 000 cm-1. Curves were obtained using Internally-Contracted Multi Reference Configuration Interaction (IC-MRCI) as implemented in the quantum chemistry package MOLPRO. The curves where used for the solution of the coupled-surface ro-vibronic problem using the in-house program DUO. DUO is a newly-developed, general program for the spectroscopy of diatomic molecules and its main functionality will be described. The resulting line lists for ScH and TiH are made available as part of the Exomol project. L. Lodi, S. N. Yurchenko and J. Tennyson, Mol. Phys. (Handy special issue) in press. S. N. Yurchenko, L. Lodi, J. Tennyson and A. V. Stolyarov, Computer Phys. Comms., to be submitted.

Vibrational Analysis of the SiCN tilde{X} ^2Π System

NASA Astrophysics Data System (ADS)

Fukushima, Masaru; Ishiwata, Takashi

2016-06-01

The laser induced fluorescence ( LIF ) spectrum of the tilde{A} 2Δ - tilde{X} ^Π transition was obtained for SiCN generated by laser ablation under supersonic free jet expansion. The vibrational structure of the dispersed fluorescence ( DF ) spectra from single vibronic levels ( SVL's ) was analyzed by numerical diagonalization procedure, in which Renner-Teller ( R-T ), anhamonicity, spin-orbit ( SO ), Herzberg-Teller ( H-T ), Fermi, and Sears interactions have been considered, where the Sears resonance is a second-order interaction combined from SO and H-T interactions with Δ K = ±1, Δ Σ = ∓1, and Δ P = 0. Four vibronic levels, (01^10) ; μ ; Σ1/2(-), κ ; Σ1/2(+), (02^00) ; μ and κ ; Π1/2, are almost closed within the four basis functions by R-T and Sears interactions ( i.e. the four-by-four transformation matrix below is close to ortho-normal ); ( |(01^10) ; μ ; ^2Σ(-)rangle |(01^10) ; κ ; ^2Σ(+)rangle |(02^00) ; μ ; ^2Π1/2rangle |(02^00) ; κ ; ^2Π1/2rangle ) ( 0.9 & -0.4 & 0.0 & 0.0 0.4 & 0.8 & 0.3 & -0.2 0.2 & 0.4 & -0.8 & 0.4 0.0 & 0.0 & -0.5 & -0.8 ) ( | - rangle | +1/2 rangle ; | 0; 1, +1 rangle | + rangle | +1/2 rangle ; | 0; 1, -1 rangle | + rangle | -1/2 rangle ; | +1; 2, 0 rangle | - rangle | -1/2 rangle ; | +1; 2, +2 rangle ), where | Λ rangle | Σ rangle | K; v_2, l rangle = | - rangle | +1/2 rangle | 0; 1, +1 rangle etc. are basis functions of the vibronic Hamiltonian for the numerical diagonalization, and | Λ rangle, | Σ rangle, and | K; v_2, l rangle are basis functions of electronic, electron spin, and two dimensional harmonic oscillator, respectively. if0 The two levels, (01^10) ; κ ; Σ1/2(+) and (02^00) ; μ ; Π1/2, with Δ K = ±1 and Δ P = 0, show typical example of Sears resonance with an almost one-to-one mixing; ( |(01^10) ; κ ; ^2Σ(+)rangle |(02^00) ; μ ; ^2Π1/2rangle ) ( 0.8 & 0.3 0.4 & -0.8 ) ( | + rangle | +1/2 rangle ; | 0; 1, -1 rangle | + rangle | -1/2 rangle ; | +1; 2, 0 rangle ) ; + ; ( 0.4 & -0.2 0.2 & 0.4 ) ( | - rangle | +1/2 rangle ; | 0; 1, +1 rangle | - rangle | -1/2 rangle ; | +1; 2, +2 rangle ) ; , where the off-diagonal terms are caused by Sears resonance, while the diagonals are came from R-T mostly. The mixing coefficients of the two vibronic levels agree with those obtained from computational studies The two levels among the four above, (01^10) ; κ ; Σ1/2(+) and (02^00) ; μ ; Π1/2, with Δ K = ±1 and Δ P = 0, show typical example of Sears resonance with an almost one-to-one mixing. Even for levels lying at ˜ 1,000 cm-1, some of them are mixed heavily and widely with several levels, and their vibrational quantum numbers are thus meaningless. V. Brites, A. O. Mitrushchenkov, and C. Léonard, J. Chem. Phys. 138, 104311 (2013); C. Léonard, Private communication.

Numerical Modeling of Fluorescence Emission Energy Dispersion in Luminescent Solar Concentrator

NASA Astrophysics Data System (ADS)

Li, Lanfang; Sheng, Xing; Rogers, John; Nuzzo, Ralph

2013-03-01

We present a numerical modeling method and the corresponding experimental results, to address fluorescence emission dispersion for applications such as luminescent solar concentrator and light emitting diode color correction. Previously established modeling methods utilized a statistic-thermodynamic theory (Kenard-Stepnov etc.) that required a thorough understanding of the free energy landscape of the fluorophores. Some more recent work used an empirical approximation of the measured emission energy dispersion profile without considering anti-Stokes shifting during absorption and emission. In this work we present a technique for modeling fluorescence absorption and emission that utilizes the experimentally measured spectrum and approximates the observable Frank-Condon vibronic states as a continuum and takes into account thermodynamic energy relaxation by allowing thermal fluctuations. This new approximation method relaxes the requirement for knowledge of the fluorophore system and reduces demand on computing resources while still capturing the essence of physical process. We present simulation results of the energy distribution of emitted photons and compare them with experimental results with good agreement in terms of peak red-shift and intensity attenuation in a luminescent solar concentrator. This work is supported by the DOE `Light-Material Interactions in Energy Conversion' Energy Frontier Research Center under grant DE-SC0001293.

High-resolution laser spectroscopy and magnetic effect of the B{sup ~2}E{sup ′}←X{sup ~2}A{sub 2}{sup ′} transition of the {sup 15}N substituted nitrate radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tada, Kohei; Teramoto, Kanon; Ishiwata, Takashi

2015-03-21

Rotationally resolved high-resolution fluorescence excitation spectra of the 0–0 band of the B{sup ~2}E{sup ′}←X{sup ~2}A{sub 2}{sup ′} transition of the {sup 15}N substituted nitrate radical were observed for the first time, by crossing a jet-cooled molecular beam and a single-mode dye laser beam at right angles. Several thousand rotational lines were detected in the 15 080–15 103 cm{sup −1} region. We observed the Zeeman splitting of intense lines up to 360 G in order to obtain secure rotational assignment. Two, nine, and seven rotational line pairs with 0.0248 cm{sup −1} spacing were assigned to the transitions from the X{supmore » ~2}A{sub 2}{sup ′} (υ″ = 0, k″ = 0, N″ = 1, J″ = 0.5 and 1.5) to the {sup 2}E{sub 3/2}{sup ′} (J′ = 1.5), {sup 2}E{sub 1/2}{sup ′} (J′ = 0.5), and {sup 2}E{sub 1/2}{sup ′} (J′ = 1.5) levels, respectively, based on the ground state combination differences and the Zeeman splitting patterns. The observed spectrum was complicated due to the vibronic coupling between the bright B{sup ~2}E{sup ′} (υ = 0) state and surrounding dark vibronic states. Some series of rotational lines other than those from the X{sup ~2}A{sub 2}{sup ′} (J = 0.5 and 1.5) levels were also assigned by the ground state combination differences and the observed Zeeman splitting. The rotational branch structures were identified, and the molecular constants of the B{sup ~2}E{sub 1/2}{sup ′} (υ = 0) state were estimated by a deperturbed analysis to be T{sub 0} = 15 098.20(4) cm{sup −1}, B = 0.4282(7) cm{sup −1}, and D{sub J} = 4 × 10{sup −4} cm{sup −1}. In the observed region, both the {sup 2}E{sub 1/2}{sup ′} and {sup 2}E{sub 3/2}{sup ′} spin-orbit components were identified, and the spin-orbit interaction constant of the B{sup ~2}E{sup ′} (υ = 0) state was estimated to be −12 cm{sup −1} as the lower limit.« less

Two-photon spectroscopy of autoionizing states of Xe² near threshold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pratt, Stephen T.; Dehmer, Patricia M.; Dehmer, Joseph L.

1990-01-01

The two-photon ionization spectrum of Xe² in the region of the first ionization threshold is presented. Vibronic bands corresponding to at least four different autoionizing electronic states of Xe² are observed for the first time and are tentatively assigned. The observed appearance potential is significantly higher (by 415 cm-1) than the earlier single-photon ionization result (Ng, Trevor, Mahan and Lee, - J. Chem. Phys. 65 (1976) 4327).

Using non-empirically tuned range-separated functionals with simulated emission bands to model fluorescence lifetimes.

PubMed

Wong, Z C; Fan, W Y; Chwee, T S; Sullivan, Michael B

2017-08-09

Fluorescence lifetimes were evaluated using TD-DFT under different approximations for the emitting molecule and various exchange-correlation functionals, such as B3LYP, BMK, CAM-B3LYP, LC-BLYP, M06, M06-2X, M11, PBE0, ωB97, ωB97X, LC-BLYP*, and ωB97X* where the range-separation parameters in the last two functionals were tuned in a non-empirical fashion. Changes in the optimised molecular geometries between the ground and electronically excited states were found to affect the quality of the calculated lifetimes significantly, while the inclusion of vibronic features led to further improvements over the assumption of a vertical electronic transition. The LC-BLYP* functional was found to return the most accurate fluorescence lifetimes with unsigned errors that are mostly within 1.5 ns of experimental values.

A new Gaussian MCTDH program: Implementation and validation on the levels of the water and glycine molecules

NASA Astrophysics Data System (ADS)

Skouteris, D.; Barone, V.

2014-06-01

We report the main features of a new general implementation of the Gaussian Multi-Configuration Time-Dependent Hartree model. The code allows effective computations of time-dependent phenomena, including calculation of vibronic spectra (in one or more electronic states), relative state populations, etc. Moreover, by expressing the Dirac-Frenkel variational principle in terms of an effective Hamiltonian, we are able to provide a new reliable estimate of the representation error. After validating the code on simple one-dimensional systems, we analyze the harmonic and anharmonic vibrational spectra of water and glycine showing that reliable and converged energy levels can be obtained with reasonable computing resources. The data obtained on water and glycine are compared with results of previous calculations using the vibrational second-order perturbation theory method. Additional features and perspectives are also shortly discussed.

Dynamics of the time-resolved stimulated Raman scattering spectrum in presence of transient vibronic inversion of population on the example of optically excited trans-β-apo-8{sup ′}-carotenal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kardaś, T. M., E-mail: kardas@chem.uw.edu.pl; Ratajska-Gadomska, B.; Gadomski, W.

2014-05-28

We have studied the effect of transient vibrational inversion of population in trans-β-apo-8{sup ′}-carotenal on the time-resolved femtosecond stimulated Raman scattering (TR-FSRS) signal. The experimental data are interpreted by applying a quantum mechanical approach, using the formalism of projection operators for constructing the theoretical model of TR-FSRS. Within this theoretical frame we explain the presence of transient Raman losses on the Stokes side of the TR-FSRS spectrum as the effect of vibrational inversion of population. In view of the obtained experimental and theoretical results, we conclude that the excited S{sub 2} electronic level of trans-β-apo-8{sup ′}-carotenal relaxes towards the S{submore » 0} ground state through a set of four vibrational sublevels of S{sub 1} state.« less

Vibron and phonon hybridization in dielectric nanostructures.

PubMed

Preston, Thomas C; Signorell, Ruth

2011-04-05

Plasmon hybridization theory has been an invaluable tool in advancing our understanding of the optical properties of metallic nanostructures. Through the prism of molecular orbital theory, it allows one to interpret complex structures as "plasmonic molecules" and easily predict and engineer their electromagnetic response. However, this formalism is limited to conducting particles. Here, we present a hybridization scheme for the external and internal vibrations of dielectric nanostructures that provides a straightforward understanding of the infrared signatures of these particles through analogy to existing hybridization models of both molecular orbitals and plasmons extending the range of applications far beyond metallic nanostructures. This method not only provides a qualitative understanding, but also allows for the quantitative prediction of vibrational spectra of complex nanoobjects from well-known spectra of their primitive building blocks. The examples of nanoshells illustrate how spectral features can be understood in terms of symmetry, number of nodal planes, and scale parameters.

The effects of vibronic coupling on the photophysics of pi-conjugated oligomers and polymers

NASA Astrophysics Data System (ADS)

Yamagata, Hajime

A theoretical model describing photophysics of pi-conjugated aggregates, such as molecular crystals and polymer thin films, is developed. A Holstein-like Hamiltonian expressed with a multi-particle basis set is used to evaluate absorption and photoluminescence (PL) spectra. An analysis with line strength ratio proves to be a powerful diagnostic tool to obtain additional spectral signatures with which to distinguish H- vs. J-aggregation. For the H-aggregates absorption peak ratio, A 0-0/A 0-1, diminishes as the excitonic coupling increases. Also the PL peak ratio, I 0-0/I 0-1, is zero at T=0K with no disorder and the value increases as temperature and disorder increase. By contrast the J-aggregates show the opposite trends. Furthermore we will show the PL peak ratio provides a direct measurement of the exciton coherence length for a linear J-aggregate and could be expressed as I0-0/I 0-1 = Ncoh/gamma2. We will also show that it is inversely proportional to square root of temperature (T-1/2). Applying our theory to the herringbone style oligoacene molecular crystals, we show the lowest singlet exciton states are highly influenced by charge transfer (CT) states and the well known energetic gap in two polarized absorption spectra, so called Davydov Splitting (DS), is a product of the interaction. We have successfully reproduced the DS for all three oligoacenes without any free parameters. Inspired by the CT contribution in oligoacene crystals, we further develop Wannier-Mott exciton model and apply to disorder-free polydiacetylene (PDA) quantum wires, which have been shown to be extremely emissive. We will show the quantum wire is a J-aggregate and we once again derive the peak ratio and the coherence size relation, I0-0/I 0-1 = kappaNcoh/gamma 2, where kappa is a prefactor close to unity. Typical photophysical properties of polymer pi-stacks such as those occurring in P3HT films are well explained by the simple linear H-aggregate model. However several groups have started seeing more J-like behaviors amongst "improved" (less disordered) polymer films such as increased values of A 0-0/A 0-1 and I 0-0/I 0-1 and higher radiative rates. With the new perception of a single polymer chain being a J-aggregate, we apply our new theory to pi-stack of polymer chains. We call this HJ-aggregate model since the interchain interaction induces H-aggregation. In the study we show a competition between intrachain and interchain interactions that leads to unique photophysical features. The new model is capable of explaining a wide range of polymer systems and most importantly the theory uncovers the mechanism of the improved polymer films; reducing disorder urges increasing intrachain reactions within each chain, thus enhancing more J-like spectral features.

Luminescence and Absorption Spectra of C sub 60 Films

DTIC Science & Technology

1991-02-01

J. McKeirnan, J.L Zink, R. Stanley Williams, W.M. Tong, D.A.A. Ohlberg and R.L. Whetten Submitted t DTIC Physical Review Letters ELECT E SFEB 2? 7,19...range at 20K. A 1400 cm"& progression in the a soccerball inflation mode is observed. The low-temperature absorption spectrum exhibits similar fine...ag soccerball inflation mode is observed. The low temperature absorption spectrum exhibits similar fine structure. The characterization of vibronic

Wave function continuity and the diagonal Born-Oppenheimer correction at conical intersections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meek, Garrett A.; Levine, Benjamin G., E-mail: levine@chemistry.msu.edu

2016-05-14

We demonstrate that though exact in principle, the expansion of the total molecular wave function as a sum over adiabatic Born-Oppenheimer (BO) vibronic states makes inclusion of the second-derivative nonadiabatic energy term near conical intersections practically problematic. In order to construct a well-behaved molecular wave function that has density at a conical intersection, the individual BO vibronic states in the summation must be discontinuous. When the second-derivative nonadiabatic terms are added to the Hamiltonian, singularities in the diagonal BO corrections (DBOCs) of the individual BO states arise from these discontinuities. In contrast to the well-known singularities in the first-derivative couplingsmore » at conical intersections, these singularities are non-integrable, resulting in undefined DBOC matrix elements. Though these singularities suggest that the exact molecular wave function may not have density at the conical intersection point, there is no physical basis for this constraint. Instead, the singularities are artifacts of the chosen basis of discontinuous functions. We also demonstrate that continuity of the total molecular wave function does not require continuity of the individual adiabatic nuclear wave functions. We classify nonadiabatic molecular dynamics methods according to the constraints placed on wave function continuity and analyze their formal properties. Based on our analysis, it is recommended that the DBOC be neglected when employing mixed quantum-classical methods and certain approximate quantum dynamical methods in the adiabatic representation.« less

Many-body and spin-orbit aspects of the alternating current phenomena

NASA Astrophysics Data System (ADS)

Glenn, Rachel M.

The thesis reports on research in the general field of light interaction with matter. According to the topics addressed, it can be naturally divided into two parts: Part I, many-body aspects of the Rabi oscillations which a two-level systems undergoes under a strong resonant drive; and Part II, absorption of the ac field between the spectrum branches of two-dimensional fermions that are split by the combined action of Zeeman and spin-orbit (SO) fields. The focus of Part I is the following many-body effects that modify the conventional Rabi oscillations: Chapter 1, coupling of a two-level system to a single vibrational mode of the environment. Chapter 2, correlated Rabi oscillations in two electron-hole systems coupled by tunneling with strong electron-hole attraction. In Chapter 1, a new effect of Rabi-vibronic resonance is uncovered. If the frequency of the Rabi oscillations, OR, is close to the frequency o0 of the vibrational mode, the oscillations acquire a collective character. It is demonstrated that the actual frequency of the collective oscillations exhibits a bistable behavior as a function of OR - o0. The main finding in Chapter 2 is, that the Fourier spectrum of the Rabi oscillations in two coupled electron-hole systems undergoes a strong transformation with increasing O R. For OR smaller than the tunneling frequency, the spectrum is dominated by a low-frequency (<< OR ) component and contains two additional weaker lines; conventional Rabi oscillations are restored only as OR exceeds the electron-hole attraction strength. The highlight of Part II is a finding that, while the spectrum of absorption between either Zeeman-split branches or SO-split branches is close to a delta-peak, in the presence of both, it transforms into a broad line with singular behavior at the edges. In particular, when the magnitudes of Zeeman and SO are equal, absorption of very low (much smaller than the splitting) frequencies become possible. The shape of the absorption spectrum is highly anisotropic with respect to the exciting field. This peculiar behavior of the absorption is also studied in wire geometry, where the interplay between two couplings (Zeeman and spin-orbit splitting) affects the shape of numerous absorption peaks.

Temperature effects on tunable cw Alexandrite lasers under diode end-pumping.

PubMed

Kerridge-Johns, William R; Damzen, Michael J

2018-03-19

Diode pumped Alexandrite is a promising route to high power, efficient and inexpensive lasers with a broad (701 nm to 858 nm) gain bandwidth; however, there are challenges with its complex laser dynamics. We present an analytical model applied to experimental red diode end-pumped Alexandrite lasers, which enabled a record 54 % slope efficiency with an output power of 1.2 W. A record lowest lasing wavelength (714 nm) and record tuning range (104 nm) was obtained by optimising the crystal temperature between 8 °C and 105 °C in the vibronic mode. The properties of Alexandrite and the analytical model were examined to understand and give general rules in optimising Alexandrite lasers, along with their fundamental efficiency limits. It was found that the lowest threshold laser wavelength was not necessarily the most efficient, and that higher and lower temperatures were optimal for longer and shorter laser wavelengths, respectively. The pump excited to ground state absorption ratio was measured to decrease from 0.8 to 0.7 by changing the crystal temperature from 10 °C to 90 °C.

Magnetostructural Properties of Colossal Magnetoresistance Manganites Under External Magnetic Fields and Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Kaplan, Michael; Zimmerman, George

2002-03-01

In the colossal magnetoresistance manganites the transport and magnetostructural properties are tightly connected [1,2]. Many magnetic field induced structural phase transitions and anomalous magnetoacoustical properties continue to be discovered in various manganite derivatives. Nevertheless the mechanism of structural transitions and microscopic theory of corresponding anomalous properties are still to be completely understood. Here we present a microscopic model of magnetic field and uniaxial pressure induced structural phase transitions in lightly doped manganites. The model is based on the cooperative Jahn-Teller effect which takes into account the Mn3+-ground doublet and excited triplet electronic states. Numerous calculations for different orientation magnetic field suggest the explanations of the origin of the structural transitions and of the measured magnetostriction data. The calculations for the two-sublattice antiferrodistortive crystals under uniaxial pressure support the idea of metaelasticity - a property typical for Jahn-Teller antiferroelastics. 1.Y. Tokura, ed. Colossal Magnetoresistance Oxides. Gordon & Breach, London, 2000. 2.M. Kaplan, G. Zimmerman, eds. Vibronic Interactions: Jahn-Teller Effect in Crystal and Molecules. NATO Science Series, Dordrecht/Boston/London, 2001

Impact of Temperature and Non-Gaussian Statistics on Electron Transfer in Donor-Bridge-Acceptor Molecules.

PubMed

Waskasi, Morteza M; Newton, Marshall D; Matyushov, Dmitry V

2017-03-30

A combination of experimental data and theoretical analysis provides evidence of a bell-shaped kinetics of electron transfer in the Arrhenius coordinates ln k vs 1/T. This kinetic law is a temperature analogue of the familiar Marcus bell-shaped dependence based on ln k vs the reaction free energy. These results were obtained for reactions of intramolecular charge shift between the donor and acceptor separated by a rigid spacer studied experimentally by Miller and co-workers. The non-Arrhenius kinetic law is a direct consequence of the solvent reorganization energy and reaction driving force changing approximately as hyperbolic functions with temperature. The reorganization energy decreases and the driving force increases when temperature is increased. The point of equality between them marks the maximum of the activationless reaction rate. Reaching the consistency between the kinetic and thermodynamic experimental data requires the non-Gaussian statistics of the donor-acceptor energy gap described by the Q-model of electron transfer. The theoretical formalism combines the vibrational envelope of quantum vibronic transitions with the Q-model describing the classical component of the Franck-Condon factor and a microscopic solvation model of the solvent reorganization energy and the reaction free energy.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waskasi, Morteza M.; Newton, Marshall D.; Matyushov, Dmitry V.

A combination of experimental data and theoretical analysis provides evidence of a bell-shaped kinetics of electron transfer in the Arrhenius coordinates ln k vs 1/T . This kinetic law is a temperature analog of the familiar Marcus bell-shaped dependence based on ln k vs the reaction free energy. These results were obtained for reactions of intramolecular charge shift between the donor and acceptor separated by a rigid spacer studied experimentally by Miller and co-workers. The non-Arrhenius kinetic law is a direct consequence of the solvent reorganization energy and reaction driving force changing approximately as hyperbolic functions with temperature. The reorganizationmore » energy decreases and the driving force increases when temperature is increased. The point of equality between them marks the maximum of the activationless reaction rate. Reaching the consistency between the kinetic and thermodynamic experimental data requires the non-Gaussian statistics of the donor-acceptor energy gap described by the Q-model of electron transfer. Furthermore, the theoretical formalism combines the vibrational envelope of quantum vibronic transitions with the Q-model describing the classical component of the Franck-Condon factor and a microscopic solvation model of the solvent reorganization energy and the reaction free energy.« less

Underlying theory of a model for the Renner-Teller effect in tetra-atomic molecules: X(2)Πu electronic state of C2H2(+).

PubMed

Perić, M; Jerosimić, S; Mitić, M; Milovanović, M; Ranković, R

2015-05-07

In the present study, we prove the plausibility of a simple model for the Renner-Teller effect in tetra-atomic molecules with linear equilibrium geometry by ab initio calculations of the electronic energy surfaces and non-adiabatic matrix elements for the X(2)Πu state of C2H2 (+). This phenomenon is considered as a combination of the usual Renner-Teller effect, appearing in triatomic species, and a kind of the Jahn-Teller effect, similar to the original one arising in highly symmetric molecules. Only four parameters (plus the spin-orbit constant, if the spin effects are taken into account), which can be extracted from ab initio calculations carried out at five appropriate (planar) molecular geometries, are sufficient for building up the Hamiltonian matrix whose diagonalization results in the complete low-energy (bending) vibronic spectrum. The main result of the present study is the proof that the diabatization scheme, hidden beneath the apparent simplicity of the model, can safely be carried out, at small-amplitude bending vibrations, without cumbersome computation of non-adiabatic matrix elements at large number of molecular geometries.

Study of hydrogen bond polarized IR spectra of cinnamic acid crystals

NASA Astrophysics Data System (ADS)

Flakus, Henryk T.; Jabłońska, Magdalena

2004-11-01

This paper presents the results of investigation of the polarized IR spectra of cinnamic acid and of its deuterium derivative crystals. The spectra were measured by a transmission method, using polarized light, at the room temperature and at 77 K, for two different crystalline faces. Theoretical analysis of the results concerned linear dichroic effects, H/D isotopic and temperature effects, observed in the spectra of the hydrogen and of the deuterium bonds in cinnamic acid crystals, at the frequency ranges of the νO-H and the νO-D bands. The basic crystal spectral properties could be satisfactorily interpreted in a quantitative way for a centrosymmetric cyclic hydrogen bond dimer model. Such a model explains not only a two-branch structure of the νO-H and νO-D bands in crystalline spectra, but also some essential linear dichroic effects in the band frequency ranges, measured for isotopically diluted crystals. Model calculations, performed within the limits of the 'strong-coupling' model, allowed for quantitative interpretation and for understanding of the basic properties of the hydrogen bond IR spectra of cinnamic acid crystals, H/D isotopic, temperature and dichroic effects included. In the scope of our studies the mechanism of H/D isotopic 'self-organization' processes, taking place in the crystal hydrogen bond lattices, was also recognized. It was proved that for isotopically diluted crystalline samples of cinnamic acid, a non-random distribution of protons and deuterons occurs exclusively in the hydrogen bond dimers. Nevertheless, these co-operative interactions between the hydrogen bonds do not involve the adjacent hydrogen bond dimers in each unit cell. The two-branch fine structure pattern of the νO-H and νO-D bands was ascribed to the vibronic mechanism of vibrational dipole selection rule breaking in centrosymmetric hydrogen bond dimers. The observed in the spectra very high intensity of the forbidden transition sub-band in the analyzed νO-H and νO-D bands is a manifestation of an extremely effective symmetry rule breaking mechanism. It correlates with a relatively large excess electron charge on the cinnamic aid dimer carboxyl groups. This effect is a result of a partial withdrawal of the electron charge, from the conjugated π-bond systems of the styryl substituents, by the carboxyl groups. This statement has been supported by ab initio calculations.

Algebraic approach to electronic spectroscopy and dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toutounji, Mohamad

Lie algebra, Zassenhaus, and parameter differentiation techniques are utilized to break up the exponential of a bilinear Hamiltonian operator into a product of noncommuting exponential operators by the virtue of the theory of Wei and Norman [J. Math. Phys. 4, 575 (1963); Proc. Am. Math. Soc., 15, 327 (1964)]. There are about three different ways to find the Zassenhaus exponents, namely, binomial expansion, Suzuki formula, and q-exponential transformation. A fourth, and most reliable method, is provided. Since linearly displaced and distorted (curvature change upon excitation/emission) Hamiltonian and spin-boson Hamiltonian may be classified as bilinear Hamiltonians, the presented algebraic algorithm (exponentialmore » operator disentanglement exploiting six-dimensional Lie algebra case) should be useful in spin-boson problems. The linearly displaced and distorted Hamiltonian exponential is only treated here. While the spin-boson model is used here only as a demonstration of the idea, the herein approach is more general and powerful than the specific example treated. The optical linear dipole moment correlation function is algebraically derived using the above mentioned methods and coherent states. Coherent states are eigenvectors of the bosonic lowering operator a and not of the raising operator a{sup +}. While exp(a{sup +}) translates coherent states, exp(a{sup +}a{sup +}) operation on coherent states has always been a challenge, as a{sup +} has no eigenvectors. Three approaches, and the results, of that operation are provided. Linear absorption spectra are derived, calculated, and discussed. The linear dipole moment correlation function for the pure quadratic coupling case is expressed in terms of Legendre polynomials to better show the even vibronic transitions in the absorption spectrum. Comparison of the present line shapes to those calculated by other methods is provided. Franck-Condon factors for both linear and quadratic couplings are exactly accounted for by the herein calculated linear absorption spectra. This new methodology should easily pave the way to calculating the four-point correlation function, F({tau}{sub 1},{tau}{sub 2},{tau}{sub 3},{tau}{sub 4}), of which the optical nonlinear response function may be procured, as evaluating F({tau}{sub 1},{tau}{sub 2},{tau}{sub 3},{tau}{sub 4}) is only evaluating the optical linear dipole moment correlation function iteratively over different time intervals, which should allow calculating various optical nonlinear temporal/spectral signals.« less

Anomalous Centrifugal Distortion in NH_2

NASA Astrophysics Data System (ADS)

Martin-Drumel, Marie-Aline; Pirali, Olivier; Coudert, L. H.

2017-06-01

The NH2 radical spectrum, first observed by Herzberg and Ramsay, is dominated by a strong Renner-Teller effect giving rise to two electronic states: the bent X ^{2}B_1 ground state and the quasi-linear A ^{2}A_1 excited state. The NH2 radical has been the subject of numerous high-resolution investigations and its electronic and ro-vibrational transitions have been measured. Using synchrotron radiation, new rotational transitions have been recently recorded and a value of the rotational quantum number N as large as 26 could be reached. In the X ^{2}B_1 ground state, the NH2 radical behaves like a triatomic molecule displaying spin-rotation splittings. Due to the lightness of the molecule, a strong coupling between the overall rotation and the bending mode arises whose effects increase with N and lead to the anomalous centrifugal distortion evidenced in the new measurements.^d In this talk the Bending-Rotation approach developed to account for the anomalous centrifugal distortion of the water molecule is modified to include spin-rotation coupling and applied to the fitting of high-resolution data pertaining to the ground electronic state of NH2. A preliminary line position analysis of the available data^{c,d} allowed us to account for 1681 transitions with a unitless standard deviation of 1.2. New transitions could also be assigned in the spectrum recorded by Martin-Drumel et al.^d In the talk, the results obtained with the new theoretical approach will be compared to those retrieved with a Watson-type Hamiltonian and the effects of the vibronic coupling between the ground X ^{2}B_1 and the excited A ^{2}A_1 electronic state will be discussed. Herzberg and Ramsay, J. Chem. Phys. 20 (1952) 347 Dressler and Ramsay, Phil. Trans. R. Soc. A 25 (1959) 553 Hadj Bachir, Huet, Destombes, and Vervloet, J. Molec. Spectrosc. 193 (1999) 326 McKellar, Vervloet, Burkholder, and Howard, J. Molec. Spectrosc. 142 (1990) 319 Morino and Kawaguchi, J. Molec. Spectrosc. 182 (1997) 428 Martin-Drumel, Pirali, and Vervloet, J. Phys. Chem. A 118 (2014) 1331 Coudert, J. Molec. Spectrosc. 165 (1994) 406

Investigating plausible mechanisms for the photo-induced partial unfolding of a globular protein

NASA Astrophysics Data System (ADS)

Parker, James E.

Two hypotheses are proposed to explain the photo-induced unfolding of β-lactoglobulin (BLG) that occurs when non-covalently bound to a dye molecule, meso-tetrakis (p-sulfonatophenyl) porphyrin (TSPP), and illuminated by a laser in the post-Tanford transition configuration. The first involves a photo-induced electron transfer from the porphyrin to the protein. The second involves the production of kynurenine by singlet oxygen that is generated during photo-excitation of the porphyrin. To evaluate these hypotheses, a series of computational and experimental results have been combined to establish the physical state of the BLG-TSPP complex and to estimate the likelihood of a post-irradiation event to initiate the partial unfolding. Determining the binding site location is crucial to establish the position of the photo-induced events and the likely end-product. A study of the vibronic state of the BLG-TSPP complex using resonant Raman and absorption spectroscopy coupled with density functional theory (DFT) and docking simulations is used to estimate the location of the binding site. Once the binding site is found, molecular dynamics simulations of the post-irradiation event relaxations in the protein are used to estimate the resulting secondary structure. This structure is compared to experimental estimates of the secondary structure of the unfolded protein to determine which hypothesis is the most likely mechanism to explain the unfolding.

Raman spectroelectrochemistry of molecules within individual electromagnetic hot spots.

PubMed

Shegai, Timur; Vaskevich, Alexander; Rubinstein, Israel; Haran, Gilad

2009-10-14

The role of chemical enhancement in surface-enhanced Raman scattering (SERS) remains a contested subject. We study SERS spectra of 4-mercaptopyridine molecules excited far from the molecular resonance, which are collected from individual electromagnetic hot spots at concentrations close to the single-molecule limit. The hot spots are created by depositing Tollen's silver island films on a transparent electrode incorporated within an electrochemical cell. Analysis of the intensity of the spectra relative to those obtained from individual rhodamine 6G molecules on the same surface provides a lower limit of approximately 3 orders of magnitude for the chemical enhancement. This large enhancement is likely to be due to a charge transfer resonance involving the transfer of an electron from the metal to an adsorbed molecule. Excitation at three different wavelengths, as well as variation of electrode potential from 0 to -1.2 V, lead to significant changes in the relative intensities of bands in the spectrum. It is suggested that while the bulk of the enhancement is due to an Albrecht A-term resonance Raman effect (involving the charge transfer transition), vibronic coupling provides additional enhancement which is sensitive to electrode potential. The measurement of potential-dependent SERS spectra from individual hot spots opens the way to a thorough characterization of chemical enhancement, as well to studies of redox phenomena at the single-molecule level.

Rotational and Fine Structure of Pseudo-Jahn Molecules with C_1 Symmetry

NASA Astrophysics Data System (ADS)

Liu, Jinjun

2016-06-01

It has been found in our previous works that rotational and fine-structure analysis of spectra involving nearly degenerate electronic states may aid in interpretation and analysis of the vibronic structure, specifically in the case of pseudo-Jahn-Teller (pJT) molecules with C_s symmetry. The spectral analysis of pJT derivatives (isopropoxy and cyclohexoxy of a prototypical JT molecule (the methoxy radical) allowed for quantitative determination of various contributions to the energy separation between the nearly degenerate electronic states, including the relativistic spin-orbit (SO) effect, the electrostatic interaction, and their zero-point energy difference. These states are coupled by SO and Coriolis interactions, which can also be determined accurately in rotational and fine structure analysis. Most recently, the spectroscopic model for rotational analysis of pJT molecules has been extended for analysis of molecules with C_1 symmetry, i.e., no symmetry. This model includes the six independently determinable components of the spin-rotation (SR) tensor and the three components of the SO and Coriolis interactions. It has been employed to simulate and fit high-resolution laser-induced fluorescence (LIF) spectra of jet-cooled alkoxy radicals with C_1 symmetry, including the 2-hexoxy and the 2-pentoxy radicals, as well as previously recorded LIF spectrum of the trans-conformer (defined by its OCCC dihedral angle) of the 2-butoxy radical. Although the LIF spectra can be reproduced by using either the SR constants or SO and Coriolis constants, the latter simulation offers results that are physically more meaningful whereas the SR constants have to be regarded as effective constants. Furthermore, we will review the SO and Coriolis constants of alkoxy radicals that have been investigated, starting from the well-studied methoxy radical (CH_3O). J. Liu, D. Melnik, and T. A. Miller, J. Chem. Phys. 139, 094308 (2013) J. Liu and T. A. Miller, J. Phys. Chem. A 118, 11871-11890 (2014) L. Stakhursky, L. Zu, J. Liu, and T. A. Miller, J. Chem. Phys. 125, 094316 (2006)

Silyl group internal rotation in S1 phenylsilane and phenylsilane cation: Experiments and ab initio calculations

NASA Astrophysics Data System (ADS)

Lu, Kueih-Tzu; Weisshaar, James C.

1993-09-01

Resonant two-photon ionization (R2PI) and pulsed field ionization (PFI) were used to measure S1-S0 and cation-S1 spectra of internally cold phenylsilane. We measure the adiabatic ionization potentials IP(phenylsilane)=73 680±5 cm-1, IP(phenylsilane ṡAr)=73 517±5 cm-1 and IP(phenylsilane ṡAr2)=73 359±5 cm-1. We assign many low lying torsion-vibration levels of the S1 (à 1A1) state and of X˜ 2B1 of phenylsilane+. In both states, the pure torsional transitions are well fit by a simple sixfold hindered rotor Hamiltonian. The results for the rotor inertial constant B and internal rotation potential barrier V6 are, in S1, B=2.7±0.2 cm-1 and V6=-44±4 cm-1; in the cation, B=2.7±0.2 cm-1 and V6=+19±3 cm-1. The sign of V6 and the conformation of minimum energy are inferred from spectral intensities of bands terminating on the 3a`1 and 3a`2 torsional levels. In S1 the staggered conformation is most stable, while in the cation ground state the eclipsed conformation is most stable. For all sixfold potentials whose absolute phase is known experimentally, the most stable conformer is staggered in the neutral states (S0 and S1 p-fluorotoluene, S1 toluene, S1 p-fluorotoluene) and eclipsed in the cationic states (ground state toluene+ and phenylsilane+). In phenylsilane+ we estimate several potential energy coupling matrix elements between torsional and vibrational states. For small V6, the term PαPa in the rigid-frame model Hamiltonian strongly mixes the 6a'1 and 6a'2 torsional states, which mediates further torsion-vibrational coupling. In addition, the cation X˜ 2B1 vibrational structure is badly perturbed, apparently by strong vibronic coupling with the low-lying à 2A2 state. Accordingly, ab initio calculations find a substantial in-plane distortion of the equilibrium geometry of the X˜ 2B1 state, while the à 2A2 state is planar and symmetric. The calculations also correctly predict the lowest energy conformer for S0 states and for cation ground states. Finally, we adapt the natural resonance theory (NRT) of Glendening and Weinhold to suggest why sixfold barriers for methyl and silyl rotors are uniformly small, while some threefold barriers are quite large. The phase of the sixfold potential is apparently determined by a subtle competition between two types of rotor-ring potential terms: attractive donor-acceptor interactions and repulsive van der Waals interactions (steric effects).

Spectral Dissimilarities Between AZULENE(C10H_8) and NAPHTHALENE(C10H_8)

NASA Astrophysics Data System (ADS)

Baba, Masaaki

2010-06-01

Polycyclic aromatic hydrocarbons (PAHs) are of great interest in the molecular structure and excited-state dynamics, and there have been extensive spectroscopic and theoretical studies. Azulene and naphthalene are bicyclic aromatic hydrocarbons composed of odd- and even-membered rings, respectively. First, they were discriminated by a theory of mutual polarizability. Naphthalene is an alternant hydrocarbon, but azulene is not. In contrast, spectral resemblances were found by John Platt et al., and were explained by their simple model of molecular orbital. However, the absorption and emission feature of the S_1 and S_2 states is completely different each other. We have investigated each rotational and vibrational structures, and radiative and nonradiative processes by means of high-resolution spectroscopy and ab initio calculation. The equilibrium structures in the S_0, S_1, and S_2 states are similar. This small structural change upon electronic excitation is common to PAH molecules composed of six-membered rings. The fluorescence quantum yield is high because radiationless transitions such as intersystem crossing (ISC) to the triplet state and internal conversion (IC) to the S_0 state are very slow in the S_1 state. In contrast, the S_1 state of azulene is nonfluorescent and the S_1 ← S_0 excitation energy is abnormally small. We consider that the potential energy curve of a b_2 vibration is shallower in the S_1 state, and therefore the vibronic coupling with the S_0 state is strong to enhance the IC process remarkably. This situation is, of course, due to its peculiar characteristics of odd-membered rings and molecular symmetry, which are completely different from the naphthalene molecule. C. A. Coulson and H. C. Longuet-Higgins, Proc. Roy. Soc. A, 191, 39 (1947) D. E. Mann, J. R. Platt, and H. B. Klevens, J. Chem. Phys., 17, 481 (1949) Y. Semba, M. Baba, et al., J. Chem. Phys., 131, 024303 (2009) K. Yoshida, M. Baba, et al., J. Chem. Phys., 130, 194304 (2009)

A unified description of the electrochemical, charge distribution, and spectroscopic properties of the special-pair radical cation in bacterial photosynthesis.

PubMed

Reimers, Jeffrey R; Hush, Noel S

2004-04-07

We apply our four-state 70-vibration vibronic-coupling model for the properties of the photosynthetic special-pair radical cation to: (1) interpret the observed correlations between the midpoint potential and the distribution of spin density between the two bacteriochlorophylls for 30 mutants of Rhodobacter sphaeroides, (2) interpret the observed average intervalence hole-transfer absorption energies as a function of spin density for six mutants, and (3) simulate the recently obtained intervalence electroabsorption Stark spectrum of the wild-type reaction center. While three new parameters describing the location of the sites of mutation with respect to the special pair are required to describe the midpoint-potential data, a priori predictions are made for the transition energies and the Stark spectrum. In general, excellent predictions are made of the observed quantities, with deviations being typically of the order of twice the experimental uncertainties. A unified description of many chemical and spectroscopic properties of the bacterial reaction center is thus provided. Central to the analysis is the assumption that the perturbations made to the reaction center, either via mutations of protein residues or by application of an external electric field, act only to independently modify the oxidation potentials of the two halves of the special pair and hence the redox asymmetry E0. While this appears to be a good approximation, clear evidence is presented that effects of mutation can be more extensive than what is allowed for. A thorough set of analytical equations describing the observed properties is obtained using the Born-Oppenheimer adiabatic approximation. These equations are generally appropriate for intervalence charge-transfer problems and include, for the first time, full treatment of both symmetric and antisymmetric vibrational motions. The limits of validity of the adiabatic approach to the full nonadiabatic problem are obtained.

Dynamics and mechanisms of interfacial photoinduced electron transfer processes of third generation photovoltaics and photocatalysis.

PubMed

Bauer, Christophe; Teuscher, Joël; Brauer, Jan C; Punzi, Angela; Marchioro, Arianna; Ghadiri, Elham; De Jonghe, Jelissa; Wielopolski, Mateusz; Banerji, Natalie; Moser, Jacques E

2011-01-01

Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aimed at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim to achieve a fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here: Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a Ru(II)(terpyridyl-PO3)(NCS)3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO2. The forward ET reaction was found to be faster than vibrational relaxation of the vibronic excited state of the donor. Instead, the back ET occurred on the micros time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor beta = 0.16 angstroms(-1) observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO2 is attributed to the coupling of electron tunneling with nonequilibrium vibrations redistributed on the bridge, giving rise to polaronic transport of charges from the donor ligand to the acceptor solid oxide surface.

Laser-saturated fluorescence of nitric oxide and chemiluminescence measurements in premixed ethanol flames

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marques, Carla S.T.; Barreta, Luiz G.; Sbampato, Maria E.

In this study, nitric oxide laser-saturated fluorescence (LSF) measurements were acquired from premixed ethanol flames at atmospheric pressure in a burner. NO-LSF experimental profiles for fuel-rich premixed ethanol flames ({phi} = 1.34 and {phi} = 1.66) were determined through the excitation/detection scheme of the Q{sub 2}(26.5) rotational line in the A{sup 2}{sigma}{sup +} - X{sup 2}{pi} (0,0) vibronic band and {gamma}(0,1) emission band. A calibration procedure by NO doping into the flame was applied to establish the NO concentration profiles in these flames. Chemiluminescent emission measurements in the (0, 0) vibronic emission bands of the OH{sup *} (A{sup 2}{sigma}{sup +}more » - X{sup 2}{pi}) and CH{sup *}(A{sup 2}{delta} - X{sup 2}{pi}) radicals were also obtained with high spatial and spectral resolution for fuel-rich premixed ethanol flames to correlate them with NO concentrations. Experimental chemiluminescence profiles and the ratios of the integrated areas under emission spectra (A{sub CH*}/A{sub CH*}(max.) and A{sub CH*}/A{sub OH*}) were determined. The relationships between chemiluminescence and NO concentrations were established along the premixed ethanol flames. There was a strong connection between CH{sup *} radical chemiluminescence and NO formation and the prompt-NO was identified as the governing mechanism for NO production. The results suggest the optimum ratio of the chemiluminescence of two radicals (A{sub CH*}/A{sub OH*}) for NO diagnostic purposes. (author)« less

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

PubMed Central

DeVine, Jessalyn A.; Levine, Daniel S.; Kim, Jongjin B.; Neumark, Daniel M.

2016-01-01

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C14H9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm−1 resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck–Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck–Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data. PMID:26792521

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weichman, Marissa L.; DeVine, Jessalyn A.; Levine, Daniel S.

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. In this paper, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C 14H 9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm -1 resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excitedmore » states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck–Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck–Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Finally and additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data.« less

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

DOE PAGES

Weichman, Marissa L.; DeVine, Jessalyn A.; Levine, Daniel S.; ...

2016-01-20

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. In this paper, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C 14H 9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm -1 resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excitedmore » states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck–Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck–Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Finally and additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data.« less

Zero-phonon-line emission of single molecules for applications in quantum information processing

NASA Astrophysics Data System (ADS)

Kiraz, Alper; Ehrl, M.; Mustecaplioglu, O. E.; Hellerer, T.; Brauchle, C.; Zumbusch, A.

2005-07-01

A single photon source which generates transform limited single photons is highly desirable for applications in quantum optics. Transform limited emission guarantees the indistinguishability of the emitted single photons. This, in turn brings groundbreaking applications in linear optics quantum information processing within an experimental reach. Recently, self-assembled InAs quantum dots and trapped atoms have successfully been demonstrated as such sources for highly indistinguishable single photons. Here, we demonstrate that nearly transform limited zero-phonon-line (ZPL) emission from single molecules can be obtained by using vibronic excitation. Furthermore we report the results of coincidence detection experiments at the output of a Michelson-type interferometer. These experiments reveal Hong-Ou-Mandel correlations as a proof of the indistinguishability of the single photons emitted consecutively from a single molecule. Therefore, single molecules constitute an attractive alternative to single InAs quantum dots and trapped atoms for applications in linear optics quantum information processing. Experiments were performed with a home-built confocal microscope keeping the sample in a superfluid liquid Helium bath at 1.4K. We investigated terrylenediimide (TDI) molecules highly diluted in hexadecane (Shpol'skii matrix). A continuous wave single mode dye laser was used for excitation of vibronic transitions of individual molecules. From the integral fluorescence, the ZPL of single molecules was selected with a spectrally narrow interference filter. The ZPL emission was then sent to a scanning Fabry-Perot interferometer for linewidth measurements or a Michelson-type interferometer for coincidence detection.

Planarizing cytosine: The S1 state structure, vibrations, and nonradiative dynamics of jet-cooled 5,6-trimethylenecytosine

NASA Astrophysics Data System (ADS)

Trachsel, Maria A.; Lobsiger, Simon; Schär, Tobias; Blancafort, Lluís; Leutwyler, Samuel

2017-06-01

We measure the S0 → S1 spectrum and time-resolved S1 state nonradiative dynamics of the "clamped" cytosine derivative 5,6-trimethylenecytosine (TMCyt) in a supersonic jet, using two-color resonant two-photon ionization (R2PI), UV/UV holeburning, and ns time-resolved pump/delayed ionization. The experiments are complemented with spin-component scaled second-order approximate coupled cluster (SCS-CC2), time-dependent density functional theory, and multi-state second-order perturbation-theory (MS-CASPT2) ab initio calculations. While the R2PI spectrum of cytosine breaks off ˜500 cm-1 above its 000 band, that of TMCyt extends up to +4400 cm-1 higher, with over a hundred resolved vibronic bands. Thus, clamping the cytosine C5-C6 bond allows us to explore the S1 state vibrations and S0 → S1 geometry changes in detail. The TMCyt S1 state out-of-plane vibrations ν1', ν3', and ν5' lie below 420 cm-1, and the in-plane ν11', ν12', and ν23' vibrational fundamentals appear at 450, 470, and 944 cm-1. S0 → S1 vibronic simulations based on SCS-CC2 calculations agree well with experiment if the calculated ν1', ν3', and ν5' frequencies are reduced by a factor of 2-3. MS-CASPT2 calculations predict that the ethylene-type S1 ⇝ S0 conical intersection (CI) increases from +366 cm-1 in cytosine to >6000 cm-1 in TMCyt, explaining the long lifetime and extended S0 → S1 spectrum. The lowest-energy S1 ⇝ S0 CI of TMCyt is the "amino out-of-plane" (OPX) intersection, calculated at +4190 cm-1. The experimental S1 ⇝ S0 internal conversion rate constant at the S1(v'=0 ) level is kI C=0.98 -2.2 ṡ1 08 s-1, which is ˜10 times smaller than in 1-methylcytosine and cytosine. The S1(v'=0 ) level relaxes into the T1(3π π *) state by intersystem crossing with kI S C=0.41 -1.6 ṡ1 08 s-1. The T1 state energy is measured to lie 24 580 ±560 cm-1 above the S0 state. The S1(v'=0 ) lifetime is τ =2.9 ns, resulting in an estimated fluorescence quantum yield of Φf l=24 %. Intense two-color R2PI spectra of the TMCyt amino-enol tautomers appear above 36 000 cm-1. A sharp S1 ionization threshold is observed for amino-keto TMCyt, yielding an adiabatic ionization energy of 8.114 ±0.002 eV.

O2-O2 and O2-N2 collision-induced absorption mechanisms unravelled

NASA Astrophysics Data System (ADS)

Karman, Tijs; Koenis, Mark A. J.; Banerjee, Agniva; Parker, David H.; Gordon, Iouli E.; van der Avoird, Ad; van der Zande, Wim J.; Groenenboom, Gerrit C.

2018-05-01

Collision-induced absorption is the phenomenon in which interactions between colliding molecules lead to absorption of light, even for transitions that are forbidden for the isolated molecules. Collision-induced absorption contributes to the atmospheric heat balance and is important for the electronic excitations of O2 that are used for remote sensing. Here, we present a theoretical study of five vibronic transitions in O2-O2 and O2-N2, using analytical models and numerical quantum scattering calculations. We unambiguously identify the underlying absorption mechanism, which is shown to depend explicitly on the collision partner—contrary to textbook knowledge. This explains experimentally observed qualitative differences between O2-O2 and O2-N2 collisions in the overall intensity, line shape and vibrational dependence of the absorption spectrum. It is shown that these results can be used to discriminate between conflicting experimental data and even to identify unphysical results, thus impacting future experimental studies and atmospheric applications.

Radiation of nitrogen molecules in a dielectric barrier discharge with small additives of chlorine and bromine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avtaeva, S. V.; Avdeev, S. M.; Sosnin, E. A.

2010-08-15

Spectral and energy characteristics of nitrogen molecule radiation in dielectric barrier discharges in Ar-N{sub 2}, Ar-N{sub 2}-Cl{sub 2}, and Ar-N{sub 2}-Br{sub 2} mixtures were investigated experimentally. Small additives of molecular chlorine or bromine to an Ar-N{sub 2} mixture are found to increase the radiation intensity of the second positive system of nitrogen. The conditions at which the radiation spectrum predominantly consists of vibronic bands of this system are determined. Using a numerical model of plasmachemical processes, it is shown that, at electron temperatures typical of gas discharges (2-4 eV), a minor additive of molecular chlorine to an Ar-N{sub 2} mixturemore » leads to an increase in the concentrations of electrons, positive ions, and metastable argon atoms. In turn, collisional energy transfer from metastable argon atoms to nitrogen molecules results in the excitation of the N{sub 2}(C{sup 3{Pi}}{sub u}) state.« less

High resolution FTIR spectroscopy of BaY2F8 single crystals doped with trivalent Er

NASA Astrophysics Data System (ADS)

Baraldi, A.; Capelletti, R.; Cornelli, M.; Ponzoni, A.; Ruffini, A.; Sperzagni, A.; Tonelli, M.

High resolution (0.04 cm-1) FTIR spectroscopy is applied to monoclinic Er3+-doped BaY2F8 single crystals in the wavenumber range 500-24000 cm-1 and temperature range 9-300 K to study the crystal field splitting of the fundamental 4I15/2 and of the excited 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2, 4F7/2, 4F5/2, and 4F3/2 states and the effects caused by increasing Er3+-concentrations (2-20% m.f.), such as inhomogeneous line-broadening and new lines due to Er3+-Er3+ interaction. In the framework of the electron-phonon interaction, the thermally induced line-broadening and -shift are detected and accounted for by the two-phonon Raman model and the vibronic replicas of a few lines are investigated.

Luminescence and energy transfer in Lu3Al5O12 scintillators co-doped with Ce3+ and Tb3+.

PubMed

Ogiegło, Joanna M; Zych, Aleksander; Ivanovskikh, Konstantin V; Jüstel, Thomas; Ronda, Cees R; Meijerink, Andries

2012-08-23

Lu(3)Al(5)O(12) (LuAG) doped with Ce(3+) is a promising scintillator material with a high density and a fast response time. The light output under X-ray or γ-ray excitation is, however, well below the theoretical limit. In this paper the influence of codoping with Tb(3+) is investigated with the aim to increase the light output. High resolution spectra of singly doped LuAG (with Ce(3+) or Tb(3+)) are reported and provide insight into the energy level structure of the two ions in LuAG. For Ce(3+) zero-phonon lines and vibronic structure are observed for the two lowest energy 5d bands and the Stokes' shift (2 350 cm(-1)) and Huang-Rhys coupling parameter (S = 9) have been determined. Tb(3+) 4f-5d transitions to the high spin (HS) and low spin (LS) states are observed (including a zero-phonon line and vibrational structure for the high spin state). The HS-LS splitting of 5400 cm(-1) is smaller than usually observed and is explained by a reduction of the 5d-4f exchange coupling parameter J by covalency. Upon replacing the smaller Lu(3+) ion with the larger Tb(3+) ion, the crystal field splitting for the lowest 5d states increases, causing the lowest 5d state to shift below the (5)D(4) state of Tb(3+) and allowing for efficient energy transfer from Tb(3+) to Ce(3+) down to the lowest temperatures. Luminescence decay measurements confirm efficient energy transfer from Tb(3+) to Ce(3+) and provide a qualitative understanding of the energy transfer process. Co-doping with Tb(3+) does not result in the desired increase in light output, and an explanation based on electron trapping in defects is discussed.

Alignment, vibronic level splitting, and coherent coupling effects on the pump-probe polarization anisotropy.

PubMed

Smith, Eric R; Jonas, David M

2011-04-28

The pump-probe polarization anisotropy is computed for molecules with a nondegenerate ground state, two degenerate or nearly degenerate excited states with perpendicular transition dipoles, and no resonant excited-state absorption. Including finite pulse effects, the initial polarization anisotropy at zero pump-probe delay is predicted to be r(0) = 3/10 with coherent excitation. During pulse overlap, it is shown that the four-wave mixing classification of signal pathways as ground or excited state is not useful for pump-probe signals. Therefore, a reclassification useful for pump-probe experiments is proposed, and the coherent anisotropy is discussed in terms of a more general transition dipole and molecular axis alignment instead of experiment-dependent ground- versus excited-state pathways. Although coherent excitation enhances alignment of the transition dipole, the molecular axes are less aligned than for a single dipole transition, lowering the initial anisotropy. As the splitting between excited states increases beyond the laser bandwidth and absorption line width, the initial anisotropy increases from 3/10 to 4/10. Asymmetric vibrational coordinates that lift the degeneracy control the electronic energy gap and off-diagonal coupling between electronic states. These vibrations dephase coherence and equilibrate the populations of the (nearly) degenerate states, causing the anisotropy to decay (possibly with oscillations) to 1/10. Small amounts of asymmetric inhomogeneity (2 cm(-1)) cause rapid (130 fs) suppression of both vibrational and electronic anisotropy beats on the excited state, but not vibrational beats on the ground electronic state. Recent measurements of conical intersection dynamics in a silicon napthalocyanine revealed anisotropic quantum beats that had to be assigned to asymmetric vibrations on the ground electronic state only [Farrow, D. A.; J. Chem. Phys. 2008, 128, 144510]. Small environmental asymmetries likely explain the observed absence of excited-state asymmetric vibrations in those experiments.

Conformational Specific Infrared and Ultraviolet Spectroscopy of Cold YA(D-Pro)AA\\cdotH+ Ions: a Sterochemical "twist" on the Proline Effect

NASA Astrophysics Data System (ADS)

Harrilal, Christopher P.; DeBlase, Andrew F.; Burke, Nicole L.; McLuckey, Scott A.; Zwier, Timothy S.

2016-06-01

The "proline effect" is a well-known fragmentation phenomenon in mass spectrometry, in which y-fragments are produced preferentially over b-fragments during the collision induced dissociation of protonated L-proline containing peptide ions. This specific fragmentation channel is favored because of the high basicity of the secondary amine intermediate and the ring instability in alternative bn+ products [ASMS 2014, 25, 1705]. In contrast, peptides containing the D-Pro stereoisomer have been shown to largely favor the production of b4+ ions over y3+ ions. This strongly suggests that differences in the conformational preferences between the D-Pro and L-Pro diastereomers are likely to be responsible but structural evidence has been lacking to date. Using tandem mass spectrometry and IR-UV double resonant action spectroscopy we are able to compare the 3D structures of cold [YA(D-Pro)AA+H]+ to [YA(L-Pro)AA+H]+ ions. The UV action spectra reveals two major conformers in [YA(D-Pro)AA+H]+ and one major conformer in [YA(L-Pro)AA+H]+. Clear differences in the hydrogen bonding patterns are apparent between the two conformers observed in the D-Pro specie which are both distinct from the L-Pro diastereomer. Furthermore, conformer and diastereomer specific photofragmentation patterns are observed. It is also noted that a ten-fold photofragment enhancement unique to one of the D-Pro conformers is observed upon absorption of a resonant IR photon after UV excitation. Differences in the excited state photophysics between the two D-Pro conformers suggest that vibrational excitation of S1 turns on coupling to the dissociative -Tyr channel in one conformer, while this coupling is already present in the vibronic ground state of the other. Calculated harmonic spectra (M052X/6-31+G*) of conformers obtained from Monte Carlo searches to the experimental spectra.

Planar imaging of OH density distributions in a supersonic combustion tunnel

NASA Technical Reports Server (NTRS)

Quagliaroli, T. M.; Laufer, G.; Krauss, R. H.; Mcdaniel, J. C., Jr.

1993-01-01

Images of absolute OH number density were obtained using planar laser-induced fluorescence (PLIF) in a supersonic H2-air combustion tunnel. A tunable KrF excimer laser was used to excite the Q2(11) ro-vibronic line. Calibration of the PLIF images was obtained by referencing the signal measured in the flame to that obtained by the excitation of OH produced by thermal dissociation of H2O in an atmospheric furnace. Measurement errors due to uncertainty in internal furnace atmospheric conditions and image temperature correction are estimated.

A study on the anisole-water complex by molecular beam-electronic spectroscopy and molecular mechanics calculations.

PubMed

Becucci, M; Pietraperzia, G; Pasquini, M; Piani, G; Zoppi, A; Chelli, R; Castellucci, E; Demtroeder, W

2004-03-22

An experimental and theoretical study is made on the anisole-water complex. It is the first van der Waals complex studied by high resolution electronic spectroscopy in which the water is seen acting as an acid. Vibronically and rotationally resolved electronic spectroscopy experiments and molecular mechanics calculations are used to elucidate the structure of the complex in the ground and first electronic excited state. Some internal dynamics in the system is revealed by high resolution spectroscopy. (c) 2004 American Institute of Physics

Kilohertz Cr:forsterite regenerative amplifier.

PubMed

Evans, J M; Petri Evi, V; Alfano, R R; Fu, Q

1998-11-01

We report on a tunable regenerative amplifier that is operational in the near-infrared spectral region from 1230 to 1280 nm based on the vibronic laser material Cr:forsterite. Utilizing the technique of chirped-pulse amplification, we generated pulses as short as 150 fs at 1255 nm at a repetition rate of 1 kHz. Pulse amplification of more than 5 x 10(5) times was observed, with recorded output pulse energies of 34 muJ . Implementation of a second-harmonic generator yielded 110-fs-duration pulses of 7-muJ energy at 625 nm.

Nonlinear thermoelectric transport in single-molecule junctions: the effect of electron-phonon interactions.

PubMed

Zimbovskaya, Natalya A

2016-07-27

In this paper, we theoretically analyze steady-state thermoelectric transport through a single-molecule junction with a vibrating bridge. The thermally induced charge current in the system is explored using a nonequilibrium Green function formalism. We study the combined effects of Coulomb interactions between charge carriers on the bridge and electron-phonon interactions on the thermocurrent beyond the linear response regime. It is shown that electron-vibron interactions may significantly affect both the magnitude and the direction of the thermocurrent, and vibrational signatures may appear.

Impact of Temperature and Non-Gaussian Statistics on Electron Transfer in Donor–Bridge–Acceptor Molecules

DOE PAGES

Waskasi, Morteza M.; Newton, Marshall D.; Matyushov, Dmitry V.

2017-03-16

A combination of experimental data and theoretical analysis provides evidence of a bell-shaped kinetics of electron transfer in the Arrhenius coordinates ln k vs 1/T . This kinetic law is a temperature analog of the familiar Marcus bell-shaped dependence based on ln k vs the reaction free energy. These results were obtained for reactions of intramolecular charge shift between the donor and acceptor separated by a rigid spacer studied experimentally by Miller and co-workers. The non-Arrhenius kinetic law is a direct consequence of the solvent reorganization energy and reaction driving force changing approximately as hyperbolic functions with temperature. The reorganizationmore » energy decreases and the driving force increases when temperature is increased. The point of equality between them marks the maximum of the activationless reaction rate. Reaching the consistency between the kinetic and thermodynamic experimental data requires the non-Gaussian statistics of the donor-acceptor energy gap described by the Q-model of electron transfer. Furthermore, the theoretical formalism combines the vibrational envelope of quantum vibronic transitions with the Q-model describing the classical component of the Franck-Condon factor and a microscopic solvation model of the solvent reorganization energy and the reaction free energy.« less

Rotational and fine structure of open-shell molecules in nearly degenerate electronic states

NASA Astrophysics Data System (ADS)

Liu, Jinjun

2018-03-01

An effective Hamiltonian without symmetry restriction has been developed to model the rotational and fine structure of two nearly degenerate electronic states of an open-shell molecule. In addition to the rotational Hamiltonian for an asymmetric top, this spectroscopic model includes the energy separation between the two states due to difference potential and zero-point energy difference, as well as the spin-orbit (SO), Coriolis, and electron spin-molecular rotation (SR) interactions. Hamiltonian matrices are computed using orbitally and fully symmetrized case (a) and case (b) basis sets. Intensity formulae and selection rules for rotational transitions between a pair of nearly degenerate states and a nondegenerate state have also been derived using all four basis sets. It is demonstrated using real examples of free radicals that the fine structure of a single electronic state can be simulated with either a SR tensor or a combination of SO and Coriolis constants. The related molecular constants can be determined precisely only when all interacting levels are simulated simultaneously. The present study suggests that analysis of rotational and fine structure can provide quantitative insights into vibronic interactions and related effects.

Comparison of the resonance-enhanced multiphoton ionization spectra of pyrrole and 2,5-dimethylpyrrole: Building toward an understanding of the electronic structure and photochemistry of porphyrins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beames, Joseph M.; Nix, Michael G. D.; Hudson, Andrew J.

The photophysical properties of porphyrins have relevance for their use as light-activated drugs in cancer treatment and sensitizers in solid-state solar cells. However, the appearance of their UV-visible spectra is usually explained inadequately by qualitative molecular-orbital theories. We intend to gain a better insight into the intense absorption bands, and excited-state dynamics, that make porphyrins appropriate for both of these applications by gradually building toward an understanding of the macrocyclic structure, starting with studies of smaller pyrrolic subunits. We have recorded the (1+1) and (2+1) resonance-enhanced multiphoton ionization (REMPI) spectra of pyrrole and 2,5-dimethylpyrrole between 25 600 cm{sup -1} (390more » nm) and 48 500 cm{sup -1} (206 nm). We did not observe a (1+1) REMPI signal through the optically bright {sup 1}B{sub 2} ({pi}{pi}*) and {sup 1}A{sub 1} ({pi}{pi}*) states in pyrrole due to ultrafast deactivation via conical intersections with the dissociative {sup 1}A{sub 2} ({pi}{sigma}*) and {sup 1}B{sub 1} ({pi}{sigma}{sup *}) states. However, we did observe (2+1) REMPI through Rydberg states with a dominant feature at 27 432 cm{sup -1} (two-photon energy, 54 864 cm{sup -1}) assigned to a 3d(leftarrow){pi} transition. In contrast, 2,5-dimethylpyrrole has a broad and structured (1+1) REMPI spectrum between 36 000 and 42 500 cm{sup -1} as a result of vibronic transitions to the {sup 1}B{sub 2} ({pi}{pi}*) state, and it does not show the 3d(leftarrow){pi} Rydberg transition via (2+1) REMPI. We have complemented the experimental studies by a theoretical treatment of the excited states of both molecules using time-dependent density functional theory (TD-DFT) and accounted for the contrasting features in the spectra. TD-DFT modeled the photochemical activity of both the optically dark {sup 1}{pi}{sigma}* states (dissociative) and optically bright {sup 1}{pi}{pi}* states well, predicting the barrierless deactivation of the {sup 1}B{sub 2} ({pi}{pi}*) state of pyrrole and the bound minimum of the {sup 1}B{sub 2} ({pi}{pi}*) state in 2,5-dimethylpyrrole. However, the quantitative agreement between vibronic transition energies and the excited-state frequencies calculated by TD-DFT was hampered by inaccurate modeling of Rydberg orbital mixing with the valence states, caused by the lack of an asymptotic correction to the exchange-correlation functionals used.« less

Vibrational Spectroscopy on Photoexcited Dye-Sensitized Films via Pump-Degenerate Four-Wave Mixing.

PubMed

Abraham, Baxter; Fan, Hao; Galoppini, Elena; Gundlach, Lars

2018-03-01

Molecular sensitization of semiconductor films is an important technology for energy and environmental applications including solar energy conversion, photocatalytic hydrogen production, and water purification. Dye-sensitized films are also scientifically complex and interesting systems with a long history of research. In most applications, photoinduced heterogeneous electron transfer (HET) at the molecule/semiconductor interface is of critical importance, and while great progress has been made in understanding HET, many open questions remain. Of particular interest is the role of combined electronic and vibrational effects and coherence of the dye during HET. The ultrafast nature of the process, the rapid intramolecular vibrational energy redistribution, and vibrational cooling present complications in the study of vibronic coupling in HET. We present the application of a time domain vibrational spectroscopy-pump-degenerate four-wave mixing (pump-DFWM)-to dye-sensitized solid-state semiconductor films. Pump-DFWM can measure Raman-active vibrational modes that are triggered by excitation of the sample with an actinic pump pulse. Modifications to the instrument for solid-state samples and its application to an anatase TiO 2 film sensitized by a Zn-porphyrin dye are discussed. We show an effective combination of experimental techniques to overcome typical challenges in measuring solid-state samples with laser spectroscopy and observe molecular vibrations following HET in a picosecond time window. The cation spectrum of the dye shows modes that can be assigned to the linker group and a mode that is localized on the Zn-phorphyrin chromophore and that is connected to photoexcitation.

Unraveling the nature of coherent beatings in chlorosomes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dostál, Jakub; Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague; Mančal, Tomáš

2014-03-21

Coherent two-dimensional (2D) spectroscopy at 80 K was used to study chlorosomes isolated from green sulfur bacterium Chlorobaculum tepidum. Two distinct processes in the evolution of the 2D spectrum are observed. The first being exciton diffusion, seen in the change of the spectral shape occurring on a 100-fs timescale, and the second being vibrational coherences, realized through coherent beatings with frequencies of 91 and 145 cm{sup −1} that are dephased during the first 1.2 ps. The distribution of the oscillation amplitude in the 2D spectra is independent of the evolution of the 2D spectral shape. This implies that the diffusionmore » energy transfer process does not transfer coherences within the chlorosome. Remarkably, the oscillatory pattern observed in the negative regions of the 2D spectrum (dominated by the excited state absorption) is a mirror image of the oscillations found in the positive part (originating from the stimulated emission and ground state bleach). This observation is surprising since it is expected that coherences in the electronic ground and excited states are generated with the same probability and the latter dephase faster in the presence of fast diffusion. Moreover, the relative amplitude of coherent beatings is rather high compared to non-oscillatory signal despite the reported low values of the Huang-Rhys factors. The origin of these effects is discussed in terms of the vibronic and Herzberg-Teller couplings.« less

Sub-Doppler rotationally resolved spectroscopy of lower vibronic bands of benzene with Zeeman effects

NASA Astrophysics Data System (ADS)

Doi, Atsushi; Kasahara, Shunji; Katô, Hajime; Baba, Masaaki

2004-04-01

Sub-Doppler high-resolution excitation spectra and the Zeeman effects of the 601, 101601, and 102601 bands of the S1 1B2u←S0 1A1g transition of benzene were measured by crossing laser beam perpendicular to a collimated molecular beam. 1593 rotational lines of the 101601 band and 928 lines of the 102601 band were assigned, and the molecular constants of the excited states were determined. Energy shifts were observed for the S1 1B2u(v1=1,v6=1,J,Kl=-11) levels, and those were identified as originating from a perpendicular Coriolis interaction. Many energy shifts were observed for the S1 1B2u(v1=2,v6=1,J,Kl) levels. The Zeeman splitting of a given J level was observed to increase with K and reach the maximum at K=J, which demonstrates that the magnetic moment lies perpendicular to the molecular plane. The Zeeman splittings of the K=J levels were observed to increase linearly with J. From the analysis, the magnetic moment is shown to be originating mostly from mixing of the S1 1B2u and S2 1B1u states by the J-L coupling (electronic Coriolis interaction). The number of perturbations was observed to increase as the excess energy increases, and all the perturbing levels were found to be a singlet state from the Zeeman spectra.

Conformation-Specific Infrared and Ultraviolet Spectroscopy of α-METHYLBENZYL Radical: Probing the State-Dependent Effects of Methyl Rocking against a Radical Site

NASA Astrophysics Data System (ADS)

Kidwell, Nathanael M.; Mehta, Deepali N.; Zwier, Timothy S.; Reilly, Neil J.; Kokkin, Damian L.; McCarthy, Michael C.

2012-06-01

Combustion processes involve a myriad of complex reaction pathways which connect smaller precursors to larger polyaromatic hydrocarbons, many of which are still unknown. In particular, benzyl-type radicals play an important role in combustible fuels due to their intrinsic resonance stabilization and consequent increase in relative concentration. Here, we present a study of the vibronic spectroscopy of α-Methylbenzyl radical (α-MeBz), in which the orientation of the methyl group adjacent to the radical site responds to the electronic interaction extending from the conjugated π-system. Probing the isolated radical, produced in an electrical discharge under jet-cooled conditions, the two-color resonant two-photon ionization, fluorescence excitation, and dispersed fluorescence spectra were obtained in order to determine the ground and excited state barriers to internal rotation and the angular change associated with electronic excitation. Resonant ion-dip infrared spectroscopy (RIDIRS) has also been implemented to elucidate the infrared signatures in the alkyl and aromatic CH stretch regions in order to probe in a complementary way the state-dependent conformational preferences of α-MeBz. We will show that the D0- and D1-RIDIR spectra report sensitively on the strong coupling between the CH stretch vibrations and the C_α-C_β torsional geometry. Furthermore, photoionization efficiency scans were carried out to reveal the adiabatic ionization threshold of α-MeBz and the quantized levels present in the radical cation state.

Rydberg states of chloroform studied by VUV photoabsorption spectroscopy

NASA Astrophysics Data System (ADS)

Singh, Param Jeet; Shastri, Aparna; D'Souza, R.; Jagatap, B. N.

2013-11-01

The VUV photoabsorption spectra of CHCl3 and CDCl3 in the energy region 6.2-11.8 eV (50,000-95,000 cm-1) have been investigated using synchrotron radiation from the Indus-1 source. Rydberg series converging to the first four ionization limits at 11.48, 11.91, 12.01 and 12.85 eV corresponding to excitation from the 1a2, 4a1, 4e, 3e, orbitals of CHCl3 respectively are identified and analyzed. Quantum defect values are observed to be consistent with excitation from the chlorine lone pair orbitals. Vibrational progressions observed in the region of 72,500-76,500 cm-1 have been reassigned to ν3 and combination modes of ν3+ν6 belonging to the 1a2→4p transition in contrast to earlier studies where they were assigned to a ν3 progression superimposed on the 3e→4p Rydberg transition. The assignments are further confirmed based on isotopic substitution studies on CDCl3 whose VUV photoabsorption spectrum is reported here for the first time. The frequencies of the ν3 and ν6 modes in the 4p Rydberg state of CHCl3 (CDCl3) are proposed to be ~454 (409) cm-1 and~130 (129) cm-1 respectively based on the vibronic analysis. DFT calculations of neutral and ionic ground state vibrational frequencies support the vibronic analysis. Experimental spectrum is found to be in good agreement with that predicted by TDDFT calculations. This work presents a consolidated analysis of the VUV photoabsorption spectrum of chloroform.

Dynamical Localization in Molecular Systems.

NASA Astrophysics Data System (ADS)

Wang, Xidi

In the first four chapters of this thesis we concentrate on the Davydov model which describes the vibrational energy quanta of Amide I bonds (C=O bonds on the alpha -helix) coupled to the acoustic phonon modes of the alpha-helix backbone in the form of a Frohlich Hamiltonian. Following a brief introduction in chapter one, in chapter two we formulate the dynamics of vibrational quanta at finite temperature by using coherent state products. The fluctuation-dissipation relation is derived. At zero temperature, in the continuum limit, we recover the original results of Davydov. We also achieve good agreement with numerical simulations. In chapter three, the net contraction of the lattice is calculated exactly at any temperature, and its relation to the so -call "topological stability" of the Davydov soliton is discussed. In the second section of the chapter three we calculate the overtone spectra of crystalline acetanilide (according to some opinions ACN provides experimental evidence for the existence of Davydov solitons). Good agreement with experimental data has been obtained. In chapter four we study the self-trapped vibrational excitations by the Quantum Monte Carlo technique. For a single excitation, the temperature dependence of different physical observables is calculated. The quasi-particle which resembles the Davydov soliton has been found to be fairly narrow using the most commonly used data for the alpha -helix; at temperatures above a few Kelvin, the quasi-particle reaches its smallest limit (extends over three sites), which implies diffusive motion of the small polaron-like quasi-particle at high temperatures. For the multi-excitation case, bound pairs and clusters of excitations are found at low temperatures; they gradually dissociate when the temperature of the system is increased as calculated from the density-density correlation function. In the last chapter of this thesis, we study a more general model of dynamical local modes in molecular systems. In particular, we study in detail the quadratic Takeno model, where the number of vibrational excitations is no longer conserved. We study the general dynamics of the system by probing the nonlinear dispersion relation with special local mode trial solutions. Our results show that, in general, the total energy favors energy localization, i.e. as time evolves, the excitations evolve into local modes, and the amplitudes of the local modes grow in time (contrary to the linear phonon picture). There is a maximum energy lowering of the excitations before the phenomenon of "bond breaking" occurs. This maximum energy lowering is about 5 percent of the bare vibron energy for the quadratic Takeno model. Our results are confirmed by numerical simulations.

Theory of optical transitions in conjugated polymers. I. Ideal systems.

PubMed

Barford, William; Marcus, Max

2014-10-28

We describe a theory of linear optical transitions in conjugated polymers. The theory is based on three assumptions. The first is that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ℏω ≪ J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. Using these assumptions we derive an expression for an effective Huang-Rhys parameter for a chain (or chromophore) of N monomers, given by S(N) = S(1)/IPR, where S(1) is the Huang-Rhys parameter for an isolated monomer. IPR is the inverse participation ratio, defined by IPR = (∑(n)|Ψ(n)|(4))(-1), where Ψ(n) is the exciton center-of-mass wavefunction. Since the IPR is proportional to the spread of the exciton center-of-mass wavefunction, this is a key result, as it shows that S(N) decreases with chain length. As in molecules, in a polymer S(N) has two interpretations. First, ℏωS(N) is the relaxation energy of an excited state caused by its coupling to the normal modes. Second, S(N) appears in the definition of an effective Franck-Condon factor, F(0v)(N) = S(N)(v)exp ( - S(N))/v! for the vth vibronic manifold. We show that the 0 - 0 and 0 - 1 optical intensities are proportional to F00(N) and F01(N), respectively, and thus the ratio of the 0 - 1 to 0 - 0 absorption and emission intensities are proportional to S(N). These analytical results are checked by extensive DMRG calculations and found to be generally valid, particularly for emission. However, for large chain lengths higher-lying quasimomentum exciton states become degenerate with the lowest vibrational excitation of the lowest exciton state. When this happens there is mixing of the electronic and nuclear states and a partial breakdown of the Born-Oppenheimer approximation, meaning that the ratio of the 0 - 0 to 0 - 1 absorption intensities no longer increases as fast as the IPR. When ℏω/J = 0.1, a value applicable to phenyl-based polymers, the critical value of N is ~20 monomers.

Theory of optical transitions in conjugated polymers. I. Ideal systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barford, William, E-mail: william.barford@chem.ox.ac.uk; Marcus, Max; Magdalen College, University of Oxford, Oxford OX1 4AU

We describe a theory of linear optical transitions in conjugated polymers. The theory is based on three assumptions. The first is that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ℏω ≪ J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. Using these assumptions we derive anmore » expression for an effective Huang-Rhys parameter for a chain (or chromophore) of N monomers, given by S(N) = S(1)/IPR, where S(1) is the Huang-Rhys parameter for an isolated monomer. IPR is the inverse participation ratio, defined by IPR = (∑{sub n}|Ψ{sub n}|{sup 4}){sup −1}, where Ψ{sub n} is the exciton center-of-mass wavefunction. Since the IPR is proportional to the spread of the exciton center-of-mass wavefunction, this is a key result, as it shows that S(N) decreases with chain length. As in molecules, in a polymer S(N) has two interpretations. First, ℏωS(N) is the relaxation energy of an excited state caused by its coupling to the normal modes. Second, S(N) appears in the definition of an effective Franck-Condon factor, F{sub 0v}(N) = S(N){sup v}exp ( − S(N))/v! for the vth vibronic manifold. We show that the 0 − 0 and 0 − 1 optical intensities are proportional to F{sub 00}(N) and F{sub 01}(N), respectively, and thus the ratio of the 0 − 1 to 0 − 0 absorption and emission intensities are proportional to S(N). These analytical results are checked by extensive DMRG calculations and found to be generally valid, particularly for emission. However, for large chain lengths higher-lying quasimomentum exciton states become degenerate with the lowest vibrational excitation of the lowest exciton state. When this happens there is mixing of the electronic and nuclear states and a partial breakdown of the Born-Oppenheimer approximation, meaning that the ratio of the 0 − 0 to 0 − 1 absorption intensities no longer increases as fast as the IPR. When ℏω/J = 0.1, a value applicable to phenyl-based polymers, the critical value of N is ∼20 monomers.« less

Fourier transform spectroscopy of the nu3 band of the N3 radical

NASA Technical Reports Server (NTRS)

Brazier, C. R.; Bernath, P. F.; Burkholder, James B.; Howard, Carleton J.

1988-01-01

The nu3 transitions of N3 radicals produced by HN3-Cl reactions in a multipass cell (effective path length 100 m) are investigated experimentally using a Fourier-transform spectrometer with maximum resolution 0.004/cm. A total of 176 rotation-vibration lines are listed in a table and used, in combination with published data on 240 optical lines (Douglas and Jones, 1965), to determine the nu3 molecular constants. The lower-than-expected value of the nu3 fundamental frequency (1644.6784/cm) is attributed to the vibronic interaction discussed by Kawaguchi et al. (1981).

Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. I - The naphthalene cation (C10H8/+/)

NASA Technical Reports Server (NTRS)

Salama, F.; Allamandola, L. J.

1991-01-01

The ultraviolet, visible, and near-infrared absorption spectra of naphthalene (C10H8) and its radical ion (C10H8/+/), formed by vacuum ultraviolet irradiation, were measured in argon and neon matrices at 4.2 K. The associated vibronic band systems and their spectroscopic assignments are discussed together with the physical and chemical conditions governing ion production in the solid phase. The absorption coefficients were calculated for the ion and found lower than previous values, presumably due to the low polarizability of the neon matrix.

Characterization of Boron Atom Aggregation

DTIC Science & Technology

2005-06-26

if it does not display a currently valid OMB control number. 1. REPORT DATE 28 JUN 2005 2. REPORT TYPE N /A 3. DATES COVERED - 4. TITLE AND...nm! n ~cm21! Dn ~cm21! 466.9 21 412 0 448.4 22 295 883 445.5 22 440 1028 440.2 22 711 1299 436.2 22 919 1507 431.9 23 147 1735 428.4 23 336 1924 427.1...absorption spectrum of B3 , vibronic symmetry G and calculated intensities. l~nm! n ~cm21! Dn~cm21! IntensityExperimenta Theory G 0 E8 1.00 230 A18 735.8 13

Spatial Quantum Beats in Vibrational Resonant Inelastic Soft X-Ray Scattering at Dissociating States in Oxygen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pietzsch, A.; Kennedy, B.; Sun, Y.-P.

2011-04-15

Resonant inelastic soft x-ray scattering (RIXS) spectra excited at the 1{sigma}{sub g}{yields}3{sigma}{sub u} resonance in gas-phase O{sub 2} show excitations due to the nuclear degrees of freedom with up to 35 well-resolved discrete vibronic states and a continuum due to the kinetic energy distribution of the separated atoms. The RIXS profile demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the atoms separate. Thomson scattering strongly affects both the spectral profile and the scattering anisotropy.

Comment on 'Ground state of octahedral platinum hexafluoride'

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gabuda, S. P.; Kozlova, S. G.

2009-05-15

It is shown that the principal results of a recent work by Alvarez-Thon et al. [Phys. Rev. A 77, 034502 (2008)] are in conflict with earlier work of the present authors [JETP Lett. 73, 35 (2001)] and also with a well known result concerning magnetic properties, NMR, and Jahn-Teller effect in the systems possessing even number of d electrons. This can be attributed to the fact that Alvarez-Thon et al. did not account for the influence of {sup 19}F and {sup 195}Pt nuclear magnetic moments and vibronic interactions on the wave function of PtF{sub 6} molecules.

2C-R4WM Spectroscopy of Jet Cooled NO_3

NASA Astrophysics Data System (ADS)

Fukushima, Masaru; Ishiwata, Takashi; Hirota, Eizi

2016-06-01

We have generated NO_3 from pyrolysis of N_2O_5 following supersonic free jet expansion, and carried out two color resonant four wave mixing ( 2C-R4WM ) spectroscopy of the tilde{B} ^2E' - tilde{X} ^2A_2' electronic transition. One laser was fixed to pump NO_3 to a ro-vibronic level of the tilde{B} state, and the other laser ( probe ) was scanned across two levels of the tilde{X} ^2A_2' state lying at 1051 and 1492 cm-1, the ν_1 (a_1') and ν_3 (e') fundamentals, respectively. The 2C-R4WM spectra have unexpected back-ground signal of NO_3 ( stray signal due to experimental set-up is also detected ) similar to laser induced fluorescence ( LIF ) excitation spectrum of the 0-0 band, although the back-ground signal was not expected in considering the 2C-R4WM scheme. Despite the back-ground interference, we have observed two peaks at 1051.61 and 1055.29 cm-1 in the ν_1 region of the spectrum, and the frequencies agree with the two bands, 1051.2 and 1055.3 cm-1, of our relatively higher resolution dispersed fluorescence spectrum, the former of which has been assigned to the ν_1 fundamental. Band width of both peaks, ˜ 0.2 cm-1, is broader than twice the experimental spectral-resolution, 0.04 cm-1 ( because this experiment is double resonance spectroscopy ), and the 1051.61 cm-1 peak is attributed to a Q branch band head ( a line-like Q branch ) of the ν_1 fundamental. The other branches are suspected to be hidden in noise of the back-ground signal. The 1055.29 cm-1 peak is also attributed to a Q band head. The tilde{B} ^2E'1/2 ( J' = 3/2, K' = 1 ) - tilde{X} ^2A_2' ( N'' = 1, K'' = 0 ) ro-vibronic transition was used as the pump transition. The dump ( probe ) transition to both a_1' and e' vibronic levels are then allowed as perpendicular transition. Accordingly, it cannot be determined from present results whether the 1055.29 cm-1 band is attributed to a_1' or e' (ν_3), unfortunately. The 2C-R4WM spectrum of the 1492 cm-1 band region shows one Q head at 1499.79 cm-1, which is consistent with our dispersed fluorescence spectrum. By considering with the ν_3 + ν_4 - ν_4 hot band, the present results suggest that both 1055.29 and 1499.79 cm-1 levels are a_1' level. K. Kawaguchi et al., J. Phys. Chem. A 117, 13732 (2013) and E. Hirota, J. Mol. Spectrosco. 310, 99 (2015).

The importance of nuclear quantum effects in spectral line broadening of optical spectra and electrostatic properties in aromatic chromophores.

PubMed

Law, Y K; Hassanali, A A

2018-03-14

In this work, we examine the importance of nuclear quantum effects on capturing the line broadening and vibronic structure of optical spectra. We determine the absorption spectra of three aromatic molecules indole, pyridine, and benzene using time dependent density functional theory with several molecular dynamics sampling protocols: force-field based empirical potentials, ab initio simulations, and finally path-integrals for the inclusion of nuclear quantum effects. We show that the absorption spectrum for all these chromophores are similarly broadened in the presence of nuclear quantum effects regardless of the presence of hydrogen bond donor or acceptor groups. We also show that simulations incorporating nuclear quantum effects are able to reproduce the heterogeneous broadening of the absorption spectra even with empirical force fields. The spectral broadening associated with nuclear quantum effects can be accounted for by the broadened distribution of chromophore size as revealed by a particle in the box model. We also highlight the role that nuclear quantum effects have on the underlying electronic structure of aromatic molecules as probed by various electrostatic properties.

The importance of nuclear quantum effects in spectral line broadening of optical spectra and electrostatic properties in aromatic chromophores

NASA Astrophysics Data System (ADS)

Law, Y. K.; Hassanali, A. A.

2018-03-01

In this work, we examine the importance of nuclear quantum effects on capturing the line broadening and vibronic structure of optical spectra. We determine the absorption spectra of three aromatic molecules indole, pyridine, and benzene using time dependent density functional theory with several molecular dynamics sampling protocols: force-field based empirical potentials, ab initio simulations, and finally path-integrals for the inclusion of nuclear quantum effects. We show that the absorption spectrum for all these chromophores are similarly broadened in the presence of nuclear quantum effects regardless of the presence of hydrogen bond donor or acceptor groups. We also show that simulations incorporating nuclear quantum effects are able to reproduce the heterogeneous broadening of the absorption spectra even with empirical force fields. The spectral broadening associated with nuclear quantum effects can be accounted for by the broadened distribution of chromophore size as revealed by a particle in the box model. We also highlight the role that nuclear quantum effects have on the underlying electronic structure of aromatic molecules as probed by various electrostatic properties.

Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

DOE PAGES

Fujihashi, Yuta; Fleming, Graham R.; Ishizaki, Akihito

2015-03-11

Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. Here in this work, we address a dimer which produces little beating of electronic origin in the absencemore » of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.« less

Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujihashi, Yuta; Ishizaki, Akihito, E-mail: ishizaki@ims.ac.jp; Fleming, Graham R.

2015-06-07

Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence ofmore » vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.« less

Orientation hydrogen-bonding effect on vibronic spectra of isoquinoline in water solvent: Franck-Condon simulation and interpretation

NASA Astrophysics Data System (ADS)

Liu, Yu-Hui; Wang, Shi-Ming; Wang, Chen-Wen; Zhu, Chaoyuan; Han, Ke-Li; Lin, Sheng-Hsien

2016-10-01

The excited-state orientation hydrogen-bonding dynamics, and vibronic spectra of isoquinoline (IQ) and its cationic form IQc in water have been investigated at the time-dependent density functional theory quantum chemistry level plus Franck-Condon simulation and interpretation. The excited-state orientation hydrogen bond strengthening has been found in IQ:H2O complex due to the charge redistribution upon excitation; this is interpreted by simulated 1:1 mixed absorption spectra of free IQ and IQ:H2O complex having best agreement with experimental results. Conversely, the orientation hydrogen bond in IQc:H2O complex would be strongly weakening in the S1 state and this is interpreted by simulated absorption spectra of free IQc having best agreement with experimental results. By performing Franck-Condon simulation, it reveals that several important vibrational normal modes with frequencies about 1250 cm-1 involving the wagging motion of the hydrogen atoms are very sensitive to the formation of the orientation hydrogen bond for the IQ/IQc:H2O complex and this is confirmed by damped Franck-Condon simulation with free IQ/IQc in water. However, the emission spectra of the IQ and IQc in water have been found differently. Upon the excitation, the simulated fluorescence of IQ in water is dominated by the IQ:H2O complex; thus hydrogen bond between IQ and H2O is much easier to form in the S1 state. While the weakened hydrogen bond in IQc:H2O complex is probably cleaved upon the laser pulse because the simulated emission spectrum of the free IQc is in better agreement with the experimental results.

The role of solitons in charge and energy transfer in 1D molecular chains

NASA Astrophysics Data System (ADS)

Ivić , Zoran

1998-03-01

The idea that polarons and solitons could play the crucial role in the transport processes in biological structures, has been critically reexamined on the basis of the general theory of self-trapping phenomena. The criteria which enable one to determine conditions for the existence and stability of polarons and solitons and to determine their character, in dependence of the values of the basic physical parameters of the system, were formulated. Validity of the so-called Davydov's soliton model was discussed on the basis of these criteria. It was found that the original Davydov's proposal, based upon the idea of the soliton creation due to the single excitation (particle, vibron, etc.) self-trapping, cannot explain the intramolecular energy transfer in α-helix and acetanilide. However, Davydov theory is flexible enough to describe the single electron transfer in some systems (α-helix and acetanilide for example). In the many-particle systems, dressing effect, due to the quantum nature of phonons, may cause the creation of the bound states of the several excitons in the molecular chain. The possibility of creation of the soliton states of this type is discussed for the simple Fröhlich's one-dimensional model. The regions of the system parameter space where different mechanisms dominate the behaviour of such entities are characterized.

Stimulated emission pumping spectroscopy of the [X](1)A' state of CHF.

PubMed

Mukarakate, Calvin; Tao, Chong; Jordan, Christopher D; Polik, William F; Reid, Scott A

2008-01-24

We have recorded stimulated emission pumping (SEP) spectra of the A1A' ' 1A' system of CHF, which reveal rich detail concerning the rovibronic structure of the 1A' state up to approximately 7000 cm-1 above the vibrationless level. Using several intermediate A1A' ' state levels, we obtained rotationally resolved spectra for 16 of the 33 levels observed in our previous single vibronic level (SVL) emission study (Fan et al., J. Chem. Phys. 2005, 123, 014314), in addition to one new level. An anharmonic effective Hamiltonian model poorly reproduces the term energies even with the improved set of data because of the extensive interactions among levels in a given polyad (p) having combinations of nu1, nu2, nu3, which satisfy the relationship p = 2nu1 + nu2 + nu3. However, the precise A rotational constants determined from the SEP data were invaluable in clarifying the assignments for these strongly perturbed levels, and the data are well reproduced using a multiresonance effective Hamiltonian model. The derived vibrational parameters are in good agreement with high level ab initio calculations. The experimental frequencies were combined with those of CDF to derive a harmonic force field and average (rz,r(z)e) structures for the ground state.

Tensor network methods for the simulation of open quantum dynamics in multichromophore systems: Application to singlet fission in novel pentacene dimers

NASA Astrophysics Data System (ADS)

Chin, Alex

Singlet fission (SF) is an ultrafast process in which a singlet exciton spontaneously converts into a pair of entangled triplet excitons on neighbouring organic molecules. As a mechanism of multiple exciton generation, it has been suggested as a way to increase the efficiency of organic photovoltaic devices, and its underlying photophysics across a wide range of molecules and materials has attracted significant theoretical attention. Recently, a number of studies using ultrafast nonlinear optics have underscored the importance of intramolecular vibrational dynamics in efficient SF systems, prompting a need for methods capable of simulating open quantum dynamics in the presence of highly structured and strongly coupled environments. Here, a combination of ab initio electronic structure techniques and a new tensor-network methodology for simulating open vibronic dynamics is presented and applied to a recently synthesised dimer of pentacene (DP-Mes). We show that ultrafast (300 fs) SF in this system is driven entirely by symmetry breaking vibrations, and our many-body approach enables the real-time identification and tracking of the ''functional' vibrational dynamics and the role of the ''bath''-like parts of the environment. Deeper analysis of the emerging wave functions points to interesting links between the time at which parts of the environment become relevant to the SF process and the optimal topology of the tensor networks, highlighting the additional insight provided by moving the problem into the natural language of correlated quantum states and how this could lead to simulations of much larger multichromophore systems Supported by The Winton Programme for the Physics of Sustainability.

Reactive carbon-chain molecules: synthesis of 1-diazo-2,4-pentadiyne and spectroscopic characterization of triplet pentadiynylidene (H-C[triple bond]C-:C-C[triple bond]C-H).

PubMed

Bowling, Nathan P; Halter, Robert J; Hodges, Jonathan A; Seburg, Randal A; Thomas, Phillip S; Simmons, Christopher S; Stanton, John F; McMahon, Robert J

2006-03-15

1-Diazo-2,4-pentadiyne (6a), along with both monodeuterio isotopomers 6b and 6c, has been synthesized via a route that proceeds through diacetylene, 2,4-pentadiynal, and 2,4-pentadiynal tosylhydrazone. Photolysis of diazo compounds 6a-c (lambda > 444 nm; Ar or N2, 10 K) generates triplet carbenes HC5H (1) and HC5D (1-d), which have been characterized by IR, EPR, and UV/vis spectroscopy. Although many resonance structures contribute to the resonance hybrid for this highly unsaturated carbon-chain molecule, experiment and theory reveal that the structure is best depicted in terms of the dominant resonance contributor of penta-1,4-diyn-3-ylidene (diethynylcarbene, H-C[triple bond]C-:C-C[triple bond]C-H). Theory predicts an axially symmetric (D(infinity h)) structure and a triplet electronic ground state for 1 (CCSD(T)/ANO). Experimental IR frequencies and isotope shifts are in good agreement with computed values. The triplet EPR spectrum of 1 (absolute value(D/hc) = 0.6157 cm(-1), absolute value(E/hc) = 0.0006 cm(-1)) is consistent with an axially symmetric structure, and the Curie law behavior confirms that the triplet state is the ground state. The electronic absorption spectrum of 1 exhibits a weak transition near 400 nm with extensive vibronic coupling. Chemical trapping of triplet HC5H (1) in an O2-doped matrix affords the carbonyl oxide 16 derived exclusively from attack at the central carbon.

Vibronic Transitions in the X-Sr Series (X=Li, Na, K, Rb): on the Accuracy of Nuclear Wavefunctions Derived from Quantum Chemistry

NASA Astrophysics Data System (ADS)

Meyer, Ralf; Pototschnig, Johann V.; Hauser, Andreas W.; Ernst, Wolfgang E.

2016-06-01

Research on ultracold molecules has seen a growing interest recently in the context of high-resolution spectroscopy and quantum computation. The preparation of molecules in low vibrational levels of the ground state is experimentally challenging, and typically achieved by population transfer using excited electronic states. On the theoretical side, highly accurate potential energy surfaces are needed for a correct description of processes such as the coherent de-excitation from the highest and therefore weakly bound vibrational levels in the electronic ground state via couplings to electronically excited states. Particularly problematic is the correct description of potential features at large intermolecular distances. Franck-Condon overlap integrals for nuclear wavefunctions in barely bound vibrational states are extremely sensitive to inaccuracies of the potential at long range. In this study, we compare the predictions of common, wavefunction-based ab initio techniques for a known de-excitation mechanism in alkali-alkaline earth dimers. It is the aim to analyze the predictive power of these methods for a preliminary evaluation of potential cooling mechanisms in heteronuclear open shell systems which offer the experimentalist an electric as well as a magnetic handle for manipulation. The series of X-Sr molecules, with X = Li, Na, K and Rb, has been chosen for a direct comparison. Quantum degenerate mixtures of Rb and Sr have already been produced, making this combination very promising for the production of ultracold molecules. B. Pasquiou, A. Bayerle, S. M. Tzanova, S. Stellmer, J. Szczepkowski, M. Parigger, R. Grimm, and F. Schreck, Phys. Rev. A, 2013, 88, 023601

Theory of exciton transfer and diffusion in conjugated polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barford, William, E-mail: william.barford@chem.ox.ac.uk; Tozer, Oliver Robert; University College, University of Oxford, Oxford OX1 4BH

We describe a theory of Förster-type exciton transfer between conjugated polymers. The theory is built on three assumptions. First, we assume that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, and described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ℏω < J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. The resulting expression for themore » exciton transfer rate has a familiar form, being a function of the exciton transfer integral and the effective Franck-Condon factors. The effective Franck-Condon factors are functions of the effective Huang-Rhys parameters, which are inversely proportional to the chromophore size. The Born-Oppenheimer expressions were checked against DMRG calculations, and are found to be within 10% of the exact value for a tiny fraction of the computational cost. This theory of exciton transfer is then applied to model exciton migration in conformationally disordered poly(p-phenylene vinylene). Key to this modeling is the assumption that the donor and acceptor chromophores are defined by local exciton ground states (LEGSs). Since LEGSs are readily determined by the exciton center-of-mass wavefunction, this theory provides a quantitative link between polymer conformation and exciton migration. Our Monte Carlo simulations indicate that the exciton diffusion length depends weakly on the conformation of the polymer, with the diffusion length increasing slightly as the chromophores became straighter and longer. This is largely a geometrical effect: longer and straighter chromophores extend over larger distances. The calculated diffusion lengths of ∼10 nm are in good agreement with experiment. The spectral properties of the migrating excitons are also investigated. The emission intensity ratio of the 0-0 and 0-1 vibronic peaks is related to the effective Huang-Rhys parameter of the emitting state, which in turn is related to the chromophore size. The intensity ratios calculated from the effective Huang-Rhys parameters are in agreement with experimental spectra, and the time-resolved trend for the intensity ratio to decrease with time was also reproduced as the excitation migrates to shorter, lower energy chromophores as a function of time. In addition, the energy of the exciton state shows a logarithmic decrease with time, in agreement with experimental observations.« less

Theory of exciton transfer and diffusion in conjugated polymers.

PubMed

Barford, William; Tozer, Oliver Robert

2014-10-28

We describe a theory of Förster-type exciton transfer between conjugated polymers. The theory is built on three assumptions. First, we assume that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, and described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ℏω < J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. The resulting expression for the exciton transfer rate has a familiar form, being a function of the exciton transfer integral and the effective Franck-Condon factors. The effective Franck-Condon factors are functions of the effective Huang-Rhys parameters, which are inversely proportional to the chromophore size. The Born-Oppenheimer expressions were checked against DMRG calculations, and are found to be within 10% of the exact value for a tiny fraction of the computational cost. This theory of exciton transfer is then applied to model exciton migration in conformationally disordered poly(p-phenylene vinylene). Key to this modeling is the assumption that the donor and acceptor chromophores are defined by local exciton ground states (LEGSs). Since LEGSs are readily determined by the exciton center-of-mass wavefunction, this theory provides a quantitative link between polymer conformation and exciton migration. Our Monte Carlo simulations indicate that the exciton diffusion length depends weakly on the conformation of the polymer, with the diffusion length increasing slightly as the chromophores became straighter and longer. This is largely a geometrical effect: longer and straighter chromophores extend over larger distances. The calculated diffusion lengths of ~10 nm are in good agreement with experiment. The spectral properties of the migrating excitons are also investigated. The emission intensity ratio of the 0-0 and 0-1 vibronic peaks is related to the effective Huang-Rhys parameter of the emitting state, which in turn is related to the chromophore size. The intensity ratios calculated from the effective Huang-Rhys parameters are in agreement with experimental spectra, and the time-resolved trend for the intensity ratio to decrease with time was also reproduced as the excitation migrates to shorter, lower energy chromophores as a function of time. In addition, the energy of the exciton state shows a logarithmic decrease with time, in agreement with experimental observations.

Excited-State Dynamics of the Thiopurine Prodrug 6-Thioguanine: Can N9-Glycosylation Affect Its Phototoxic Activity?

PubMed

Ashwood, Brennan; Jockusch, Steffen; Crespo-Hernández, Carlos E

2017-02-28

6-Thioguanine, an immunosuppressant and anticancer prodrug, has been shown to induce DNA damage and cell death following exposure to UVA radiation. Its metabolite, 6-thioguanosine, plays a major role in the prodrug's overall photoreactivity. However, 6-thioguanine itself has proven to be cytotoxic following UVA irradiation, warranting further investigation into its excited-state dynamics. In this contribution, the excited-state dynamics and photochemical properties of 6-thioguanine are studied in aqueous solution following UVA excitation at 345 nm in order to provide mechanistic insight regarding its photochemical reactivity and to scrutinize whether N9-glycosylation modulates its phototoxicity in solution. The experimental results are complemented with time-dependent density functional calculations that include solvent dielectric effects by means of a reaction-field solvation model. UVA excitation results in the initial population of the S₂(ππ*) state, which is followed by ultrafast internal conversion to the S₁(nπ*) state and then intersystem crossing to the triplet manifold within 560 ± 60 fs. A small fraction (ca. 25%) of the population that reaches the S₁(nπ*) state repopulates the ground state. The T₁(ππ*) state decays to the ground state in 1.4 ± 0.2 μs under N₂-purged conditions, using a 0.2 mM concentration of 6-thioguanine, or it can sensitize singlet oxygen in 0.21 ± 0.02 and 0.23 ± 0.02 yields in air- and O₂-saturated solution, respectively. This demonstrates the efficacy of 6-thioguanine to act as a Type II photosensitizer. N9-glycosylation increases the rate of intersystem crossing from the singlet to triplet manifold, as well as from the T₁(ππ*) state to the ground state, which lead to a ca. 40% decrease in the singlet oxygen yield under air-saturated conditions. Enhanced vibronic coupling between the singlet and triplet manifolds due to a higher density of vibrational states is proposed to be responsible for the observed increase in the rates of intersystem crossing in 6-thioguanine upon N9-glycosylation.

The pure rotational spectrum of CaNC

NASA Astrophysics Data System (ADS)

Scurlock, C. T.; Steimle, T. C.; Suenram, R. D.; Lovas, F. J.

1994-03-01

The pure rotational spectrum of calcium isocyanide, CaNC, in its (0,0,0) X 2Σ+ vibronic state was measured using a combination of Fourier transform microwave (FTMW) and pump/probe microwave-optical double resonance (PPMODR) spectroscopy. Gaseous CaNC was generated using a laser ablation/supersonic expansion source. The determined spectroscopic parameters are (in MHz), B=4048.754 332 (29); γ=18.055 06 (23); bF=12.481 49 (93); c=2.0735 (14); and eQq0=-2.6974 (11). The hyperfine parameters are qualitatively interpreted in terms of a plausible molecular orbital descriptions and a comparison with the alkaline earth monohalides and the alkali monocyanides is given.

A study of complex scaling transformation using the Wigner representation of wavefunctions.

PubMed

Kaprálová-Ždánská, Petra Ruth

2011-05-28

The complex scaling operator exp(-θ ̂x̂p/ℏ), being a foundation of the complex scaling method for resonances, is studied in the Wigner phase-space representation. It is shown that the complex scaling operator behaves similarly to the squeezing operator, rotating and amplifying Wigner quasi-probability distributions of the respective wavefunctions. It is disclosed that the distorting effect of the complex scaling transformation is correlated with increased numerical errors of computed resonance energies and widths. The behavior of the numerical error is demonstrated for a computation of CO(2+) vibronic resonances. © 2011 American Institute of Physics

QED Effects in Molecules: Test on Rotational Quantum States of H2

NASA Astrophysics Data System (ADS)

Salumbides, E. J.; Dickenson, G. D.; Ivanov, T. I.; Ubachs, W.

2011-07-01

Quantum electrodynamic effects have been systematically tested in the progression of rotational quantum states in the XΣg+1, v=0 vibronic ground state of molecular hydrogen. High-precision Doppler-free spectroscopy of the EFΣg+1-XΣg+1 (0,0) band was performed with 0.005cm-1 accuracy on rotationally hot H2 (with rotational quantum states J up to 16). QED and relativistic contributions to rotational level energies as high as 0.13cm-1 are extracted, and are in perfect agreement with recent calculations of QED and high-order relativistic effects for the H2 ground state.

Conformationally resolved spectroscopy of jet-cooled methacetin

NASA Astrophysics Data System (ADS)

Moon, Cheol Joo; Ahn, Ahreum; Min, Ahreum; Seong, Yeon Guk; Kim, Ju Hyun; Choi, Myong Yong

2017-11-01

The excitation spectra of jet-cooled methacetin (MA) have been measured using a combination of mass-selected resonant two-photon ionization and ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy in the gas phase. Four different UV-UV HB spectra originating from two conformers of MA (syn- and anti-MA) with their fundamental and hot transitions have been obtained. IR-dip spectroscopy has conclusively confirmed the coexistence of the two conformers with the aid of theoretical calculations. Vibronic band assignments in the low frequency region caused by internal methyl group rotation in the methyl-capped peptide group, which originate from the 1e rotational level, are presented.

High-Pressure Synchrotron Infrared Absorption and Raman Spectroscopy of ζ-N_2

NASA Astrophysics Data System (ADS)

Gregoryanz, E.; Goncharov, A. F.; Mao, H. K.; Hemley, R. J.

2000-03-01

Infrared mid-IR and Raman spectra of high-pressure, low-temperature phases of solid nitrogen have been measured to above 40 GPa. The transition to the lower-symmetry ordered phase ζ at 21 GPa, reported by Schiferl et al. [1]. has been confirmed. We observe three Raman-active and two IR components of the nu2 stretching mode (disk-like molecules) and only one Raman-active component of the nu1 mode (sphere-like molecules). All the vibron modes increase frequency with pressure. The structure of ζ-N2 phase is discussed. [1] Schiferl et al., J. Phys. Chem., 89, 2324 (1985).

The Production of Polycyclic Aromatic Hydrocarbon Anions in Inert Gas Matrices Doped with Alkali Metals. Electronic Absorption Spectra of the Pentacene Anion (C22H14(-))

NASA Technical Reports Server (NTRS)

Halasinski, Thomas M.; Hudgins, Douglas M.; Salama, Farid; Allamandola, Louis J.; Mead, Susan (Technical Monitor)

1999-01-01

The absorption spectra of pentacene (C22H14) and its radical cation (C22H14(+)) and anion (C22H14(-)) isolated in inert-gas matrices of Ne, Ar, and Kr are reported from the ultraviolet to the near-infrared. The associated vibronic band systems and their spectroscopic assignments are discussed together with the physical and chemical conditions governing ion (and counterion) production in the solid matrix. In particular, the formation of isolated pentacene anions is found to be optimized in matrices doped with alkali metal (Na and K).

Primary photoexcitations and the origin of the photocurrent in rubrene single crystals.

PubMed

Najafov, Hikmat; Biaggio, Ivan; Podzorov, Vitaly; Calhoun, Matthew F; Gershenson, Michael E

2006-02-10

By simultaneously measuring the excitation spectra of transient luminescence and transient photoconductivity after picosecond pulsed excitation in rubrene single crystals, we show that free excitons are photoexcited starting at photon energies above 2.0 eV. We observe a competition between photoexcitation of free excitons and photoexcitation into vibronic states that subsequently decays into free carriers, while molecular excitons are instead formed predominantly through the free exciton. At photon energies below 2.25 eV, free charge carriers are created only through a long-lived intermediate state with a lifetime of up to 0.1 ms and no free carriers appear during the exciton lifetime.

Low-lying singlet states of carotenoids having 8-13 conjugated double bonds as determined by electronic absorption spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Peng; Nakamura, Ryosuke; Kanematsu, Yasuo; Koyama, Yasushi; Nagae, Hiroyoshi; Nishio, Tomohiro; Hashimoto, Hideki; Zhang, Jian-Ping

2005-07-01

Electronic absorption spectra were recorded at room temperature in solutions of carotenoids having different numbers of conjugated double bonds, n = 8-13, including a spheroidene derivatives, neurosporene, spheroidene, lycopene, anhydrorhodovibrin and spirilloxanthin. The vibronic states of 1Bu+(v=0-4), 2Ag-(v=0-3), 3Ag- (0) and 1Bu- (0) were clearly identified. The arrangement of the four electronic states determined by electronic absorption spectroscopy was identical to that determined by measurement of resonance Raman excitation profiles [K. Furuichi et al., Chem. Phys. Lett. 356 (2002) 547] for carotenoids in crystals.

Free H₂ rotation vs Jahn-Teller constraints in the nonclassical trigonal (TPB)Co-H₂ complex.

PubMed

Gunderson, William A; Suess, Daniel L M; Fong, Henry; Wang, Xiaoping; Hoffmann, Christina M; Cutsail, George E; Peters, Jonas C; Hoffman, Brian M

2014-10-22

Proton exchange within the M-H2 moiety of (TPB)Co(H2) (Co-H2; TPB = B(o-C6H4P(i)Pr2)3) by 2-fold rotation about the M-H2 axis is probed through EPR/ENDOR studies and a neutron diffraction crystal structure. This complex is compared with previously studied (SiP(iPr)3)Fe(H2) (Fe-H2) (SiP(iPr)3 = [Si(o-C6H4P(i)Pr2)3]). The g-values for Co-H2 and Fe-H2 show that both have the Jahn-Teller (JT)-active (2)E ground state (idealized C3 symmetry) with doubly degenerate frontier orbitals, (e)(3) = [|mL ± 2>](3) = [x(2) - y(2), xy](3), but with stronger linear vibronic coupling for Co-H2. The observation of (1)H ENDOR signals from the Co-HD complex, (2)H signals from the Co-D2/HD complexes, but no (1)H signals from the Co-H2 complex establishes that H2 undergoes proton exchange at 2 K through rotation around the Co-H2 axis, which introduces a quantum-statistical (Pauli-principle) requirement that the overall nuclear wave function be antisymmetric to exchange of identical protons (I = 1/2; Fermions), symmetric for identical deuterons (I = 1; Bosons). Analysis of the 1-D rotor problem indicates that Co-H2 exhibits rotor-like behavior in solution because the underlying C3 molecular symmetry combined with H2 exchange creates a dominant 6-fold barrier to H2 rotation. Fe-H2 instead shows H2 localization at 2 K because a dominant 2-fold barrier is introduced by strong Fe(3d)→ H2(σ*) π-backbonding that becomes dependent on the H2 orientation through quadratic JT distortion. ENDOR sensitively probes bonding along the L2-M-E axis (E = Si for Fe-H2; E = B for Co-H2). Notably, the isotropic (1)H/(2)H hyperfine coupling to the diatomic of Co-H2 is nearly 4-fold smaller than for Fe-H2.

Energy and radiative properties of the (3 )1Π and (5 )+1Σ states of RbCs: Experiment and theory

NASA Astrophysics Data System (ADS)

Alps, K.; Kruzins, A.; Nikolayeva, O.; Tamanis, M.; Ferber, R.; Pazyuk, E. A.; Stolyarov, A. V.

2017-08-01

We combined high-resolution Fourier-transform spectroscopy and large-scale electronic structure calculation to study energy and radiative properties of the high-lying (3 )1Π and (5 )+1Σ states of the RbCs molecule. The laser-induced (5 )+1Σ,(4 )+1Σ,(3 )1Π→A (2 )+1Σ˜ b (1 )3Π fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer in the frequency range ν ∈[5500 ,10 000 ] cm-1 with the instrumental resolution of 0.03 cm-1. The rotational assignment of the observed LIF progressions, which exhibit irregular vibrational-rotational spacing due to strong spin-orbit interaction between A +1Σ and b 3Π states was based on the coincidences between observed and calculated energy differences. The required rovibronic term values of the strongly perturbed A ˜b complex have been calculated by a coupled-channels approach for both 85Rb133Cs and 87Rb133Cs isotopologs with accuracy of about 0.01 cm-1, as demonstrated in A. Kruzins et al. [J. Chem. Phys. 141, 184309 (2014), 10.1063/1.4901327]. The experimental energies of the upper (3 )1Π and (5 )+1Σ states were involved in a direct-potential-fit analysis performed in the framework of inverted perturbation approach. Quasirelativistic ab initio calculations of the spin-allowed (3 )1Π,(5 )+1Σ→ (1-4)+1Σ,(1-3)1Π transition dipole moments were performed. Radiative lifetimes and vibronic branching ratios of radiative transitions from the (3 )1Π and (5 )+1Σ states were evaluated. To elucidate the origin of the Λ -doubling effect in the (3 )1Π state, the angular coupling (3 )1Π -(1-5)+1Σ electronic matrix elements were calculated and applied for the relevant q -factors estimate. The intensity distributions simulated for the particular (5 )+1Σ ;(3 )1Π→A ˜b LIF progressions have been found to be remarkably close to their experimental counterparts.

Using the Model Coupling Toolkit to couple earth system models

USGS Publications Warehouse

Warner, J.C.; Perlin, N.; Skyllingstad, E.D.

2008-01-01

Continued advances in computational resources are providing the opportunity to operate more sophisticated numerical models. Additionally, there is an increasing demand for multidisciplinary studies that include interactions between different physical processes. Therefore there is a strong desire to develop coupled modeling systems that utilize existing models and allow efficient data exchange and model control. The basic system would entail model "1" running on "M" processors and model "2" running on "N" processors, with efficient exchange of model fields at predetermined synchronization intervals. Here we demonstrate two coupled systems: the coupling of the ocean circulation model Regional Ocean Modeling System (ROMS) to the surface wave model Simulating WAves Nearshore (SWAN), and the coupling of ROMS to the atmospheric model Coupled Ocean Atmosphere Prediction System (COAMPS). Both coupled systems use the Model Coupling Toolkit (MCT) as a mechanism for operation control and inter-model distributed memory transfer of model variables. In this paper we describe requirements and other options for model coupling, explain the MCT library, ROMS, SWAN and COAMPS models, methods for grid decomposition and sparse matrix interpolation, and provide an example from each coupled system. Methods presented in this paper are clearly applicable for coupling of other types of models. ?? 2008 Elsevier Ltd. All rights reserved.

The Challenges to Coupling Dynamic Geospatial Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldstein, N

2006-06-23

Many applications of modeling spatial dynamic systems focus on a single system and a single process, ignoring the geographic and systemic context of the processes being modeled. A solution to this problem is the coupled modeling of spatial dynamic systems. Coupled modeling is challenging for both technical reasons, as well as conceptual reasons. This paper explores the benefits and challenges to coupling or linking spatial dynamic models, from loose coupling, where information transfer between models is done by hand, to tight coupling, where two (or more) models are merged as one. To illustrate the challenges, a coupled model of Urbanizationmore » and Wildfire Risk is presented. This model, called Vesta, was applied to the Santa Barbara, California region (using real geospatial data), where Urbanization and Wildfires occur and recur, respectively. The preliminary results of the model coupling illustrate that coupled modeling can lead to insight into the consequences of processes acting on their own.« less

Analytical gradients for MP2, double hybrid functionals, and TD‐DFT with polarizable embedding described by fluctuating charges

PubMed Central

Carnimeo, Ivan; Cappelli, Chiara

2015-01-01

A polarizable quantum mechanics (QM)/ molecular mechanics (MM) approach recently developed for Hartree–Fock (HF) and Kohn–Sham (KS) methods has been extended to energies and analytical gradients for MP2, double hybrid functionals, and TD‐DFT models, thus allowing the computation of equilibrium structures for excited electronic states together with more accurate results for ground electronic states. After a detailed presentation of the theoretical background and of some implementation details, a number of test cases are analyzed to show that the polarizable embedding model based on fluctuating charges (FQ) is remarkably more accurate than the corresponding electronic embedding based on a fixed charge (FX) description. In particular, a set of electronegativities and hardnesses has been optimized for interactions between QM and FQ regions together with new repulsion–dispersion parameters. After validation of both the numerical implementation and of the new parameters, absorption electronic spectra have been computed for representative model systems including vibronic effects. The results show remarkable agreement with full QM computations and significant improvement with respect to the corresponding FX results. The last part of the article provides some hints about computation of solvatochromic effects on absorption spectra in aqueous solution as a function of the number of FQ water molecules and on the use of FX external shells to improve the convergence of the results. © 2015 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc. PMID:26399473

Depth-resolved incoherent and coherent wide-field high-content imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

So, Peter T.

2016-03-01

Recent advances in depth-resolved wide-field imaging technique has enabled many high throughput applications in biology and medicine. Depth resolved imaging of incoherent signals can be readily accomplished with structured light illumination or nonlinear temporal focusing. The integration of these high throughput systems with novel spectroscopic resolving elements further enable high-content information extraction. We will introduce a novel near common-path interferometer and demonstrate its uses in toxicology and cancer biology applications. The extension of incoherent depth-resolved wide-field imaging to coherent modality is non-trivial. Here, we will cover recent advances in wide-field 3D resolved mapping of refractive index, absorbance, and vibronic components in biological specimens.

Optical vortex generation from a diode-pumped alexandrite laser

NASA Astrophysics Data System (ADS)

Thomas, G. M.; Minassian, A.; Damzen, M. J.

2018-04-01

We present the demonstration of an optical vortex mode directly generated from a diode-pumped alexandrite slab laser, operating in the bounce geometry. This is the first demonstration of an optical vortex mode generated from an alexandrite laser or from any other vibronic laser. An output power of 2 W for a vortex mode with a ‘topological charge’ of 1 was achieved and the laser was made to oscillate with both left- and right-handed vorticity. The laser operated at two distinct wavelengths simultaneously, 755 and 759 nm, due to birefringent filtering in the alexandrite gain medium. The result offers the prospect of broadly wavelength tunable vortex generation directly from a laser.

ExoCross: Spectra from molecular line lists

NASA Astrophysics Data System (ADS)

Yurchenko, Sergei N.; Al-Refaie, Ahmed; Tennyson, Jonathan

2018-03-01

ExoCross generates spectra and thermodynamic properties from molecular line lists in ExoMol, HITRAN, or several other formats. The code is parallelized and also shows a high degree of vectorization; it works with line profiles such as Doppler, Lorentzian and Voigt and supports several broadening schemes. ExoCross is also capable of working with the recently proposed method of super-lines. It supports calculations of lifetimes, cooling functions, specific heats and other properties. ExoCross converts between different formats, such as HITRAN, ExoMol and Phoenix, and simulates non-LTE spectra using a simple two-temperature approach. Different electronic, vibronic or vibrational bands can be simulated separately using an efficient filtering scheme based on the quantum numbers.

Spectroscopic evidence of α-methylbenzyl radical in the gas phase

NASA Astrophysics Data System (ADS)

Lee, Gi Woo; Ahn, Hyeon Geun; Kim, Tae Kyu; Lee, Sang Kuk

2008-11-01

We report the observation of the spectroscopic evidence of the α-methylbenzyl radical in a corona excited supersonic expansion using a pinhole-type glass nozzle for the first time. The precursors, toluene, ethylbenzene, and isopropylbenzene, seeded in a large amount of inert carrier gas helium, were electrically discharged to produce benzyl-type radicals as a result of the breaking off of a C-H or a C-C bond from the alkyl chain. The vibronic emission spectra, obtained in the visible region from the precursors, were compared to identify the species generated in the corona discharge of the precursors, from which we found the spectroscopic evidence of the α-methylbenzyl radical.

Simulation of femtosecond two-dimensional electronic spectra of conical intersections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krčmář, Jindřich; Gelin, Maxim F.; Domcke, Wolfgang

2015-08-21

We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed.

Self-cavity lasing in optically pumped single crystals of p-sexiphenyl

NASA Astrophysics Data System (ADS)

Yanagi, Hisao; Tamura, Kenji; Sasaki, Fumio

2016-08-01

Organic single-crystal self-cavities are prepared by solution growth of p-sexiphenyl (p-6P). Based on Fabry-Pérot feedback inside a quasi-lozenge-shaped platelet crystal, edge-emitting laser is obtained under optical pumping. The multimode lasing band appears at the 0-1 or 0-2 vibronic progressions depending on the excitation conditions which affect the self-absorption effect. Cavity-size dependence of amplified spontaneous emission (ASE) is investigated with laser-etched single crystals of p-6P. As the cavity length of square-shaped crystal is reduced from 100 to 10 μm, ASE threshold fluence is decreased probably due to size-dependent light confinement in the crystal cavity.

Two-photon excitation of nitric oxide fluorescence as a temperature indicator in unsteady gas-dynamic processes

NASA Technical Reports Server (NTRS)

Mckenzie, R. L.; Gross, K. P.

1980-01-01

A laser induced fluorescence technique, suitable for measuring fluctuating temperatures in cold turbulent flows containing very low concentrations of nitric oxide is described. Temperatures below 300 K may be resolved with signal to noise ratios greater than 50 to 1 using high peak power, tunable dye lasers. The method relies on the two photon excitation of selected ro-vibronic transitions. The analysis includes the effects of fluorescence quenching and shows the technique to be effective at all densities below ambient. Signal to noise ratio estimates are based on a preliminary measurement of the two photon absorptivity for a selected rotational transition in the NO gamma (0,0) band.

State interference in resonance Auger and x-ray emission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cesar, A.; Agren, H.

1992-03-01

Starting from a scattering-theory formulation, cross sections for Auger and x-ray decay from energetically shifted inner-shell states are derived. Two situations are studied: (i) when there are several close-lying intermediate core-hole states with no vibrational excitations, in which case a {ital state} {ital interference} effect is identified; and (ii) when there are several close-lying intermediate states with vibrational excitations, in which case a {ital vibronic} {ital interference} effect is identified. In the latter case, the present formalism is a many-state generalization of the {ital vibrational} {ital interference} {ital effects} derived from the same type of scattering formalism in our previousmore » paper (A. Cesar, H. Agren, and V. Carravetta, Phys. Rev. A 40, 187 (1989)). Applications are carried out for spectra of some few-state model systems. It is found that a conventional analysis in terms of discrete noninteracting (noninterfering) states, such as the one-center decomposition model, is only valid when the ratio ({ital R}) between energy shift and lifetime is sufficiently large. For states with small {ital R}, a more complete theoretical account must be undertaken, including, e.g., the calculation of phases of the respective transition moments. The presented formalism applies to resonance Auger or x-ray emission spectra, to Auger and x-ray emission from core-electron shake-up states, and also, under certain circumstances, to emission from chemically shifted core-hole states.« less

Spectral and thermodynamic properties for the exciplexes of N-alkyl carbazoles with dicyanobenzenes in THF

NASA Astrophysics Data System (ADS)

Asim, Sadia; Mansha, Asim; Landgraf, Stephan; Grampp, Günter; Zahid, Muhammad; Bhatti, Haq Nawaz

2014-01-01

The exciplex emission spectra of N-ethylcarbazole with 1,2-dicyanobenzene (NEC/1,2-DCB), N-methylcarbazole with 1,2-dicyanobenzene (NMC/1,2-DCB), 1,3-dicyanobenzene (NMC/1,3-DCB), and 1,4-dicyanobenzene (NMC/1,4-DCB) are studied in tetrahydrofuran (THF) for the temperature range starting from 253 K to 334 K. Thermochromic shifts along with the spectral properties including change in peak intensities and the ratio of exciplex peak intensity to fluorophore peak intensity are studied. Effect of temperature on the energy of zero-zero transitions hνo‧, Huang-Rhys factor (S), Gauss broadening of vibronic level (σ) and the dominant high-frequency vibration (hνν) are also part of investigation. Enthalpy of exciplex formation (ΔHEX∗) calculated by the model proposed by A. Weller and the Gibb's energy of electron transfer (ΔGet∗) for all exciplex systems are also discussed in the present paper. All the exciplexes under study were observed to be dipolar in nature. The exciplex of the N-methylcarbazole/1,4-dicyanobenzene was found to be the most stable and the N-methylcarbazole/1,3-dicyanobenzene was the weakest exciplex system.

One step Pd(0)-catalyzed synthesis, X-ray analysis, and photophysical properties of cyclopent[hi]aceanthrylene: fullerene-like properties in a nonalternant cyclopentafused aromatic hydrocarbon.

PubMed

Dang, Hung; Levitus, Marcia; Garcia-Garibay, Miguel A

2002-01-09

A simple procedure for the synthesis of cyclopentafused polycyclic aromatic hydrocarbons (CP-PAH) with Pd(PPh(3))(2)Cl(2) catalyst has been applied to the one-pot palladium(0)-catalyzed coupling of 9,10-dibromoanthracene (1) with 2-methyl-3-butyn-2-ol. Reactions carried out in refluxing benzene in the presence of CuSO(4)/Al(2)O(3) yielded 9,10-dialkynylanthracene 2a, alkynyl aceanthrylene 2b, and 2,7-disubstituted cyclopent[hi]aceanthrylene 2c in 13%, 23%, and 19% purified yields, respectively, with total conversions of 80-90%. Sealed tube reactions without copper at 110 degrees C improved the yield of 2c up to >75%. Single-crystal X-ray analyses of 2a and 2c reveal a three-dimensional hydrogen bonding network, producing a unique crystal packing. The packing structure of 2b is dominated by pi-pi stacking interactions between two aceanthrylene molecules. CP-PAHs 2b and 2c have potentially interesting fullerene-like photophysics. While the UV-vis and fluorescence spectra of 2a (Phi(F) = 0.87) show the characteristic vibronic structure of anthracene, the UV-vis spectra of ruby-red aceanthrylene 2b and greenish-black cyclopent[hi]aceanthrylene 2c extend well into the visible range. Isomers 2b and 2c showed no detectable fluorescence emission. Unlike fullerenes, compounds 2b and 2c are poor singlet oxygen sensitizers with measured (1)O(2) quantum yields of 0.02 and 0.06, respectively. As expected from a simple Hückel analysis, 2c has relatively low two-electron reduction potentials as determined by cyclic voltammetry.

Studies of atomic and molecular dynamics using photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Canton, Sophie E.

Photoexcitation and photoionization studies of free atoms and molecules in the gas phase provide a unique view into various aspects of radiation-matter interactions that are used as basic building blocks in many branches of physics, such as Solid State, Plasma Physics, Photochemistry or Astrophysics. With the advent of third generation synchrotron light sources delivering high photon flux (>1015 photons/s) with unprecedented resolving power over a broad energy range, it has become possible to investigate in great detail not only the internal structure of the targets, but also the dynamics of the process. Born in the 1960s, photoelectron spectroscopy specifically analyzes the kinetic energy and emission angle of the ionized electrons. It is now coming to maturity with the availability of spectrometers designed to achieve high performances. This thesis work presents three examples of experiments made possible by the combination of the radiation from the Advanced Light Source with state of the art spectrometers. First, the measurements of the partial photoionization cross sections below the second ionization potential in argon and neon have uncovered weak and narrow resonances. Their mirroring profiles in the two open channels, which had prevented them from being detected in non-differential measurements, have been explained by their LS-forbidden nature. Second, the Auger spectra produced by decay of core-excited HF have revealed specific nuclear wavepacket interferences that occur when the electronic lifetime, the nuclear dynamics and the excitation prolongation, defined as the inverse of the photon bandwidth, have comparable time scales. Third, the analysis of the underlying structure in the first ionization band for free C60 has allowed the vibronic coupling of the singly charged molecular ion to be characterized.

Crystal Chemistry of the Potassium and Rubidium Uranyl Borate Families Derived from Boric Acid Fluxes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shuao; Alekseev, Evgeny V.; Stritzinger, Jared T.

2010-07-19

The reaction of uranyl nitrate with a large excess of molten boric acid in the presence of potassium or rubidium nitrate results in the formation of three new potassium uranyl borates, K{sub 2}[(UO{sub 2}){sub 2}B{sub 12}O{sub 19}(OH){sub 4}]·0.3H{sub 2}O (KUBO-1), K[(UO{sub 2}){sub 2}B{sub 10}O{sub 15}(OH){sub 5}] (KUBO-2), and K[(UO{sub 2}){sub 2}B{sub 10}O{sub 16}(OH){sub 3}]·0.7H{sub 2}O (KUBO-3) and two new rubidium uranyl borates Rb{sub 2}[(UO{sub 2}){sub 2}B{sub 13}O{sub 20}(OH){sub 5}] (RbUBO-1) and Rb[(UO{sub 2}){sub 2}B{sub 10}O{sub 16}(OH){sub 3}]·0.7H{sub 2}O (RbUBO-2). The latter is isotypic with KUBO-3. These compounds share a common structural motif consisting of a linear uranyl, UO{sub 2}{sup 2+},more » cation surrounded by BO{sub 3} triangles and BO{sub 4} tetrahedra to create an UO{sub 8} hexagonal bipyramidal environment around uranium. The borate anions bridge between uranyl units to create sheets. Additional BO{sub 3} triangles extend from the polyborate layers and are directed approximately perpendicular to the sheets. All of these compounds adopt layered structures. With the exception of KUBO-1, the structures are all centrosymmetric. All of these compounds fluoresce when irradiated with long-wavelength UV light. The fluorescence spectrum yields well-defined vibronically coupled charge-transfer features.« less

The COSMO-CLM 4.8 regional climate model coupled to regional ocean, land surface and global earth system models using OASIS3-MCT: description and performance

NASA Astrophysics Data System (ADS)

Will, Andreas; Akhtar, Naveed; Brauch, Jennifer; Breil, Marcus; Davin, Edouard; Ho-Hagemann, Ha T. M.; Maisonnave, Eric; Thürkow, Markus; Weiher, Stefan

2017-04-01

We developed a coupled regional climate system model based on the CCLM regional climate model. Within this model system, using OASIS3-MCT as a coupler, CCLM can be coupled to two land surface models (the Community Land Model (CLM) and VEG3D), the NEMO-MED12 regional ocean model for the Mediterranean Sea, two ocean models for the North and Baltic seas (NEMO-NORDIC and TRIMNP+CICE) and the MPI-ESM Earth system model.We first present the different model components and the unified OASIS3-MCT interface which handles all couplings in a consistent way, minimising the model source code modifications and defining the physical and numerical aspects of the couplings. We also address specific coupling issues like the handling of different domains, multiple usage of the MCT library and exchange of 3-D fields.We analyse and compare the computational performance of the different couplings based on real-case simulations over Europe. The usage of the LUCIA tool implemented in OASIS3-MCT enables the quantification of the contributions of the coupled components to the overall coupling cost. These individual contributions are (1) cost of the model(s) coupled, (2) direct cost of coupling including horizontal interpolation and communication between the components, (3) load imbalance, (4) cost of different usage of processors by CCLM in coupled and stand-alone mode and (5) residual cost including i.a. CCLM additional computations.Finally a procedure for finding an optimum processor configuration for each of the couplings was developed considering the time to solution, computing cost and parallel efficiency of the simulation. The optimum configurations are presented for sequential, concurrent and mixed (sequential+concurrent) coupling layouts. The procedure applied can be regarded as independent of the specific coupling layout and coupling details.We found that the direct cost of coupling, i.e. communications and horizontal interpolation, in OASIS3-MCT remains below 7 % of the CCLM stand-alone cost for all couplings investigated. This is in particular true for the exchange of 450 2-D fields between CCLM and MPI-ESM. We identified remaining limitations in the coupling strategies and discuss possible future improvements of the computational efficiency.

Measurement and analysis of electronic energy transfer between Tb 3+ and Eu 3+ ions in Cs 2NaY 1-x-y Tb xEu yCl 6

NASA Astrophysics Data System (ADS)

Moran, Diane M.; May, P. Stanley; Richardson, F. S.

1994-08-01

Electronic energy-transfer processes between Tb 3+5D 4) and Eu 3+ ( 7F 0, 7F 1) ions in crystalline Cs 2NaY 1-x-yTb xEu yCl 6 compounds are examined over a wide range of relative Tb 3+ and Eu 3+ concentrations (at sample temperature of 77 and 295 K). In these systems, the Tb 3+ and Eu 3+ ions are located at centrosymmetric (O h) sites surrounded by six Cl - ions, and the minimum distance between these sites is ≈ 7.6 Å. The host lattice has a cubic structure (space group O h5-Fm3m), and the phonon spectrum of this lattice has a cut-off frequency of ≈ 300 cm -1. The optical spectra of Tb 3+ and Eu 3+ in Cs 2NaYCl 6 exhibit relatively sparse line structures, consisting almost entirely of magnetic-dipole origin lines and one-phonon-assisted electric-dipole vibronic lines that reflect O h selection rules and have relatively low oscillator strenghts. Overlap between Tb 3+ ( 5D 4) emission and Eu 3+ ( 7F 0, 7F 1) absorption spectra occurs only within the Tb 3+ ( 5D 4 → 7 F 4 and Eu 3+ ( 7F 0, 7F 1 → 5D 0 transition regions, and resonances between individual lines in these regions are used to identify possible pathways for Tb 3+ ( 5D 4)-to-Eu 3+ ( 7F 0, 7F 1) energy transfer. Rates of energy transfer are determined from time-resolved Tb 3+ ( 5D 4) luminescence intersity measurements, analyzed in terms of two different models for representing donor (Tb 3+)-acceptor (Eu 3+) site distributions in Cs 2NaY 1-x-yTb xEu yCl 6 systems. In one model, donor-accepator site distances are represented by a continuous radial distribution function, whereas in the second model, these distances are represented by a discrete distribution function. Both models are used to analyze donor luminescence decay data in terms of rate parameters that reflect specific mechanistic contributions to electronic energy transfer. Both electron-exchange and multipole-multipole mechanisms are considered in the analyses. Results from these analyses, combined with spectral overlap considerations and comparisons of 77 versus 295 K rate data, suggest an electric-quadrupole/electric-dipole mechanism in which a 5D 4(T 1g → 7F 4(T 1g) electric-quadrupole transition on Tb 3+ excites a 7F 0(A 1g) + v4(t 1u → 5D 0(A 1g) electric-dipole (vibronic) transition on Eu 3+. Rate data obtained on systems of stoichiometric formulae Cs 2NaY 0.95-xTb xEu 0.05Cl 6 show that Tb 3+( 5D 4)- to-Eu 3+ ( 7F 0, 7F 1) energy-transfer rates a Tb 3+-Tb 3+ energy-migration processes when tx > 0.05. Direct calculations of Tb 3+ ( 5D 4)-Eu 3+ ( 7F 0, 7F 1) and Tb 3+ ( 5D 4-Tb 3+ ( 7F 6) multipole-multipole interaction parameters are performed, and the parameters obtained from these calculations are compared to those derived from parametric fits of experimentally observed rate data. Discrepancies between calculated and ovserved rate parameters are large, and possible explanations for these discrepancies are discussed.

Persistent optical hole-burning spectroscopy of nano-confined dye molecules in liquid at room temperature: Spectral narrowing due to a glassy state and extraordinary relaxation in a nano-cage

NASA Astrophysics Data System (ADS)

Murakami, Hiroshi

2018-04-01

Persistent optical hole-burning spectroscopy has been conducted for a dye molecule within a very small (˜1 nm) reverse micelle at room temperature. The spectra show a spectral narrowing due to site-selective excitation. This definitely demonstrates that the surroundings of the dye molecule are in a glassy state regardless of a solution at room temperature. On the other hand, the hole-burning spectra exhibit large shifts from excitation frequencies, and their positions are almost independent of excitation frequencies. The hole-burning spectra have been theoretically calculated by taking account of a vibronic absorption band of the dye molecule under the assumption that the surroundings of the dye molecule are in a glassy state. The calculated results agree with the experimental ones that were obtained for the dye molecule in a polymer glass for comparison, where it has been found that the ratio of hole-burning efficiencies of vibronic- to electronic-band excitations is quite high. On the other hand, the theoretical results do not explain the large spectral shift from the excitation frequency and small spectral narrowing observed in the hole-burning spectra measured for the dye-containing reverse micelle. It is thought that the spectral shift and broadening occur within the measurement time owing to the relaxation process of the surroundings that are hot with the thermal energy deposited by the dye molecule optically excited. Furthermore, the relaxation should be temporary because the cooling of the inside of the reverse micelle takes place with the dissipation of the excess thermal energy to the outer oil solvent, and so the surroundings of the dye molecule return to the glassy state and do not attain the thermal equilibrium. These results suggest that a very small reverse micelle provides a unique reaction field in which the diffusional motion can be controlled by light in a glassy state.

Magnetosphere - Ionosphere - Thermosphere (MIT) Coupling at Jupiter

NASA Astrophysics Data System (ADS)

Yates, J. N.; Ray, L. C.; Achilleos, N.

2017-12-01

Jupiter's upper atmospheric temperature is considerably higher than that predicted by Solar Extreme Ultraviolet (EUV) heating alone. Simulations incorporating magnetosphere-ionosphere coupling effects into general circulation models have, to date, struggled to reproduce the observed atmospheric temperatures under simplifying assumptions such as azimuthal symmetry and a spin-aligned dipole magnetic field. Here we present the development of a full three-dimensional thermosphere model coupled in both hemispheres to an axisymmetric magnetosphere model. This new coupled model is based on the two-dimensional MIT model presented in Yates et al., 2014. This coupled model is a critical step towards to the development of a fully coupled 3D MIT model. We discuss and compare the resulting thermospheric flows, energy balance and MI coupling currents to those presented in previous 2D MIT models.

Design of Soil Salinity Policies with Tinamit, a Flexible and Rapid Tool to Couple Stakeholder-Built System Dynamics Models with Physically-Based Models

NASA Astrophysics Data System (ADS)

Malard, J. J.; Baig, A. I.; Hassanzadeh, E.; Adamowski, J. F.; Tuy, H.; Melgar-Quiñonez, H.

2016-12-01

Model coupling is a crucial step to constructing many environmental models, as it allows for the integration of independently-built models representing different system sub-components to simulate the entire system. Model coupling has been of particular interest in combining socioeconomic System Dynamics (SD) models, whose visual interface facilitates their direct use by stakeholders, with more complex physically-based models of the environmental system. However, model coupling processes are often cumbersome and inflexible and require extensive programming knowledge, limiting their potential for continued use by stakeholders in policy design and analysis after the end of the project. Here, we present Tinamit, a flexible Python-based model-coupling software tool whose easy-to-use API and graphical user interface make the coupling of stakeholder-built SD models with physically-based models rapid, flexible and simple for users with limited to no coding knowledge. The flexibility of the system allows end users to modify the SD model as well as the linking variables between the two models themselves with no need for recoding. We use Tinamit to couple a stakeholder-built socioeconomic model of soil salinization in Pakistan with the physically-based soil salinity model SAHYSMOD. As climate extremes increase in the region, policies to slow or reverse soil salinity buildup are increasing in urgency and must take both socioeconomic and biophysical spheres into account. We use the Tinamit-coupled model to test the impact of integrated policy options (economic and regulatory incentives to farmers) on soil salinity in the region in the face of future climate change scenarios. Use of the Tinamit model allowed for rapid and flexible coupling of the two models, allowing the end user to continue making model structure and policy changes. In addition, the clear interface (in contrast to most model coupling code) makes the final coupled model easily accessible to stakeholders with limited technical background.

Tinamit: Making coupled system dynamics models accessible to stakeholders

NASA Astrophysics Data System (ADS)

Malard, Julien; Inam Baig, Azhar; Rojas Díaz, Marcela; Hassanzadeh, Elmira; Adamowski, Jan; Tuy, Héctor; Melgar-Quiñonez, Hugo

2017-04-01

Model coupling is increasingly used as a method of combining the best of two models when representing socio-environmental systems, though barriers to successful model adoption by stakeholders are particularly present with the use of coupled models, due to their high complexity and typically low implementation flexibility. Coupled system dynamics - physically-based modelling is a promising method to improve stakeholder participation in environmental modelling while retaining a high level of complexity for physical process representation, as the system dynamics components are readily understandable and can be built by stakeholders themselves. However, this method is not without limitations in practice, including 1) inflexible and complicated coupling methods, 2) difficult model maintenance after the end of the project, and 3) a wide variety of end-user cultures and languages. We have developed the open-source Python-language software tool Tinamit to overcome some of these limitations to the adoption of stakeholder-based coupled system dynamics - physically-based modelling. The software is unique in 1) its inclusion of both a graphical user interface (GUI) and a library of available commands (API) that allow users with little or no coding abilities to rapidly, effectively, and flexibly couple models, 2) its multilingual support for the GUI, allowing users to couple models in their preferred language (and to add new languages as necessary for their community work), and 3) its modular structure allowing for very easy model coupling and modification without the direct use of code, and to which programming-savvy users can easily add support for new types of physically-based models. We discuss how the use of Tinamit for model coupling can greatly increase the accessibility of coupled models to stakeholders, using an example of a stakeholder-built system dynamics model of soil salinity issues in Pakistan coupled with the physically-based soil salinity and water flow model SAHYSMOD. Different socioeconomic and environmental policies for soil salinity remediation are tested within the coupled model, allowing for the identification of the most efficient actions from an environmental and a farmer economy standpoint while taking into account the complex feedbacks between socioeconomics and the physical environment.

Effect of oxygen concentration on the magnetic properties of La2CoMnO6 thin films

NASA Astrophysics Data System (ADS)

Guo, H. Z.; Gupta, A.; Zhang, Jiandi; Varela, M.; Pennycook, S. J.

2007-11-01

The dependence of the magnetic properties on oxygen concentration in epitaxial La2CoMnO6 thin films deposited on (100)-oriented SrTiO3 substrates has been investigated by varying the oxygen background pressure during growth using pulsed laser deposition. Two distinct ferromagnetic (FM) phases are revealed, and the relative fraction varies with the oxygen concentration. The existence of oxygen vacancies induces the local vibronic Mn3+-O -Co3+ superexchange interactions in direct competition with the static FM Mn4+-O-Co2+ interactions. This results in the appearance of a new low temperature FM phase and suppression of the high-temperature FM phase, creating two distinct magnetic phase transitions.

Rotationally-resolved excitation spectroscopy of the alkoxy and alkylthio radicals in a supersonic jet

NASA Technical Reports Server (NTRS)

Misra, Prabhakar; Zhu, Xinming; Bryant, Hosie L.; Kamal, Mohammed M.

1993-01-01

Rotationally-resolved laser excitation spectra have been obtained for the alkoxy radicals (CH3O, C2H5O, i-C3H7O) and the alkylthio radicals (CH3S, C2H5S, i-C3H7S) in a supersonic jet expansion. Low resolution (0.2/cm) excitation spectra have helped identify several vibronic bands belonging to the A-X electronic system for these jet-cooled free radicals. High resolution (0.07/cm) laser-induced fluorescence excitation spectra have aided the unraveling of the associated rotational structure and in certain cases (CH3O and CH3S, for example) enabled explicit rotational (J,K) assignments of the transitions.

Absorption spectra of PTCDI: A combined UV-Vis and TD-DFT study

NASA Astrophysics Data System (ADS)

Oltean, Mircea; Calborean, Adrian; Mile, George; Vidrighin, Mihai; Iosin, Monica; Leopold, Loredana; Maniu, Dana; Leopold, Nicolae; Chiş, Vasile

2012-11-01

Absorption spectra of PTCDI (3,4,9,10-perylene-tetracarboxylic-diimide) have been investigated in chloroform, N,N'-dimethylformamide (DMF) and dimethylsulfoxide (DMSO). While no signature of assembled PTCDI molecules is observed in chloroform solution, distinct bands assigned to their aggregation have been identified in DMF and DMSO solutions. PTCDI monomers show very similar absorption patterns in chloroform and DMSO solutions. Experimental data, including the vibronic structure of the absorption spectra were explained based on the Franck-Condon approximation and quantum chemical results obtained at PBE0-DCP/6-31+G(d,p) level of theory. Geometry optimization of the first excited state leads to a nice agreement between the calculated adiabatic transition energies and experimental data.

A classical phase r-centroid approach to molecular wave packet dynamics illustrating the danger of using an incomplete set of initial states for thermal averaging

NASA Astrophysics Data System (ADS)

Hansson, Tony

1999-08-01

An inexpensive semiclassical method to simulate time-resolved pump-probe spectroscopy on molecular wave packets is applied to NaK molecules at high temperature. The method builds on the introduction of classical phase factors related to the r-centroids for vibronic transitions and assumes instantaneous laser-molecule interaction. All observed quantum mechanical features are reproduced - for short times where experimental data are available even quantitatively. Furthermore, it is shown that fully quantum dynamical molecular wave packet calculations on molecules at elevated temperatures, which do not include all rovibrational states, must be regarded with caution, as they easily might yield even qualitatively incorrect results.

Raman scattering and anti-Stokes luminescence in poly-paraphenylene vinylene/carbon nanotubes composites

NASA Astrophysics Data System (ADS)

Baibarac, M.; Massuyeau, F.; Wery, J.; Baltog, I.; Lefrant, S.

2012-04-01

In this paper, we present Raman scattering and luminescence of poly-paraphenylene vinylene/single-walled carbon nanotubes composites, focused on data recorded in the anti-Stokes branch. We demonstrate that, when the excitation energy is in the long wavelength tail of the fundamental absorption edge, an anti-Stokes signal is generated, whose origin is a photon absorption accompanied by a phonon process from lower to upper vibronic states. The efficiency of this anti-Stokes photo-luminescence is increased when composites films are deposited onto an Au rough surface acting as a surface enhanced Raman scattering substrate. This mechanism is explained by a coherent anti-Stokes Raman scattering-like process, as observed in other nano-structured materials.

Inelastic X-ray scattering of RTAl3 (R = La, Ce, T = Cu, Au)

NASA Astrophysics Data System (ADS)

Tsutsui, Satoshi; Kaneko, Koji; Pospisil, Jiri; Haga, Yoshinori

2018-05-01

Inelastic X-ray scattering (IXS) experiments of RTAl3 (R = La Ce, T = Cu, Au) were carried out at 300 and 5.5 K. The spectra between LaCuAl3 and CeCuAl3 (LaAuAl3 and CeAuAl3) are nearly identical at both temperatures except for temperature factors such as temperature dependence of Bose factor in IXS spectra and effect on thermal expansion. This means that no evident temperature dependence of IXS spectra was observed in CeTAl3 (T = Cu, Au). Since the major contribution of scattering cross section in IXS measurements is Thomson scattering, the present results failed to confirm the presence of vibron in these compounds.

Excited State Intramolecular Proton Transfer of 2,5-bis(5-ethyl-2-benzoxazolyl)-hydroquinone and its OH/OD-isotopomers studied in supersonic jets

NASA Astrophysics Data System (ADS)

Peukert, Sebastian; Gil, Michał; Kijak, Michał; Sepioł, Jerzy

2015-11-01

The Excited State Intramolecular Proton Transfer (ESIPT) reactions of dually fluorescent 2,5-bis(5-ethyl-2-benzoxazolyl)-hydroquinone (DE-BBHQ) and its isotopomers have been studied in the supersonic jet applying laser induced fluorescence (LIF) and fluorescence-depletion (F-D) spectroscopy. LIF-spectra measured at photo-tautomeric (red) fluorescence exhibit a characteristic triplet pattern of vibronic bands, which gradually collapses upon successive deuteration. Complementary TDDFT calculations indicate the possibility of 2 consecutive ESIPT reactions yielding an excited state diketo-tautomer. However, concerning this matter the present experimental results are not unambiguous and could be also rationalized without assuming the formation of an additional photo-tautomer.

Nonlinear interaction between underwater explosion bubble and structure based on fully coupled model

NASA Astrophysics Data System (ADS)

Zhang, A. M.; Wu, W. B.; Liu, Y. L.; Wang, Q. X.

2017-08-01

The interaction between an underwater explosion bubble and an elastic-plastic structure is a complex transient process, accompanying violent bubble collapsing, jet impact, penetration through the bubble, and large structural deformation. In the present study, the bubble dynamics are modeled using the boundary element method and the nonlinear transient structural response is modeled using the explicit finite element method. A new fully coupled 3D model is established through coupling the equations for the state variables of the fluid and structure and solving them as a set of coupled linear algebra equations. Based on the acceleration potential theory, the mutual dependence between the hydrodynamic load and the structural motion is decoupled. The pressure distribution in the flow field is calculated with the Bernoulli equation, where the partial derivative of the velocity potential in time is calculated using the boundary integral method to avoid numerical instabilities. To validate the present fully coupled model, the experiments of small-scale underwater explosion near a stiffened plate are carried out. High-speed imaging is used to capture the bubble behaviors and strain gauges are used to measure the strain response. The numerical results correspond well with the experimental data, in terms of bubble shapes and structural strain response. By both the loosely coupled model and the fully coupled model, the interaction between a bubble and a hollow spherical shell is studied. The bubble patterns vary with different parameters. When the fully coupled model and the loosely coupled model are advanced with the same time step, the error caused by the loosely coupled model becomes larger with the coupling effect becoming stronger. The fully coupled model is more stable than the loosely coupled model. Besides, the influences of the internal fluid on the dynamic response of the spherical shell are studied. At last, the case that the bubble interacts with an air-backed stiffened plate is simulated. The associated interesting physical phenomenon is obtained and expounded.

The Met Office Coupled Atmosphere/Land/Ocean/Sea-Ice Data Assimilation System

NASA Astrophysics Data System (ADS)

Lea, Daniel; Mirouze, Isabelle; King, Robert; Martin, Matthew; Hines, Adrian

2015-04-01

The Met Office has developed a weakly-coupled data assimilation (DA) system using the global coupled model HadGEM3 (Hadley Centre Global Environment Model, version 3). At present the analysis from separate ocean and atmosphere DA systems are combined to produced coupled forecasts. The aim of coupled DA is to produce a more consistent analysis for coupled forecasts which may lead to less initialisation shock and improved forecast performance. The HadGEM3 coupled model combines the atmospheric model UM (Unified Model) at 60 km horizontal resolution on 85 vertical levels, the ocean model NEMO (Nucleus for European Modelling of the Ocean) at 25 km (at the equator) horizontal resolution on 75 vertical levels, and the sea-ice model CICE at the same resolution as NEMO. The atmosphere and the ocean/sea-ice fields are coupled every 1-hour using the OASIS coupler. The coupled model is corrected using two separate 6-hour window data assimilation systems: a 4D-Var for the atmosphere with associated soil moisture content nudging and snow analysis schemes on the one hand, and a 3D-Var FGAT for the ocean and sea-ice on the other hand. The background information in the DA systems comes from a previous 6-hour forecast of the coupled model. To isolate the impact of the coupled DA, 13-month experiments have been carried out, including 1) a full atmosphere/land/ocean/sea-ice coupled DA run, 2) an atmosphere-only run forced by OSTIA SSTs and sea-ice with atmosphere and land DA, and 3) an ocean-only run forced by atmospheric fields from run 2 with ocean and sea-ice DA. In addition, 5-day and 10-day forecast runs, have been produced from initial conditions generated by either run 1 or a combination of runs 2 and 3. The different results have been compared to each other and, whenever possible, to other references such as the Met Office atmosphere and ocean operational analyses or the OSTIA SST data. The performance of the coupled DA is similar to the existing separate ocean and atmosphere DA systems. This is despite the fact that the assimilation error covariances have not yet been tuned for coupled DA. In addition, the coupled model also exhibits some biases which do not affect the uncoupled models. An example is precipitation and run off errors affecting the ocean salinity. This of course impacts the performance of the ocean data assimilation. This does, however, highlight a particular benefit of data assimilation in that it can help to identify short term model biases by using, for example, the differences between the observations and model background (innovations) and the mean increments. Coupled DA has the distinct advantage that this gives direct information about the coupled model short term biases. By identifying the biases and developing solutions this will improve the short range coupled forecasts, and may also improve the coupled model on climate timescales.

Reducing the Dynamical Degradation by Bi-Coupling Digital Chaotic Maps

NASA Astrophysics Data System (ADS)

Liu, Lingfeng; Liu, Bocheng; Hu, Hanping; Miao, Suoxia

A chaotic map which is realized on a computer will suffer dynamical degradation. Here, a coupled chaotic model is proposed to reduce the dynamical degradation. In this model, the state variable of one digital chaotic map is used to control the parameter of the other digital map. This coupled model is universal and can be used for all chaotic maps. In this paper, two coupled models (one is coupled by two logistic maps, the other is coupled by Chebyshev map and Baker map) are performed, and the numerical experiments show that the performances of these two coupled chaotic maps are greatly improved. Furthermore, a simple pseudorandom bit generator (PRBG) based on coupled digital logistic maps is proposed as an application for our method.

Exploring coupled 4D-Var data assimilation using an idealised atmosphere-ocean model

NASA Astrophysics Data System (ADS)

Smith, Polly; Fowler, Alison; Lawless, Amos; Haines, Keith

2014-05-01

The successful application of data assimilation techniques to operational numerical weather prediction and ocean forecasting systems has led to an increased interest in their use for the initialisation of coupled atmosphere-ocean models in prediction on seasonal to decadal timescales. Coupled data assimilation presents a significant challenge but offers a long list of potential benefits including improved use of near-surface observations, reduction of initialisation shocks in coupled forecasts, and generation of a consistent system state for the initialisation of coupled forecasts across all timescales. In this work we explore some of the fundamental questions in the design of coupled data assimilation systems within the context of an idealised one-dimensional coupled atmosphere-ocean model. The system is based on the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) atmosphere model and a K-Profile Parameterisation (KKP) mixed layer ocean model developed by the National Centre for Atmospheric Science (NCAS) climate group at the University of Reading. It employs a strong constraint incremental 4D-Var scheme and is designed to enable the effective exploration of various approaches to performing coupled model data assimilation whilst avoiding many of the issues associated with more complex models. Working with this simple framework enables a greater range and quantity of experiments to be performed. Here, we will describe the development of our simplified single-column coupled atmosphere-ocean 4D-Var assimilation system and present preliminary results from a series of identical twin experiments devised to investigate and compare the behaviour and sensitivities of different coupled data assimilation methodologies. This includes comparing fully and weakly coupled assimilations with uncoupled assimilation, investigating whether coupled assimilation can eliminate or lessen initialisation shock in coupled model forecasts, and exploring the effect of the assimilation window length in coupled assimilations. These experiments will facilitate a greater theoretical understanding of the coupled atmosphere-ocean data assimilation problem and thus help guide the design and implementation of different coupling strategies within operational systems. This research is funded by the European Space Agency (ESA) and the UK Natural Environment Research Council (NERC). The ESA funded component is part of the Data Assimilation Projects - Coupled Model Data Assimilation initiative whose goal is to advance data assimilation techniques in fully coupled atmosphere-ocean models (see http://www.esa-da.org/). It is being conducted in parallel to the development of prototype weakly coupled data assimilation systems at both the UK Met Office and ECMWF.

Coupled intertwiner dynamics: A toy model for coupling matter to spin foam models

NASA Astrophysics Data System (ADS)

Steinhaus, Sebastian

2015-09-01

The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretization. However, extracting these mutual dynamics is crucial in testing the viability of the spin foam approach and also establishing connections to other discrete approaches such as lattice gauge theories. Therefore, we introduce a simple two-dimensional toy model for Yang-Mills coupled to spin foams, namely an Ising model coupled to so-called intertwiner models defined for SU (2 )k. The two systems are coupled by choosing the Ising coupling constant to depend on spin labels of the background, as these are interpreted as the edge lengths of the discretization. We coarse grain this toy model via tensor network renormalization and uncover an interesting dynamics: the Ising phase transition temperature turns out to be sensitive to the background configurations and conversely, the Ising model can induce phase transitions in the background. Moreover, we observe a strong coupling of both systems if close to both phase transitions.

Study on the Vehicle Dynamic Load Considering the Vehicle-Pavement Coupled Effect

NASA Astrophysics Data System (ADS)

Xu, H. L.; He, L.; An, D.

2017-11-01

The vibration of vehicle-pavement interaction system is sophisticated random vibration process and the vehicle-pavement coupled effect was not considered in the previous study. A new linear elastic model of the vehicle-pavement coupled system was established in the paper. The new model was verified with field measurement which could reflect the real vibration between vehicle and pavement. Using the new model, the study on the vehicle dynamic load considering the vehicle-pavement coupled effect showed that random forces (centralization) between vehicle and pavement were influenced largely by vehicle-pavement coupled effect. Numerical calculation indicated that the maximum of random forces in coupled model was 2.4 times than that in uncoupled model. Inquiring the reason, it was found that the main vibration frequency of the vehicle non-suspension system was similar with that of the vehicle suspension system in the coupled model and the resonance vibration lead to vehicle dynamic load increase significantly.

Hierarchical and coupling model of factors influencing vessel traffic flow.

PubMed

Liu, Zhao; Liu, Jingxian; Li, Huanhuan; Li, Zongzhi; Tan, Zhirong; Liu, Ryan Wen; Liu, Yi

2017-01-01

Understanding the characteristics of vessel traffic flow is crucial in maintaining navigation safety, efficiency, and overall waterway transportation management. Factors influencing vessel traffic flow possess diverse features such as hierarchy, uncertainty, nonlinearity, complexity, and interdependency. To reveal the impact mechanism of the factors influencing vessel traffic flow, a hierarchical model and a coupling model are proposed in this study based on the interpretative structural modeling method. The hierarchical model explains the hierarchies and relationships of the factors using a graph. The coupling model provides a quantitative method that explores interaction effects of factors using a coupling coefficient. The coupling coefficient is obtained by determining the quantitative indicators of the factors and their weights. Thereafter, the data obtained from Port of Tianjin is used to verify the proposed coupling model. The results show that the hierarchical model of the factors influencing vessel traffic flow can explain the level, structure, and interaction effect of the factors; the coupling model is efficient in analyzing factors influencing traffic volumes. The proposed method can be used for analyzing increases in vessel traffic flow in waterway transportation system.

Simulation of seasonal anomalies of atmospheric circulation using coupled atmosphere-ocean model

NASA Astrophysics Data System (ADS)

Tolstykh, M. A.; Diansky, N. A.; Gusev, A. V.; Kiktev, D. B.

2014-03-01

A coupled atmosphere-ocean model intended for the simulation of coupled circulation at time scales up to a season is developed. The semi-Lagrangian atmospheric general circulation model of the Hydrometeorological Centre of Russia, SLAV, is coupled with the sigma model of ocean general circulation developed at the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), INMOM. Using this coupled model, numerical experiments on ensemble modeling of the atmosphere and ocean circulation for up to 4 months are carried out using real initial data for all seasons of an annual cycle in 1989-2010. Results of these experiments are compared to the results of the SLAV model with the simple evolution of the sea surface temperature. A comparative analysis of seasonally averaged anomalies of atmospheric circulation shows prospects in applying the coupled model for forecasts. It is shown with the example of the El Niño phenomenon of 1997-1998 that the coupled model forecasts the seasonally averaged anomalies for the period of the nonstationary El Niño phase significantly better.

Hierarchical and coupling model of factors influencing vessel traffic flow

PubMed Central

Liu, Jingxian; Li, Huanhuan; Li, Zongzhi; Tan, Zhirong; Liu, Ryan Wen; Liu, Yi

2017-01-01

Understanding the characteristics of vessel traffic flow is crucial in maintaining navigation safety, efficiency, and overall waterway transportation management. Factors influencing vessel traffic flow possess diverse features such as hierarchy, uncertainty, nonlinearity, complexity, and interdependency. To reveal the impact mechanism of the factors influencing vessel traffic flow, a hierarchical model and a coupling model are proposed in this study based on the interpretative structural modeling method. The hierarchical model explains the hierarchies and relationships of the factors using a graph. The coupling model provides a quantitative method that explores interaction effects of factors using a coupling coefficient. The coupling coefficient is obtained by determining the quantitative indicators of the factors and their weights. Thereafter, the data obtained from Port of Tianjin is used to verify the proposed coupling model. The results show that the hierarchical model of the factors influencing vessel traffic flow can explain the level, structure, and interaction effect of the factors; the coupling model is efficient in analyzing factors influencing traffic volumes. The proposed method can be used for analyzing increases in vessel traffic flow in waterway transportation system. PMID:28414747

[Individualized fluid-solid coupled model of intracranial aneurysms based on computed tomography angiography data].

PubMed

Wang, Fuyu; Xu, Bainan; Sun, Zhenghui; Liu, Lei; Wu, Chen; Zhang, Xiaojun

2012-10-01

To establish an individualized fluid-solid coupled model of intracranial aneurysms based on computed tomography angiography (CTA) image data. The original Dicom format image data from a patient with an intracranial aneurysm were imported into Mimics software to construct the 3D model. The fluid-solid coupled model was simulated with ANSYS and CFX software, and the sensitivity of the model was analyzed. The difference between the rigid model and fluid-solid coupled model was also compared. The fluid-solid coupled model of intracranial aneurysm was established successfully, which allowed direct simulation of the blood flow of the intracranial aneurysm and the deformation of the solid wall. The pressure field, stress field, and distribution of Von Mises stress and deformation of the aneurysm could be exported from the model. A small Young's modulus led to an obvious deformation of the vascular wall, and the walls with greater thicknesses had smaller deformations. The rigid model and the fluid-solid coupled model showed more differences in the wall shear stress and blood flow velocity than in pressure. The fluid-solid coupled model more accurately represents the actual condition of the intracranial aneurysm than the rigid model. The results of numerical simulation with the model are reliable to study the origin, growth and rupture of the aneurysms.

Session on coupled atmospheric/chemistry coupled models

NASA Technical Reports Server (NTRS)

Thompson, Anne

1993-01-01

The session on coupled atmospheric/chemistry coupled models is reviewed. Current model limitations, current issues and critical unknowns, and modeling activity are addressed. Specific recommendations and experimental strategies on the following are given: multiscale surface layer - planetary boundary layer - chemical flux measurements; Eulerian budget study; and Langrangian experiment. Nonprecipitating cloud studies, organized convective systems, and aerosols - heterogenous chemistry are also discussed.

Electron Scattering by biomass molecular fragments

NASA Astrophysics Data System (ADS)

Lima, Marco

2015-09-01

The replacement of fossil fuels by biofuels from renewable sources may not be a definite answer for greenhouse gas emissions problems, but it is a good step towards a sustainable energy strategy. Few per cent of ethanol is being mixed to gasoline in many countries and in some of them, like Brazil, a very aggressive program has been developed, using, in large scale, flex fuel engines that can run with any mixture of gasoline and ethanol, including 100% ethanol. Important points are how to produce ethanol in a sustainable way and with which technology? Biomass is a good candidate to enhance the first generation (produced from Corn in USA and from sugarcane in Brazil) production towards the so-called second-generation ethanol, since it has cellulose and hemicellulose as source of sugars. In order to liberate these sugars for fermentation, it is important to learn how to separate the main components. Chemical routes (acid treatment) and biological routes (enzymatic hydrolysis) are combined and used for these purposes. Atmospheric plasmas can be useful for attacking the biomass in a controlled manner and low energy electrons may have an important role in the process. Recently, we have been studying the interaction of electrons with lignin subunits (phenol, guaiacol, p-coumaryl alcohol), cellulose components, β-D-glucose and cellobiose (β(1-4) linked glucose dimer) and hemicellulose components [2] (β-D-xylose). We also obtained results for the amylose subunits α-D-glucose and maltose (α(1-4) linked glucose dimer). Altogether, the resonance spectra of lignin, cellulose and hemicellulose components establish a physical-chemical basis for electron-induced biomass pretreatment that could be applied to biofuel production. In order to describe a more realistic system (where molecules are ``wet''), we have obtained the shape resonance spectra of phenol-water clusters, as obtained previously from elastic electron scattering calculations. Our results, obtained in a simple model (phenol in the presence of one and two water molecules), indicate that the well-known indirect mechanism for hydrogen elimination in the gas phase is significantly impacted on by microsolvation, due to the competition between vibronic couplings on the solute and solvent molecules. This fact suggested how relevant the solvation effects could be for the electron-driven damage of biomolecules and the biomass delignification. We have also discussed microsolvation signatures in the differential cross sections that could help to identify the solvated complexes and access the composition of gaseous admixtures of these species. In a collaboration project involving Australia (within the Brazilian Science Without Borders program), Portugal, Spain and Brazil, we have focused on obtaining theoretical and experimental electronic excitation cross sections of phenol and furfural for 10-50 eV electron impact energies. Convergence on electronic multichannel coupling stands as the biggest challenge to obtain agreement between theory and experiments. In my presentation, I will discuss the current status of this project.

Magnetic structures and excitations in CePd2(Al,Ga)2 series: Development of the "vibron" states

NASA Astrophysics Data System (ADS)

Klicpera, M.; Boehm, M.; Doležal, P.; Mutka, H.; Koza, M. M.; Rols, S.; Adroja, D. T.; Puente Orench, I.; Rodríguez-Carvajal, J.; Javorský, P.

2017-02-01

CePd2Al2 -xGax compounds crystallizing in the tetragonal CaBe2Ge2 -type structure (space group P 4 /n m m ) and undergoing a structural phase transition to an orthorhombic structure (C m m e ) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd2Al2 is described by an incommensurate propagation vector k ⃗=(δx,1/2 +δy,0 ) with δx=0.06 and δy=0.04 . The magnetic moments order antiferromagnetically within the a b planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) μB/Ce3 +. CePd2Ga2 reveals a magnetic structure composed of two components: the first is described by the propagation vector k1⃗=(1/2 ,1/2 ,0 ) , and the second one propagates with k2⃗=(0 ,1/2 ,0 ) . The magnetic moments of both components are aligned along the same direction—the orthorhombic [100] direction—and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors k1⃗ and k2⃗ describe also the magnetic structure of substituted CePd2Al2 -xGax compounds, except the one with x =0.1 .CePd2Al1.9Ga0.1 with magnetic structure described by k ⃗ and k1⃗ stays on the border between pure CePd2Al2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd2Al2 , while only two crystal field (CF) excitations are expected from the splitting of ground state J =5/2 of the Ce3 + ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd2Al2 . A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound CePd2Ga2 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the CePd2Al2 -xGax series is discussed and crystal field parameters determined.

Couples Counseling Directive Technique: A (Mis)communication Model to Promote Insight, Catharsis, Disclosure, and Problem Resolution

ERIC Educational Resources Information Center

Mahaffey, Barbara A.

2010-01-01

A psychoeducational model for improving couple communication is proposed. An important goal in couples counseling is to assist couples in resolving communication conflicts. The proposed communication model helps to establish a therapeutic environment that encourages insight, therapeutic alliance formation, catharsis, self-disclosure, symptom…

From global circulation to flood loss: Coupling models across the scales

NASA Astrophysics Data System (ADS)

Felder, Guido; Gomez-Navarro, Juan Jose; Bozhinova, Denica; Zischg, Andreas; Raible, Christoph C.; Ole, Roessler; Martius, Olivia; Weingartner, Rolf

2017-04-01

The prediction and the prevention of flood losses requires an extensive understanding of underlying meteorological, hydrological, hydraulic and damage processes. Coupled models help to improve the understanding of such underlying processes and therefore contribute the understanding of flood risk. Using such a modelling approach to determine potentially flood-affected areas and damages requires a complex coupling between several models operating at different spatial and temporal scales. Although the isolated parts of the single modelling components are well established and commonly used in the literature, a full coupling including a mesoscale meteorological model driven by a global circulation one, a hydrologic model, a hydrodynamic model and a flood impact and loss model has not been reported so far. In the present study, we tackle the application of such a coupled model chain in terms of computational resources, scale effects, and model performance. From a technical point of view, results show the general applicability of such a coupled model, as well as good model performance. From a practical point of view, such an approach enables the prediction of flood-induced damages, although some future challenges have been identified.

An extension of the standard model with a single coupling parameter

NASA Astrophysics Data System (ADS)

Atance, Mario; Cortés, José Luis; Irastorza, Igor G.

1997-02-01

We show that it is possible to find an extension of the matter content of the standard model with a unification of gauge and Yukawa couplings reproducing their known values. The perturbative renormalizability of the model with a single coupling and the requirement to accommodate the known properties of the standard model fix the masses and couplings of the additional particles. The implications on the parameters of the standard model are discussed.

Atmosphere-Wave-Ocean Coupling from Regional to Global Earth System Models for High-Impact Extreme Weather Prediction

NASA Astrophysics Data System (ADS)

Chen, S. S.; Curcic, M.

2017-12-01

The need for acurrate and integrated impact forecasts of extreme wind, rain, waves, and storm surge is growing as coastal population and built environment expand worldwide. A key limiting factor in forecasting impacts of extreme weather events associated with tropical cycle and winter storms is fully coupled atmosphere-wave-ocean model interface with explicit momentum and energy exchange. It is not only critical for accurate prediction of storm intensity, but also provides coherent wind, rian, ocean waves and currents forecasts for forcing for storm surge. The Unified Wave INterface (UWIN) has been developed for coupling of the atmosphere-wave-ocean models. UWIN couples the atmosphere, wave, and ocean models using the Earth System Modeling Framework (ESMF). It is a physically based and computationally efficient coupling sytem that is flexible to use in a multi-model system and portable for transition to the next generation global Earth system prediction mdoels. This standardized coupling framework allows researchers to develop and test air-sea coupling parameterizations and coupled data assimilation, and to better facilitate research-to-operation activities. It has been used and extensively tested and verified in regional coupled model forecasts of tropical cycles and winter storms (Chen and Curcic 2016, Curcic et al. 2016, and Judt et al. 2016). We will present 1) an overview of UWIN and its applications in fully coupled atmosphere-wave-ocean model predictions of hurricanes and coastal winter storms, and 2) implenmentation of UWIN in the NASA GMAO GEOS-5.

Photodissociation spectroscopy of the Mg + -CO2 complex and its isotopic analogs

NASA Astrophysics Data System (ADS)

Yeh, C. S.; Willey, K. F.; Robbins, D. L.; Pilgrim, J. S.; Duncan, M. A.

1993-02-01

Mg+-CO2 ion-molecule cluster complexes are produced by laser vaporization in a pulsed nozzle cluster source. The vibronic spectroscopy in these complexes is studied with mass-selected photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer. Two excited electronic states are observed (2) 2Σ+ and 2Π. The 2Π state has a vibrational progression in the metal-CO2 stretching mode (ωe'=381.8 cm-1). The complexes are linear (Mg+-OCO) and are bound by the charge-quadrupole interaction. The dissociation energy (D0`) is 14.7 kcal/mol. Corresponding spectra are measured for each of the 24, 25, and 26 isotopes of magnesium. These results are compared to theoretical predictions made by Bauschlicher and co-workers.

Manifestation of Molecular Chromophore Polymorphism in Diffuse Vibronic Spectra

NASA Astrophysics Data System (ADS)

Tolkachev, V. A.

2018-05-01

The location of the purely electronic 0-0-transition v0 for homomorphic chromophores is defined in the transition cross-section spectrum σ(ν) by the extremum ( ∂φ/ ∂v = 0) of the function [σ(ν)/ν] exp ((∓ hv/2 kT) = φ(| v - v 0|) and "-" for absorption, ν < ν0 and "+" for emission) for the dipole Frank-Condon transition with thermal distribution among the initial-state sublevels. The observed effective cross section and spectrum with polymorphism are formed by partial contributions of electronic transitions of the separate species with different ν i0. In this instance, the homomorphic extremum is distorted, i.e., broadened, weakened, or absent, which is also indicative of a polymorphic chromophore. Examples of these distortions of the functions calculated from the experimental spectra are given.

Discovery of the Electronic Spectra of Hps and Dps

NASA Astrophysics Data System (ADS)

Grimminger, Robert A.; Wei, Jie; Ellis, Blaine; Clouthier, Dennis J.; Wang, Zhong; Sears, Trevor

2009-06-01

The hitherto unknown electronic spectrum of the closed shell transient molecule HPS has been observed in the 685 - 846 nm region by laser-induced fluorescence and single vibronic level emission techniques. HPS (and DPS) were produced in a pulsed electric discharge jet using a precursor mixture of 3% PH_3 and 1% H_2S (or PD_3 and D_2S) in high pressure argon. The weak set of observed bands are assigned to the à ^1A^''-X˜ ^1A^' electronic transition on the basis of chemical evidence, isotope shifts and the correspondence of the vibrational frequencies, excitation energy, and band contours with predictions based on our own high level ab initio calculations. Theory predicts that the HPS bond angle decreases on electronic excitation, contrary to expectations based on Walsh diagrams.

LABORATORY MEASUREMENTS OF NiH BY FOURIER TRANSFORM DISPERSED FLUORESCENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vallon, Raphael; Richard, Cyril; Crozet, Patrick

2009-05-01

Red and orange bands of laser-induced fluorescence in NiH have been recorded on a Fourier transform interferometer at Doppler resolution. The spectra show strong transitions to low-lying vibronic states which are not thermally populated in a laboratory source, and therefore do not appear in laser excitation spectra, but which would be expected to contribute significantly to any stellar spectrum. The strongest bands belong to the G[{omega}' 5/2]-X {sub 2} {sup 2}{delta}{sub 3/2}, I[{omega}' 3/2]-X {sub 2}, and {sup 2}{delta}{sub 3/2} I[{omega}' 3/2]-W {sub 1} {sup 2}{pi}{sub 3/2} systems. Measurements are reported for {sup 58}NiH, {sup 60}NiH, and {sup 62}NiH.

Manifestation of Molecular Chromophore Polymorphism in Diffuse Vibronic Spectra

NASA Astrophysics Data System (ADS)

Tolkachev, V. A.

2018-05-01

The location of the purely electronic 0-0-transition v0 for homomorphic chromophores is defined in the transition cross-section spectrum σ(ν) by the extremum (∂φ/∂v = 0) of the function [σ(ν)/ν] exp ((∓hv/2kT) = φ(|v - v 0|) and "-" for absorption, ν < ν0 and "+" for emission) for the dipole Frank-Condon transition with thermal distribution among the initial-state sublevels. The observed effective cross section and spectrum with polymorphism are formed by partial contributions of electronic transitions of the separate species with different ν i0. In this instance, the homomorphic extremum is distorted, i.e., broadened, weakened, or absent, which is also indicative of a polymorphic chromophore. Examples of these distortions of the functions calculated from the experimental spectra are given.

Spectroscopic identification of jet-cooled p-fluoro-α-methylbenzyl radical in corona discharge

NASA Astrophysics Data System (ADS)

Lee, Gi Woo; Lee, Sang Kuk

2009-02-01

We report the first spectroscopic identification of the p-fluoro-α-methylbenzyl radical in the gas phase. Precursor p-fluoro-ethylbenzene seeded in a large amount of carrier gas was electrically discharged to produce the benzyl-type radicals in a corona excited supersonic expansion using a pinhole-type glass nozzle, from which the vibronic emission spectrum was recorded in the visible region. From an analysis of the spectrum observed, we identified spectroscopically the formation of the p-fluoro-α-methylbenzyl, in which the energy of the D 1 → D 0 electronic transition and a few vibrational mode frequencies in the ground electronic state were determined by comparison with those from an ab initio calculation and with those from the known data of the precursor.

Bis-pyridinium quadrupolar derivatives. High Stokes shift selective probes for bio-imaging

NASA Astrophysics Data System (ADS)

Salice, Patrizio; Versari, Silvia; Bradamante, Silvia; Meinardi, Francesco; Macchi, Giorgio; Pagani, Giorgio A.; Beverina, Luca

2013-11-01

We describe the design, synthesis and characterization of five high Stokes shift quadrupolar heteroaryl compounds suitable as fluorescent probes in bio-imaging. In particular, we characterize the photophysical properties and the intracellular localization in Human Umbilical Vein Endothelial Cells (HUVEC) and Human Mesenchymal Stem Cells (HMSCs) for each dye. We show that, amongst all of the investigated derivatives, the 2,5-bis[1-(4-N-methylpyridinium)ethen-2-yl)]- N-methylpyrrole salt is the best candidates as selective mitochondrial tracker. Finally, we recorded the full emission spectrum of the most performing - exclusively mitochondrial selective - fluorescent probe directly from HUVEC stained cells. The emission spectrum collected from the stained mitochondria shows a remarkably more pronounced vibronic structure with respect to the emission of the free fluorophore in solution.

Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. II. The phenanthrene cation (C14H10+) and its 1-methyl derivative

NASA Technical Reports Server (NTRS)

Salama, F.; Joblin, C.; Allamandola, L. J.

1994-01-01

The ultraviolet, visible, and near infrared absorption spectra of phenanthrene (C14H10), 1-methylphenanthrene [(CH3)C14H9], and their radical ions [C14H10+; (CH3)C14H9+], formed by vacuum-ultraviolet irradiation, were measured in neon matrices at 4.2 K. The associated vibronic band systems and their spectroscopic assignments are discussed. The oscillator strengths were calculated for the phenanthrene ion and found lower than the theoretical predictions. This study presents the first spectroscopic data for phenanthrene and its methyl derivative trapped in a neon matrix where the perturbation of the isolated species by its environment is minimum; a condition crucial to astrophysical applications.

Time-dependent nonlinear Jaynes-Cummings dynamics of a trapped ion

NASA Astrophysics Data System (ADS)

Krumm, F.; Vogel, W.

2018-04-01

In quantum interaction problems with explicitly time-dependent interaction Hamiltonians, the time ordering plays a crucial role for describing the quantum evolution of the system under consideration. In such complex scenarios, exact solutions of the dynamics are rarely available. Here we study the nonlinear vibronic dynamics of a trapped ion, driven in the resolved sideband regime with some small frequency mismatch. By describing the pump field in a quantized manner, we are able to derive exact solutions for the dynamics of the system. This eventually allows us to provide analytical solutions for various types of time-dependent quantities. In particular, we study in some detail the electronic and the motional quantum dynamics of the ion, as well as the time evolution of the nonclassicality of the motional quantum state.

Effect of land model ensemble versus coupled model ensemble on the simulation of precipitation climatology and variability

NASA Astrophysics Data System (ADS)

Wei, Jiangfeng; Dirmeyer, Paul A.; Yang, Zong-Liang; Chen, Haishan

2017-10-01

Through a series of model simulations with an atmospheric general circulation model coupled to three different land surface models, this study investigates the impacts of land model ensembles and coupled model ensemble on precipitation simulation. It is found that coupling an ensemble of land models to an atmospheric model has a very minor impact on the improvement of precipitation climatology and variability, but a simple ensemble average of the precipitation from three individually coupled land-atmosphere models produces better results, especially for precipitation variability. The generally weak impact of land processes on precipitation should be the main reason that the land model ensembles do not improve precipitation simulation. However, if there are big biases in the land surface model or land surface data set, correcting them could improve the simulated climate, especially for well-constrained regional climate simulations.

SURFEX v8.0 interface with OASIS3-MCT to couple atmosphere with hydrology, ocean, waves and sea-ice models, from coastal to global scales

NASA Astrophysics Data System (ADS)

Voldoire, Aurore; Decharme, Bertrand; Pianezze, Joris; Lebeaupin Brossier, Cindy; Sevault, Florence; Seyfried, Léo; Garnier, Valérie; Bielli, Soline; Valcke, Sophie; Alias, Antoinette; Accensi, Mickael; Ardhuin, Fabrice; Bouin, Marie-Noëlle; Ducrocq, Véronique; Faroux, Stéphanie; Giordani, Hervé; Léger, Fabien; Marsaleix, Patrick; Rainaud, Romain; Redelsperger, Jean-Luc; Richard, Evelyne; Riette, Sébastien

2017-11-01

This study presents the principles of the new coupling interface based on the SURFEX multi-surface model and the OASIS3-MCT coupler. As SURFEX can be plugged into several atmospheric models, it can be used in a wide range of applications, from global and regional coupled climate systems to high-resolution numerical weather prediction systems or very fine-scale models dedicated to process studies. The objective of this development is to build and share a common structure for the atmosphere-surface coupling of all these applications, involving on the one hand atmospheric models and on the other hand ocean, ice, hydrology, and wave models. The numerical and physical principles of SURFEX interface between the different component models are described, and the different coupled systems in which the SURFEX OASIS3-MCT-based coupling interface is already implemented are presented.

Representing grounding line migration in synchronous coupling between a marine ice sheet model and a z-coordinate ocean model

NASA Astrophysics Data System (ADS)

Goldberg, D. N.; Snow, K.; Holland, P.; Jordan, J. R.; Campin, J.-M.; Heimbach, P.; Arthern, R.; Jenkins, A.

2018-05-01

Synchronous coupling is developed between an ice sheet model and a z-coordinate ocean model (the MITgcm). A previously-developed scheme to allow continuous vertical movement of the ice-ocean interface of a floating ice shelf ("vertical coupling") is built upon to allow continuous movement of the grounding line, or point of floatation of the ice sheet ("horizontal coupling"). Horizontal coupling is implemented through the maintenance of a thin layer of ocean ( ∼ 1 m) under grounded ice, which is inflated into the real ocean as the ice ungrounds. This is accomplished through a modification of the ocean model's nonlinear free surface evolution in a manner akin to a hydrological model in the presence of steep bathymetry. The coupled model is applied to a number of idealized geometries and shown to successfully represent ocean-forced marine ice sheet retreat while maintaining a continuous ocean circulation.

Simulated E-Bomb Effects on Electronically Equipped Targets

DTIC Science & Technology

2009-09-01

coupling model program (CEMPAT), pursuing a feasible geometry of attack, practical antennas, best coupling approximations of ground conductivity and...procedure to determine these possible effects is to estimate the electromagnetic coupling from first principles and simulations using a coupling model ...Applications .................................... 16 B. SYSTEM OF INTEREST MODEL AS A TARGET ............................. 16 1. Shielding Methods, as

Coupled Vortex-Lattice Flight Dynamic Model with Aeroelastic Finite-Element Model of Flexible Wing Transport Aircraft with Variable Camber Continuous Trailing Edge Flap for Drag Reduction

NASA Technical Reports Server (NTRS)

Nguyen, Nhan; Ting, Eric; Nguyen, Daniel; Dao, Tung; Trinh, Khanh

2013-01-01

This paper presents a coupled vortex-lattice flight dynamic model with an aeroelastic finite-element model to predict dynamic characteristics of a flexible wing transport aircraft. The aircraft model is based on NASA Generic Transport Model (GTM) with representative mass and stiffness properties to achieve a wing tip deflection about twice that of a conventional transport aircraft (10% versus 5%). This flexible wing transport aircraft is referred to as an Elastically Shaped Aircraft Concept (ESAC) which is equipped with a Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for active wing shaping control for drag reduction. A vortex-lattice aerodynamic model of the ESAC is developed and is coupled with an aeroelastic finite-element model via an automated geometry modeler. This coupled model is used to compute static and dynamic aeroelastic solutions. The deflection information from the finite-element model and the vortex-lattice model is used to compute unsteady contributions to the aerodynamic force and moment coefficients. A coupled aeroelastic-longitudinal flight dynamic model is developed by coupling the finite-element model with the rigid-body flight dynamic model of the GTM.

Seizure Dynamics of Coupled Oscillators with Epileptor Field Model

NASA Astrophysics Data System (ADS)

Zhang, Honghui; Xiao, Pengcheng

The focus of this paper is to investigate the dynamics of seizure activities by using the Epileptor coupled model. Based on the coexistence of seizure-like event (SLE), refractory status epilepticus (RSE), depolarization block (DB), and normal state, we first study the dynamical behaviors of two coupled oscillators in different activity states with Epileptor model by linking them with slow permittivity coupling. Our research has found that when one oscillator in normal states is coupled with any oscillator in SLE, RSE or DB states, these two oscillators can both evolve into SLE states under appropriate coupling strength. And then these two SLE oscillators can perform epileptiform synchronization or epileptiform anti-synchronization. Meanwhile, SLE can be depressed when considering the fast electrical or chemical coupling in Epileptor model. Additionally, a two-dimensional reduced model is also given to show the effect of coupling number on seizures. Those results can help to understand the dynamical mechanism of the initiation, maintenance, propagation and termination of seizures in focal epilepsy.