Excited states in the soliton bag model
Saly, R.; Sundaresan, M.K.
1984-02-01
Numerical analysis of the solutions of the soliton bag model of Friedberg and Lee is performed. The recent analysis of Goldflam and Wilets is extended to include even-parity as well as odd-parity radially excited states. It is shown that the existence of the solutions (especially the odd-parity ones) restrict severely the allowed range of parameters.
Excited states of ribosome translocation revealed through integrative molecular modeling
Whitford, Paul C.; Ahmed, Aqeel; Yu, Yanan; Hennelly, Scott P.; Tama, Florence; Spahn, Christian M. T.; Onuchic, José N.; Sanbonmatsu, Karissa Y.
2011-01-01
The dynamic nature of biomolecules leads to significant challenges when characterizing the structural properties associated with function. While X-ray crystallography and imaging techniques (such as cryo-electron microscopy) can reveal the structural details of stable molecular complexes, strategies must be developed to characterize configurations that exhibit only marginal stability (such as intermediates) or configurations that do not correspond to minima on the energy landscape (such as transition-state ensembles). Here, we present a methodology (MDfit) that utilizes molecular dynamics simulations to generate configurations of excited states that are consistent with available biophysical and biochemical measurements. To demonstrate the approach, we present a sequence of configurations that are suggested to be associated with transfer RNA (tRNA) movement through the ribosome (translocation). The models were constructed by combining information from X-ray crystallography, cryo-electron microscopy, and biochemical data. These models provide a structural framework for translocation that may be further investigated experimentally and theoretically to determine the precise energetic character of each configuration and the transition dynamics between them. PMID:22080606
Excited states of ribosome translocation revealed through integrative molecular modeling.
Whitford, Paul C; Ahmed, Aqeel; Yu, Yanan; Hennelly, Scott P; Tama, Florence; Spahn, Christian M T; Onuchic, José N; Sanbonmatsu, Karissa Y
2011-11-22
The dynamic nature of biomolecules leads to significant challenges when characterizing the structural properties associated with function. While X-ray crystallography and imaging techniques (such as cryo-electron microscopy) can reveal the structural details of stable molecular complexes, strategies must be developed to characterize configurations that exhibit only marginal stability (such as intermediates) or configurations that do not correspond to minima on the energy landscape (such as transition-state ensembles). Here, we present a methodology (MDfit) that utilizes molecular dynamics simulations to generate configurations of excited states that are consistent with available biophysical and biochemical measurements. To demonstrate the approach, we present a sequence of configurations that are suggested to be associated with transfer RNA (tRNA) movement through the ribosome (translocation). The models were constructed by combining information from X-ray crystallography, cryo-electron microscopy, and biochemical data. These models provide a structural framework for translocation that may be further investigated experimentally and theoretically to determine the precise energetic character of each configuration and the transition dynamics between them. PMID:22080606
Shukla, S.
1994-12-31
Characteristics of mass spectra and decays of orbitally excited charm mesons and baryons, expected on the basis of quark models and Heavy Quark Symmetry, are briefly described. The difficulties associated with measurements on these excited states are discussed. The accuracy and reliability of currently available experimental information is examined. The reasons, for the widely accepted spin-parity assignments to the observed excited mesons and baryons, are stated. Finally, the experimental data, with the accepted spin-parity assignments, is compared with expectations based on quark models and Heavy Quark Symmetry.
NASA Astrophysics Data System (ADS)
Zhang, Yu; Zuo, Yan; Pan, Feng; Draayer, J. P.
2016-04-01
The spectral characteristics of the Lπ=0+ excited states in the interacting boson model are systematically investigated. It is found that various types of excited-state quantum phase transitions may widely occur in the model as functions of the excitation energy, which indicates that the phase diagram of the interacting boson model can be dynamically extended along the direction of the excitation energy. It has also been justified that the d -boson occupation probability ρ (E ) is qualified to be taken as the effective order parameter to identify these excited-state quantum phase transitions. In addition, the underlying relation between the excite-state quantum phase transition and the chaotic dynamics is also stated.
Wang, D.F.; Liu, J.T.
1996-07-01
We examine the ground state and excitations of the one-dimensional supersymmetric extended Hubbard model with long-range interaction. The ground state wave-function and low lying excitations are given explicitly in the form of a Jastrow product of two-body terms. This result motivates an asymptotic Bethe ansatz solution for the model. We present evidence that this solution is in fact exact and spans the complete spectrum of states. {copyright} {ital 1996 The American Physical Society.}
Entropy, chaos, and excited-state quantum phase transitions in the Dicke model.
Lóbez, C M; Relaño, A
2016-07-01
We study nonequilibrium processes in an isolated quantum system-the Dicke model-focusing on the role played by the transition from integrability to chaos and the presence of excited-state quantum phase transitions. We show that both diagonal and entanglement entropies are abruptly increased by the onset of chaos. Also, this increase ends in both cases just after the system crosses the critical energy of the excited-state quantum phase transition. The link between entropy production, the development of chaos, and the excited-state quantum phase transition is more clear for the entanglement entropy. PMID:27575109
Excited states of many-body systems in the fermion dynamical symmetry model with random interactions
NASA Astrophysics Data System (ADS)
Fu, G. J.; Zhao, Y. M.; Ping, J. L.; Arima, A.
2013-09-01
In this Brief Report we investigate excited yrast states under random interactions in the framework of the fermion dynamical symmetry model, for the ensemble with spin-0 ground states. Interesting correlations are seen between R6 and R4 (where RI≡EI1+/E21+) by using the Mallmann plot, for cases with both SP(6) symmetry and SO(8) symmetry.
Excited-state PAW Potentials: Modelling Hot-Dense Plasmas From First Principles
NASA Astrophysics Data System (ADS)
Hollebon, Patrick; Vinko, Sam; Ciricosta, Orlando; Wark, Justin
2015-11-01
Finite temperature density functional theory has proven to be a successful means of modelling warm and hot dense plasma systems, including the calculation of transport properties, equation of state and ionization potential depression. Such methods take into account the non-negligible influence of quantum mechanics on the electronic structure of these strongly coupled systems. We apply excited state frozen core potentials to model general core-hole states in high density plasma, allowing for the calculation of the electronic structure of a range of ionic configurations. The advantages of using excited-state potentials are explored and we investigate their application towards various response function calculations, with the results shown to be in good agreement with all-electron calculations at finite-temperatures.
Shell-model description of the charge form factor and the first excited state in /sup 4/He
Bevelacqua, J.J.
1982-09-01
A /sup 4/He shell-model formalism, including two- and three-body forces, is used to calculate ground and first excited state properties. Inclusion of the three-body force improves the calculated ground state rms radius, ground state form factor, and position of the /sup 4/He first excited state.
Compressed simulation of thermal and excited states of the one-dimensional X Y model
NASA Astrophysics Data System (ADS)
Boyajian, W. L.; Kraus, B.
2015-09-01
Since several years, the preparation and manipulation of a small number of quantum systems in a controlled and coherent way is feasible in many experiments. In fact, these experiments are nowadays commonly used for quantum simulation and quantum computation. As recently shown, such a system can, however, also be utilized to simulate specific behaviors of exponentially larger systems. That is, certain quantum computations can be performed by an exponentially smaller quantum computer. This compressed quantum computation can be employed to observe, for instance, the quantum phase transition of the one-dimensional (1D) X Y model using very few qubits. We extend here this notion to simulate the behavior of thermal as well as excited states of the 1D X Y model. In particular, we consider the 1D X Y model of a spin chain of n qubits and derive a quantum circuit processing only log(n ) qubits which simulates the original system. We demonstrate how the behavior of thermal as well as any eigenstate of the system can be efficiently simulated in this compressed fashion and present a quantum circuit on log(n ) qubits to measure the magnetization, the number of kinks, and correlations occurring in the thermal as well as any excited state of the original systems. Moreover, we derive compressed circuits to study time evolutions.
NASA Astrophysics Data System (ADS)
Jiménez, Andrea
2014-02-01
We study the unexpected asymptotic behavior of the degeneracy of the first few energy levels in the antiferromagnetic Ising model on triangulations of closed Riemann surfaces. There are strong mathematical and physical reasons to expect that the number of ground states (i.e., degeneracy) of the antiferromagnetic Ising model on the triangulations of a fixed closed Riemann surface is exponential in the number of vertices. In the set of plane triangulations, the degeneracy equals the number of perfect matchings of the geometric duals, and thus it is exponential by a recent result of Chudnovsky and Seymour. From the physics point of view, antiferromagnetic triangulations are geometrically frustrated systems, and in such systems exponential degeneracy is predicted. We present results that contradict these predictions. We prove that for each closed Riemann surface S of positive genus, there are sequences of triangulations of S with exactly one ground state. One possible explanation of this phenomenon is that exponential degeneracy would be found in the excited states with energy close to the ground state energy. However, as our second result, we show the existence of a sequence of triangulations of a closed Riemann surface of genus 10 with exactly one ground state such that the degeneracy of each of the 1st, 2nd, 3rd and 4th excited energy levels belongs to O( n), O( n 2), O( n 3) and O( n 4), respectively.
Das, Mousumi
2014-03-28
We studied the nature of the ground state and low-lying excited states of armchair polyacene oligomers (Polyphenanthrene) within long-range Pariser-Parr-Pople model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. The ground state of all armchair polyacenes studied is found to be singlet. The results show that lowest singlet dipole allowed excited state has higher energy for armchair polyacenes as compared to linear fused polyacenes. Moreover, unlike linear fused polyacenes, the lowest singlet excited state of these oligomers is always found to lie below the lowest dipole forbidden two-photon state indicating that these armchair polyacene oligomers strongly fluoresce. The calculations of low-lying excitations on singly and triply electron doped armchair polyacene oligomers show a low energy band with strong transition dipole moment that coupled to charge conductivity. This implies armchair polyacene posses novel field-effect transistor properties. PMID:24697451
Das, Mousumi
2014-03-28
We studied the nature of the ground state and low-lying excited states of armchair polyacene oligomers (Polyphenanthrene) within long-range Pariser-Parr-Pople model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. The ground state of all armchair polyacenes studied is found to be singlet. The results show that lowest singlet dipole allowed excited state has higher energy for armchair polyacenes as compared to linear fused polyacenes. Moreover, unlike linear fused polyacenes, the lowest singlet excited state of these oligomers is always found to lie below the lowest dipole forbidden two-photon state indicating that these armchair polyacene oligomers strongly fluoresce. The calculations of low-lying excitations on singly and triply electron doped armchair polyacene oligomers show a low energy band with strong transition dipole moment that coupled to charge conductivity. This implies armchair polyacene posses novel field-effect transistor properties.
NASA Astrophysics Data System (ADS)
Corral, Inés; González, Leticia
2007-10-01
The vertical excited spectrum of a model endoperoxide (cyclohexadieneendoperoxide) has been calculated using time dependent density functional theory (TD-DFT), resolution of the identity second order approximate coupled-cluster theory (RI-CC2), multiconfigurational complete active space self consistent field (CASSCF) and second order multi-state perturbation theory (MS-CASPT2). All theoretical methods predict the charge transfer πOO∗→πCC∗, and the πOO∗→σOO∗ excitation to be the lowest absorbing excited states. CASSCF optimized geometries for these states provide some hints about the photodissociation mechanisms as well as the emission spectrum of the molecule.
Decay widths of ground-state and excited {Xi}{sub b} baryons in a nonrelativistic quark model
Limphirat, Ayut; Kobdaj, Chinorat; Suebka, Prasart; Yan, Yupeng
2010-11-15
Decay processes of ground and excited bottom baryons are studied in the {sup 3}P{sub 0} nonrelativistic quark model with all model parameters fixed in the sector of light quarks. Using as an input the recent mass of {Xi}{sub b} and the theoretical masses of {Xi}{sub b}{sup *} and {Xi}{sub b}{sup '}, narrow decay widths are predicted for the ground-state bottom baryons {Xi}{sub b}{sup *} and {Xi}{sub b}{sup '}. The work predicts large decay widths, about 100 MeV for the {rho}-type orbital excitation states of {Xi}{sub b}.
A Dipole Model for Negative Steady-State Resistance in Excitable Membranes
Hamel, Bernard B.; Zimmerman, Irwin
1970-01-01
A dipole model is presented for ion flow in excitable membranes. This model considers the membrane to be composed of two distinct regions: a polar region and a nonpolar region. Further, the construction of an electrodiffusive formalism which takes explicit account of the energy of partition required by an ion for passage from external fluid to nonpolar region is presented. In the polar region a cooperative effect is considered which produces a configurational transition of the polar group dependent only on membrane voltage. A resulting change in voltage drop across the polar group is brought about by this configurational transition. This gives rise to a negative steady-state resistance for the equimolar case, in reasonable agreement with observation. The theory, in addition, is in reasonable accord with nonequimolar ion flow, and provides an explanation for such effects as the following: the intercept of the voltage-current characteristic, the ion membrane concentrations inferred from electrodiffusion theories, and the effects of polyvalent cations PMID:5471696
Girardeau, M. D.
2006-11-24
The ground and excited states of a one-dimensional (1D) spin-(1/2) Fermi gas (SFG) with both attractive zero-range odd-wave interactions and repulsive zero-range even-wave interactions are mapped exactly to a 1D Lieb-Liniger-Heisenberg (LLH) model with delta-function repulsions depending on isotropic Heisenberg spin-spin interactions, such that the complete SFG and LLH energy spectra are identical. The ground state in the ferromagnetic phase is given exactly by the Lieb-Liniger (LL) Bethe ansatz, and that in the antiferromagnetic phase by a variational method combining Bethe ansatz solutions of the LL and 1D Heisenberg models. There are excitation branches corresponding to LL type I and II phonons and spin waves, the latter behaving quadratically for small wave numbers in the ferromagnetic phase and linearly in the antiferromagnetic phase.
Charmonium excited state spectrum in lattice QCD
Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards
2008-02-01
Working with a large basis of covariant derivative-based meson interpolating fields we demonstrate the feasibility of reliably extracting multiple excited states using a variational method. The study is performed on quenched anisotropic lattices with clover quarks at the charm mass. We demonstrate how a knowledge of the continuum limit of a lattice interpolating field can give additional spin-assignment information, even at a single lattice spacing, via the overlap factors of interpolating field and state. Excited state masses are systematically high with respect to quark potential model predictions and, where they exist, experimental states. We conclude that this is most likely a result of the quenched approximation.
Jorner, Kjell; Emanuelsson, Rikard; Dahlstrand, Christian; Tong, Hui; Denisova, Aleksandra V; Ottosson, Henrik
2014-07-21
A new qualitative model for estimating the properties of substituted cyclopentadienes and siloles in their lowest ππ* excited states is introduced and confirmed through quantum chemical calculations, and then applied to explain earlier reported experimental excitation energies. According to our model, which is based on excited-state aromaticity and antiaromaticity, siloles and cyclopentadienes are cross-hyperconjugated "aromatic chameleons" that adapt their electronic structures to conform to the various aromaticity rules in different electronic states (Hückel's rule in the π(2) electronic ground state (S0) and Baird's rule in the lowest ππ* excited singlet and triplet states (S1 and T1)). By using pen-and-paper arguments, one can explain polarity changes upon excitation of substituted cyclopentadienes and siloles, and one can tune their lowest excitation energies by combined considerations of ground- and excited-state aromaticity/antiaromaticity effects. Finally, the "aromatic chameleon" model can be extended to other monocyclic compound classes of potential use in organic electronics, thereby providing a unified view of the S0, T1, and S1 states of a range of different cyclic cross-π-conjugated and cross-hyperconjugated compound classes. PMID:25043523
Ishow, Eléna; Clavier, Gilles; Miomandre, Fabien; Rebarz, Mateusz; Buntinx, Guy; Poizat, Olivier
2013-09-01
A series of emitting push-pull triarylamine derivatives, models of their widely used homologues in photonics and organic electronics, was investigated by steady-state and time-resolved spectroscopy. Their structural originality stems from the sole change of the electron-withdrawing substituent X (-H: 1, -CN: 2, -NO2: 3, -CHC(CN)2: 4), giving rise to efficient emission tuning from blue to red upon increasing the X electron-withdrawing character. All compounds are highly fluorescent in alkanes. The more polar compounds 2-4 undergo considerable Stokes shift and emission quenching in polar solvents. Femtosecond transient absorption data allowed us to identify the nature of the emissive state which varies as a function of the compound and surrounding polarity. A long-lived ππ* excited state with weak charge transfer character was found for 1. This excited state evolves into a long-lived ICT state with red-shifted emission for 2 in polar solvents. For 3 and 4, the ICT state is directly populated in all solvents. Long-lived and emissive in n-hexane, it relaxes in toluene to a new ICT' conformation with stronger charge transfer character and enhanced Stokes shift. In more polar THF, ethanol, and nitrile solvents, ICT relaxes to a dark excited state ICT'' with viscosity-dependent kinetics (<10 ps). The ICT'' state lifetime drops with increasing solvent polarity (150 ps for 3 in THF, 8.5 ps in butyronitrile, 1.9 ps in acetonitrile), denoting an efficient radiationless deactivation to the ground state (back charge transfer). This result reveals a very small S0-S1 energy gap at the relaxed ICT'' geometry, with a possible close-lying S0-S1 conical intersection, which suggests that the ICT → ICT'' process results from a structural change involving a large-amplitude molecular distortion. This fast structural change can account for the strong fluorescence quenching observed for 3 and 4 in polar solvents. Finally, the magnitude of intersystem crossing between the singlet and
NASA Astrophysics Data System (ADS)
Kurosaki, Yuzuru; Ho, Tak-San; Rabitz, Herschel
2016-05-01
The prospect of performing the open → cyclic ozone isomerization has attracted much research attention. Here we explore this consideration theoretically by performing quantum optimal control calculations to demonstrate the important role that excited-state dissociation channels could play in the isomerization transformation. In the calculations we use a three-state, one-dimensional dynamical model constructed from the lowest five 1A‧ potential energy curves obtained with high-level ab initio calculations. Besides the laser field-dipole couplings between all three states, this model also includes the diabatic coupling between the two excited states at an avoided crossing leading to competing dissociation channels that can further hinder the isomerization process. The present three-state optimal control simulations examine two possible control pathways previously considered in a two-state model, and reveal that only one of the pathways is viable, achieving a robust ∼95% yield to the cyclic target in the three-state model. This work represents a step towards an ultimate model for the open → cyclic ozone transformation capable of giving adequate guidance about the necessary experimental control field resources as well as an estimate of the ro-vibronic spectral character of cyclic ozone as a basis for an appropriate probe of its formation.
Identification of excited states and shell model description of the N=Z+1 nucleus {sup 91}Rh
Marginean, N.; Rusu, C.; Bucurescu, D.; Ionescu-Bujor, M.; Iordachescu, A.; Alvarez, C. Rossi; Bazzacco, D.; Lunardi, S.; Pavan, P.; Farnea, E.; Lenzi, S.M.; Menegazzo, R.; Ur, C.A.; De Angelis, G.; Axiotis, M.; Gadea, A.; Martinez, T.; Napoli, D.R.; Spolaore, P.; Zhang, Y.H.
2005-07-01
High-spin excited states have been identified in the N=Z+1 nucleus {sup 91}Rh with the reaction {sup 54}Fe({sup 40}Ca,p2n{gamma}) at 130 MeV, using the GASP array, the ISIS silicon array, and the n-ring detector system. Two structures have been observed, the positive-parity yrast sequence above the (9/2{sup +}) ground state and a sequence assigned to negative parity that is built on a possible (1/2{sup -}) isomeric state. The observed structures are compared with various shell-model calculations in the (p{sub 1/2},g{sub 9/2}) space.
Excited intruder states in {sup 32}Mg
Tripathi, Vandana; Tabor, S. L.; Bender, P.; Hoffman, C. R.; Lee, Sangjin; Pepper, K.; Perry, M.; Utsuno, Y.; Otsuka, T.; Mantica, P. F.; Pinter, J. S.; Stoker, J. B.; Cook, J. M.; Pereira, J.; Weisshaar, D.
2008-03-15
The low energy level structure of N=20 {sup 32}Mg obtained via {beta}-delayed {gamma} spectroscopy is reported. The level structure of {sup 32}Mg is found to be completely dominated by intruders. An inversion between the 1p-1h and 3p-3h states is observed for the negative parity states, similar to the 0p-0h and 2p-2h inversion for the positive parity states in these N{approx}20 nuclei. The intruder excited states, both positive and negative parity, are reasonably explained by Monte Carlo shell model calculations, which suggest a shrinking N=20 shell gap with decreasing Z.
Theoretical studies of electronically excited states
Besley, Nicholas A.
2014-10-06
Time-dependent density functional theory is the most widely used quantum chemical method for studying molecules in electronically excited states. However, excited states can also be computed within Kohn-Sham density functional theory by exploiting methods that converge the self-consistent field equations to give excited state solutions. The usefulness of single reference self-consistent field based approaches for studying excited states is demonstrated by considering the calculation of several types of spectroscopy including the infrared spectroscopy of molecules in an electronically excited state, the rovibrational spectrum of the NO-Ar complex, core electron binding energies and the emission spectroscopy of BODIPY in water.
Stochastic flow modeling : Quasi-Geostrophy, Taylor state and torsional wave excitation
NASA Astrophysics Data System (ADS)
gillet, N.; Jault, D.; Finlay, C. C.
2013-12-01
We reconstruct the core flow evolution over the period 1840-2010 under the quasi-geostrophic assumption, from the stochastic magnetic field model COV-OBS and its full model error covariance matrix. We make use of a prior information on the flow temporal power spectrum compatible with that of observed geomagnetic series. We account for errors of representativeness (subgrid processes associated with the unresolved field at small length-scales) that are correlated in space and time, using an iterative scheme. An ensemble approach allows us to measure the uncertainties within the recovered motions. Large length-scales flow features are naturally dominated by their equatorially symmetric component from about 1900 when the symmetry constraint is relaxed. Equipartition of the kinetic energy in both symmetries coincides with the poor prediction of decadal length-of-day changes in the XIXth century. We interpret this as an evidence for quasi-geostrophic rapid flow changes, and the consequence of a too loose data constraint during the oldest period. We manage to retrieve rapid flow changes over the past 60 yrs, and in particular modulated torsional waves predicting correctly interannual length-of day variations from 1950 onward. We propose a triggering mechanism for these waves involving non-zonal motions in the framework of Taylor's state.
Resource Paper: Molecular Excited State Relaxation Processes.
ERIC Educational Resources Information Center
Rhodes, William
1979-01-01
Develops the concept of oscillatory v dissipative limits as it applies to electronic excited state processes in molecular systems. Main emphasis is placed on the radiative and nonradiative dynamics of the excited state of a molecule prepared by interaction with light or some other excitation source. (BT)
NASA Astrophysics Data System (ADS)
Zschocke, Fabian; Vojta, Matthias
2015-07-01
Kitaev's compass model on the honeycomb lattice realizes a spin liquid whose emergent excitations are dispersive Majorana fermions and static Z2 gauge fluxes. We discuss the proper selection of physical states for finite-size simulations in the Majorana representation, based on a recent paper by F. L. Pedrocchi, S. Chesi, and D. Loss [Phys. Rev. B 84, 165414 (2011), 10.1103/PhysRevB.84.165414]. Certain physical observables acquire large finite-size effects, in particular if the ground state is not fermion-free, which we prove to generally apply to the system in the gapless phase and with periodic boundary conditions. To illustrate our findings, we compute the static and dynamic spin susceptibilities for finite-size systems. Specifically, we consider random-bond disorder (which preserves the solubility of the model), calculate the distribution of local flux gaps, and extract the NMR line shape. We also predict a transition to a random-flux state with increasing disorder.
Excited state baryon spectroscopy from lattice QCD
Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.
2011-10-31
Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting of levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.
Excited state baryon spectroscopy from lattice QCD
Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.
2011-10-31
Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting ofmore » levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.« less
Mohammed, Omar F; Xiao, Dequan; Batista, Victor S; Nibbering, Erik T J
2014-05-01
We combine ultrafast electronic and vibrational spectroscopy and computational modeling to investigate the photoinduced excited-state intramolecular hydrogen-transfer dynamics in 1,8-dihydroxy-9,10-anthraquinone (DHAQ) in tetrachloroethene, acetonitrile, dimethyl sulfoxide, and methanol. We analyze the electronic excited states of DHAQ with various possible hydrogen-bonding schemes and provide a general description of the electronic excited-state dynamics based on a systematic analysis of femtosecond UV/vis and UV/IR pump-probe spectroscopic data. Upon photoabsorption at 400 nm, the S2 electronic excited state is initially populated, followed by a rapid equilibration within 150 fs through population transfer to the S1 state where DHAQ exhibits ESIHT dynamics. In this equilibration process, the excited-state population is distributed between the 9,10-quinone (S2) and 1,10-quinone (S1) states while undergoing vibrational energy redistribution, vibrational cooling, and solvation dynamics on the 0.1-50 ps time scale. Transient UV/vis pump-probe data in methanol also suggest additional relaxation dynamics on the subnanosecond time scale, which we tentatively ascribe to hydrogen bond dynamics of DHAQ with the protic solvent, affecting the equilibrium population dynamics within the S2 and S1 electronic excited states. Ultimately, the two excited singlet states decay with a solvent-dependent time constant ranging from 139 to 210 ps. The concomitant electronic ground-state recovery is, however, only partial because a large fraction of the population relaxes to the first triplet state. From the similarity of the time scales involved, we conjecture that the solvent plays a crucial role in breaking the intramolecular hydrogen bond of DHAQ during the S2/S1 relaxation to either the ground or triplet state. PMID:24684387
Novoderezhkin, Vladimir I; Doust, Alexander B; Curutchet, Carles; Scholes, Gregory D; van Grondelle, Rienk
2010-07-21
We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex. PMID:20643051
NASA Astrophysics Data System (ADS)
Butel, Arnaud; Annaloro, Julien; Schneider, Ioan F.; Benredgem, Djamel
2011-08-01
In relation with the problem of space vehicles re-entry into the earth atmosphere, we have developed a nonlinear electronic and vibrational specific time-dependent Collisional-Radiative (CR) model for air plasma working between 100 Pa and atmospheric pressure and between 2000 K and 20000 K for the translation temperatures. 13 species are considered: N2, O2, NO, N, O, Ar, N+2 , O+2 , NO+ , N+ , O+ , Ar+ and electrons. This model takes into account a total of 335 different states separated in excited electronic states and vibrational states of N2, O2 and NO on their electronic ground state. Owing to the temperature levels involved, many elementary processes are considered. The CR model is partially validated by comparison with experimental results under atmospheric pressure. Time scales to reach the final steady state are derived. Two models of dissociation are tested with respect to the vibration-translation transfers. The excitation and vibrational temperature results are analyzed in a typical Heaviside-like case at constant pressure and temperature.
Radiative and Excited State Charmonium Physics
Jozef Dudek
2007-07-30
Renewed interest in the spectroscopy of charmonium has arisen from recent unexpected observations at $e^+e^-$ colliders. Here we report on a series of works from the previous two years examining the radiative physics of charmonium states as well as the mass spectrum of states of higher spin and internal excitation. Using new techniques applied to Domain-Wall and Clover quark actions on quenched isotropic and anisotropic lattices, radiative transitions and two-photon decays are considered for the first time. Comparisons are made with experimental results and with model approaches. Forthcoming application to the light-quark sector of relevance to experiments like Jefferson Lab's GlueX is discussed.
Computing electronic structures: A new multiconfiguration approach for excited states
Cances, Eric . E-mail: cances@cermics.enpc.fr; Galicher, Herve . E-mail: galicher@cermics.enpc.fr; Lewin, Mathieu . E-mail: lewin@cermic.enpc.fr
2006-02-10
We present a new method for the computation of electronic excited states of molecular systems. This method is based upon a recent theoretical definition of multiconfiguration excited states [due to one of us, see M. Lewin, Solutions of the multiconfiguration equations in quantum chemistry, Arch. Rat. Mech. Anal. 171 (2004) 83-114]. Our algorithm, dedicated to the computation of the first excited state, always converges to a stationary state of the multiconfiguration model, which can be interpreted as an approximate excited state of the molecule. The definition of this approximate excited state is variational. An interesting feature is that it satisfies a non-linear Hylleraas-Undheim-MacDonald type principle: the energy of the approximate excited state is an upper bound to the true excited state energy of the N-body Hamiltonian. To compute the first excited state, one has to deform paths on a manifold, like this is usually done in the search for transition states between reactants and products on potential energy surfaces. We propose here a general method for the deformation of paths which could also be useful in other settings. We also compare our method to other approaches used in Quantum Chemistry and give some explanation of the unsatisfactory behaviours which are sometimes observed when using the latter. Numerical results for the special case of two-electron systems are provided: we compute the first singlet excited state potential energy surface of the H {sub 2} molecule.
Excited states in DNA strands investigated by ultrafast laser spectroscopy.
Chen, Jinquan; Zhang, Yuyuan; Kohler, Bern
2015-01-01
Ultrafast laser experiments on carefully selected DNA model compounds probe the effects of base stacking, base pairing, and structural disorder on excited electronic states formed by UV absorption in single and double DNA strands. Direct π-orbital overlap between two stacked bases in a dinucleotide or in a longer single strand creates new excited states that decay orders of magnitude more slowly than the generally subpicosecond excited states of monomeric bases. Half or more of all excited states in single strands decay in this manner. Ultrafast mid-IR transient absorption experiments reveal that the long-lived excited states in a number of model compounds are charge transfer states formed by interbase electron transfer, which subsequently decay by charge recombination. The lifetimes of the charge transfer states are surprisingly independent of how the stacked bases are oriented, but disruption of π-stacking, either by elevating temperature or by adding a denaturing co-solvent, completely eliminates this decay channel. Time-resolved emission measurements support the conclusion that these states are populated very rapidly from initial excitons. These experiments also reveal the existence of populations of emissive excited states that decay on the nanosecond time scale. The quantum yield of these states is very small for UVB/UVC excitation, but increases at UVA wavelengths. In double strands, hydrogen bonding between bases perturbs, but does not quench, the long-lived excited states. Kinetic isotope effects on the excited-state dynamics suggest that intrastrand electron transfer may couple to interstrand proton transfer. By revealing how structure and non-covalent interactions affect excited-state dynamics, on-going experimental and theoretical studies of excited states in DNA strands can advance understanding of fundamental photophysics in other nanoscale systems. PMID:25326834
Excited state mass spectra of Λc+ baryon
NASA Astrophysics Data System (ADS)
Shah, Zalak; Thakkar, Kaushal; Rai, Ajay Kumar; Vinodkumar, P. C.
2016-05-01
The radial and orbital excited state masses of singly charmed Λc+ baryon is calculated using the Hypercentral Constituent Quark Model (hCQM). The first order correction is applied to the confinement coulomb plus power potential. The ground and excited state masses for JP=3/2+ are calculated. Our results are in good agreement with experimental and other theoretical predictions.
Excited States of Non-Isolated Chromophores
NASA Astrophysics Data System (ADS)
Matsika, S.; Kozak, C.; Kistler, K.
2009-06-01
The photophysical and photochemical behavior of nucleobases is very important because of their biological role as the building blocks in DNA and RNA. Great progress has been made in understanding the excited-state properties of single bases. In order to understand the photophysical properties of nucleobases in complex environments we have investigated their excited states (a) in aqueous solutions and (b) as π-stacked dimers in DNA. The solvatochromic shifts of the excited states of pyrimidine nucleobases in aqueous solution have been investigated using a combined QM/MM procedure where the quantum mechanical solute is described using high level multireference configuration interaction methods while molecular dynamics simulations are used to obtain the structure of the solvent around the solute in an average way. The excited states of π-stacked nucleobases have also been investigated using various ab initio methods. The effect of the environment on the excited states and conical intersections is investigated.
NASA Astrophysics Data System (ADS)
Liu, Jie; Liang, WanZhen
2013-01-01
This work extends our previous works [J. Liu and W. Z. Liang, J. Chem. Phys. 135, 014113 (2011), 10.1063/1.3605504; J. Liu and W. Z. Liang, J. Chem. Phys. 135, 184111 (2011)], 10.1063/1.3659312 on analytical excited-state Hessian within the framework of time-dependent density functional theory (TDDFT) to couple with a conductor-like polarizable continuum model (CPCM). The formalism, implementation, and application of analytical first and second energy derivatives of TDDFT/CPCM excited state with respect to the nuclear and electric perturbations are presented. Their performances are demonstrated by the calculations of excitation energies, excited-state geometries, and harmonic vibrational frequencies for a number of benchmark systems. The calculated results are in good agreement with the corresponding experimental data or other theoretical calculations, indicating the reliability of the current computer implementation of the developed algorithms. Then we made some preliminary applications to calculate the resonant Raman spectrum of 4-hydroxybenzylidene-2,3-dimethyl-imidazolinone in ethanol solution and the infrared spectra of ground and excited states of 9-fluorenone in methanol solution.
New Insights in 4f(12)5d(1) Excited States of Tm(2+) through Excited State Excitation Spectroscopy.
de Jong, Mathijs; Biner, Daniel; Krämer, Karl W; Barandiarán, Zoila; Seijo, Luis; Meijerink, Andries
2016-07-21
Optical excitation of ions or molecules typically leads to an expansion of the equilibrium bond lengths in the excited electronic state. However, for 4f(n-1)5d(1) excited states in lanthanide ions both expansion and contraction relative to the 4f(n) ground state have been reported, depending on the crystal field and nature of the 5d state. To probe the equilibrium distance offset between different 4f(n-1)5d(1) excited states, we report excited state excitation (ESE) spectra for Tm(2+) doped in CsCaBr3 and CsCaCl3 using two-color excited state excitation spectroscopy. The ESE spectra reveal sharp lines at low energies, confirming a similar distance offset for 4f(n-1)5d(t2g)(1) states. At higher energies, broader bands are observed, which indicate the presence of excited states with a different offset. On the basis of ab initio embedded-cluster calculations, the broad bands are assigned to two-photon d-d absorption from the excited state. In this work, we demonstrate that ESE is a powerful spectroscopic tool, giving access to information which cannot be obtained through regular one-photon spectroscopy. PMID:27347766
NASA Astrophysics Data System (ADS)
Guo, Y. Q.; Bhattacharya, A.; Bernstein, E. R.
2008-01-01
We report the first experimental and theoretical study of gas phase excited electronic state decomposition of a furazan based, high nitrogen content energetic material, 3,3'-diamino-4,4'-azoxyfurazan (DAAF), and its model systems, diaminofurazan (DAF) and furazan (C2H2N2O). DAAF has received major attention as an insensitive high energy explosive; however, the mechanism and dynamics of the decomposition of this material are not clear yet. In order to understand the initial decomposition mechanism of DAAF and those of its model systems, nanosecond energy resolved and femtosecond time resolved spectroscopies and complete active space self-consistent field (CASSCF) calculations have been employed to investigate the excited electronic state decomposition of these materials. The NO molecule is observed as an initial decomposition product from DAAF and its model systems at three UV excitation wavelengths (226, 236, and 248nm) with a pulse duration of 8ns. Energies of the three excitation wavelengths coincide with the (0-0), (0-1), and (0-2) vibronic bands of the NO A∑+2←X∏2 electronic transition, respectively. A unique excitation wavelength independent dissociation channel is observed for DAAF, which generates the NO product with a rotationally cold (20K ) and a vibrationally hot (1265K) distribution. On the contrary, excitation wavelength dependent dissociation channels are observed for the model systems, which generate the NO product with both rotationally cold and hot distributions depending on the excitation wavelengths. Potential energy surface calculations at the CASSCF level of theory illustrates that two conical intersections between the excited and ground electronic states are involved in two different excitation wavelength dependent dissociation channels for the model systems. Femtosecond pump-probe experiments at 226nm reveal that the NO molecule is still the main observed decomposition product from the materials of interest and that the formation
Guo, Y Q; Bhattacharya, A; Bernstein, E R
2008-01-21
We report the first experimental and theoretical study of gas phase excited electronic state decomposition of a furazan based, high nitrogen content energetic material, 3,3'-diamino-4,4'-azoxyfurazan (DAAF), and its model systems, diaminofurazan (DAF) and furazan (C2H2N2O). DAAF has received major attention as an insensitive high energy explosive; however, the mechanism and dynamics of the decomposition of this material are not clear yet. In order to understand the initial decomposition mechanism of DAAF and those of its model systems, nanosecond energy resolved and femtosecond time resolved spectroscopies and complete active space self-consistent field (CASSCF) calculations have been employed to investigate the excited electronic state decomposition of these materials. The NO molecule is observed as an initial decomposition product from DAAF and its model systems at three UV excitation wavelengths (226, 236, and 248 nm) with a pulse duration of 8 ns. Energies of the three excitation wavelengths coincide with the (0-0), (0-1), and (0-2) vibronic bands of the NO A 2Sigma+<--X 2Pi electronic transition, respectively. A unique excitation wavelength independent dissociation channel is observed for DAAF, which generates the NO product with a rotationally cold (20 K) and a vibrationally hot (1265 K) distribution. On the contrary, excitation wavelength dependent dissociation channels are observed for the model systems, which generate the NO product with both rotationally cold and hot distributions depending on the excitation wavelengths. Potential energy surface calculations at the CASSCF level of theory illustrates that two conical intersections between the excited and ground electronic states are involved in two different excitation wavelength dependent dissociation channels for the model systems. Femtosecond pump-probe experiments at 226 nm reveal that the NO molecule is still the main observed decomposition product from the materials of interest and that the formation
Influence of collective effects on lifetimes of condensed excited states
NASA Technical Reports Server (NTRS)
Zmuidzinas, Jonas Stasys
1987-01-01
The possibility that collective effects may dramatically influence autoionization-limited lifetimes of condensed excited states is investigated in the context of a two-band model of an insulator in a strong magnetic field. Two different mechanisms for suppressing autoionization are discussed which may prevent the potentially catastrophic destruction of the excited state. Under appropriate circumstances, the residual low-density Auger electrons may be confined in a superconducting state and paired by excitonic fluctuations in the conduction band.
Study of excited nucleon states at EBAC: status and plans
Hiroyuki Kamano
2009-12-01
We present an overview of a research program for the excited nucleon states in Excited Baryon Analysis Center (EBAC) at Jefferson Lab. Current status of our analysis of the meson production reactions based on the unitary dynamical coupled-channels model is summarized, and the N* pole positions extracted from the constructed scattering amplitudes are presented. Our plans for future developments are also discussed.
Isomeric States and Collective Excitations of Heaviest Nuclei
NASA Astrophysics Data System (ADS)
Adamian, G. G.; Antonenko, N. V.; Jolos, R. V.; Kuzmina, A. N.; Malov, L. A.; Shirikova, N. Yu.; Sushkov, A. V.
2013-03-01
The isotopic dependence of two-quasiparticle isomeric states in Fm and No is treated. An α-decay chain through the isomeric states of super-heavy nuclei is demonstrated. The excitation energies and the structure of the low lying states with Kπ = 0‒ 1‒ 2‒ are calculated with the quasiparticle phonon model.
Electronically excited states of PANH anions.
Theis, Mallory L; Candian, Alessandra; Tielens, Alexander G G M; Lee, Timothy J; Fortenberry, Ryan C
2015-06-14
The singly deprotonated anion derivatives of nitrogenated polycyclic aromatic hydrocarbons (PANHs) are investigated for their electronically excited state properties. These include single deprotonation of the two unique arrangements of quinoline producing fourteen different isomers. This same procedure is also undertaken for single deprotonation of the three nitrogenation isomers of acridine and the three of pyrenidine. It is shown quantum chemically that the quinoline-class of PANH anion derivatives can only produce a candidate dipole-bound excited state each, a state defined as the interaction of an extra electron with the dipole moment of the corresponding neutral. However, the acridine- and pyrenidine-classes possess valence excited states as well as the possible dipole-bound excited states where the latter is only possible if the dipole moment is sufficiently large to retain the extra electron; the valence excitation is independent of the radical dipolar strength. As a result, the theoretical vertically computed electronic spectra of deprotonated PANH anion derivatives is fairly rich in the 1.5 eV to 2.5 eV range significantly opening the possibilities for these molecules to be applied to longer wavelength studies of visible and near-IR spectroscopy. Lastly, the study of these systems is also enhanced by the inclusion of informed orbital arrangements in a simply constructed basis set that is shown to be more complete and efficient than standard atom-centered functions. PMID:25975430
Electron excitation from ground state to first excited state: Bohmian mechanics method
NASA Astrophysics Data System (ADS)
Yang, Song; Shuang, Zhao; Fu-Ming, Guo; Yu-Jun, Yang; Su-Yu, Li
2016-03-01
The excitation process of electrons from the ground state to the first excited state via the resonant laser pulse is investigated by the Bohmian mechanics method. It is found that the Bohmian particles far away from the nucleus are easier to be excited and are excited firstly, while the Bohmian particles in the ground state is subject to a strong quantum force at a certain moment, being excited to the first excited state instantaneously. A detailed analysis for one of the trajectories is made, and finally we present the space and energy distribution of 2000 Bohmian particles at several typical instants and analyze their dynamical process at these moments. Project supported by the Doctoral Research Start-up Funding of Northeast Dianli University, China (Grant No. BSJXM-201332), the National Natural Science Foundation of China (Grant Nos. 11547114, 11534004, 11474129, 11274141, 11447192, and 11304116), and the Graduate Innovation Fund of Jilin University, China (Grant No. 2015091).
Carlotti, B; Cesaretti, A; Gentili, P L; Marrocchi, A; Elisei, F; Spalletti, A
2016-08-17
The peculiar photobehaviour of a symmetrical arylenevinylene anthracene derivative bearing mild electron donors (alkoxy groups) at the sides of its structure has been fully comprehended through this study. An investigation into the effect of solvent polarity and temperature on the stationary fluorescence spectrum allowed a clear dual emission to be revealed. A further valuable insight was obtained, thanks to the employment of ultrafast spectroscopies. Fluorescence up-conversion measurements and the Time Resolved Area Normalised Spectra analysis provided a clear-cut proof of the presence of two distinct fluorescent states ((1)A* and (1)B*), with (1)A* being responsible for the steady-state emission in highly polar and viscous media. Femtosecond transient absorption spectra were acquired in several organic solvents of different polarity and viscosity. Interestingly, the lifetime of (1)A* was found to be dependent on solvent viscosity whereas the lifetime of (1)B* showed a trend which matches the change in solvent polarity. Indeed, the Density functional theory calculations predicted a structural rearrangement in the fully relaxed lowest excited singlet state. The (1)A* → (1)B* transition is thus likely accompanied by large amplitude motions of the molecular structure, with the (1)B* state also exhibiting a small intramolecular charge transfer character. The investigated flexible quadrupolar D-π-D system arouses therefore great interest as a novel material for applications in organic electronics and photonics. PMID:27499254
Investigation into chromophore excited-state coupling in allophycocyanin
NASA Astrophysics Data System (ADS)
Zheng, Xiguang; Zhao, Fuli; Wang, He Z.; Gao, Zhaolan; Yu, Zhenxin; Zhu, Jinchang; Xia, Andong; Jiang, Lijin
1994-08-01
Both theoretical and experimental studies are presented on chromophore excited-state coupling in linker-free allophycocyanin (APC), one of the antenna phycobiliproteins in algal photosynthesis. A three-site-coupling model has been introduced to describe the exciton interaction mechanism amoung the excited (beta) chromophore in APC, and the exciton energy splitting is estimated. Picosecond polarized fluorescence experiments both on monomeric and trimeric APC isolated from alga Spirulina platensis have been performed. The experimental results show that APC monomer and trimer exhibit remarkedly different spectropic characteristics, and satisfy the suggestion of strong excited- state coupling among chromophores in APC.
Alpha-cluster excited states in 32S
NASA Astrophysics Data System (ADS)
Yoshida, Yuta; Y. Kanada-En'yo Collaboration; F. Kobayashi Collaboration
2014-09-01
Excited states having core +alpha cluster structure called the alpha-cluster excited state are known to exist in such nuclei as 16O and 20Ne. Meanwhile, the existence of alpha-cluster excited states in the middle of sd-shell nuclei is an open problem. Recently, the alpha-cluster excited state in 32S is suggested by experiments. In order to understand the dynamics of the core-alpha relative motion, we focus on the structure change of the core nuclei and the breaking of the alpha-cluster. In the present work, we construct 28Si +alpha model which has the structure change of the 28Si core and the alpha-cluster breaking. Using the present model, we calculate the energy expectation value of 28Si +alpha system. We found that the structure change of the core nuclei is energetically rather important while the alpha-cluster breaking is not significant when the alpha-cluster exists at the surface of the 28Si core. We calculate the ground and excited states with the generator coordinate method. As a result, we suggest the existence of alpha-cluster excited states in 32S.
Direct observation of photoinduced bent nitrosyl excited-state complexes
Sawyer, Karma R.; Steele, Ryan P.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Head-Gordon, Martin; Harris, Charles B.
2008-06-28
Ground state structures with side-on nitrosyl ({eta}{sup 2}-NO) and isonitrosyl (ON) ligands have been observed in a variety of transition-metal complexes. In contrast, excited state structures with bent-NO ligands have been proposed for years but never directly observed. Here we use picosecond time-resolved infrared spectroscopy and density functional theory (DFT) modeling to study the photochemistry of Co(CO){sub 3}(NO), a model transition-metal-NO compound. Surprisingly, we have observed no evidence for ON and {eta}{sup 2}-NO structural isomers, but have observed two bent-NO complexes. DFT modeling of the ground and excited state potentials indicates that the bent-NO complexes correspond to triplet excited states. Photolysis of Co(CO){sub 3}(NO) with a 400-nm pump pulse leads to population of a manifold of excited states which decay to form an excited state triplet bent-NO complex within 1 ps. This structure relaxes to the ground triplet state in ca. 350 ps to form a second bent-NO structure.
Photoacoustic imaging of the excited state lifetime of fluorophores
NASA Astrophysics Data System (ADS)
Märk, Julia; Schmitt, Franz-Josef; Laufer, Jan
2016-05-01
Photoacoustic (PA) imaging using pump-probe excitation has been shown to allow the detection and visualization of fluorescent contrast agents. The technique relies upon inducing stimulated emission using pump and probe pulses at excitation wavelengths that correspond to the absorption and fluorescence spectra. By changing the time delay between the pulses, the excited state lifetime of the fluorophore is modulated to vary the amount of thermalized energy, and hence PA signal amplitude, to provide fluorophore-specific PA contrast. In this study, this approach was extended to the detection of differences in the excited state lifetime of fluorophores. PA waveforms were measured in solutions of a near-infrared fluorophore using simultaneous and time-delayed pump-probe excitation. The lifetime of the fluorophore solutions was varied by using different solvents and quencher concentrations. By calculating difference signals and by plotting their amplitude as a function of pump-probe time delay, a correlation with the excited state lifetime of the fluorophore was observed. The results agreed with the output of a forward model of the PA signal generation in fluorophores. The application of this method to tomographic PA imaging of differences in the excited state lifetime was demonstrated in tissue phantom experiments.
On the Electronically Excited States of Uracil
Epifanovsky, Evgeny; Kowalski, Karol; Fan, Peng-Dong; Valiev, Marat; Matsika, Spiridoula; Krylov, Anna
2008-10-09
Vertical excitation energies in uracil in the gas phase and in water solution are investigated by the equation-of-motion coupled-cluster and multi-reference configuration interaction methods. Basis set effects are found to be important for converged results. The analysis of electronic wave functions reveals that the lowest singlet states are predominantly of a singly excited character and are therefore well described by single-reference equation-of-motion methods augmented by a perturbative triples correction to account for dynamical correlation. Our best estimates for the vertical excitation energies for the lowest singlet n and are 5.0±0.1 eV and 5.3±0.1 eV, respectively. The solvent effects for these states are estimated to be +0.5 eV and ±0.1 eV, respectively. We attribute the difference between the computed vertical excitations and the maximum of the experimental absorption to strong vibronic interaction between the lowest A00 and A0 states leading to intensity borrowing by the forbidden transition.
NASA Astrophysics Data System (ADS)
Koh, Yang Wei
2016-04-01
We present an extensive numerical study of the Sherrington-Kirkpatrick model in a transverse field. Recent numerical studies of quantum spin glasses have focused on exact diagonalization of the full Hamiltonian for small systems (≈20 spins). However, such exact numerical treatments are difficult to apply on larger systems. We propose making an approximation by using only a subspace of the full Hilbert space spanned by low-lying excitations consisting of one-spin-flipped and two-spin-flipped states. The approximation procedure is carried out within the theoretical framework of the Hartree-Fock approximation and configuration interaction. Although not exact, our approach allows us to study larger system sizes comparable to that achievable by state-of-the-art quantum Monte Carlo simulations. We calculate two quantities of interest due to recent advances in quantum annealing, the ground-state energy and the energy gap between the ground and first excited states. For the energy gap, we derive a formula that enables it to be calculated using just the ground-state wave function, thereby circumventing the need to diagonalize the Hamiltonian. We calculate the scalings of the energy gap and the leading correction to the extensive part of the ground-state energy with system size, which are difficult to obtain with current methods.
STIRAP on helium: Excitation to Rydberg states
NASA Astrophysics Data System (ADS)
Yuan, Deqian
Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S→33P→nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of ~ 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable ~790 nm IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S → 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections.
Accelerating slow excited state proton transfer.
Stewart, David J; Concepcion, Javier J; Brennaman, M Kyle; Binstead, Robert A; Meyer, Thomas J
2013-01-15
Visible light excitation of the ligand-bridged assembly [(bpy)(2)Ru(a)(II)(L)Ru(b)(II)(bpy)(OH(2))(4+)] (bpy is 2,2'-bipyridine; L is the bridging ligand, 4-phen-tpy) results in emission from the lowest energy, bridge-based metal-to-ligand charge transfer excited state (L(-•))Ru(b)(III)-OH(2) with an excited-state lifetime of 13 ± 1 ns. Near-diffusion-controlled quenching of the emission occurs with added HPO(4)(2-) and partial quenching by added acetate anion (OAc(-)) in buffered solutions with pH control. A Stern-Volmer analysis of quenching by OAc(-) gave a quenching rate constant of k(q) = 4.1 × 10(8) M(-1) • s(-1) and an estimated pK(a)* value of ~5 ± 1 for the [(bpy)(2)Ru(a)(II)(L(•-))Ru(b)(III)(bpy)(OH(2))(4+)]* excited state. Following proton loss and rapid excited-state decay to give [(bpy)(2)Ru(a)(II)(L)Ru(b)(II)(bpy)(OH)(3+)] in a H(2)PO(4)(-)/HPO(4)(2-) buffer, back proton transfer occurs from H(2)PO(4)(-) to give [(bpy)(2)Ru(a)(II)(L)Ru(b)(bpy)(OH(2))(4+)] with k(PT,2) = 4.4 × 10(8) M(-1) • s(-1). From the intercept of a plot of k(obs) vs. [H(2)PO(4)(-)], k = 2.1 × 10(6) s(-1) for reprotonation by water providing a dramatic illustration of kinetically limiting, slow proton transfer for acids and bases with pK(a) values intermediate between pK(a)(H(3)O(+)) = -1.74 and pK(a)(H(2)O) = 15.7. PMID:23277551
Controlling chimera states: The influence of excitable units
NASA Astrophysics Data System (ADS)
Isele, Thomas; Hizanidis, Johanne; Provata, Astero; Hövel, Philipp
2016-02-01
We explore the influence of a block of excitable units on the existence and behavior of chimera states in a nonlocally coupled ring-network of FitzHugh-Nagumo elements. The FitzHugh-Nagumo system, a paradigmatic model in many fields from neuroscience to chemical pattern formation and nonlinear electronics, exhibits oscillatory or excitable behavior depending on the values of its parameters. Until now, chimera states have been studied in networks of coupled oscillatory FitzHugh-Nagumo elements. In the present work, we find that introducing a block of excitable units into the network may lead to several interesting effects. It allows for controlling the position of a chimera state as well as for generating a chimera state directly from the synchronous state.
Shoeb, Mohammad; Sonika
2009-08-15
The energies of the ground and excited 2{sup +} states of {sub {lambda}}{sub {lambda}}{sup 10}Be have been calculated variationally in the Monte Carlo framework. The hypernucleus is treated as a partial ten-body problem in the {lambda}{lambda}+{alpha}{alpha} model where nucleonic degrees of freedom of {alpha}'s are taken into consideration ignoring the antisymmetrization between two {alpha}'s. The central two-body {lambda}N and {lambda}{lambda} and the three-body dispersive and two-pion exchange {lambda}NN forces, constrained by the {lambda}p scattering data and the observed ground state energies of {sub {lambda}}{sup 5}He and {sub {lambda}}{sub {lambda}}{sup 6}He, are employed. The product-type trial wave function predicts binding energy for the ground state considerably less than for the event reported by Danysz et al.; however, it is consistent with the value deduced assuming a {gamma} ray of 3.04 MeV must have escaped undetected in the decay of the product {sub {lambda}}{sup 9}Be* {yields} {sub {lambda}}{sup 9}Be+{gamma} of the emulsion event {sub {lambda}}{sub {lambda}}{sup 10}Be{yields} {pi}{sup -}+p+{sub {lambda}}{sup 9}Be* and for the excited 2{sup +} state closer to the value measured in the Demachi-Yanagi event. The hypernucleus {sub {lambda}}{sub {lambda}}{sup 10}Be has an oblate shape in the excited state. These results are consistent with the earlier four-body {alpha} cluster model approach where {alpha}'s are assumed to be structureless entities.
Tuning ground states and excitations in complex electronic materials
Bishop, A.R.
1996-09-01
Modern electronic materials are characterized by a great variety of broken-symmetry ground states and excitations. Their control requires understanding and tuning underlying driving forces of spin-charge-lattice coupling, critical to macroscopic properties and applications. We report representative model calculations which demonstrate some of the richness of the phenomena and the challenges for successful microscopic modeling.
Photoionization from excited states of helium
NASA Technical Reports Server (NTRS)
Jacobs, V. L.
1973-01-01
The cross sections for photoionization from the 2 1S, 2 3S, 2 1P and 2 3P excited states of helium are calculated for photoelectron energies below the n = 2 threshold of He(+) using Hylleraas bound state wave functions and 1s-2s-2p close coupling final state wave functions. The resonant structures associated with the lowest-lying 1S, 1P, 3P, and 1D autoionizing states of helium are found to be characterized by large values of the line profile parameter q. The cross sections and the photoelectron angular distribution asymmetry parameters for the P-states are calculated for various polarization states of the target atom and the incident photon. Experiments which would lead to the separate determinations of the S- and D- wave partial photoionization cross sections are discussed.
α-cluster excited states in 32S
NASA Astrophysics Data System (ADS)
Yoshida, Yuta; Kanada-En'yo, Yoshiko; Kobayashi, Fumiharu
2016-04-01
α -cluster excited states in ^{32}S are investigated with an extended ^{28}Si+α cluster model, in which the ^{28}Si core deformation and rotation and the α -cluster breaking are incorporated. In the generator coordinate method calculation with the extended ^{28}Si+α cluster model, the α -cluster excited states are obtained near the ^{28}Si+α threshold energy. The ^{28}Si core deformation and rotation effects, and also the α -clusters breaking in the ^{28}Si+α system, are discussed. It is found that the rotation of the oblately deformed ^{28}Si core has a significant effect on the α -cluster excited states whereas the α -cluster breaking has only a minor effect.
Intermediate Excited States in Rhodopsin Photochemistry
NASA Astrophysics Data System (ADS)
Rothberg, L. J.; Yan, M.; Jedju, T. M.; Callender, R. H.; Chao, H.; Alfano, R. R.
1996-03-01
Recent work by Wang et.al. footnote Q. Wang et.al., Science 266, 422 (1994) reports rapid coherent photoisomerization in rhodopsin. The bathorhodopsin photoproduct appears in 200 fs and exhibits torsional oscillations which remain synchronized with the initial photoexcitation. We report transient absorption experiments which suggest that the fraction of excited rhodopsin molecules which does not isomerize in this fashion (approximately 1/3) remains in an electronically excited state, probably the twisted state described by Birge and Hubbard,footnote R. R. Birge and L. M. Hubbard, J. Am. Chem. Soc. 102, 2195 (1980) for ~ 3 ps and then reforms rhodopsin. This picture explains the long bleaching recovery time for rhodopsin and the controversial spectral dynamics which are observed in the red.
Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene
2015-05-14
State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor–acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene–perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.
Modeling Excited States in TiO2 Nanoparticles: On the Accuracy of a TD-DFT Based Description
Berardo, Enrico; Hu, Hanshi; Shevlin, S. A.; Woodley, Scott M.; Kowalski, Karol; Zwijnenburg, Martijn A.
2014-03-11
We have investigated the suitability of Time-Dependent Density Functional Theory (TD-DFT) to describe vertical low-energy excitations in naked and hydrated titanium dioxide nanoparticles through a comparison with results from Equation-of-Motion Coupled Cluster (EOM-CC) quantum chemistry methods. We demonstrate that for most TiO2 nanoparticles TD-DFT calculations with commonly used exchange-correlation (XC-)potentials (e.g. B3LYP) and EOM-CC methods give qualitatively similar results. Importantly, however, we also show that for an important subset of structures, TD-DFT gives qualitatively different results depending upon the XC-potential used and that in this case only TD-CAM-B3LYP and TD-BHLYP calculations yield results that are consistent with those obtained using EOM-CC theory. Moreover, we demonstrate that the discrepancies for such structures arise from a particular combination of defects, excitations involving which are charge-transfer excitations and hence are poorly described by XC-potentials that contain no or low fractions of Hartree-Fock like exchange. Finally, we discuss that such defects are readily healed in the presence of ubiquitously present water and that as a result the description of vertical low-energy excitations for hydrated TiO2 nanoparticles is hence non-problematic.
Ultrafast excited-state dynamics of isocytosine.
Szabla, Rafał; Góra, Robert W; Šponer, Jiří
2016-07-27
The alternative nucleobase isocytosine has long been considered as a plausible component of hypothetical primordial informational polymers. To examine this hypothesis we investigated the excited-state dynamics of the two most abundant forms of isocytosine in the gas phase (keto and enol). Our surface-hopping nonadiabatic molecular dynamics simulations employing the algebraic diagrammatic construction to the second order [ADC(2)] method for the electronic structure calculations suggest that both tautomers undergo efficient radiationless deactivation to the electronic ground state with time constants which amount to τketo = 182 fs and τenol = 533 fs. The dominant photorelaxation pathways correspond to ring-puckering (ππ* surface) and C[double bond, length as m-dash]O stretching/N-H tilting (nπ* surface) for the enol and keto forms respectively. Based on these findings, we infer that isocytosine is a relatively photostable compound in the gas phase and in these terms resembles biologically relevant nucleobases. The estimated S1 [radiolysis arrow - arrow with voltage kink] T1 intersystem crossing rate constant of 8.02 × 10(10) s(-1) suggests that triplet states might also play an important role in the overall excited-state dynamics of the keto tautomer. The reliability of ADC(2)-based surface-hopping molecular dynamics simulations was tested against multireference quantum-chemical calculations and the potential limitations of the employed ADC(2) approach are briefly discussed. PMID:27346684
Formation of metastable excited states during sputtering of transition metals
Wucher, A.; Sroubek, Z.
1997-01-01
We propose a simple model which treats the formation of metastable excited neutral atoms during sputtering of a transition metal as a two step process. First, the energy deposited into the electronic system of the solid by electronic energy losses of all moving particles in the collision cascade is considered to lead to a locally altered equilibrium electronic state of the solid. It is found that this step is dominated by collective interaction with the conduction band electrons rather than by electron promotion in binary atom-atom collisions. Second, sputtered excited atoms are assumed to be formed by resonant neutralization of excited ions (reflecting the altered equilibrium state) while crossing the surface. It is shown that this model explains the total as well as the velocity dependent excitation probability observed in recent experiments on sputtered neutral silver atoms, which cannot be understood in terms of existing theories describing the formation of excited states in sputtering. {copyright} {ital 1996} {ital The American Physical Society}
Quenching of excited triplet states by dissolved natural organic matter.
Wenk, Jannis; Eustis, Soren N; McNeill, Kristopher; Canonica, Silvio
2013-11-19
Excited triplet states of aromatic ketones and quinones are used as proxies to assess the reactivity of excited triplet states of the dissolved organic matter ((3)DOM*) in natural waters. (3)DOM* are crucial transients in environmental photochemistry responsible for contaminant transformation, production of reactive oxygen species, and potentially photobleaching of DOM. In recent photochemical studies aimed at clarifying the role of DOM as an inhibitor of triplet-induced oxidations of organic contaminants, aromatic ketones have been used in the presence of DOM, and the question of a possible interaction between their excited triplet states and DOM has emerged. To clarify this issue, time-resolved laser spectroscopy was applied to measure the excited triplet state quenching of four different model triplet photosensitizers induced by a suite of DOM from various aquatic and terrestrial sources. While no quenching for the anionic triplet sensitizers 4-carboxybenzophenone (CBBP) and 9,10-anthraquinone-2,6-disulfonic acid (2,6-AQDS) was detected, second-order quenching rate constants with DOM for the triplets of 2-acetonaphthone (2AN) and 3-methoxyacetophenone (3MAP) in the range of 1.30-3.85 × 10(7) L mol(C)(-1) s(-1) were determined. On the basis of the average molecular weight of DOM molecules, the quenching for these uncharged excited triplet molecules is nearly diffusion-controlled, but significant quenching (>10%) in aerated water is not expected to occur below DOM concentrations of 22-72 mg(C) L(-1). PMID:24083647
Direct Lifetime Measurements of the Excited States in (72)Ni.
Kolos, K; Miller, D; Grzywacz, R; Iwasaki, H; Al-Shudifat, M; Bazin, D; Bingham, C R; Braunroth, T; Cerizza, G; Gade, A; Lemasson, A; Liddick, S N; Madurga, M; Morse, C; Portillo, M; Rajabali, M M; Recchia, F; Riedinger, L L; Voss, P; Walters, W B; Weisshaar, D; Whitmore, K; Wimmer, K; Tostevin, J A
2016-03-25
The lifetimes of the first excited 2^{+} and 4^{+} states in ^{72}Ni were measured at the National Superconducting Cyclotron Laboratory with the recoil-distance Doppler-shift method, a model-independent probe to obtain the reduced transition probability. Excited states in ^{72}Ni were populated by the one-proton knockout reaction of an intermediate energy ^{73}Cu beam. γ-ray-recoil coincidences were detected with the γ-ray tracking array GRETINA and the S800 spectrograph. Our results provide evidence of enhanced transition probability B(E2;2^{+}→0^{+}) as compared to ^{68}Ni, but do not confirm the trend of large B(E2) values reported in the neighboring isotope ^{70}Ni obtained from Coulomb excitation measurement. The results are compared to shell model calculations. The lifetime obtained for the excited 4_{1}^{+} state is consistent with models showing decay of a seniority ν=4, 4^{+} state, which is consistent with the disappearance of the 8^{+} isomer in ^{72}Ni. PMID:27058074
Direct Lifetime Measurements of the Excited States in 72Ni
NASA Astrophysics Data System (ADS)
Kolos, K.; Miller, D.; Grzywacz, R.; Iwasaki, H.; Al-Shudifat, M.; Bazin, D.; Bingham, C. R.; Braunroth, T.; Cerizza, G.; Gade, A.; Lemasson, A.; Liddick, S. N.; Madurga, M.; Morse, C.; Portillo, M.; Rajabali, M. M.; Recchia, F.; Riedinger, L. L.; Voss, P.; Walters, W. B.; Weisshaar, D.; Whitmore, K.; Wimmer, K.; Tostevin, J. A.
2016-03-01
The lifetimes of the first excited 2+ and 4+ states in 72>Ni were measured at the National Superconducting Cyclotron Laboratory with the recoil-distance Doppler-shift method, a model-independent probe to obtain the reduced transition probability. Excited states in 72Ni were populated by the one-proton knockout reaction of an intermediate energy 73Cu beam. γ -ray-recoil coincidences were detected with the γ -ray tracking array GRETINA and the S800 spectrograph. Our results provide evidence of enhanced transition probability B (E 2 ;2+→0+) as compared to 68Ni, but do not confirm the trend of large B (E 2 ) values reported in the neighboring isotope 70Ni obtained from Coulomb excitation measurement. The results are compared to shell model calculations. The lifetime obtained for the excited 41+ state is consistent with models showing decay of a seniority ν =4 , 4+ state, which is consistent with the disappearance of the 8+ isomer in 72Ni.
NASA Astrophysics Data System (ADS)
Andzelm, Jan; Russo, Nino; Salahub, Dennis R.
1987-12-01
LCGTO-MP-LSD results are reported for the spectroscopic constants and electronic structure of the diatomic molecules Si2, Ge2, Sn2, SiGe, SiSn, and GeSn in their low-lying electronic states. For the homonuclear molecules we found that the ground state is 3Σ-g with the most important lower-lying excited states being 3Πu, 1Πu, and 1Σ+g, respectively. Our results are in good agreement with the available experimental data and also in qualitative agreement with other theoretical studies. We present here the first theoretical study on the heteronuclear molecules, for which experimental data are not available. We found the 3Σ- state to be the lowest, followed by 3Π and 1Σ+ states. Model potentials (MP) are reported for the Si, Ge, and Sn atoms. The reliable results for molecules complement those for the atoms and show that the LSD model potentials presented here allow for an accurate description of chemical bonding and spectroscopic properties in the title molecules.
Calculation of neutral beam deposition accounting for excited states
Gianakon, T.A.
1992-09-01
Large-scale neutral-beam auxillary heating of plasmas has led to new plasma operational regimes which are often dominated by fast ions injected via the absorption of an energetic beam of hydrogen neutrals. An accurate simulation of the slowing down and transport of these fast ions requires an intimate knowledge of the hydrogenic neutral deposition on each flux surface of the plasma. As a refinement to the present generation of transport codes, which base their beam deposition on ground-state reaction rates, a new set of routines, based on the excited states of hydrogen, is presented as mechanism for computing the attenuation and deposition of a beam of energetic neutrals. Additionally, the numerical formulations for the underlying atomic physics for hydrogen impacting on the constiuent plasma species is developed and compiled as a numerical database. Sample results based on this excited state model are compared with the ground-state model for simple plasma configurations.
Modeling Excited States in TiO2 Nanoparticles: On the Accuracy of a TD-DFT Based Description
2014-01-01
We have investigated the suitability of Time-Dependent Density Functional Theory (TD-DFT) to describe vertical low-energy excitations in naked and hydrated titanium dioxide nanoparticles. Specifically, we compared TD-DFT results obtained using different exchange-correlation (XC) potentials with those calculated using Equation-of-Motion Coupled Cluster (EOM-CC) quantum chemistry methods. We demonstrate that TD-DFT calculations with commonly used XC potentials (e.g., B3LYP) and EOM-CC methods give qualitatively similar results for most TiO2 nanoparticles investigated. More importantly, however, we also show that, for a significant subset of structures, TD-DFT gives qualitatively different results depending upon the XC potential used and that only TD-CAM-B3LYP and TD-BHLYP calculations yield results that are consistent with those obtained using EOM-CC theory. Moreover, we demonstrate that the discrepancies for such structures originate from a particular combination of defects that give rise to charge-transfer excitations, which are poorly described by XC potentials that do not contain sufficient Hartree–Fock like exchange. Finally, we consider that such defects are readily healed in the presence of ubiquitously present water and that, as a result, the description of vertical low-energy excitations for hydrated TiO2 nanoparticles is nonproblematic. PMID:24795544
Three Long Lived Excited States of Tm^-
NASA Astrophysics Data System (ADS)
O'Malley, Steven M.; Beck, Donald R.
2004-05-01
Recent measurements(V. T. Davis and J. S. Thompson, Phys. Rev. A 65), 010501 (2001). have yielded 2 Tm^- states with lifetimes >50 μs [2] with estimated electron affinities of ˜1 eV. Theory does not support a 4f attachment to the ground state(D. Datta and D. R. Beck, Phys. Rev. A 47), 5198 (1993)., and at most only a weak (<100 meV) 6p attachment(J. A. Chevary and S. H. Vosko, J. Phys. B 27), 657 (1994).. Our more accurate calculations for 4f, 5d, and 6p attachment to the ground state find no evidence of any bound state associated with these attachments. We then turned to attachment to ``low lying'' Tm I excited states. Candidates must have lifetimes >50 μs, unusually long for simpler species except for He^-, Be^-, and Ba^- (T. Andersen et al., J. Phys. Chem. Ref. Data 28), 1511 (1999).. Using a relativistic configuration interaction in the continuum methodology (Z. Cai, D. R. Beck, and W. F. Perger, Phys. Rev. A 43), 4660 (1991)., we have found 3 states, 4f^125d6s^26p (J=8,9,10), with lifetimes of 10 μs, 5 ms, and 3 ms, respectively. These are bound to their natural thresholds by 254, 258, and 173 meV and may represent what is being observed [2].
Description of electronic excited states using electron correlation operator.
Nichols, Bryan; Rassolov, Vitaly A
2013-09-14
The electron correlation energy in a chemical system is defined as a difference between the energy of an exact energy for a given Hamiltonian, and a mean-field, or single determinant, approximation to it. A promising way to model electron correlation is through the expectation value of a linear two-electron operator for the Kohn-Sham single determinant wavefunction. For practical reasons, it is desirable for such an operator to be universal, i.e., independent of the positions and types of nuclei in a molecule. The correlation operator models the effect of electron correlation on the interaction energy in a electron pair. We choose an operator expanded in a small number of Gaussians as a model for electron correlation, and test it by computing atomic and molecular adiabatic excited states. The computations are performed within the Δ Self-Consistent Field (ΔSCF) formalism, and are compared to the time-dependent density functional theory model with popular density functionals. The simplest form of the correlation operator contains only one parameter derived from the helium atom ground state correlation energy. The correlation operator approach significantly outperforms other methods in computation of atomic excitation energies. The accuracy of molecular excitation energies computed with the correlation operator is limited by the shortcomings of the ΔSCF methodology in describing excited states. PMID:24050332
Note: Excited State Studies of Ozone using State-Specific Multireference Coupled Cluster Methods
Bhaskaran-Nair, Kiran; Kowalski, Karol
2012-12-07
Vertical excitation energies obtained with state-specific multi-reference coupled cluster (MRCC) methods are reported for the ozone molecule. Using state-specific MRCC non-iterative methods with singles, doubles, and non-iterative triples (MRCCSD(T)) we obtain 4.40 eV for the challenging doubly excited 21A1 state when using a reliable model space. This estimate is in good agreement with experiment (4.5 eV). We also compare our MRCC results with the excitation energies obtained with high-order equation-of-motion coupled cluster methods
Pahari, Biswa Pathik; Chaudhuri, Sudip; Chakraborty, Sandipan; Sengupta, Pradeep K
2015-02-12
We performed spectroscopic and molecular modeling studies to explore the interaction of the bioactive plant flavonol robinetin (3,7,3',4',5'-OH flavone), with the carrier protein human serum albumin (HSA). Multiparametric fluorescence sensing, exploiting the intrinsic "two color" fluorescence of robinetin (comprising excited state intramolecular proton transfer (ESIPT) and charge transfer (CT) emissions) reveals that binding to HSA significantly affects the emission and excitation profiles, with strongly blue-shifted (∼29 nm) normal fluorescence and remarkable increase in the ESIPT fluorescence anisotropy (r) and lifetime (τ). Flavonol-induced HSA (tryptophan) fluorescence quenching data yield the dynamic quenching constant (KD) as 5.42 × 10(3) M(-1) and the association constant (Ks) as 5.59 × 10(4) M(-1). Time-resolved fluorescence anisotropy decay studies show dramatic (∼170 times) increase in the rotational correlation time (τ(rot)), reflecting greatly enhanced restrictions in motion of robinetin in the protein matrix. Furthermore, prominent induced circular dichroism (ICD) bands appear, indicating that the chiral environment of HSA strongly perturbs the electronic transitions of the intrinsically achiral robinetin molecule. Molecular docking calculations suggest that robinetin binds in subdomain IIA of HSA, where specific interactions with basic residues promote ground state proton abstraction and stabilize an anionic species, which is consistent with spectroscopic observations. PMID:25313717
Shoeb, Mohammad
2006-12-15
The energies of the degenerate spin-flip doublet (3{sup +}/2,5{sup +}/2) of {sub {lambda}}{sup 9}Be and of the 2{sup +} state of {sub {lambda}}{sub {lambda}}{sup 10}Be are analyzed in the {alpha} cluster model using a phenomenological dispersive three-body {lambda}{alpha}{alpha} force that reproduces the ground state energy of {sub {lambda}}{sup 9}Be. Two types of phenomenological {lambda}{alpha} and {alpha}{alpha} potentials and a few s-state {lambda}{lambda} potentials are taken as input. The energies of the excited states of the hypernuclei, treated as three- and four-body systems, calculated using the Variational Monte Carlo method, are in good agreement with the experimental values. Our results demonstrate that the existing data are insensitive to whether one employs a dispersive {lambda}{alpha}{alpha} force along with potentials in the relative angular momentum state l=0 and 2 as in the present work or whether one uses nonlocal {lambda}{alpha} potential as in earlier analyses.
Protein-induced excited-state dynamics of protochlorophyllide.
Hanf, Robert; Fey, Sonja; Dietzek, Benjamin; Schmitt, Michael; Reinbothe, Christiane; Reinbothe, Steffen; Hermann, Gudrun; Popp, Jürgen
2011-07-14
The light-driven NADPH:protochlorophyllide oxidoreductase (POR) is a key enzyme of chlorophyll biosynthesis in angiosperms. POR's unique requirement for light to become catalytically active makes the enzyme an attractive model to study the dynamics of enzymatic reactions in real time. Here, we use picosecond time-resolved fluorescence and femtosecond pump-probe spectroscopy to examine the influence of the protein environment on the excited-state dynamics of the substrate, protochlorophyllide (PChlide), in the enzyme/substrate (PChlide/POR) and pseudoternary complex including the nucleotide cofactor NADP(+) (PChlide/NADP(+)/ POR). In comparison with the excited-state processes of unbound PChlide, the lifetime of the thermally equilibrated S(1) excited state is lengthened from 3.4 to 4.4 and 5.4 ns in the PChlide/POR and PChlide/NADP(+)/POR complex, whereas the nonradiative rates are decreased by ∼30 and 40%, respectively. This effect is most likely due to the reduced probability of nonradiative decay into the triplet excited state, thus keeping the risk of photosensitized side reactions in the enzyme low. Further, the initial reaction path involves the formation of an intramolecular charge-transfer state (S(ICT)) as an intermediate product. From a strong blue shift in the excited-state absorption, it is concluded that the S(ICT) state is stabilized by local interactions with specific protein sites in the catalytic pocket. The possible relevance of this result for the catalytic reaction in the enzyme POR is discussed. PMID:21678944
Excited states of the odd-odd nucleus 230Pa
NASA Astrophysics Data System (ADS)
Kotthaus, T.; Reiter, P.; Hess, H.; Kalkühler, M.; Wendt, A.; Wiens, A.; Hertenberger, R.; Morgan, T.; Thirolf, P. G.; Wirth, H.-F.; Faestermann, T.
2013-04-01
The completely unknown spectrum of excited states of the odd-odd nucleus 230Pa was studied employing the one-neutron transfer reaction 231Pa(d,t)230Pa at a beam energy of 22 MeV. The excitation energy and the cross section were measured for, in total, 81 states below 1.4 MeV. Level assignments of these states are based on a semiempirical model and comparison with theoretical predictions, based on distorted-wave Born approximation (DWBA) calculations for the cross sections. For 12 rotational bands the band-head energy and the rotational parameter are determined. The K quantum numbers and the Nilsson configurations are established. Empirical values for the Gallagher-Moszkowski splittings and for Newby shifts are obtained.
Excited states in large molecular systems through polarizable embedding.
List, Nanna Holmgaard; Olsen, Jógvan Magnus Haugaard; Kongsted, Jacob
2016-07-27
In this perspective, we provide an overview of recent work within the polarizable embedding scheme to describe properties of molecules in realistic environments of increasing complexity. After an outline of the theoretical basis for the polarizable embedding model, we discuss the importance of using an accurate embedding potential, and how this may be used to significantly reduce the size of the part of the system treated using quantum mechanics without compromising the accuracy of the final results. Furthermore, we discuss the calculation of local electronic excited states based on response theory. We finally discuss aspects related to two recent extensions of the model (i) effective external field and (ii) polarizable density embedding emphasizing their importance for efficient yet accurate description of excited-state properties in complex environments. PMID:27416749
Gieseking, Rebecca L; Ratner, Mark A; Schatz, George C
2016-07-01
Quantum mechanical studies of Ag nanoclusters have shown that plasmonic behavior can be modeled in terms of excited states where collectivity among single excitations leads to strong absorption. However, new computational approaches are needed to provide understanding of plasmonic excitations beyond the single-excitation level. We show that semiempirical INDO/CI approaches with appropriately selected parameters reproduce the TD-DFT optical spectra of various closed-shell Ag clusters. The plasmon-like states with strong optical absorption comprise linear combinations of many singly excited configurations that contribute additively to the transition dipole moment, whereas all other excited states show significant cancellation among the contributions to the transition dipole moment. The computational efficiency of this approach allows us to investigate the role of double excitations at the INDO/SDCI level. The Ag cluster ground states are stabilized by slight mixing with doubly excited configurations, but the plasmonic states generally retain largely singly excited character. The consideration of double excitations in all cases improves the agreement of the INDO/CI absorption spectra with TD-DFT, suggesting that the SDCI calculation effectively captures some of the ground-state correlation implicit in DFT. These results provide the first evidence to support the commonly used assumption that single excitations are in many cases sufficient to describe the optical spectra of plasmonic excitations quantum mechanically. PMID:27259004
Lombardi, A; Faginas-Lago, N; Pacifici, L; Grossi, G
2015-07-21
Carbon dioxide molecules can store and release tens of kcal/mol upon collisions, and such an energy transfer strongly influences the energy disposal and the chemical processes in gases under the extreme conditions typical of plasmas and hypersonic flows. Moreover, the energy transfer involving CO2 characterizes the global dynamics of the Earth-atmosphere system and the energy balance of other planetary atmospheres. Contemporary developments in kinetic modeling of gaseous mixtures are connected to progress in the description of the energy transfer, and, in particular, the attempts to include non-equilibrium effects require to consider state-specific energy exchanges. A systematic study of the state-to-state vibrational energy transfer in CO2 + CO2 collisions is the focus of the present work, aided by a theoretical and computational tool based on quasiclassical trajectory simulations and an accurate full-dimension model of the intermolecular interactions. In this model, the accuracy of the description of the intermolecular forces (that determine the probability of energy transfer in molecular collisions) is enhanced by explicit account of the specific effects of the distortion of the CO2 structure due to vibrations. Results show that these effects are important for the energy transfer probabilities. Moreover, the role of rotational and vibrational degrees of freedom is found to be dominant in the energy exchange, while the average contribution of translations, under the temperature and energy conditions considered, is negligible. Remarkable is the fact that the intramolecular energy transfer only involves stretching and bending, unless one of the colliding molecules has an initial symmetric stretching quantum number greater than a threshold value estimated to be equal to 7. PMID:26203027
Lombardi, A. Faginas-Lago, N.; Pacifici, L.; Grossi, G.
2015-07-21
Carbon dioxide molecules can store and release tens of kcal/mol upon collisions, and such an energy transfer strongly influences the energy disposal and the chemical processes in gases under the extreme conditions typical of plasmas and hypersonic flows. Moreover, the energy transfer involving CO{sub 2} characterizes the global dynamics of the Earth-atmosphere system and the energy balance of other planetary atmospheres. Contemporary developments in kinetic modeling of gaseous mixtures are connected to progress in the description of the energy transfer, and, in particular, the attempts to include non-equilibrium effects require to consider state-specific energy exchanges. A systematic study of the state-to-state vibrational energy transfer in CO{sub 2} + CO{sub 2} collisions is the focus of the present work, aided by a theoretical and computational tool based on quasiclassical trajectory simulations and an accurate full-dimension model of the intermolecular interactions. In this model, the accuracy of the description of the intermolecular forces (that determine the probability of energy transfer in molecular collisions) is enhanced by explicit account of the specific effects of the distortion of the CO{sub 2} structure due to vibrations. Results show that these effects are important for the energy transfer probabilities. Moreover, the role of rotational and vibrational degrees of freedom is found to be dominant in the energy exchange, while the average contribution of translations, under the temperature and energy conditions considered, is negligible. Remarkable is the fact that the intramolecular energy transfer only involves stretching and bending, unless one of the colliding molecules has an initial symmetric stretching quantum number greater than a threshold value estimated to be equal to 7.
NASA Astrophysics Data System (ADS)
Lombardi, A.; Faginas-Lago, N.; Pacifici, L.; Grossi, G.
2015-07-01
Carbon dioxide molecules can store and release tens of kcal/mol upon collisions, and such an energy transfer strongly influences the energy disposal and the chemical processes in gases under the extreme conditions typical of plasmas and hypersonic flows. Moreover, the energy transfer involving CO2 characterizes the global dynamics of the Earth-atmosphere system and the energy balance of other planetary atmospheres. Contemporary developments in kinetic modeling of gaseous mixtures are connected to progress in the description of the energy transfer, and, in particular, the attempts to include non-equilibrium effects require to consider state-specific energy exchanges. A systematic study of the state-to-state vibrational energy transfer in CO2 + CO2 collisions is the focus of the present work, aided by a theoretical and computational tool based on quasiclassical trajectory simulations and an accurate full-dimension model of the intermolecular interactions. In this model, the accuracy of the description of the intermolecular forces (that determine the probability of energy transfer in molecular collisions) is enhanced by explicit account of the specific effects of the distortion of the CO2 structure due to vibrations. Results show that these effects are important for the energy transfer probabilities. Moreover, the role of rotational and vibrational degrees of freedom is found to be dominant in the energy exchange, while the average contribution of translations, under the temperature and energy conditions considered, is negligible. Remarkable is the fact that the intramolecular energy transfer only involves stretching and bending, unless one of the colliding molecules has an initial symmetric stretching quantum number greater than a threshold value estimated to be equal to 7.
Neutral Excitations in the Gaffnian state
NASA Astrophysics Data System (ADS)
Kang, Byungmin; Moore, Joel E.
The Fractional Quantum Hall Effect (FQHE) is one of the most well-studied systems having topological order. Starting with the pioneering work by Laughlin, the model wave function approach has been shown to provide essential information for understanding topological order in gapped incompressible states. We study a model wave function called the Gaffnian state which is believed to represent a gapless, strongly correlated state that is very different from conventional metals. To understand this exotic gapless state better, we provide a representation in which the pairing structure of the Gaffnian state becomes more explicit. We employ the single-mode approximation of the Girvin-MacDonald-Platzman (GMP) mode, which is a neutral collective exitation mode, in order to have a physical picture of the gaplessness of the Gaffnian state. In particular, we discuss how to extract systematically the relevant physics in the long-distance, large electron number limit of the FQH states using a numerical calculation with relatively few electrons.
NASA Astrophysics Data System (ADS)
Gammel, J. Tinka; Saxena, A.; Batistić, I.; Bishop, A. R.; Phillpot, S. R.
1992-03-01
We consider a 3/4-filled, two-band discrete tight-binding Peierls-Hubbard model for an isolated chain of a halogen-bridged, mixed-valence, transition-metal linear-chain complex (HMMC or MX chain). We have employed the adiabatic approximation in which the quantum fluctuations associated with phonons are implicitly treated as an external field for the electrons, and treat electron-electron effects in the Hartree-Fock approximation. We investigate ground states as functions of the model parameters and doping-induced and photoinduced excitations-kinks, polarons, bipolarons, and excitons. Results for several experimental observables, including the lattice distortion, the excess charge and spin densities of defects, and the optical absorption, are compiled. For the ground state, we find that the bond-order-wave (BOW) portion of the one-band phase diagram is eliminated from the two-band phase diagram, in agreement with the lack of real materials in the pure BOW phase. The extent of electron-hole asymmetry and of spatial localization or delocalization of defects is explored. Two separate solitons or polarons are compared with corresponding bipolarons. We demonstrate explicitly the need to employ the two-band model for a realistic modeling of the MX systems, focusing on three specific systems: (a) highly distorted, valence-localized (strongly charge-disproportionated) PtCl, (b) moderately distorted PtBr, and (c) weakly distorted, valence-delocalized (weak charge-density wave) PtI. The compilation of results reported here constitutes a reference resource against which the rapidly expanding experimental data can be compared.
Ground State and Excited State H-Atom Temperatures in a Microwave Plasma Diamond Deposition Reactor
NASA Astrophysics Data System (ADS)
Gicquel, A.; Chenevier, M.; Breton, Y.; Petiau, M.; Booth, J. P.; Hassouni, K.
1996-09-01
Ground electronic state and excited state H-atom temperatures are measured in a microwave plasma diamond deposition reactor as a function of a low percentage of methane introduced in the feed gas and the averaged input microwave power density. Ground state H-atom temperatures (T_H) and temperature of the H-atom in the n=3 excited state (T_{Hα}) are obtained from the measurements respectively of the excitation profile by Two-photon Allowed transition Laser Induced Fluorescence (TALIF) and the Hα line broadening by Optical Emission Spectroscopy (OES). They are compared to gas temperatures calculated with a 1D diffusive non equilibrium H{2} plasma flow model and to ground electronic state rotational temperatures of molecular hydrogen measured previously by Coherent Anti-Stokes Raman Spectroscopy.
Sub-50 fs excited state dynamics of 6-chloroguanine upon deep ultraviolet excitation.
Mondal, Sayan; Puranik, Mrinalini
2016-05-18
The photophysical properties of natural nucleobases and their respective nucleotides are ascribed to the sub-picosecond lifetime of their first singlet states in the UV-B region (260-350 nm). Electronic transitions of the ππ* type, which are stronger than those in the UV-B region, lie at the red edge of the UV-C range (100-260 nm) in all isolated nucleobases. The lowest energetic excited states in the UV-B region of nucleobases have been investigated using a plethora of experimental and theoretical methods in gas and solution phases. The sub-picosecond lifetime of these molecules is not a general attribute of all nucleobases but specific to the five primary nucleobases and a few xanthine and methylated derivatives. To determine the overall UV photostability, we aim to understand the effect of more energetic photons lying in the UV-C region on nucleobases. To determine the UV-C initiated photophysics of a nucleobase system, we chose a halogen substituted purine, 6-chloroguanine (6-ClG), that we had investigated previously using resonance Raman spectroscopy. We have performed quantitative measurements of the resonance Raman cross-section across the Bb absorption band (210-230 nm) and constructed the Raman excitation profiles. We modeled the excitation profiles using Lee and Heller's time-dependent theory of resonance Raman intensities to extract the initial excited state dynamics of 6-ClG within 30-50 fs after photoexcitation. We found that imidazole and pyrimidine rings of 6-ClG undergo expansion and contraction, respectively, following photoexcitation to the Bb state. The amount of distortions of the excited state structure from that of the ground state structure is reflected by the total internal reorganization energy that is determined at 112 cm(-1). The contribution of the inertial component of the solvent response towards the total reorganization energy was obtained at 1220 cm(-1). In addition, our simulation also yields an instantaneous response of the first
Excited-State Effective Masses in Lattice QCD
George Fleming, Saul Cohen, Huey-Wen Lin
2009-10-01
We apply black-box methods, i.e. where the performance of the method does not depend upon initial guesses, to extract excited-state energies from Euclidean-time hadron correlation functions. In particular, we extend the widely used effective-mass method to incorporate multiple correlation functions and produce effective mass estimates for multiple excited states. In general, these excited-state effective masses will be determined by finding the roots of some polynomial. We demonstrate the method using sample lattice data to determine excited-state energies of the nucleon and compare the results to other energy-level finding techniques.
Characterization of weakly excited final states by shakedown spectroscopy of laser-excited potassium
Schulz, J.; Heinaesmaeki, S.; Aksela, S.; Aksela, H.; Sankari, R.; Rander, T.; Lindblad, A.; Bergersen, H.; Oehrwall, G.; Svensson, S.; Kukk, E.
2006-07-15
3p shakedown spectra of laser excited potassium atoms as well as direct 3p photoemission of ground state potassium have been studied. These two excitation schemes lead to the same final states and thereby provide a good basis for a detailed study of the 3p{sup 5}(4s3d){sup 1} configurations of singly ionized potassium and the photoemission processes leading to these configurations. The comparison of direct photoemission from the ground state and conjugate shakedown spectra from 4p{sub 1/2} laser excited potassium made it possible to experimentally determine the character of final states that are only weakly excited in the direct photoemission but have a much higher relative intensity in the shakedown spectrum. Based on considerations of angular momentum and parity conservation the excitation scheme of the final states can be understood.
Excited State Properties of Hybrid Perovskites.
Saba, Michele; Quochi, Francesco; Mura, Andrea; Bongiovanni, Giovanni
2016-01-19
Metal halide perovskites have come to the attention of the scientific community for the progress achieved in solar light conversion. Energy sustainability is one of the priorities of our society, and materials advancements resulting in low-cost but efficient solar cells and large-area lighting devices represent a major goal for applied research. From a basic point of view, perovskites are an exotic class of hybrid materials combining some merits of organic and inorganic semiconductors: large optical absorption, large mobilities, and tunable band gap together with the possibility to be processed in solution. When a novel class of promising semiconductors comes into the limelight, lively discussions ensue on the photophysics of band-edge excitations, because just the states close to the band edge are entailed in energy/charge transport and light emission. This was the case several decades ago for III-V semiconductors, it has been up to 10 years ago for organics, and it is currently the case for perovskites. Our aim in this Account is to rationalize the body of experimental evidence on perovskite photophysics in a coherent theoretical framework, borrowing from the knowledge acquired over the years in materials optoelectronics. A crucial question is whether photon absorption leads to a population of unbound, conductive free charges or instead excitons, neutral and insulating bound states created by Coulomb interaction just below the energy of the band gap. We first focus on the experimental estimates of the exciton binding energy (Eb): at room temperature, Eb is comparable to the thermal energy kBT in MAPbI3 and increases up to values 2-3kBT in wide band gap MAPbBr3 and MAPbCl3. Statistical considerations predict that these values, even though comparable to or larger than thermal energy, let free carriers prevail over bound excitons for all levels of excitation densities relevant for devices. The analysis of photophysics evidence confirms that all hybrid halide
Generic two-variable model of excitability
NASA Astrophysics Data System (ADS)
Ventura, A. C.; Mindlin, G. B.; Dawson, S. Ponce
2002-04-01
We present a simple model that displays all classes of two-dimensional excitable regimes. One of the variables of the model displays the usual spikes observed in excitable systems. Since the model is written in terms of a ``standard'' vector field, it is always possible to fit it to experimental data displaying spikes in an algorithmic way. In fact, we use it to fit a series of membrane potential recordings obtained in the medicinal leech and time series generated with the FitzHugh-Nagumo equations and the excitability model of Eguía et al. [Phys. Rev. E 58, 2636 (1998)]. In each case, we determine the excitability class of the corresponding system.
NASA Astrophysics Data System (ADS)
Azuma, T.; Nakano, Y.; Metoki, K.; Hatakeyama, A.; Nakai, Y.; Komaki, K.; Yamazaki, Y.; Takada, E.; Murakami, T.
2009-11-01
Convoy electrons emitted from 416 MeV/u heliumlike Ar16+ ions excited by three-dimensional resonant coherent excitation (3D-RCE) have been explored. The 1s electron in the ground state was excited to the 2p state by a periodic crystal field during the passage through a Si crystal and released into the continuum by collisions with target atoms to form a cusp-shaped peak in the energy distribution, referred to as convoy electron. Under the resonance condition, we found not only enhancement of the convoy electron yield but also significant narrowing in the energy distribution, reflecting the initial bound state momentum distribution of the excited ions. This suggests that RCE is well-suited to study fast ion collisions involving the specific excited state.
Radiative Decays of Low-Lying Excited-State Hyperons
Simon Taylor
2000-05-01
The quark wave-functions of the lower-lying excited-state hyperons Lambda(1405), Sigma(1385), and Lambda(1520) are not well understood. For example, the Lambda(1405) may not be a regular three-quark state but a {bar K}N molecule. Several competing models have been proposed, but none have been convincingly eliminated. Measuring radiative decays provides a means of discriminating between the models. The radiative branching of ratios are predicted to be small ({approx}1%), but the radiative widths vary by factors of 2-10 from model to model. The existing experimental data is sparse and inconsistent; moreover, the radiative decay of the Sigma(1385) has never been observed before (except for one event). These lower-lying excited state hypersons were produced in a tagged photon-beam experiment in the CLAS detector at TJNAF in the reaction gamma p {yields} K{sup +} Y* for photon energies from threshold to 2.4 GeV. The radiative branching ration for the Sigma{sup 0}(1385) relative to the Sigma{sup 0}(1385) {yields} Lambda pi{sup 0} channel was measured to be 0.021 {+-} 0.008{sub -0.007}{sup +0.004}, corresponding to a partial width of 640 {+-} 270{sub -220}{sup +130} keV.
The triplet excited state of Bodipy: formation, modulation and application.
Zhao, Jianzhang; Xu, Kejing; Yang, Wenbo; Wang, Zhijia; Zhong, Fangfang
2015-12-21
Boron dipyrromethene (Bodipy) is one of the most extensively investigated organic chromophores. Most of the investigations are focused on the singlet excited state of Bodipy, such as fluorescence. In stark contrast, the study of the triplet excited state of Bodipy is limited, but it is an emerging area, since the triplet state of Bodipy is tremendously important for several areas, such as the fundamental photochemistry study, photodynamic therapy (PDT), photocatalysis and triplet-triplet annihilation (TTA) upconversion. The recent developments in the study of the production, modulation and application of the triplet excited state of Bodipy are discussed in this review article. The formation of the triplet state of Bodipy upon photoexcitation, via the well known approach such as the heavy atom effect (including I, Br, Ru, Ir, etc.), and the new methods, such as using a spin converter (e.g. C60), charge recombination, exciton coupling and the doubly substituted excited state, are summarized. All the Bodipy-based triplet photosensitizers show strong absorption of visible or near IR light and the long-lived triplet excited state, which are important for the application of the triplet excited state in PDT or photocatalysis. Moreover, the methods for switching (or modulation) of the triplet excited state of Bodipy were discussed, such as those based on the photo-induced electron transfer (PET), by controlling the competing Förster-resonance-energy-transfer (FRET), or the intermolecular charge transfer (ICT). Controlling the triplet excited state will give functional molecules such as activatable PDT reagents or molecular devices. It is worth noting that switching of the singlet excited state and the triplet state of Bodipy may follow different principles. Application of the triplet excited state of Bodipy in PDT, hydrogen (H2) production, photoredox catalytic organic reactions and TTA upconversion were discussed. The challenges and the opportunities in these areas were
Quenching rate constants of excited halogen atoms in quartet states
NASA Astrophysics Data System (ADS)
Mizuta, K.; Kuramasu, T.; Ishikawa, Y.; Arai, S.
1994-04-01
Excited halogen atoms in quartet spin states F*(2p43s, 4P5/2), Cl*(3p44s, 4P5/2), and Br*(4p45s, 4P5/2) were produced from helium sensitized radiation chemical decomposition of SF6, CF3Cl, CF3Br, and CF2Br2. Quenching rate constants of these excited halogen atoms by simple gas molecules such as O2, N2, H2, CO, CO2, NO, NO2, N2O, CH4, C2H6, and Xe including parent molecules were determined from absorption decay curves at 685.8 nm for F*, 837.5 nm for Cl*, and 827.4 nm for Br*. The optical densities were assumed to be proportional to (number of excited atoms per one cubic centimeter)0.9. The quenching rate constants obtained here were compared to those reported of metastable rare-gas atoms and an excited oxygen atom O*(2p33s, 5S2), and further discussed in terms of several theoretical kinetic models.
Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHS) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calcu...
Radiative recombination and excited-state photoionization of lithium
Lahiri, J. ); Manson, S.T. )
1993-11-01
The radiative-recombination rate coefficients for electrons impinging on Li[sup +], along with the associated excited-state photoionization cross sections for Li, are calculated in the low-energy region. In addition to the totals, the contribution of the recombination of individual excited states to the total is discussed.
Experimental Investigation of Excited-State Lifetimes in Atomic Ytterbium
Bowers, C.J.; Budker, D.; Commins, E.D.; DeMille, D.; Freedman, S.J.; Nguyen, A.-T.; Shang, S.-Q.; Zolotorev, M.; /SLAC
2011-11-15
Lifetimes of 21 excited states in atomic Yb were measured using time-resolved fluorescence detection following pulsed laser excitation. The lifetime of the 4f{sup 14}5d6s {sup 3}D{sub 1} state, which is of particular importance for a proposed study of parity nonconservation in atoms, was measured to be 380(30) ns.
Excited State Isomerization of a Stilbene Analog: E / Z Phenylvinylacetylene
NASA Astrophysics Data System (ADS)
Newby, Josh J.; Müller, Christian W.; Liu, Ching-Ping; Lee, Hsiupu D.; Zwier, Timothy S.
2009-06-01
The excited state isomerization of the E and Z forms of phenylvinylacetylene (PVA, 1-phenyl-1-buten-3-yne) has been studied using ultraviolet population transfer spectroscopy (UVPT). UVPT is a pump-probe experiment, where single isomers are selectively excited and after a wait time, the induced change in population of reactant and product isomers is probed. In these experiments, after initial cooling, an isomer of PVA is selectively excited to vibrational levels in the S_{1} electronic state. If the energy supplied by the excitation is above the barrier to isomerization population can be transferred into a product well. Excited molecules are collisionally cooled via supersonic expansion and a new population distribution can be detected downstream via R2PI spectroscopy. From these experiments, product isomerization quantum yields have been determined for both E to Z and Z to E excited state pathways as a function of excess energy above the S_{1} origin.
Charge-displacement analysis for excited states
Ronca, Enrico Tarantelli, Francesco; Pastore, Mariachiara Belpassi, Leonardo; De Angelis, Filippo; Angeli, Celestino; Cimiraglia, Renzo
2014-02-07
We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.
Charge-displacement analysis for excited states
NASA Astrophysics Data System (ADS)
Ronca, Enrico; Pastore, Mariachiara; Belpassi, Leonardo; De Angelis, Filippo; Angeli, Celestino; Cimiraglia, Renzo; Tarantelli, Francesco
2014-02-01
We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.
Excited state lifetime during photostimulated desorption of no from a Pt surface
NASA Astrophysics Data System (ADS)
Magkoev, T. T.
1998-07-01
We analyze the rotational energy distribution N(J) for NO molecules desorbed from a Pt (111) surface, taking into account the valence electron excitations, using a simple impulse model. We find a linear dependence between ln N(J) and (Er)1/2, where Er is the rotational energy of the desorbed molecules. The excited state lifetime and the critical residence time in the excited state, evaluated from the given dependences, are close to each other, and in order of magnitude are 10-15 s. We also estimate the frequency and amplitude of the tilting vibrations of the adsorbed molecules in the excited state.
Four-body model for transfer excitation
Harris, A. L.; Peacher, J. L.; Madison, D. H.; Colgan, J.
2009-12-15
We present here a four-body model for transfer-excitation collisions, which we call the four-body transfer-excitation (4BTE) model. Each two-body interaction is explicitly included in the 4BTE model, allowing us to study the effects of individual two-body interactions. We apply our model to fully differential cross sections for proton+helium collisions, and study the effect of the incident projectile-atom interaction, the scattered projectile-ion interaction, the projectile-nuclear interaction, and electron correlation within the target atom.
Preparation of stable excited states in an optical lattice via sudden quantum quench
Wang, Li; Chen, Shu; Hao, Yajiang
2010-06-15
We study how stable excited many-body states of the Bose-Hubbard model, including both the gaslike state for strongly attractive bosons and bound cluster state for repulsive bosons, can be produced with cold bosonic atoms in an one-dimensional optical lattice. Starting from the initial ground states of strongly interacting bosonic systems, we can achieve stable excited states of the systems with opposite interaction strength by suddenly switching the interaction to the opposite limit. By exactly solving dynamics of the Bose-Hubbard model, we demonstrate that the produced excited state can be a very stable dynamic state. This allows the experimental study of excited state properties of ultracold atoms system in optical lattices.
Excited states of methylene from quantum Monte Carlo.
Zimmerman, Paul M; Toulouse, Julien; Zhang, Zhiyong; Musgrave, Charles B; Umrigar, C J
2009-09-28
The ground and lowest three adiabatic excited states of methylene are computed using the variational Monte Carlo and diffusion Monte Carlo (DMC) methods using progressively larger Jastrow-Slater multideterminant complete active space (CAS) wave functions. The highest of these states has the same symmetry, (1)A(1), as the first excited state. The DMC excitation energies obtained using any of the CAS wave functions are in excellent agreement with experiment, but single-determinant wave functions do not yield accurate DMC energies of the states of (1)A(1) symmetry, indicating that it is important to include in the wave function Slater determinants that describe static (strong) correlation. Excitation energies obtained using recently proposed pseudopotentials [Burkatzki et al., J. Chem. Phys. 126, 234105 (2007)] differ from the all-electron excitation energies by at most 0.04 eV. PMID:19791848
Self-scattering for Dark Matter with an excited state
Schutz, Katelin; Slatyer, Tracy R. E-mail: tslatyer@mit.edu
2015-01-01
Self-interacting dark matter scenarios have recently attracted much attention, as a possible means to alleviate the tension between N-body simulations and observations of the dark matter distribution on galactic and sub-galactic scales. The presence of internal structure for the dark matter—for example, a nearly-degenerate state in the spectrum that could decay, or be collisionally excited or de-excited—has also been proposed as a possible means to address these discrepancies. Such internal structure can be a source of interesting signatures in direct and indirect dark matter searches, for example providing a novel explanation for the 3.5 keV line recently observed in galaxies and galaxy clusters. We analyze a simple model of dark matter self-scattering including a nearly-degenerate excited state, and develop an accurate analytic approximation for the elastic and inelastic s-wave cross sections, which is valid outside the perturbative regime provided the particle velocity is sufficiently low (this condition is also required for the s-wave to dominate over higher partial waves). We anticipate our results will be useful in incorporating inelastic self-scattering into N-body simulations, in order to study the quantitative impact of nearly-degenerate states in the dark matter spectrum on galactic structure and dynamics, and in computing the indirect signatures of multi-state dark matter.
Large degeneracy of excited hadrons and quark models
Bicudo, P.
2007-11-01
The pattern of a large approximate degeneracy of the excited hadron spectra (larger than the chiral restoration degeneracy) is present in the recent experimental report of Bugg. Here we try to model this degeneracy with state of the art quark models. We review how the Coulomb Gauge chiral invariant and confining Bethe-Salpeter equation simplifies in the case of very excited quark-antiquark mesons, including angular or radial excitations, to a Salpeter equation with an ultrarelativistic kinetic energy with the spin-independent part of the potential. The resulting meson spectrum is solved, and the excited chiral restoration is recovered, for all mesons with J>0. Applying the ultrarelativistic simplification to a linear equal-time potential, linear Regge trajectories are obtained, for both angular and radial excitations. The spectrum is also compared with the semiclassical Bohr-Sommerfeld quantization relation. However, the excited angular and radial spectra do not coincide exactly. We then search, with the classical Bertrand theorem, for central potentials producing always classical closed orbits with the ultrarelativistic kinetic energy. We find that no such potential exists, and this implies that no exact larger degeneracy can be obtained in our equal-time framework, with a single principal quantum number comparable to the nonrelativistic Coulomb or harmonic oscillator potentials. Nevertheless we find it plausible that the large experimental approximate degeneracy will be modeled in the future by quark models beyond the present state of the art.
18Ne Excited States Two-Proton Decay
NASA Astrophysics Data System (ADS)
de Napoli, M.; Rapisarda, E.; Raciti, G.; Cardella, G.; Amorini, F.; Giacoppo, F.; Sfienti, C.
2008-04-01
Two-proton radioactivity studies have been performed on excited states of 18Ne produced by 20Ne fragmentation at the FRS of the Laboratori Nazionali del Sud and excited via Coulomb excitation on a 209Pb target. The 18Ne levels decay has been studied by complete kinematical reconstruction. In spite of the low statistic, the energy and angular correlations of the emitted proton pairs indicate the presence of 2He emission toghether with the democratic decay.
NASA Astrophysics Data System (ADS)
Casida, Mark E.; Gutierrez, Fabien; Guan, Jingang; Gadea, Florent-Xavier; Salahub, Dennis; Daudey, Jean-Pierre
2000-11-01
Time-dependent density-functional theory (TDDFT) is an increasingly popular approach for calculating molecular excitation energies. However, the TDDFT lowest triplet excitation energy, ωT, of a closed-shell molecule often falls rapidly to zero and then becomes imaginary at large internuclear distances. We show that this unphysical behavior occurs because ωT2 must become negative wherever symmetry breaking lowers the energy of the ground state solution below that of the symmetry unbroken solution. We use the fact that the ΔSCF method gives a qualitatively correct first triplet excited state to derive a "charge-transfer correction" (CTC) for the time-dependent local density approximation (TDLDA) within the two-level model and the Tamm-Dancoff approximation (TDA). Although this correction would not be needed for the exact exchange-correlation functional, it is evidently important for a correct description of molecular excited state potential energy surfaces in the TDLDA. As a byproduct of our analysis, we show why TDLDA and LDA ΔSCF excitation energies are often very similar near the equilibrium geometries. The reasoning given here is fairly general and it is expected that similar corrections will be needed in the case of generalized gradient approximations and hybrid functionals.
Closser, Kristina D; Ge, Qinghui; Mao, Yuezhi; Shao, Yihan; Head-Gordon, Martin
2015-12-01
We develop a local excited-state method, based on the configuration interaction singles (CIS) wave function, for large atomic and molecular clusters. This method exploits the properties of absolutely localized molecular orbitals (ALMOs), which strictly limits the total number of excitations, and results in formal scaling with the third power of the system size for computing the full spectrum of ALMO-CIS excited states. The derivation of the equations and design of the algorithm are discussed in detail, with particular emphasis on the computational scaling. Clusters containing ∼500 atoms were used in evaluating the scaling, which agrees with the theoretical predictions, and the accuracy of the method is evaluated with respect to standard CIS. A pioneering application to the size dependence of the helium cluster spectrum is also presented for clusters of 25-231 atoms, the largest of which results in the computation of 2310 excited states per sampled cluster geometry. PMID:26609558
Vander Wal, R.L.; Scott, J.L.; Crim, F.F. )
1991-02-01
The state resolved photodissociation of highly vibrationally excited water molecules using laser induced fluorescence detection of the OH product demonstrates the control that the initially selected state exerts over product state populations. These vibrationally mediated photodissociation experiments, in which one photon prepares a highly vibrationally excited molecule and a second photon dissociates it, determine the role of overall rotations and of O--H stretching vibrations as well as measure the relative cross section for the photodissociation of water. The {ital rotational} {ital state} of the vibrationally excited water molecule governs the rotational state of the OH product of the dissociation, in agreement with {ital ab} {ital initio} calculations and previous measurements on single rotational states excited in the fundamental asymmetric stretching vibration band. The initially selected {ital vibrational} {ital state} of the water molecule determines the vibrational energy disposal in the products, which agrees with a simple qualitative model based on the pattern of the initially selected vibrational wave function. Dissociating vibrational states with similar energies but very different nuclear motions produces dramatically different product vibrational state populations. The vibrational energy initially present in the surviving bond primarily appears as vibrational excitation of the product. Dissociation of the {vert bar}04{r angle}{sup {minus}} state produces no vibrationally excited OH, but dissociation of the {vert bar}13{r angle}{sup {minus}} state produces mostly vibrationally excited products.
An 'all pigment' model of excitation quenching in LHCII.
Chmeliov, Jevgenij; Bricker, William P; Lo, Cynthia; Jouin, Elodie; Valkunas, Leonas; Ruban, Alexander V; Duffy, Christopher D P
2015-06-28
The rapid, photoprotective down-regulation of plant light-harvesting in bright light proceeds via the non-photochemical quenching of chlorophyll excitation energy in the major photosystem II light-harvesting complex LHCII. However, there is currently no consensus regarding the precise mechanism by which excess energy is quenched. Current X-ray structures of this complex correspond to a dissipative conformation and therefore correct microscopic theoretical modelling should capture this property. Despite their accuracy in explaining the steady state spectroscopy of this complex, chlorophyll-only models (those that neglect the energetic role of carotenoids) do not explain the observed fluorescence quenching. To address this gap, we have used a combination of the semi-empirical MNDO-CAS-CI and the Transition Density Cube method to model all chlorophyll-carotenoid energy transfer pathways in the highly quenched LHCII X-ray structure. Our simulations reveal that the inclusion of carotenoids in this microscopic model results in profound excitation quenching, reducing the predicted excitation lifetime of the complex from 4 ns (chlorophyll-only) to 67 ps. The model indicates that energy dissipation proceeds via slow excitation transfer (>20 ps) from chlorophyll to the forbidden S1 excited state of the centrally bound lutein molecules followed by the rapid (∼10 ps) radiationless decay to the ground state, with the latter being assumed from experimental measurements of carotenoid excited state lifetimes. Violaxanthin and neoxanthin do not contribute to this quenching. This work presents the first all-pigment microscopic model of LHCII and the first attempt to capture the dissipative character of the known structure. PMID:26017055
NASA Astrophysics Data System (ADS)
Kushner, Mark; Cooley, James; Xue, Jun; Urdhal, Randall
2011-10-01
Low pressure plasmas sustained in rare gases and rare gas mixtures can be efficient sources of VUV light from resonant optical transitions. Many applications would benefit from having small, inexpensive sources of plasma produced VUV light. To address this need, microwave wave excited microplasma sources in rare gases operating at pressures of <10 Torr are being developed. The microplasmas are sustained in ceramic cavities having cross sectional dimensions of <=1 mm, excited by a split-ring resonator antenna operated at 2.45 GHz. Power deposition is a few W. Hybrid computer modeling of microplasmas sustained in Ar has been performed to develop scaling laws for increasing the efficiency of VUV light production. The model includes a Monte Carlo simulation for the electron energy distribution and for radiation transport. Results from those studies will be discussed for plasma densities, electron energy distributions, VUV light production and excited state densities as a function of power, pressure and aspect ratio of the microplasma cavities. Modeling results will be compared to laser absorption spectroscopy of Ar excited state densities. Work supported by Agilent Technologies.
Vibronic coupling in the excited-states of carotenoids.
Miki, Takeshi; Buckup, Tiago; Krause, Marie S; Southall, June; Cogdell, Richard J; Motzkus, Marcus
2016-04-28
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 S2 to the optically dark state S1. Extending this picture, some additional dark states (3A(g)(-) and 1B(u)(-)) and their interaction with the S2 state have also been suggested to play a major role in the ultrafast deactivation of carotenoids and their properties. Here, we investigate the interaction between such dark and bright electronic excited states of open chain carotenoids, particularly its dependence on the number of conjugated double bonds (N). We focus on the ultrafast wave packet motion on the excited potential surface, which is modified by the interaction between bright and dark electronic states. Such a coupling between electronic states leads to a shift of the vibrational frequency during the excited-state evolution. In this regard, pump-degenerate four-wave mixing (pump-DFWM) is applied to a series of carotenoids with different numbers of conjugated double bonds N = 9, 10, 11 and 13 (neurosporene, spheroidene, lycopene and spirilloxanthin, respectively). Moreover, we demonstrate in a closed-chain carotenoid (lutein) that the coupling strength and therefore the vibrational shift can be tailored by changing the energy degeneracy between the 1B(u)(+) and 1B(u)(-) states via solvent interaction. PMID:27055720
On the excitation energy of deep-hole states in medium-heavy-mass spherical nuclei
NASA Astrophysics Data System (ADS)
Kolomiytsev, G. V.; Igashov, S. Yu.; Urin, M. H.
2016-01-01
Within the particle-hole dispersive optical model it is shown that the spreading effect determines a significant part of the anomalously large excitation energy of deep-hole states in the 90Zr and 208Pb parent nuclei.
Quantification of Entanglement Entropies for Doubly Excited States in Helium
NASA Astrophysics Data System (ADS)
Lin, Chien-Hao; Ho, Yew Kam
2015-05-01
In this work, we study the quantum entanglement for doubly excited resonance states in helium by using highly correlated Hylleraas type functions to represent such states of the two-electron system. The doubly-excited resonance states are determined by calculation of density of resonance states under the framework of the stabilization method. The spatial (electron-electron orbital) entanglement measures for the low-lying doubly excited 2 s 2, 2 s3 s, and 2 p 2 1 S e states are carried out. Once a resonance state wave function is obtained, the linear entropy and von Neumann entropy for such a state are quantified using the Schmidt-Slater decomposition method. To check the consistence, linear entropy is also determined by solving analytically the needed four-electron (12-dimensional) integrals.
The examination of berberine excited state by laser flash photolysis
NASA Astrophysics Data System (ADS)
Cheng, Lingli; Wang, Mei; Zhao, Ping; Zhu, Hui; Zhu, Rongrong; Sun, Xiaoyu; Yao, Side; Wang, Shilong
2009-07-01
The property of the excited triplet state of berberine (BBR) was investigated by using time-resolved laser flash photolysis of 355 nm in acetonitrile. The transient absorption spectra of the excited triplet BBR were obtained in acetonitrile, which have an absorption maximum at 420 nm. And the ratio of excitation to ionization of BBR in acetonitrile solvent was calculated. The self-decay and self-quenching rate constants, and the absorption coefficient of 3BBR* were investigated and the excited state quantum yield was determined. Furthermore utilizing the benzophenone (BEN) as a triplet sensitizer, and the β-carotene (Car) as an excited energy transfer acceptor, the assignment of 3BBR* was further confirmed and the related energy transfer rate constants were also determined.
Copan, Andreas V.; Wiens, Avery E.; Nowara, Ewa M.; Schaefer, Henry F.; Agarwal, Jay
2015-02-07
Peroxyacetyl radical [CH{sub 3}C(O)O{sub 2}] is among the most abundant peroxy radicals in the atmosphere and is involved in OH-radical recycling along with peroxyacetyl nitrate formation. Herein, the ground (X{sup ~}) and first (A{sup ~}) excited state surfaces of cis and trans peroxyacetyl radical are characterized using high-level ab initio methods. Geometries, anharmonic vibrational frequencies, and adiabatic excitation energies extrapolated to the complete basis-set limit are reported from computations with coupled-cluster theory. Excitation of the trans conformer is found to induce a symmetry-breaking conformational change due to second-order Jahn-Teller interactions with higher-lying excited states. Additional benchmark computations are provided to aid future theoretical work on peroxy radicals.
Electron-impact excitation and ionization cross sections for ground state and excited helium atoms
Ralchenko, Yu. Janev, R.K.; Kato, T.; Fursa, D.V.; Bray, I.; Heer, F.J. de
2008-07-15
Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n{<=}4 are treated individually, while the states with n{>=}5 are considered degenerate. For the processes involving transitions to and from n{>=}5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.
Metastable states of highly excited heavy ions
NASA Technical Reports Server (NTRS)
Pegg, D. J.; Griffin, P. M.; Sellin, I. A.; Smith, W. W.; Donnally, B.
1973-01-01
Description of the method used and results obtained in an experimental study of the metastable states of highly stripped heavy ions, aimed at determining the lifetimes of such states by the rates of autoionization and radiation. The significance and limitations of the results presented are discussed.
Excited state dynamics of thulium ions in yttrium aluminum garnets
NASA Technical Reports Server (NTRS)
Armagan, G.; Buoncristiani, A. M.; Dibartolo, B.
1991-01-01
The processes that take place in the excited states of a trivalent Thulium (Tm) ion in an Yttrium Aluminum Garnet (YAG) crystal, being relevant to the use of this system for laser applications, have been the object of several studies. We have reexamined this system focusing our attention on the dynamics of Tm following its excitation in the H-3(sub 4) level. Under these conditions the system relaxes through a cross-relaxation process. H-3(sub 4) yields F-3(sub 4), H-3(sub 6) yields F-3(sub 4), whose rate depends upon both the concentration of the Tm ion and the temperature of the crystal. The excitation spectrum obtained by monitoring the 1.8 micron emission of Tm (due to the F-3(sub 4) yields H-3(sub 6) transition) indicates an increase in the contribution to this emission from the H-3(sub 4) level relative to the H-3(sub 5) level as the Tm concentration increases; this shows the increased role played by the H-3(sub 4) level in pumping the infrared emission. Correspondingly, the duration of the luminescence originating in the H-3(sub 4) level is shortened as the concentration of Tm increases. The concentration quenching of this lifetime can be fit to a model which assumes that the cross-relaxation is due to a dipole-dipole interaction; from this fit, the intrinsic Tm lifetime in the absence of cross relaxation can be derived. We have used this lifetime to calculate the rate of the cross-relaxation process. We have evaluated this rate as a function of the temperature and found it to be fastest at 77 K. We have also calculated the microscopic interaction parameters for the cross-relaxation process by using two independent experimental features: (1) the time evolution of the emission from the H-3(sub 4) level; and (2) the spectral overlap between the H-3(sub 4) yields F-3(sub 4) emission and the H-3(sub 6) yields F-3(sub 4) absorption. We have also considered the migration of excitation among the Tm ions in the F-3(sub 4) level and calculated the relevant
Microwave spectroscopy of furfural in vibrationally excited states
NASA Astrophysics Data System (ADS)
Motiyenko, R. A.; Alekseev, E. A.; Dyubko, S. F.
2007-07-01
The results of microwave spectrum investigation of the excited vibrational states of furfural in the frequency range between 49 and 149 GHz are reported. In total 15 excited vibrational states (9 for trans-furfural and 6 for cis-furfural) were assigned and analyzed. Six of the 15 investigated states were assigned for the first time. Accurate values of rigid rotor and quartic centrifugal distortion constants of asymmetric top Hamiltonian have been determined for 13 excited states. Also for some states several sextic and octic level constants were needed in order to fit the data within experimental accuracy. The vt = 3 and vs = 1, va = 1 states of trans-furfural were found to be strongly perturbed and only rotational transitions with low Ka values can be reliably identified in this study.
Characterizing RNA Excited States using NMR Relaxation Dispersion
Xue, Yi; Kellogg, Dawn; Kimsey, Isaac J; Sathyamoorthy, Bharathwaj; Stein, Zachary W; McBrairty, Mitchell; Al-Hashimi, Hashim M.
2016-01-01
Changes in RNA secondary structure play fundamental roles in the cellular functions of a growing number of non-coding RNAs. This chapter describes NMR-based approaches for characterizing microsecond-to-millisecond changes in RNA secondary structure that are directed toward short-lived and low-populated species often referred to as “excited states”. Compared to larger-scale changes in RNA secondary structure, transitions towards excited states do not require assistance from chaperones, are often orders of magnitude faster, and are localized to a small number of nearby base pairs in and around non-canonical motifs. Here we describe a procedure for characterizing RNA excited states using off-resonance R1ρ NMR relaxation dispersion utilizing low-to-high spin-lock fields (25–3000 Hz). R1ρ NMR relaxation dispersion experiments are used to measure carbon and nitrogen chemical shifts in base and sugar moieties of the excited state. The chemical shift data is then interpreted with the aid of secondary structure prediction to infer potential excited states that feature alternative secondary structures. Candidate structures are then tested by using mutations, single-atom substitutions, or by changing physiochemical conditions, such as pH and temperature, to either stabilize or destabilize the candidate excited state. The resulting chemical shifts of the mutants or under different physiochemical conditions are then compared to those of the ground and excited state. Application is illustrated with a focus on the transactivation response element (TAR) from the human immune deficiency virus type 1 (HIV-1), which exists in dynamic equilibrium with at least two distinct excited states. PMID:26068737
NASA Astrophysics Data System (ADS)
Seybold, P. G.; Kier, L. B.; Cheng, C.-K.
1999-12-01
Emissions from the 1S and 1D excited states of atomic oxygen play a prominent role in creating the dramatic light displays (aurora borealis) seen in the skies over polar regions of the Northern Hemisphere. A probabilistic asynchronous cellular automaton model described previously has been applied to the excited-state dynamics of atomic oxygen. The model simulates the time-dependent variations in ground (3P) and excited-state populations that occur under user-defined probabilistic transition rules for both pulse and steady-state conditions. Although each trial simulation is itself an independent "experiment", deterministic values for the excited-state emission lifetimes and quantum yields emerge as limiting cases for large numbers of cells or large numbers of trials. Stochastic variations in the lifetimes and emission yields can be estimated from repeated trials.
Nitrogen molecule activation by excited states of copper
Sanchez-Zamora, M.; Novaro, O.; Ruiz, M.E. )
1990-04-05
Ab initio molecular orbital studies that include variational (with a multiconfiguration reference state of 200 states) and perturbational (including over 3 million configurations) configuration interaction calculations were addressed to the interaction of nitrogen molecules with copper. The Cu ground state {sup 2}S and first two excited states {sup 2}P and {sup 2}D were studied as they interact in different geometrical approaches (including side-on and end-on geometries) with ground-state N{sub 2} molecules.
Information resonance in a model excitable system
NASA Astrophysics Data System (ADS)
Gorecki, Jerzy; Gorecki, Adam; Lemarchand, Annie; Nowakowski, Bogdan
2013-06-01
We consider a simple mesoscopic model of an excitable thermochemical system for which the system temperature as a function of time has a form of irregular spikes. The interspike intervals are mapped onto elements of a formal alphabet. The time evolution of system temperature is represented by a string over this alphabet. We demonstrate that the entropy of such string reaches a minimum for the values of model parameters where the coherence resonance of interspike intervals is observed.
Excited state dynamics in photosynthetic reaction center and light harvesting complex 1
NASA Astrophysics Data System (ADS)
Strümpfer, Johan; Schulten, Klaus
2012-08-01
Key to efficient harvesting of sunlight in photosynthesis is the first energy conversion process in which electronic excitation establishes a trans-membrane charge gradient. This conversion is accomplished by the photosynthetic reaction center (RC) that is, in case of the purple photosynthetic bacterium Rhodobacter sphaeroides studied here, surrounded by light harvesting complex 1 (LH1). The RC employs six pigment molecules to initiate the conversion: four bacteriochlorophylls and two bacteriopheophytins. The excited states of these pigments interact very strongly and are simultaneously influenced by the surrounding thermal protein environment. Likewise, LH1 employs 32 bacteriochlorophylls influenced in their excited state dynamics by strong interaction between the pigments and by interaction with the protein environment. Modeling the excited state dynamics in the RC as well as in LH1 requires theoretical methods, which account for both pigment-pigment interaction and pigment-environment interaction. In the present study we describe the excitation dynamics within a RC and excitation transfer between light harvesting complex 1 (LH1) and RC, employing the hierarchical equation of motion method. For this purpose a set of model parameters that reproduce RC as well as LH1 spectra and observed oscillatory excitation dynamics in the RC is suggested. We find that the environment has a significant effect on LH1-RC excitation transfer and that excitation transfers incoherently between LH1 and RC.
The excited state antiaromatic benzene ring: a molecular Mr Hyde?
Papadakis, Raffaello; Ottosson, Henrik
2015-09-21
The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas. PMID:25960203
Photocyclization Reactions of Diarylethenes via the Excited Triplet State.
Murata, Ryutaro; Yago, Tomoaki; Wakasa, Masanobu
2015-11-12
Cyclization reactions of three diarylethene derivatives, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT), 1,2-bis(2-hexyl-3-benzothienyl)perfluorocyclopentene (BTHex), and 1,2-bis(2-isopropyl-3-benzothienyl)perfluorocyclopentene (BTiPr), via their excited triplet states were studied by means of steady-state and nanosecond transient absorption spectroscopy. The excited triplet states of BT, BTHex, and BTiPr were generated by energy transfer from the photoexcited triplet states of sensitizers such as xanthone, phenanthrene, and pyrene. The single-step quantum yields of the cyclization reactions from the excited triplet states of BT, BTHex, and BTiPr were determined to be 0.34, 0.53, and 0.65, respectively. The triplet energies of these three BTs were estimated to be 190-200 kJ mol(-1). PMID:26490486
Brown, S.S.; Cheatum, C.M.; Fitzwater, D.A.; Crim, F.F.
1996-12-01
Recent state-selected photodissociation experiments on isocyanic acid, HNCO, have provided a wealth of data on its photochemistry and dissociation dynamics. The excited state potential energy surface on which the dissociation occurs is central to these observations but is relatively uncharacterized. We construct a two-dimensional analytical model for the excited state potential that is consistent with experimental observations, including the ultraviolet absorption spectrum and the dynamics of the C{endash}N and N{endash}H bond dissociations. We then test this surface by running classical trajectories on it, using Morse oscillator vibrational wave functions from the ground electronic state to determine the probability distributions of initial conditions. The trajectory calculation reproduces the experimentally observed variation in the photochemical branching with photolysis wavelength. It also reproduces the bond selectivity in the photodissociation of HNCO molecules containing three quanta of N{endash}H stretching excitation (3{nu}{sub 1}) that we observed experimentally. Although the model for the surface is very simple and includes only two degrees of freedom, it captures the essential features that determine the photochemical branching in a direct dissociation. {copyright} {ital 1996 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Guevara, Z. E.; Torres, D. A.
2016-07-01
In this contribution the challenges in the use of a setup to simultaneously measure lifetimes and g-factor values will be presented. The simultaneous use of the transient field technique and the Doppler Shift Attenuation Method, to measure magnetic moments and lifetimes respectively, allows to obtain a complete characterization of the currents of nucleons and the deformation in excited states close to the ground state. The technique is at the moment limited to Coulomb excitation and alpha-transfer reactions, what opens an interesting perspective to consider this type of experiments with radioactive beams. The use of deep-inelastic and fusion-evaporation reactions will be discussed. An example of a setup that makes use of a beam of 106Cd to study excited states of 110Sn and the beam nuclei itself will be presented.
Liquid ground state, gap, and excited states of a strongly correlated spin chain.
Lesanovsky, Igor
2012-03-01
We present an exact solution of an experimentally realizable and strongly interacting one-dimensional spin system which is a limiting case of a quantum Ising model with long range interaction in a transverse and longitudinal field. Pronounced quantum fluctuations lead to a strongly correlated liquid ground state. For open boundary conditions the ground state manifold consists of four degenerate sectors whose quantum numbers are determined by the orientation of the edge spins. Explicit expressions for the entanglement properties, the exact excitation gap, as well as the exact wave functions for a couple of excited states are analytically derived and discussed. We outline how this system can be experimentally realized in a lattice gas of Rydberg atoms. PMID:22463419
Shape vibration and quasiparticle excitations in the lowest 0+ excited state in erbium isotopes
NASA Astrophysics Data System (ADS)
Chen, Fang-Qi; Egido, J. Luis
2016-06-01
The ground and first excited 0+ states of the -172Er156 isotopes are analyzed in the framework of the generator coordinate method. The shape parameter β is used to generate wave functions with different deformations which together with the two-quasiparticle states built on them provide a set of states. An angular momentum and particle number projection of the latter spawn the basis states of the generator coordinate method. With this ansatz and using the separable pairing plus quadrupole interaction we obtain a good agreement with the experimental spectra and E 2 transition rates up to moderate spin values. The structure of the wave functions suggests that the first excited 0+ states in the soft Er isotopes are dominated by shape fluctuations, while in the well deformed Er isotopes the two-quasiparticle states are more relevant. In between, both degrees of freedom are necessary.
Nature of ground and electronic excited states of higher acenes.
Yang, Yang; Davidson, Ernest R; Yang, Weitao
2016-08-30
Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particle-particle random-phase approximation calculation. The (1)Ag ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state (3)B2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state (1)B2u is a zwitterionic state to the short axis. The excited (1)Ag state gradually switches from a double-excitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the (1)B2u and excited (1)Ag states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved. PMID:27528690
Two-photon transitions to excited states in atomic hydrogen
Quattropani, A.; Bassani, F.; Carillo, S.
1982-06-01
Resonant two-photon transition rates from the ground state of atomic hydrogen to ns excited states have been computed as a function of photon frequencies in the length and velocity gauges in order to test the accuracy of the calculation and to discuss the rate of convergence over the intermediate states. The dramatic structure of the transition rates produced by intermediate-state resonances is exhibited. A two-photon transparency is found in correspondence to each resonance.
Masses of Ground- and Excited-State Hadrons
NASA Astrophysics Data System (ADS)
Roberts, Hannes L. L.; Chang, Lei; Cloët, Ian C.; Roberts, Craig D.
2011-07-01
We present the first Dyson-Schwinger equation calculation of the light hadron spectrum that simultaneously correlates the masses of meson and baryon ground- and excited-states within a single framework. At the core of our analysis is a symmetry-preserving treatment of a vector-vector contact interaction. In comparison with relevant quantities the root-mean-square-relative-error/degree-of freedom is 13%. Notable amongst our results is agreement between the computed baryon masses and the bare masses employed in modern dynamical coupled-channels models of pion-nucleon reactions. Our analysis provides insight into numerous aspects of baryon structure; e.g., relationships between the nucleon and Δ masses and those of the dressed-quark and diquark correlations they contain.
Dynamics and spectroscopy of CH₂OO excited electronic states.
Kalinowski, Jaroslaw; Foreman, Elizabeth S; Kapnas, Kara M; Murray, Craig; Räsänen, Markku; Gerber, R Benny
2016-04-28
The excited states of the Criegee intermediate CH2OO are studied in molecular dynamics simulations using directly potentials from multi-reference perturbation theory (MR-PT2). The photoexcitation of the species is simulated, and trajectories are propagated in time on the excited state. Some of the photoexcitation events lead to direct fragmentation of the molecule, but other trajectories describe at least several vibrations in the excited state, that may terminate by relaxation to the ground electronic state. Limits on the role of non-adiabatic contributions to the process are estimated by two different simulations, one that forces surface-hopping at potential crossings, and another that ignores surface hopping altogether. The effect of non-adiabatic transitions is found to be small. Spectroscopic implications and consequences for the interpretation of experimental results are discussed. PMID:27040614
Excited states of the 5-chlorophyll photosystem II reaction center
Jankowiak, R.; Raetsep, M.; Picorel, R.; Seibert, M.; Small, G.J.
1999-11-04
Results of 4.2 K hole burning, chemical reduction (sodium dithionite, in dark and with illumination), and oxidation (ferricyanide) experiments are reported for the isolated PS II reaction center containing five chlorophyll (Chl) molecules (RC-5). Q{sub y} states at 679.6 and 668.3 nm are identified as being highly localized on pheophytin a of the D{sub 1} branch (Pheo{sub 1}) and pheophytin a of the D{sub 2} branch (Pheo{sub 2}), respectively. The Pheo{sub 1}-Q{sub x} and Pheo{sub 2}-Q{sub x} transitions were found to lie on the low and high energy sides of the single Pheo-Q{sub x} absorption band, at 544.4 and 541.2 nm, respectively. The Q{sub y} band of the 684 nm absorbing Chl, which is more apparent in absorption in RC-5 than in RC-6 samples, is assigned to the peripheral Chl on the D{sub 1} side. The results are consistent with that peripheral Chl being Chl{sub z}. The results indicate that P680, the primary electron donor, is the main acceptor for energy transfer from the Pheo{sub 1}-Q{sub y} state and that excitation energy transfer from the Pheo{sub 1}-Q{sub y} state and P680* to the 684 nm Chl is inefficient. It is concluded that the procedure used to prepare RC-5 has only a small effect on the energies of the Q{sub y} states associated with the core cofactors of the 6-Chl RC as well as the 684 nm Chl. Implications of the results for the multimer model are considered. In that model the Q{sub y}-states of the core are significantly delocalized over several cofactors. The results presented provide no support for this model.
Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme
Theophilou, Iris; Tassi, M.; Thanos, S.
2014-04-28
Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.
Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme.
Theophilou, Iris; Tassi, M; Thanos, S
2014-04-28
Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations. PMID:24784248
Microwave Spectroscopy of the Excited Vibrational States of Methanol
NASA Astrophysics Data System (ADS)
Pearson, John; Daly, Adam M.; Bermúdez, Celina
2015-06-01
Methanol is the simplest molecule with a three-fold internal rotation and the observation of its νb{8} band served the primary catalyst for the development of internal rotation theory(a,b). The 75 subsequent years of investigation into the νb{8} band region have yielded a large number assignments, numerous high precision energy levels and a great deal of insight into the coupling of νb{t}=3 & 4 with νb{8}, νb{7}, νb{11} and other nearby states(c). In spite of this progress numerous assignment mysteries persist, the origin of almost half the far infrared laser lines remain unknown and all attempts to model the region quantum mechanically have had very limited success. The C3V internal rotation Hamiltonian has successfully modeled the νb{t}=0,1 & 2 states of methanol and other internal rotors(d). However, successful modeling of the coupling between torsional bath states and excited small amplitude motion remains problematic and coupling of multiple interacting excited small amplitude vibrations featuring large amplitude motions remains almost completely unexplored. Before such modeling can be attempted, identifying the remaining low lying levels of νb{7} and νb{11} is necessary. We present an investigation into the microwave spectrum of νb{7}, νb{8} and νb{11} along with the underlying torsional bath states in νb{t}=3 and νb{t}= 4. (a) A. Borden, E.F. Barker J. Chem. Phys., 6, 553 (1938). (b) J. S. Koehler and D. M. Dennison, Phys. Rev. 57, 1006 (1940). (c) R. M. Lees, Li-Hong Xu, J. W. C. Johns, B. P. Winnewisser, and M. Lock, J. Mol. Spectrosc. 243, 168 (2007). (d) L.-H. Xu, J. Fisher, R.M. Lees, H.Y. Shi, J.T. Hougen, J.C. Pearson, B.J. Drouin, G.A. Blake, R. Braakman J. Mol. Spectrosc., 251, 305 (2008).
Excited-state entanglement and thermal mutual information in random spin chains
NASA Astrophysics Data System (ADS)
Huang, Yichen; Moore, Joel E.
2014-12-01
Entanglement properties of excited eigenstates (or of thermal mixed states) are difficult to study with conventional analytical methods. We approach this problem for random spin chains using a recently developed real-space renormalization group technique for excited states ("RSRG-X"). For the random XX and quantum Ising chains, which have logarithmic divergences in the entanglement entropy of their (infinite-randomness) critical ground states, we show that the entanglement entropy of excited eigenstates retains a logarithmic divergence while the mutual information of thermal mixed states does not. However, in the XX case the coefficient of the logarithmic divergence extends from the universal ground-state value to a universal interval due to the degeneracy of excited eigenstates. These models are noninteracting in the sense of having free-fermion representations, allowing strong numerical checks of our analytical predictions.
Multiscale excited state lifetimes of protonated dimethyl aminopyridines.
Soorkia, Satchin; Broquier, Michel; Grégoire, Gilles
2016-09-14
The excited state dynamics of protonated ortho (2-) and para (4-) dimethyl aminopyridine molecules (DMAPH(+)) has been studied through pump-probe photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Multiscale temporal dynamics has been recorded over 9 orders of magnitude from subpicosecond to millisecond. The initially locally excited ππ* state rapidly decays within about 100 fs into a charge transfer state following 90° twist motion of the dimethyl amino group. While this twisted intramolecular charge transfer (TICT) state does not trigger any fragmentation, it selectively leads to specific two-color photofragments through absorption of the probe photon at 355 nm. Besides, the optically dark TICT state provides an efficient deactivation path with high intersystem probability to non-dissociative long-lived triplet states. Such a multiscale pump-probe photodissociation scheme paves the way to systematic studies of charge transfer reactions in the excited state of cold ionic systems stored in a cryogenic cooled ion trap and probed continuously up to the millisecond time scale. PMID:27524459
Lifetime of the Excited State In Vivo
Mar, T.; Govindjee; Singhal, G. S.; Merkelo, H.
1972-01-01
Using a mode-locked laser (λ, 632.8 nm), fluorescence decay of chlorophyll (Chl) a in the green alga Chlorella pyrenoidosa, the red alga Porphyridium cruentum, and the blue-green alga Anacystis nidulans was measured by the phase-shift method under conditions when photosynthesis was not operative (3-(3,4-dichlorophenyl)-1,1-dimethylurea [DCMU] poisoning, or cooling to 77°K). In the presence of 10-5 M DCMU, the lifetime of Chl a fluorescence (τ) at room temperature is about 1.7 nsec in Chlorella, 1.0 nsec in Porphyridium, and 0.7 nsec in Anacystis. At 77°K, τ is 1.4 nsec (for fluorescence at about 685 nm, F-685) and 2.3 nsec (for F-730) in Chlorella, 0.9 nsec (F-685) and 1.2 nsec (F-730) in Porphyridium, and 0.8 nsec (F-685 and F-730) in Anacystis. From the above measurement, and the assumption that τ0 (the intrinsic fluorescence lifetime) for Chl a in all three algae is 15.2 nsec, we have calculated the rate constants of radiationless transition (that includes energy transfer to weakly fluorescent system I) processes competing with fluorescence at room temperature to be about 5 × 108 sec-1 in Chlorella, 9 × 108 sec-1 in Porphyridium, and 13 × 108 sec-1 in Anacystis. At 77°K, this rate constant for Chl a that fluoresces at 685 nm remains, in the first approximation, the same as at room temperature. From the τ data, the rate constant for the trapping of excitation energy is calculated to be about 1.2 × 109 sec-1 for Chlorella, 2 × 109 sec-1 for Porphyridium, and 2 × 109 sec-1 for Anacystis. The efficiency of trapping is calculated to be about 66% (Chlorella), 68% (Porphyridium), and 60% (Anacystis). (It is recognized that variations in the above values are to be expected if algae grown under different conditions are used for experimentation.) The maximum quantum yield of Chl a fluorescence for system II (λ, 632.8 nm), calculated from τ measurements, is about 10% in Chlorella, 6-7% in Porhyridium, and 5% in Anacystis under conditions when photosynthesis
NASA Astrophysics Data System (ADS)
Zhu, Xi-Ming; Cheng, Zhi-Wen; Carbone, Emile; Pu, Yi-Kang; Czarnetzki, Uwe
2016-08-01
Electron-impact excitation processes play an important role in low-temperature plasma physics. Cross section and rate coefficient data for electron-impact processes from the ground state to excited states or between two excited states are required for both diagnostics and modeling works. However, the collisional processes between excited states are much less investigated than the ones involving the ground state due to various experimental challenges. Recently, a method for determining electron excitation rate coefficients between Ar excited states in afterglow plasmas was successfully implemented and further developed to obtain large sets of collisional data. This method combines diagnostics for electron temperature, electron density, and excited species densities and kinetic modeling of excited species, from which the electron excitation rate coefficients from one of the 1s states to the other 1s states or to one of 2p or 3p states are determined (states are in Paschen’s notation). This paper reviews the above method—namely the combined diagnostics and modeling in afterglow plasmas. The results from other important approaches, including electron-beam measurement of cross sections, laser pump-probe technique for measuring rate coefficients, and theoretical calculations by R-matrix and distorted-wave models are also discussed. From a comparative study of these results, a fitted mathematical expression of excitation rate coefficients is obtained for the electron temperature range of 1–5 eV, which can be used for the collisional-radiative modeling of low-temperature Ar plasmas. At last, we report the limitations in the present dataset and give some suggestions for future work in this area.
Electronic excited states and relaxation dynamics in polymer heterojunction systems
NASA Astrophysics Data System (ADS)
Ramon, John Glenn Santos
The potential for using conducting polymers as the active material in optoelectronic devices has come to fruition in the past few years. Understanding the fundamental photophysics behind their operations points to the significant role played by the polymer interface in their performance. Current device architectures involve the use of bulk heterojunctions which intimately blend the donor and acceptor polymers to significantly increase not only their interfacial surface area but also the probability of exciton formation within the vicinity of the interface. In this dissertation, we detail the role played by the interface on the behavior and performance of bulk heterojunction systems. First, we explore the relation between the exciton binding energy to the band offset in determining device characteristics. As a general rule, when the exciton binding energy is greater than the band offset, the exciton remains the lowest energy excited state leading to efficient light-emitting properties. On the other hand, if the offset is greater than the binding energy, charge separation becomes favorable leading to better photovoltaic behavior. Here, we use a Wannier function, configuration interaction based approach to examine the essential excited states and predict the vibronic absorption and emission spectra of the PPV/BBL, TFB/F8BT and PFB/F8BT heterojunctions. Our results underscore the role of vibrational relaxation in the formation of charge-transfer states following photoexcitation. In addition, we look at the relaxation dynamics that occur upon photoexcitation. For this, we adopt the Marcus-Hush semiclassical method to account for lattice reorganization in the calculation of the interconversion rates in TFB/F8BT and PFB/F8BT. We find that, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, a regeneration pathway to the optically active lowest excitonic state in TFB/F8BT is possible via thermal repopulation from the exciplex. Finally
Excited-state dynamics of astaxanthin aggregates
NASA Astrophysics Data System (ADS)
Fuciman, Marcel; Durchan, Milan; Šlouf, Václav; Keşan, Gürkan; Polívka, Tomáš
2013-05-01
Astaxanthin forms three types of aggregates in hydrated dimethyl sulfoxide (DMSO). In DMSO/water ratio of 1:1, a red-shifted J-aggregate with maximum at 570 nm is generated, while a ratio of 1:9 produces blue-shifted H-aggregates with peaks at 386 nm (H1) and 460 nm (H2). Monomeric astaxanthin in DMSO has an S1 lifetime of 5.3 ps, but a long-lived (33 ps) S∗ signal was also identified. Aggregation changes the S1 lifetimes to 17 ps (H1), 30 ps (H2), and 14 ps (J). Triplet state of astaxanthin, most likely generated via singlet homofission, was observed in H1 and H2 aggregates.
Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A
2015-04-15
A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. PMID:25731863
Model for the hyperfine structure of electronically excited KCs molecules
NASA Astrophysics Data System (ADS)
Orbán, A.; Vexiau, R.; Krieglsteiner, O.; Nägerl, H.-C.; Dulieu, O.; Crubellier, A.; Bouloufa-Maafa, N.
2015-09-01
A model for determining the hyperfine structure of the excited electronic states of diatomic bialkali heteronuclear molecules is formulated from the atomic hyperfine interactions and is applied to the case of bosonic 39KCs and fermionic 40KCs molecules. The hyperfine structure of the potential-energy curves of the states correlated to the K (4 s 2S1 /2) +Cs (6 p 2P1 /2 ,3 /2) dissociation limits is described in terms of different coupling schemes depending on the internuclear distance R . These results provide a step in the calculation of the hyperfine structure of rovibrational levels of these excited molecular states in the perspective of the identification of efficient paths for creating ultracold ground-state KCs molecules.
Quantum entanglement of localized excited states at finite temperature
NASA Astrophysics Data System (ADS)
Caputa, Pawel; Simón, Joan; Štikonas, Andrius; Takayanagi, Tadashi
2015-01-01
In this work we study the time evolutions of (Renyi) entanglement entropy of locally excited states in two dimensional conformal field theories (CFTs) at finite temperature. We consider excited states created by acting with local operators on thermal states and give both field theoretic and holographic calculations. In free field CFTs, we find that the growth of Renyi entanglement entropy at finite temperature is reduced compared to the zero temperature result by a small quantity proportional to the width of the localized excitations. On the other hand, in finite temperature CFTs with classical gravity duals, we find that the entanglement entropy approaches a characteristic value at late time. This behaviour does not occur at zero temperature. We also study the mutual information between the two CFTs in the thermofield double (TFD) formulation and give physical interpretations of our results.
Coulombic Effects on Excited States in a Small Quantum Dot
NASA Astrophysics Data System (ADS)
Goldhaber-Gordon, David; Duncan, David; Westervelt, R. M.; Maranowski, K. M.; Gossard, A. C.
2000-03-01
The excitation spectrum of a quantum dot varies with the addition of electrons, as successive single-particle eigenstates become filled in the ground state and so cannot accomodate additional electrons. Previous experiments have observed that each spatial state becomes unavailable for transport of further electrons after only one electron has occupied it. We have investigated state occupancy in the excitation spectrum of a small (200 nm X 200 nm) quantum dot laterally defined by capacitively coupled gate electrodes in a GaAs/AlGaAs heterostructure. For our dots, quantized level spacing Δ E ≈ 300 μeV and charging energy Ec ≈ 2 meV. We have studied the evolution of features in the excitation spectrum with magnetic field and equilibrium occupancy and have identified the pattern of spins for the added electrons. These results test the applicability of the spin-degenerate constant interaction picture as well as its limitations.
State-Selective Excitation of Quantum Systems via Geometrical Optimization.
Chang, Bo Y; Shin, Seokmin; Sola, Ignacio R
2015-09-01
We lay out the foundations of a general method of quantum control via geometrical optimization. We apply the method to state-selective population transfer using ultrashort transform-limited pulses between manifolds of levels that may represent, e.g., state-selective transitions in molecules. Assuming that certain states can be prepared, we develop three implementations: (i) preoptimization, which implies engineering the initial state within the ground manifold or electronic state before the pulse is applied; (ii) postoptimization, which implies engineering the final state within the excited manifold or target electronic state, after the pulse; and (iii) double-time optimization, which uses both types of time-ordered manipulations. We apply the schemes to two important dynamical problems: To prepare arbitrary vibrational superposition states on the target electronic state and to select weakly coupled vibrational states. Whereas full population inversion between the electronic states only requires control at initial time in all of the ground vibrational levels, only very specific superposition states can be prepared with high fidelity by either pre- or postoptimization mechanisms. Full state-selective population inversion requires manipulating the vibrational coherences in the ground electronic state before the optical pulse is applied and in the excited electronic state afterward, but not during all times. PMID:26575896
Foil dissociation of fast molecular ions into atomic excited states
Berry, H.G.; Gay, T.J.; Brooks, R.L.
1980-01-01
The intensity and polarizations of light emitted from atomic excited states of dissociated molecular ions were measured. The dissociations are induced when fast molecular ions (50 to 500 keV/amu) are transmitted through thin carbon foils. A calculation of multiple scattering and the Coulomb explosion gives the average internuclear separation of the projectile at the foil surface. Experimentally, the foil thickness is varied to give varying internuclear separations at the foil surface and observe the consequent variation in light yield and optical polarization. Using HeH/sup +/ projectiles, factors of 1 to 5 enhancements of the light yields from n = 3, /sup 1/ /sup 3/P,D states of He I and some He II and H I emissions were observed. The results can be explained in terms of molecular level crossings which provide mixings of the various final states during dissociation of the molecular ions at the exit surface. They suggest a short range surface interaction of the electron pick-up followed by a slow molecular dissociation. Alignment measurements confirm the essential features of the model. Observations of Lyman ..cap alpha.. emission after dissociation of H/sub 2//sup +/ amd H/sub 3//sup +/ show rapid variations in light yield for small internuclear separations at the foil surface.
Photoionization of furan from the ground and excited electronic states
NASA Astrophysics Data System (ADS)
Ponzi, Aurora; Sapunar, Marin; Angeli, Celestino; Cimiraglia, Renzo; Došlić, Nada; Decleva, Piero
2016-02-01
Here we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy.
Calculating helium atomic excited states in coordinate space
NASA Astrophysics Data System (ADS)
Hall, Shane; Siegel, P. B.
2015-12-01
Two coupled Schrödinger equations are used to calculate excited states of atomic helium. Using product state functions for the two-electron state, the shooting method is used to numerically determine the energies of the allowed singlet and triplet levels. The calculations agree well with the data, and the coordinate-space basis yields Schrödinger equations for helium that are familiar to students who have used similar methods for the hydrogen atom.
Coherent excitation of a single atom to a Rydberg state
Miroshnychenko, Y.; Gaeetan, A.; Evellin, C.; Grangier, P.; Wilk, T.; Browaeys, A.; Comparat, D.; Pillet, P.
2010-07-15
We present the coherent excitation of a single Rubidium atom to the Rydberg state 58d{sub 3/2} using a two-photon transition. The experimental setup is described in detail, as are experimental techniques and procedures. The coherence of the excitation is revealed by observing Rabi oscillations between ground and Rydberg states of the atom. We analyze the observed oscillations in detail and compare them to numerical simulations which include imperfections of our experimental system. Strategies for future improvements on the coherent manipulation of a single atom in our settings are given.
2{sup +} excitation of the {sup 12}C Hoyle state
Freer, M.; Fujita, H.; Carter, J.; Usman, I.; Buthelezi, Z.; Foertsch, S. V.; Neveling, R.; Perez, S. M.; Smit, F. D.; Fearick, R. W.; Papka, P.; Swartz, J. A.
2009-10-15
A high-energy-resolution magnetic spectrometer has been used to measure the {sup 12}C excitation energy spectrum to search for the 2{sup +} excitation of the 7.65 MeV, 0{sup +} Hoyle state. By measuring in the diffractive minimum of the angular distribution for the broad 0{sup +} background, evidence is found for a possible 2{sup +} state at 9.6(1) MeV with a width of 600(100) keV. The implications for the {sup 8}Be+{sup 4}He reaction rate in stellar environments are discussed.
First-principles Calculation of Excited State Spectra in QCD
Jozef Dudek,Robert Edwards,Michael Peardon,David Richards,Christopher Thomas
2011-05-01
Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi-hadron contributions, and describe a recent calculation of the I=2 pion-pion energy-dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.
First-principles Calculation of Excited State Spectra in QCD
Dudek, Jozef J.; Edwards, Robert G.; Richards, David G.; Thomas, Christopher E.; Peardon, Michael J.
2011-05-24
Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi-hadron contributions, and describe a recent calculation of the I = 2{pi}{pi} energy-dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.
Accurate Excited State Geometries within Reduced Subspace TDDFT/TDA.
Robinson, David
2014-12-01
A method for the calculation of TDDFT/TDA excited state geometries within a reduced subspace of Kohn-Sham orbitals has been implemented and tested. Accurate geometries are found for all of the fluorophore-like molecules tested, with at most all valence occupied orbitals and half of the virtual orbitals included but for some molecules even fewer orbitals. Efficiency gains of between 15 and 30% are found for essentially the same level of accuracy as a standard TDDFT/TDA excited state geometry optimization calculation. PMID:26583218
NASA Astrophysics Data System (ADS)
Koyama, Y.; Mukai, Yumiko; Kuki, Michitaka
1993-06-01
Both experimental and theoretical results which indicate the presence of the triplet-excited region in retinoids and carotenoids are reviewed. The triplet- excited region is defined as a region where changes in the bond order take place, upon triplet excitation, toward its inversion, i.e., a double bond becomes more signal bond-like and a single bond becomes more double bond-like. (1) It has a span of approximately six conjugated double bonds, (2) it is localized in the central part of a conjugated chain, and (3) it triggers `cis' to `trans' isomerization in the T1 state. The experimental and theoretical results include: (1) the T1 Raman spectra of all-trans-retinal and its homologues; (2) the T1-state isomerization of isomeric retinal; (3) the T1-state isomerization of isomeric (beta) -carotene; (4) the PPP-SD-CI calculations of the bond orders of the carbon-carbon bonds in a set of model polyenes; and (5) the normal-coordinate analysis of the T1 Raman lines of undeuterated and deuterated all-trans-retinal. Finally, (6) the biological implication of 'the triplet-excited region' is discussed in relation to the photo-protective function of a 15-cis carotenoid bound to the bacterial photoreaction center.
NASA Astrophysics Data System (ADS)
Kumar, Anupriya; Kołaski, Maciej; Kim, Kwang S.
2008-01-01
Structures of the ground state pyrrole-(H2O)n clusters are investigated using ab initio calculations. The charge-transfer driven femtosecond scale dynamics are studied with excited state ab initio molecular dynamics simulations employing the complete-active-space self-consistent-field method for pyrrole-(H2O)n clusters. Upon the excitation of these clusters, the charge density is located over the farthest water molecule which is repelled by the depleted π-electron cloud of pyrrole ring, resulting in a highly polarized complex. For pyrrole-(H2O), the charge transfer is maximized (up to 0.34a.u.) around ˜100fs and then oscillates. For pyrrole-(H2O)2, the initial charge transfer occurs through the space between the pyrrole and the π H-bonded water molecule and then the charge transfer takes place from this water molecule to the σ H-bonded water molecule. The total charge transfer from the pyrrole to the water molecules is maximized (up to 0.53a.u.) around ˜100fs.
Unbound excited states of the N =16 closed shell nucleus 24O
NASA Astrophysics Data System (ADS)
Rogers, W. F.; Garrett, S.; Grovom, A.; Anthony, R. E.; Aulie, A.; Barker, A.; Baumann, T.; Brett, J. J.; Brown, J.; Christian, G.; DeYoung, P. A.; Finck, J. E.; Frank, N.; Hamann, A.; Haring-Kaye, R. A.; Hinnefeld, J.; Howe, A. R.; Islam, N. T.; Jones, M. D.; Kuchera, A. N.; Kwiatkowski, J.; Lunderberg, E. M.; Luther, B.; Meyer, D. A.; Mosby, S.; Palmisano, A.; Parkhurst, R.; Peters, A.; Smith, J.; Snyder, J.; Spyrou, A.; Stephenson, S. L.; Strongman, M.; Sutherland, B.; Taylor, N. E.; Thoennessen, M.
2015-09-01
Two low-lying neutron-unbound excited states of 24O, populated by proton-knockout reactions on 26F, have been measured using the MoNA and LISA arrays in combination with the Sweeper Magnet at the Coupled Cyclotron Facility at the NSCL using invariant mass spectroscopy. The current measurement confirms the separate identity of two states with decay energies 0.51(5) MeV and 1.20(7) MeV, and provides support for theoretical model calculations, which predict a 2+ first excited state and a 1+ higher-energy state. The measured excitation energies for these states, 4.70(15) MeV for the 2+ level and 5.39(16) MeV for the 1+ level, are consistent with previous lower-resolution measurements, and are compared with five recent model predictions.
The Millimeter-Wave Spectrum of Methacrolein. Torsion-Rotation Effects in the Excited States
NASA Astrophysics Data System (ADS)
Zakharenko, Olena; Motiyenko, R. A.; Aviles Moreno, Juan-Ramon; Huet, T. R.
2015-06-01
Last year we reported the analysis of the rotational spectrum of s-trans conformer of methacrolein CH2=C(CH3)CHO in the ground vibrational state. In this talk we report the study of its low lying excited vibrational states. The study is based on room-temperature absorption spectra of methacrolein recorded in the frequency range 150 - 465 GHz using the spectrometer in Lille. The new results include assignment of the first excited torsional state (131 cm-1), and the joint analysis of the vt = 0 and vt = 1 states, that allowed us to improve the model in the frame of Rho-Axis-Method (RAM) Hamiltonian and to remove some strong correlations between parameters. Also we assigned the first excited vibrational state of the skeletal torsion mode (170 cm-1). The inverse sequence of A and E tunneling substates as well as anomalous A-E splittings observed for the rotational lines of vsk = 1 state clearly indicate a coupling between methyl torsion and skeletal torsion. However we were able to fit within experimental accuracy the rotational lines of vsk = 1 state using the RAM Hamiltonian. Because of the inversion of the A and E tunneling substates the rotational lines of the vsk = 1 states were assumed to belong to a virtual first excited torsional state. Finally, we assigned several low-Ka rotational transitions of the excited vibrational states above 200 cm-1 but their analysis is complicated by different rotation-vibration interactions. In particular there is an evidence of the Fermi-type resonance between the second excited torsional state and the first excited state of the in-plane skeletal bending mode (265 cm-1). Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged. Zakharenko O. et al., 69th ISMS, 2014, TI01
Excited states in the proton-unbound nuclide 158Ta
NASA Astrophysics Data System (ADS)
Carroll, R. J.; Page, R. D.; Joss, D. T.; O'Donnell, D.; Uusitalo, J.; Darby, I. G.; Andgren, K.; Auranen, K.; Bönig, S.; Cederwall, B.; Doncel, M.; Drummond, M. C.; Eeckhaudt, S.; Grahn, T.; Gray-Jones, C.; Greenlees, P. T.; Hadinia, B.; HerzáÅ, A.; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Konki, J.; Kröll, T.; Leino, M.; Leppänen, A.-P.; McPeake, C.; Nyman, M.; Pakarinen, J.; Partanen, J.; Peura, P.; Rahkila, P.; Revill, J.; Ruotsalainen, P.; Sandzelius, M.; Sarén, J.; Sayǧi, B.; Scholey, C.; Seweryniak, D.; Simpson, J.; Sorri, J.; Stolze, S.; Taylor, M. J.; Thornthwaite, A.
2016-03-01
Excited states in the neutron-deficient odd-odd proton-unbound nuclide 158Ta have been investigated in two separate experiments. In the first experiment, 166Ir nuclei were produced in the reactions of 380 MeV 78Kr ions with an isotopically enriched 92Mo target. The α -decay chain of the 9+ state in 166Ir was analyzed. Fine structure in the α decay of the 9+ state in 162Re established a 66 keV difference in excitation energy between the lowest-lying 9+ and 10+ states in 158Ta. Higher-lying states in 158Ta were populated in the reactions of 255 MeV 58Ni ions with an isotopically enriched 102Pd target. Gamma-ray decay paths that populate, depopulate, and bypass a 19- isomeric state have been identified. The general features of the deduced level scheme are discussed and the prospects for observing proton emission branches from excited states are considered.
Thermally induced excited-state coherent raman spectra of solids
NASA Astrophysics Data System (ADS)
Andrews, J. R.; Hochstrasser, R. M.
1981-09-01
A difference frequency resonance has been observed for the 747 cm -1 vibration in the first excited singlet state of pentacene in benzoic acid. The resonance is absent at low temperature (4.5 K) and its appearance is exponentially activated with an activation energy of 13.8 cm -1. These observations are compared to theoretical expectations.
Detection of excited-state electron bubbles in superfluid helium.
Konstantinov, Denis; Maris, Humphrey J
2003-01-17
We report on experiments in which the pressure oscillation associated with a sound wave is used to explode electron bubbles in liquid helium. Using this technique, we are able to detect the presence of electron bubbles in excited states. PMID:12570553
Adhikary, Amitava; Kumar, Anil; Palmer, Brian J.; Todd, Andrew D.; Heizer, Alicia N.; Sevilla, Michael D.
2014-01-01
Purpose To study the formation and subsequent reactions of the 5-methyl-2′-deoxycytidine cation radical (5-Me-2′-dC•+) in nucleosides and DNA-oligomers and compare to one electron oxidized thymidine. Materials and methods Employing electron spin resonance (ESR), cation radical formation and its reactions were investigated in 5-Me-2′-dC, thymidine (Thd) and their derivatives, in fully double stranded (ds) d[GC*GC*GC*GC*]2 and in the 5-Me-C/A mismatched, d[GGAC*AAGC:CCTAATCG], where C* = 5-Me-C. Results We report 5-Me-2′-dC•+ production by one-electron oxidation of 5-Me-2′-dC by Cl2•− via annealing in the dark at 155 K. Progressive annealing of 5-Me-2′-dC•+ at 155 K produces the allylic radical (C-CH2•). However, photoexcitation of 5-Me-2′-dC•+ by 405 nm laser or by photoflood lamp leads to only C3′• formation. Photoexcitation of N3-deprotonated thyminyl radical in Thd and its 5′-nucleotides leads to C3′• formation but not in 3′-TMP which resulted in the allylic radical (U-CH2•) and C5′• production. For excited 5-Me-2′,3′-ddC•+, absence of the 3′-OH group does not prevent C3′• formation. For d[GC*GC*GC*GC*]2 and d[GGAC*AAGC:CCTAATCG], intra-base paired proton transferred form of G cation radical (G(N1-H)•:C(+H+)) is found with no observable 5-Me-2′-dC•+ formation. Photoexcitation of (G(N1-H)•:C(+H+)) in d[GC*GC*GC*GC*]2 produced only C1′• and not the expected photoproducts from 5-Me-2′-dC•+. However, photoexcitation of (G(N1-H)•:C(+H+)) in d[GGAC*AAGC:CCTAATCG] led to C5′• and C1′• formation. Conclusions C-CH2• formation from 5-Me-2′-dC•+ occurs via ground state deprotonation from C5-methyl group on the base. In the excited 5-Me-2′-dC•+ and 5-Me-2′,3′-ddC•+, spin and charge localization at C3′ followed by deprotonation leads to C3′• formation. Thus, deprotonation from C3′ in the excited cation radical is kinetically controlled and sugar C-H bond energies are
First observation of excited states in {sup 12}Li
Hall, C. C.; Lunderberg, E. M.; DeYoung, P. A.; Denby, D. H.; Baumann, T.; Bazin, D.; Blanchon, G.; Bonaccorso, A.; Brown, B. A.; Christian, G.; Frank, N.; Gade, A.; Mosby, S.; Peters, W. A.; Spyrou, A.; Thoennessen, M.; Brown, J.; Finck, J.; Hinnefeld, J.; Hoffman, C. R.
2010-02-15
The neutron-unbound ground state and two excited states of {sup 12}Li were formed by the two-proton removal reaction from a 53.4-MeV/u {sup 14}B beam. The decay energy spectrum of {sup 12}Li was measured with the Modular Neutron Array (MoNA) and the Sweeper dipole superconducting magnet at the National Superconducting Cyclotron Laboratory. Two excited states at resonance energies of 250 +- 20 keV and 555 +- 20 keV were observed for the first time and the data are consistent with the previously reported s-wave ground state with a scattering length of a{sub s}=-13.7 fm.
Lattice QCD determination of patterns of excited baryon states
Subhasish Basak; Robert Edwards; George Fleming; Keisuke Juge; Adam Lichtl; Colin Morningstar; David Richards; Ikuro Sato; Stephen Wallace
2007-10-01
Energies for excited isospin I = 1/2 and I = 3/2 states that include the nucleon and Delta families of baryons are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G2 irreducible representations of the octahedral group. The decomposition of spin 5/2 or higher spin states is realized for the first time in a lattice QCD calculation. We observe patterns of degenerate energies in the irreducible representations of the octahedral group that correspond to the subduction of the continuum spin 5/2 or higher. The overall pattern of low-lying excited states corresponds well to the pattern of physical states subduced to the irreducible representations of the octahedral group.
Direct excitation of butterfly states in Rydberg molecules
NASA Astrophysics Data System (ADS)
Lippe, Carsten; Niederpruem, Thomas; Thomas, Oliver; Eichert, Tanita; Ott, Herwig
2016-05-01
Since their first theoretical prediction Rydberg molecules have become an increasing field of research. These exotic states originate from the binding of a ground state atom in the electronic wave function of a highly-excited Rydberg atom mediated by a Fermi contact type interaction. A special class of long-range molecular states, the butterfly states, were first proposed by Greene et al.. These states arise from a shape resonance in the p-wave scattering channel of a ground state atom and a Rydberg electron and are characterized by an electron wavefunction whose density distribution resembles the shape of a butterfly. We report on the direct observation of deeply bound butterfly states of Rydberg molecules of 87 Rb. The butterfly states are studied by high resolution spectroscopy of UV-excited Rydberg molecules. We find states bound up to - 50 GHz from the 25 P1/2 , F = 1 state, corresponding to binding lengths of 50a0 to 500a0 and with permanent electric dipole moments of up to 500 Debye. This distinguishes the observed butterfly states from the previously observed long range Rydberg molecules in rubidium.
Radiative HELIUM-3 Capture by CARBON-12 to Excited States in OXYGEN-15
NASA Astrophysics Data System (ADS)
Abduljalil, Amir M.
The radiative ^3He capture reaction on ^{12}C was measured over the energy region E_{ rm 3_{He}} = 12-25 MeV. The gamma-ray was measured by two 25.4 cm long and 25.4 cm in diameter NaI(Tl) spectrometers surrounded by anticoincidence plastic shields. Excitation functions at theta_{rm lab} = 60^circ and 105 ^circ have been measured for captures populating the ground and various excited states of ^{15}O. Angular distribution have been measured at E_{rm 3 _{He}} = 18.9 MeV. The existence of giant resonances built on the excited states of ^{15}O was investigated. Calculations from a phenomenological direct-semidirect cluster model were performed to bound and unbound final states in ^{15}O to determine the magnitude and the energy dependence of the cross section as well as the angular distributions. The calculations showed a reasonable agreement with the excitation function.
Ultrafast excited-state dynamics of copper(I) complexes.
Iwamura, Munetaka; Takeuchi, Satoshi; Tahara, Tahei
2015-03-17
Bis-diimine Cu(I) complexes exhibit strong absorption in the visible region owing to the metal-to-ligand charge transfer (MLCT) transitions, and the triplet MLCT ((3)MLCT) states have long lifetimes. Because these characteristics are highly suitable for photosensitizers and photocatalysts, bis-diimine Cu(I) complexes have been attracting much interest. An intriguing feature of the Cu(I) complexes is the photoinduced structural change called "flattening". Bis-diimine Cu(I) complexes usually have tetrahedron-like D2d structures in the ground (S0) state, in which two ligands are perpendicularly attached to the Cu(I) ion. With MLCT excitation, the central Cu(I) ion is formally oxidized to Cu(II), which induces the structural change to the "flattened" square-planar-like structure that is seen for usual Cu(II) complexes. In this Account, we review our recent studies on ultrafast excited-state dynamics of bis-diimine Cu(I) complexes carried out using femtosecond time-resolved optical spectroscopy. Focusing on three prototypical bis-diimine Cu(I) complexes that have 1,10-phenanthroline ligands with different substituents at the 2,9-positions, i.e., [Cu(phen)2](+) (phen = 1,10-phenanthroline), [Cu(dmphen)2](+) (dmphen = 2,9-dimethyl-1,10-phenanthroline), and [Cu(dpphen)2](+) (dpphen = 2,9-diphenyl-1,10-phenanthroline), we examined their excited-state dynamics by time-resolved emission and absorption spectroscopies with 200 fs time resolution, observed the excited-state coherent nuclear motion with 30 fs time resolution and performed complementary theoretical calculations. This combined approach vividly visualizes excited-state processes in the MLCT state of bis-diimine Cu(I) complexes. It was demonstrated that flattening distortion, internal conversion, and intersystem crossing occur on the femtosecond-early picosecond time scale, and their dynamics is clearly identified separately. The flattening distortion predominantly occurs in the S1 state on the subpicosecond time
Excited States of the Diatomic Molecule CrHe
NASA Astrophysics Data System (ADS)
Pototschnig, Johann V.; Ratschek, Martin; Hauser, Andreas W.; Ernst, Wolfgang E.
2013-06-01
Chromium (Cr) atoms embedded in superfluid helium nanodroplets (He_N) have been investigated by laser induced fluorescence, beam depletion and resonant two-photon ionization spectroscopy in current experiments at our institute. Cr is found to reside inside the He_N in the a^7S ground state. Two electronically excited states, z^7P and y^7P, are involved in a photoinduced ejection process which allowed us to study Fano resonances in the photoionisation spectra The need for a better understanding of the experimental observations triggered a theoretical approach towards the computation of electronically excited states via high-level methods of computational chemistry. Two well-established, wave function-based methods, CASSCF and MRCI, are combined to calculate the potential energy curves for the three states involved. The character of the two excited states z^7P and y^7P turns out to be significantly different. Theory predicts the ejection of the Cr atom in the case of an y^7P excitation as was observed experimentally. The quasi-inert helium environment is expected to weaken spin selection rules, allowing a coupling between different spin states especially during the ejection process. We therefore extend our theoretical analysis to the lowest state in the triplet- and quintet- manifold. Most of these alternative states show very weak bonding of only a few wn. A. Kautsch, M. Hasewend, M. Koch and W. E. Ernst, Phys. Rev. A 86, 033428 (2012). A. Kautsch, M. Koch and W. E. Ernst, J. Phys. Chem. A, accepted, doi:10.1021/jp312336m}.
NASA Astrophysics Data System (ADS)
Montoya, G. A.; Carreras-Sospedra, M.; Montoya, J.; Dabdub, D.; Foster, K. L.
2014-12-01
Complex reactions between hydroxyl radicals (OH) and volatile organic compounds (VOCs) in the lower atmosphere have a high impact on the formation/fates of airborne toxic chemicals, polycyclic aromatic hydrocarbons (PAHs), and particulate matter.1 Recently, air quality models have been implemented to identify OH sources, but have underpredicted OH concentrations. Studies suggest that O2 (1Δg) is produced via an energy transfer (ET) mechanism initiated by the electronic excitation of PAH and oxygenated-PAH. Energy transfer involves the formation of triplet excited state PAH which is then quenched by the surrounding ground state O2 (3∑g) resulting in excited state O2 (1Δg) formation. Excited state O2 (1Δg) is known to readily react with mono-olefins to produce organic hydroperoxides.2,3 Furthermore, the organic hydroperoxide can photodegrade to yield OH. In this study, a Nd:YAG laser coupled to a time-resolved near infrared detector was used to obtain quantum yields of O2 (1Δg) production by irradiating PAHs and oxy-PAHs at both 355 nm and 532 nm in different solvents. Select PAHs, primarily emitted by combustion engines (e.g. pyrene and benzo[a]pyrene), and their oxygenated forms (oxy-PAHs) have been identified as highly efficient O2 (1Δg) photosensitizers. For example, the measured quantum yield for pyrene in toluene was 0.90 ± 0.02. The measured quantum yields were used to calculate the photochemical rate constants for O2 (1Δg) production via ET from electronically excited PAHs and oxy-PAHs. These results were incorporated into the University of California, Irvine-California Institute of Technology (UCI-CIT) model to assess the impact on OH concentrations and the overall air quality of the South Coast Air Basin of California. References 1 Finlayson-Pitts, B.J., and J. N. Pitts (1997), Science, 276(5315),1045-1052. 2 Foote, C. S. (1968), Accts. Chem. Res., 1, 104-110; Gollnick, K. (1968), Adv. Photochem., 6, 1-112; Kearns, D. R. (1971), Chem. Rev., 71, 395
Integrating proton coupled electron transfer (PCET) and excited states
Gagliardi, Christopher J.; Westlake, Brittany C.; Kent, Caleb A.; Paul, Jared J.; Papanikolas, John M.; Meyer, Thomas J.
2010-11-01
In many of the chemical steps in photosynthesis and artificial photosynthesis, proton coupled electron transfer (PCET) plays an essential role. An important issue is how excited state reactivity can be integrated with PCET to carry out solar fuel reactions such as water splitting into hydrogen and oxygen or water reduction of CO_{2} to methanol or hydrocarbons. The principles behind PCET and concerted electron–proton transfer (EPT) pathways are reasonably well understood. In Photosystem II antenna light absorption is followed by sensitization of chlorophyll P_{680} and electron transfer quenching to give P_{680}^{+}. The oxidized chlorophyll activates the oxygen evolving complex (OEC), a CaMn4 cluster, through an intervening tyrosine–histidine pair, Y_{Z}. EPT plays a major role in a series of four activation steps that ultimately result in loss of 4e^{-}/4H^{+} from the OEC with oxygen evolution. The key elements in photosynthesis and artificial photosynthesis – light absorption, excited state energy and electron transfer, electron transfer activation of multiple-electron, multiple-proton catalysis – can also be assembled in dye sensitized photoelectrochemical synthesis cells (DS-PEC). In this approach, molecular or nanoscale assemblies are incorporated at separate electrodes for coupled, light driven oxidation and reduction. Separate excited state electron transfer followed by proton transfer can be combined in single semi-concerted steps (photo-EPT) by photolysis of organic charge transfer excited states with H-bonded bases or in metal-to-ligand charge transfer (MLCT) excited states in pre-associated assemblies with H-bonded electron transfer donors or acceptors. In these assemblies, photochemically induced electron and proton transfer occur in a single, semi-concerted event to give high-energy, redox active intermediates.
Ground and Excited State Spectra of a Quantum Dot
NASA Astrophysics Data System (ADS)
Stewart, D. R.; Sprinzak, D.; Patel, S. R.; Marcus, C. M.; Duruoz, C. I.; Harris, J. S.
1998-03-01
We present linear and nonlinear magnetoconductance measurements of the ground and excited state spectra for successive electron occupancy in a gate defined lateral quantum dot. Previous measurementsfootnote D.R. Stewart, D. Sprinzak, C.M. Marcus, C.I. Duruoz and J.S. Harris Jr., Science 278, (1997). showed a direct correlation between the mth excited state of the N-electron system and the ground state of the (N+m)-electron system for m up to 4, consistent to a large degree with a single-particle picture. Here we report quantitative deviations of the excited state spectra from the spectrum of ground state magnetoconductances, attributed to many-body interactions in the finite system of N ~200 electrons. We also describe the behaviour of anticrossings in the ground state magnetoconductances. We acknowledge the support of JSEP (DAAH04-94-G-0058), ARO (DAAH04-95-1-0331), ONR-YIP (N00014-94-1-0622) and the NSF-PECASE program. D.S. acknowledges the support of MINERVA grant.
Photodissociation of N2O: excitation of 1A" states.
Schinke, Reinhard; Schmidt, Johan A
2012-11-26
We investigate the contributions of the lowest two (1)A" states in the UV photodissociation of N(2)O employing three-dimensional potential energy surfaces and transition dipole moment functions. Because the transition dipole moments are much smaller than for the 2 (1)A' state, we conclude that excitation of the (1)A" states has a marginal effect. The dense vibrational spectrum of the quasi-bound 2(1)A" state possibly explains some of the tiny, noise-like structures of the measured absorption spectrum. PMID:22536943
Excited S-symmetry states of positronic lithium and beryllium
NASA Astrophysics Data System (ADS)
Strasburger, Krzysztof
2016-04-01
The possibility of the existence of excited S-symmetry states of positronic lithium and beryllium, resulting from the positron attachment to high-spin P parent atomic states, is examined and confirmed with variational calculations in the basis of explicitly correlated Gaussian functions. The unexpectedly different order of the energies of the S and P states is explained by the formation of the positronium cluster structure and associated disappearance of the destabilizing centrifugal force. The annihilation properties of newly discovered states are discussed in the context of prospective experimental detection.
Excited S-symmetry states of positronic lithium and beryllium.
Strasburger, Krzysztof
2016-04-14
The possibility of the existence of excited S-symmetry states of positronic lithium and beryllium, resulting from the positron attachment to high-spin P parent atomic states, is examined and confirmed with variational calculations in the basis of explicitly correlated Gaussian functions. The unexpectedly different order of the energies of the S and P states is explained by the formation of the positronium cluster structure and associated disappearance of the destabilizing centrifugal force. The annihilation properties of newly discovered states are discussed in the context of prospective experimental detection. PMID:27083730
Novelli, Fabio; Nazir, Ahsan; Richards, Gethin H; Roozbeh, Ashkan; Wilk, Krystyna E; Curmi, Paul M G; Davis, Jeffrey A
2015-11-19
Until recently it was believed that photosynthesis, a fundamental process for life on earth, could be fully understood with semiclassical models. However, puzzling quantum phenomena have been observed in several photosynthetic pigment-protein complexes, prompting questions regarding the nature and role of these effects. Recent attention has focused on discrete vibrational modes that are resonant or quasi-resonant with excitonic energy splittings and strongly coupled to these excitonic states. Here we unambiguously identify excited state coherent superpositions in photosynthetic light-harvesting complexes using a new experimental approach. Decoherence on the time scale of the excited state lifetime allows low energy (56 cm(-1)) oscillations on the signal intensity to be observed. In conjunction with an appropriate model, these oscillations provide clear and direct experimental evidence that the persistent coherences observed originate from quantum superpositions among vibronic excited states. PMID:26528956
Super-atom molecular orbital excited states of fullerenes.
Johansson, J Olof; Bohl, Elvira; Campbell, Eleanor E B
2016-09-13
Super-atom molecular orbitals are orbitals that form diffuse hydrogenic excited electronic states of fullerenes with their electron density centred at the centre of the hollow carbon cage and a significant electron density inside the cage. This is a consequence of the high symmetry and hollow structure of the molecules and distinguishes them from typical low-lying molecular Rydberg states. This review summarizes the current experimental and theoretical studies related to these exotic excited electronic states with emphasis on femtosecond photoelectron spectroscopy experiments on gas-phase fullerenes.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. PMID:27501970
Subpicosecond Excited State Lifetimes in DNA Polymers Require Unstacked Bases
NASA Astrophysics Data System (ADS)
de La Harpe, Kimberly; Su, Charlene; Kohler, Bern
2009-06-01
The femtosecond lifetimes of excited states of monomeric DNA bases are the result of nuclear motions that lead to one or more conical intersections (CIs). Surprisingly, femtosecond pump-probe experiments reveal that excitations in DNA base polymers, including ones with genomic or 'natural' sequences of the four bases, decay at least an order of magnitude more slowly. Although the reasons for this dramatic change in photophysics are unclear, evidence strongly suggests that the long-lived states are exciplexes formed when an electron is partially transferred from one base to its π-stacked neighbor. Experiments also show that monomer-like subpicosecond decay to the ground state is frequently observed in many DNA oligomers and polymers in addition to exciplex formation. We will present results from high-temperature and other experiments suggesting that monomer-like, CI-mediated dynamics are only possible when unstacked bases are present.
Embedding potentials for excited states of embedded species
Wesolowski, Tomasz A.
2014-05-14
Frozen-Density-Embedding Theory (FDET) is a formalism to obtain the upper bound of the ground-state energy of the total system and the corresponding embedded wavefunction by means of Euler-Lagrange equations [T. A. Wesolowski, Phys. Rev. A 77(1), 012504 (2008)]. FDET provides the expression for the embedding potential as a functional of the electron density of the embedded species, electron density of the environment, and the field generated by other charges in the environment. Under certain conditions, FDET leads to the exact ground-state energy and density of the whole system. Following Perdew-Levy theorem on stationary states of the ground-state energy functional, the other-than-ground-state stationary states of the FDET energy functional correspond to excited states. In the present work, we analyze such use of other-than-ground-state embedded wavefunctions obtained in practical calculations, i.e., when the FDET embedding potential is approximated. Three computational approaches based on FDET, that assure self-consistent excitation energy and embedded wavefunction dealing with the issue of orthogonality of embedded wavefunctions for different states in a different manner, are proposed and discussed.
Controlling excited-state contamination in nucleon matrix elements
NASA Astrophysics Data System (ADS)
Yoon, Boram; Gupta, Rajan; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank; Nucleon Matrix Elements NME Collaboration
2016-06-01
We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2 +1 -flavor ensemble with lattices of size 323×64 generated using the rational hybrid Monte Carlo algorithm at a =0.081 fm and with Mπ=312 MeV . The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a 2-state fit to data at multiple values of the source-sink separation tsep. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of tsep needed to demonstrate convergence of the isovector charges of the nucleon to the tsep→∞ estimates is presented.
Valence and excited states of LiH-
NASA Astrophysics Data System (ADS)
Gutsev, Gennady L.; Nooijen, Marcel; Bartlett, Rodney J.
1998-03-01
Valence and excited dipole-bound states of the LiH- anion are calculated with the recently developed electron-attachment equation-of-motion coupled-cluster technique. It is found that the first dipole-bound state of LiH- corresponds to the second dissociation channel LiH--->Li-(1S)+H(2S). The second (excited) dipole-bound state of LiH- is below the neutral ground-state potential energy curve only for some range of the Li-H internuclear distance. This state appears at bond lengths larger than ~2.0 Å and decays at Li-H distances longer than ~4.2 Å, where the dipole moment of LiH becomes smaller than the critical value of 2.5 D. The adiabatic electron affinity of LiH calculated at the coupled-cluster level with the iterative inclusion of all single, double, and triple excitations and a large atomic natural orbital basis set is 0.327 eV, almost matching the recently obtained experimental value of 0.342+/-0.012 eV.
Excited state dynamics of the astaxanthin radical cation
NASA Astrophysics Data System (ADS)
Amarie, Sergiu; Förster, Ute; Gildenhoff, Nina; Dreuw, Andreas; Wachtveitl, Josef
2010-07-01
Femtosecond transient absorption spectroscopy in the visible and NIR and ultrafast fluorescence spectroscopy were used to examine the excited state dynamics of astaxanthin and its radical cation. For neutral astaxanthin, two kinetic components corresponding to time constants of 130 fs (decay of the S 2 excited state) and 5.2 ps (nonradiative decay of the S 1 excited state) were sufficient to describe the data. The dynamics of the radical cation proved to be more complex. The main absorption band was shifted to 880 nm (D 0 → D 3 transition), showing a weak additional band at 1320 nm (D 0 → D 1 transition). We found, that D 3 decays to the lower-lying D 2 within 100 fs, followed by a decay to D 1 with a time constant of 0.9 ps. The D 1 state itself exhibited a dual behavior, the majority of the population is transferred to the ground state in 4.9 ps, while a small population decays on a longer timescale of 40 ps. Both transitions from D 1 were found to be fluorescent.
Reexamination of the excited states of {sup 12}C
Freer, M.; Munoz-Britton, T.; Nicoli, M. P.; Singer, S. M.; Sparks, N.; Boztosun, I.; Bremner, C. A.; Chappell, S. P. G.; Rae, W. D. M.; Cowin, R. L.; Dillon, G. K.; Fulton, B. R.; Greenhalgh, B. J.; Watson, D. L.; Weisser, D. C.
2007-09-15
An analysis of the {sup 12}C({sup 12}C,3{alpha}){sup 12}C reaction was made at beam energies between 82 and 106 MeV. Decays to both the ground state and the excited states of {sup 8}Be were isolated, allowing states of different characters to be identified. In particular, evidence was found for a previously observed state at 11.16 MeV. An analysis of the angular distributions of the unnatural parity states at 11.83 and 13.35 MeV, previously assigned J{sup {pi}}=2{sup -}, calls into question the validity of these assignments, suggesting that at least one of the states may correspond to J{sup {pi}}=4{sup -}. Evidence is also found for 1{sup -} and 3{sup -} strengths associated with broad states between 11 and 14 MeV.
A new record excited state (3)MLCT lifetime for metalorganic iron(ii) complexes.
Liu, Li; Duchanois, Thibaut; Etienne, Thibaud; Monari, Antonio; Beley, Marc; Assfeld, Xavier; Haacke, Stefan; Gros, Philippe C
2016-05-14
Herein we report the synthesis and time-resolved spectroscopic characterization of a homoleptic Fe(ii) complex exhibiting a record (3)MLCT lifetime of 26 ps promoted by benzimidazolylidene-based ligands. Time dependent density functional molecular modeling of the triplet excited state manifold clearly reveals that, at equilibrium geometries, the lowest (3)MC state lies higher in energy than the lowest (3)MLCT one. This unprecedented energetic reversal in a series of iron complexes, with the stabilization of the charge-transfer state, opens up new perspectives towards iron-made excitonic and photonic devices, hampering the deactivation of the excitation via metal centered channels. PMID:27086578
Excitation on the Coherent States of Pseudoharmonic Oscillator
Popov, Dusan; Pop, Nicolina; Sajfert, Vjekoslav
2009-05-22
In the last decades, much attention has been paid to the excitation on coherent states, especially for coherent states of the harmonic oscillator ([1] and references therein). But an interesting anharmonic oscillator with many potential applications is also the pseudoharmonic oscillator (PHO). So, in the present paper we have defined the excitation on the Klauder-Perelomov coherent states (E-KP-CSs) for the PHO. These states are obtained by repeatedly operating the raising operator K{sub +} on a usual Klauder-Perelomov coherent state (KP-CS) of the PHO [2]. We have verified that really, the E-KP-CSs fulfill all the properties of the coherent states, as stated by Klauder [3]. We have examined the nonclassical properties of the E-KP-CSs, by using the density matrix formalism and examining the dependence of the Mandel parameter Q{sub z,k;m}(|z|{sup 2}) on the |z|{sup 2} and on the m. It seems that these states can be used in optical communication field and in the physics of quantum information, as signal beams, due to the fact that in these fields the nonclassicality plays an important role.
Hermite polynomial excited squeezed vacuum as quantum optical vortex states
NASA Astrophysics Data System (ADS)
Li, Ya-Zhou; Jia, Fang; Zhang, Hao-Liang; Huang, Jie-Hui; Hu, Li-Yun
2015-11-01
We introduce theoretically a kind of Hermite polynomial excited squeezed vacuum by extending the wave-packet states with a vortex structure to a general case. Its normalised factor is found to be the Legendre polynomial and the condition converting the general case to a special one is achieved. Then we consider its statistical properties according to the photon number distribution and the Wigner function. As an application, we investigate the performance of the teleportation of the coherent state. It is shown that these parameters in the generalised state can modulate all the above properties including the vortex structure.
Strong-Field Photoionization as Excited-State Tunneling.
Serebryannikov, E E; Zheltikov, A M
2016-03-25
We show that, in an intense laser field, ultrafast photoionization can occur through quantum pathways that cannot be categorized as multiphoton ionization or ground-state tunneling. In this regime, the subcycle electron-wave-packet dynamics leading to photoionization occurs via electron excited states, from where the electrons tunnel to the continuum within a tiny fraction of the field cycle. For high field intensities, this ionization pathway is shown to drastically enhance the dynamic leakage of the electron wave packet into the continuum, opening an ionization channel that dominates over ground-state electron tunneling. PMID:27058079
Strong-Field Photoionization as Excited-State Tunneling
NASA Astrophysics Data System (ADS)
Serebryannikov, E. E.; Zheltikov, A. M.
2016-03-01
We show that, in an intense laser field, ultrafast photoionization can occur through quantum pathways that cannot be categorized as multiphoton ionization or ground-state tunneling. In this regime, the subcycle electron-wave-packet dynamics leading to photoionization occurs via electron excited states, from where the electrons tunnel to the continuum within a tiny fraction of the field cycle. For high field intensities, this ionization pathway is shown to drastically enhance the dynamic leakage of the electron wave packet into the continuum, opening an ionization channel that dominates over ground-state electron tunneling.
Controlling autoionization in strontium two-electron-excited states
NASA Astrophysics Data System (ADS)
Fields, Robert; Zhang, Xinyue; Dunning, F. Barry; Yoshida, Shuhei; Burgdörfer, Joachim
2016-05-01
One challenge in engineering long-lived two-electron-excited states, i.e., so-called planetary atoms, is autoionization. Autoionization, however, can be suppressed if the outermost electron is placed in a high- n, n ~ 300 - 600 , high- L state because such states have only a very small overlap with the inner electron, even when this is also excited to a state of relatively high n and hence of relatively long lifetime. Here the L-dependence of the autoionization rate for high- n strontium Rydberg atoms is examined during excitation of the core ion 5 s 2S1 / 2 - 5 p 2P3 / 2 transition. Measurements in which the angular momentum of the Rydberg electron is controlled using a pulsed electric field show that the autoionization rate decreases rapidly with increasing L and becomes very small for values larger than ~ 20 . The data are analyzed with the aid of calculations undertaken using complex scaling. Research supported by the NSF and Robert A. Welch Foundation.
A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems
NASA Astrophysics Data System (ADS)
Liu, Wenlan; Lunkenheimer, Bernd; Settels, Volker; Engels, Bernd; Fink, Reinhold F.; Köhn, Andreas
2015-08-01
We present a general method for analyzing the character of singly excited states in terms of charge transfer (CT) and locally excited (LE) configurations. The analysis is formulated for configuration interaction singles (CIS) singly excited wave functions of aggregate systems. It also approximately works for the second-order approximate coupled cluster singles and doubles and the second-order algebraic-diagrammatic construction methods [CC2 and ADC(2)]. The analysis method not only generates a weight of each character for an excited state, but also allows to define the related quasi-diabatic states and corresponding coupling matrix elements. In the character analysis approach, we divide the target system into domains and use a modified Pipek-Mezey algorithm to localize the canonical MOs on each domain, respectively. The CIS wavefunction is then transformed into the localized basis, which allows us to partition the wavefunction into LE configurations within domains and CT configuration between pairs of different domains. Quasi-diabatic states are then obtained by mixing excited states subject to the condition of maximizing the weight of one single LE or CT configuration (localization in configuration space). Different aims of such a procedure are discussed, either the construction of pure LE and CT states for analysis purposes (by including a large number of excited states) or the construction of effective models for dynamics calculations (by including a restricted number of excited states). Applications are given to LE/CT mixing in π-stacked systems, charge-recombination matrix elements in a hetero-dimer, and excitonic couplings in multi-chromophoric systems.
A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems
Liu, Wenlan; Köhn, Andreas; Lunkenheimer, Bernd; Settels, Volker; Engels, Bernd; Fink, Reinhold F.
2015-08-28
We present a general method for analyzing the character of singly excited states in terms of charge transfer (CT) and locally excited (LE) configurations. The analysis is formulated for configuration interaction singles (CIS) singly excited wave functions of aggregate systems. It also approximately works for the second-order approximate coupled cluster singles and doubles and the second-order algebraic-diagrammatic construction methods [CC2 and ADC(2)]. The analysis method not only generates a weight of each character for an excited state, but also allows to define the related quasi-diabatic states and corresponding coupling matrix elements. In the character analysis approach, we divide the target system into domains and use a modified Pipek-Mezey algorithm to localize the canonical MOs on each domain, respectively. The CIS wavefunction is then transformed into the localized basis, which allows us to partition the wavefunction into LE configurations within domains and CT configuration between pairs of different domains. Quasi-diabatic states are then obtained by mixing excited states subject to the condition of maximizing the weight of one single LE or CT configuration (localization in configuration space). Different aims of such a procedure are discussed, either the construction of pure LE and CT states for analysis purposes (by including a large number of excited states) or the construction of effective models for dynamics calculations (by including a restricted number of excited states). Applications are given to LE/CT mixing in π-stacked systems, charge-recombination matrix elements in a hetero-dimer, and excitonic couplings in multi-chromophoric systems.
NASA Astrophysics Data System (ADS)
Jing, Yuanyuan; Chen, Liping; Bai, Shuming; Shi, Qiang
2013-01-01
The hierarchical equations of motion (HEOM) method was applied to calculate the emission spectra of molecular aggregates using the Frenkel exciton model. HEOM equations for the one-exciton excited state were first propagated until equilibration. The reduced density operator and auxiliary density operators (ADOs) were used to characterize the coupled system-bath equilibrium. The dipole-dipole correlation functions were then calculated to obtain the emission spectra of model dimers, and the B850 band of light-harvesting complex II (LH2) in purple bacteria. The effect of static disorder on equilibrium excited state and the emission spectra of LH2 was also explicitly considered. Several approximation schemes, including the high temperature approximation (HTA) of the HEOM, a modified version of the HTA, the stochastic Liouville equation approach, the perturbative time-local and time-nonlocal generalized quantum master equations, were assessed in the calculation of the equilibrium excited state and emission spectra.
Is dipole moment a valid descriptor of excited state's charge-transfer character?
Petelenz, Piotr; Pac, Barbara
2013-11-20
In the ongoing discussion on excited states of the pentacene crystal, dipole moment values have been recently invoked to gauge the CT admixture to excited states of Frenkel parentage in a model cluster. In the present paper, a simple dimer model is used to show that, in general, the dipole moment is not a valid measure of the CT contribution. This finding eliminates some apparent disagreement between the computational results published by different research groups. The implications of our results and other related aspects of cluster-type quantum chemistry calculations are discussed in the context of the standing literature dispute concerning the mechanism of singlet fission in the pentacene crystal, notably the role of charge transfer contributions vs the involvement of an excimer-like doubly excited intermediate (D state). PMID:24138489
Wenzel, Jan; Dreuw, Andreas
2016-03-01
The theoretical simulation of X-ray absorption spectra is in general a challenging task. However, for small and medium-sized organic molecules, the algebraic diagrammatic construction scheme (ADC) for the polarization operator in combination with the core-valence separation approximation (CVS) has proven to yield core-excitation energies and transition moments with almost quantitative accuracy allowing for reliable construction of X-ray absorption spectra. Still, to understand core-excitation processes in detail, it is not sufficient to only compute energies, but also properties like static dipole moments and state densities are important as they provide deeper insight into the nature of core-excited states. Here, we present for the first time an implementation of the intermediate state representation (ISR) approach in combination with the CVS approximation (CVS-ISR), which gives, in combination with the CVS-ADC method, direct access to core-excited state properties. The performance of the CVS-ADC/CVS-ISR approach is demonstrated by means of small- and medium-sized organic molecules. Besides the calculation of core-excited state dipole moments, advanced analyses of core-excited state densities are performed using descriptors like exciton sizes and distances. Plotting electron and hole densities helps to determine the character of the state, and in particular, the investigation of detachment/attachment densities provides information about orbital relaxation effects that are crucial for understanding core excitations. PMID:26845396
Photoionization of potassium atoms from the ground and excited states
Zatsarinny, O.; Tayal, S. S.
2010-04-15
The Dirac-based B-spline R-matrix method is used to investigate the photoionization of atomic potassium from the 4s ground and 4p, 5s-7s, 3d-5d excited states. The effect of the core polarization by the outer electron is included through the polarized pseudostates. Besides the dipole core polarization, we also found a noticeable influence of the quadrupole core polarization. We obtained excellent agreement with experiment for cross sections of the 4s photoionization, including accurate description of the near-threshold Cooper-Seaton minimum. We also obtained close agreement with experiment for the 4p photoionization, but there are unexpectedly large discrepancies with available experimental data for photoionization of the 5d and 7s excited states.
Tunable rubidium excited state Voigt atomic optical filter.
Yin, Longfei; Luo, Bin; Xiong, Junyu; Guo, Hong
2016-03-21
A tunable rubidium excited state Voigt atomic optical filter working at optical communication wavelength (1.5 μm) is realized. The filter achieves a peak transmittance of 57.6% with a double-peak structure, in which each one has a bandwidth of 600 MHz. Benefiting from the Voigt type structure, the magnetic field of the filter can be tuned from 0 to 1600 gauss, and a peak transmittance tunability of 1.6 GHz can thus be realized. Different from the excited state Faraday type filter, the pump efficiency in the Voigt filter is affected a lot by the pump polarization. Measured absorption results of the pump laser and transmittances of the signal laser both prove that the vertical linear polarization pumping is the most efficient in the Voigt filter. PMID:27136803
Precision Study of Excited State Effects in Nucleon Matrix Elements
Simon Dinter, Constantia Alexandrou, Martha Constantinou, Vincent Drach, Karl Jansen, Dru B. Renner
2011-10-01
We present a dedicated precision analysis of the influence of excited states on the calculation of several nucleon matrix elements. This calculation is performed at fixed values of the lattice spacing, volume and pion mass that are typical of contemporary lattice computations. We focus on the nucleon axial charge, g{sub A}, for which we use 7,500 measurements, and on the average momentum of the unpolarized isovector parton distribution, x{sub u-d}, for which we use 23,000 measurements. All computations are done employing N{sub f}=2+1+1 maximally-twisted-mass Wilson fermions and non-perturbatively calculated renormalization factors. We find that excited state effects are negligible for g{sub A} and lead to a O(10%) downward shift for x{sub u-d}.
Electro-optical parameters in excited states of some spectrally active molecules
NASA Astrophysics Data System (ADS)
Benchea, Andreea Celia; Closca, Valentina; Rusu, Cristina Marcela; Morosanu, Cezarina; Dorohoi, Dana Ortansa
2014-08-01
The spectral shifts measured in different solvents are expressed as functions of the solvent macroscopic parameters. The value of the correlation coefficient multiplying the functions of electric permittivity was determined by statistical means. The correlation coefficient depends on the electric dipole moment of the spectrally active molecules. The electro-optical parameters in the ground state of the solute molecules can be approximated by molecular modeling. The excited state parameters are usually estimated using the results obtained both by HyperChem Programme and solvatochromic study. The importance of this approximate method is that it offers information about of the excited state of solute molecule for which our measuring possibilities are very restrictive. The information about the excited electronic state is affected by the limits in which the theories of liquid solutions are developed. Our results refer to two molecules of vitamins from B class, namely B3 and B6.
Communication: Hartree-Fock description of excited states of H{sub 2}
Barca, Giuseppe M. J.; Gilbert, Andrew T. B.; Gill, Peter M. W.
2014-09-21
Hartree-Fock (HF) theory is most often applied to study the electronic ground states of molecular systems. However, with the advent of numerical techniques for locating higher solutions of the self-consistent field equations, it is now possible to examine the extent to which such mean-field solutions are useful approximations to electronic excited states. In this Communication, we use the maximum overlap method to locate 11 low-energy solutions of the HF equation for the H{sub 2} molecule and we find that, with only one exception, these yield surprisingly accurate models for the low-lying excited states of this molecule. This finding suggests that the HF solutions could be useful first-order approximations for correlated excited state wavefunctions.
Temperature dependence of the excited state absorption of alexandrite
Shand, M.L.; Jenssen, H.P.
1983-03-01
The temperature dependence from 28 to 290/sup 0/C of the excited-state absorption cross section sigma /SUB 2a/ (E) in the gain wavelength region of alexandrite has been determined from the temperature dependence of the single pass gain (SPG) and of the fluorescence. sigma /SUB 2a/ (E) and the emission cross section increase with temperature at approximately the same rate.
Minimal-excitation states for electron quantum optics using levitons
NASA Astrophysics Data System (ADS)
Dubois, J.; Jullien, T.; Portier, F.; Roche, P.; Cavanna, A.; Jin, Y.; Wegscheider, W.; Roulleau, P.; Glattli, D. C.
2013-10-01
The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the
Stretching of hydrogen-bonded OH in the lowest singlet excited electronic state of water dimer.
Chipman, Daniel M
2006-01-28
The lowest singlet excited electronic state of water monomer in the gas phase is strictly dissociative along a OH stretch coordinate but changes its nature when the stretched OH moiety is hydrogen bonded to a neighboring water molecule. This work extends previous exploration of the water dimer excited singlet potential-energy surface, using computational methods that are reliable even at geometries well removed from the ground-state equilibrium. First, the hydrogen-bonded OH moiety is stretched far enough to establish the existence of a barrier that is sufficient to support a quasibound vibrational state of the OH oscillator near the Franck-Condon region. Second, the constraint of an icelike structure is relaxed, and it is found that a substantial fraction of liquidlike structures also supports a quasibound vibrational state. These potential-energy explorations on stretching of the hydrogen-bonded OH moiety in a water dimer are discussed as a model for understanding the initial dynamics upon excitation into the lowest excited singlet state of condensed water. The possibility is raised that the excited-state lifetime may be long enough to allow for exciton migration, which would provide a mechanism for energy transport in condensed water phases. PMID:16460160
Ground- and excited-state electronic structure of an iron-containing molecular spin photoswitch
NASA Astrophysics Data System (ADS)
Rodriguez, Jorge H.
2005-09-01
The electronic structure of the cation of [Fe(ptz)6](BF4)2, a prototype of a class of complexes that display light-induced excited-state spin trapping (LIESST), has been investigated by time-independent and time-dependent density-functional theories. The density of states of the singlet ground state reveals that the highest occupied orbitals are metal centered and give rise to a low spin configuration Fe2+(3dxy↑↓3dxz↑↓3dyz↑↓) in agreement with experiment. Upon excitation with light in the 2.3-3.3eV range, metal-centered spin-allowed but parity-forbidden ligand field (LF) antibonding states are populated which, in conjunction with electron-phonon coupling, explain the experimental absorption intensities. The computed excitation energies are in excellent agreement with experiment. Contrary to simpler models we show that the LF absorption bands, which are important for LIESST, do not originate in transitions from the ground to a single excited state but from transitions to manifolds of nearly degenerate excited singlets. Consistent with crystallography, population of the LF states promotes a drastic dilation of the ligand cage surrounding the iron.
Spin radical enhanced magnetocapacitance effect in intermolecular excited states.
Zang, Huidong; Wang, Jianguo; Li, Mingxing; He, Lei; Liu, Zitong; Zhang, Deqing; Hu, Bin
2013-11-14
This article reports the magnetocapacitance effect (MFC) based on both pristine polymer MEH-PPV and its composite system doped with spin radicals (6R-BDTSCSB). We observed that a photoexcitation leads to a significant positive MFC in the pristine MEH-PPV. Moreover, we found that a low doping of spin radicals in polymer MEH-PPV causes a significant change on the MFC signal: an amplitude increase and a line-shape narrowing under light illumination at room temperature. However, no MFC signal was observed under dark conditions in either the pristine MEH-PPV or the radical-doped MEH-PPV. Furthermore, the magnitude increase and line-shape narrowing caused by the doped spin radicals are very similar to the phenomena induced by increasing the photoexcitation intensity. Our studies suggest that the MFC is essentially originated from the intermolecular excited states, namely, intermolecular electron-hole pairs, generated by a photoexcitation in the MEH-PPV. More importantly, by comparing the effects of spin radicals and electrically polar molecules on the MFC magnitude and line shape, we concluded that the doped spin radicals can have the spin interaction with intermolecular excited states and consequently affect the internal spin-exchange interaction within intermolecular excited states in the development of MFC. Clearly, our experimental results indicate that dispersing spin radicals forms a convenient method to enhance the magnetocapacitance effect in organic semiconducting materials. PMID:24144347
Imaging Excited State Dynamics with 2d Electronic Spectroscopy
NASA Astrophysics Data System (ADS)
Engel, Gregory S.
2012-06-01
Excited states in the condensed phase have extremely high chemical potentials making them highly reactive and difficult to control. Yet in biology, excited state dynamics operate with exquisite precision driving solar light harvesting in photosynthetic complexes though excitonic transport and photochemistry through non-radiative relaxation to photochemical products. Optimized by evolution, these biological systems display manifestly quantum mechanical behaviors including coherent energy transfer, steering wavepacket trajectories through conical intersections and protection of long-lived quantum coherence. To image the underlying excited state dynamics, we have developed a new spectroscopic method allowing us to capture excitonic structure in real time. Through this method and other ultrafast multidimensional spectroscopies, we have captured coherent dynamics within photosynthetic antenna complexes. The data not only reveal how biological systems operate, but these same spectral signatures can be exploited to create new spectroscopic tools to elucidate the underlying Hamiltonian. New data on the role of the protein in photosynthetic systems indicates that the chromophores mix strongly with some bath modes within the system. The implications of this mixing for excitonic transport will be discussed along with prospects for transferring underlying design principles to synthetic systems.
The excited-state chemistry of protochlorophyllide a: a time-resolved fluorescence study.
Dietzek, Benjamin; Kiefer, Wolfgang; Yartsev, Arkady; Sundström, Villy; Schellenberg, Peter; Grigaravicius, Paulius; Hermann, Gudrun; Popp, Jürgen; Schmitt, Michael
2006-08-11
The excited-state processes of protochlorophyllide a, the precursor of chlorophyll a in chlorophyll biosynthesis, are studied using picosecond time-resolved fluorescence spectroscopy. Following excitation into the Soret band, two distinct fluorescence components, with emission maxima at 640 and 647 nm, are observed. The 640 nm emitting component appears within the time resolution of the experiment and then decays with a time constant of 27 ps. In contrast, the 647 nm emitting component is built up with a 3.5 ps rise time and undergoes a subsequent decay with a time constant of 3.5 ns. The 3.5 ps rise kinetics are attributed to relaxations in the electronically excited state preceding the nanosecond fluorescence, which is ascribed to emission out of the thermally equilibrated S(1) state. The 27 ps fluorescence, which appears within the experimental response of the streak camera, is suggested to originate from a second minimum on the excited-state potential-energy surface. The population of the secondary excited state is suggested to reflect a very fast motion out of the Franck-Condon region along a reaction coordinate different from the one connecting the Franck-Condon region with the S(1) potential-energy minimum. The 27 ps-component is an emissive intermediate on the reactive excited-state pathway, as its decay yields the intermediate photoproduct, which has been identified previously (J. Phys. Chem. B 2006, 110, 4399-4406). No emission of the photoproduct is observed. The results of the time-resolved fluorescence study allow a detailed spectral characterization of the emission of the excited states in protochlorophyllide a, and the refinement of the kinetic model deduced from ultrafast absorption measurements. PMID:16841352
Low-Lying ππ* States of Heteroaromatic Molecules: A Challenge for Excited State Methods.
Prlj, Antonio; Sandoval-Salinas, María Eugenia; Casanova, David; Jacquemin, Denis; Corminboeuf, Clémence
2016-06-14
The description of low-lying ππ* states of linear acenes by standard electronic structure methods is known to be challenging. Here, we broaden the framework of this problem by considering a set of fused heteroaromatic rings and demonstrate that standard electronic structure methods do not provide a balanced description of the two (typically) lowest singlet state (La and Lb) excitations. While the Lb state is highly sensitive to correlation effects, La suffers from the same drawbacks as charge transfer excitations. We show that the comparison between CIS/CIS(D) can serve as a diagnostic for detecting the two problematic excited states. Standard TD-DFT and even its spin-flip variant lead to inaccurate excitation energies and interstate gaps, with only a double hybrid functional performing somewhat better. The complication inherent to a balanced description of these states is so important that even CC2 and ADC(2) do not necessarily match the ADC(3) reference. PMID:27144975
An incompressible state of a photo-excited electron gas
Chepelianskii, Alexei D.; Watanabe, Masamitsu; Nasyedkin, Kostyantyn; Kono, Kimitoshi; Konstantinov, Denis
2015-01-01
Two-dimensional electrons in a magnetic field can form new states of matter characterized by topological properties and strong electronic correlations as displayed in the integer and fractional quantum Hall states. In these states, the electron liquid displays several spectacular characteristics, which manifest themselves in transport experiments with the quantization of the Hall resistance and a vanishing longitudinal conductivity or in thermodynamic equilibrium when the electron fluid becomes incompressible. Several experiments have reported that dissipationless transport can be achieved even at weak, non-quantizing magnetic fields when the electrons absorb photons at specific energies related to their cyclotron frequency. Here we perform compressibility measurements on electrons on liquid helium demonstrating the formation of an incompressible electronic state under these resonant excitation conditions. This new state provides a striking example of irradiation-induced self-organization in a quantum system. PMID:26007282
Modular Hamiltonian for Excited States in Conformal Field Theory.
Lashkari, Nima
2016-07-22
We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Z_{n} replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories. PMID:27494465
Modular Hamiltonian for Excited States in Conformal Field Theory
NASA Astrophysics Data System (ADS)
Lashkari, Nima
2016-07-01
We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Zn replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories.
NASA Astrophysics Data System (ADS)
Kondo, Jorge M.; Šibalić, Nikola; Guttridge, Alexander; Wade, Christopher G.; De Melo, Natalia R.; Adams, Charles S.; Weatherill, Kevin J.
2015-12-01
We report on the observation of electromagnetically induced transparency (EIT) and absorption (EIA) of highly excited Rydberg states in thermal Cs vapor using a four-step excitation scheme. The advantage of this four-step scheme is that the final transition to the Rydberg state has a large dipole moment and one can achieve similar Rabi frequencies to two- or three-step excitation schemes using two orders of magnitude less laser power. This scheme enables new applications such as dephasing free Rydberg excitation. The observed lineshapes are in good agreement with simulations based on multilevel optical Bloch equations.
Branching ratios of {alpha} decay to excited states of even-even nuclei
Wang, Y. Z.; Zhang, H. F.; Dong, J. M.; Royer, G.
2009-01-15
Branching ratios of {alpha} decay to members of the ground state rotational band and excited 0{sup +} states of even-even nuclei are calculated in the framework of the generalized liquid drop model (GLDM) by taking into account the angular momentum of the {alpha} particle and the excitation probability of the daughter nucleus. The calculation covers isotopic chains from Hg to Fm in the mass regions 180=}224. The calculated branching ratios of the {alpha} transitions are in good agreement with the experimental data and some useful predictions are provided for future experiments.
Controlling the Excited-State Dynamics of Nuclear Spin Isomers Using the Dynamic Stark Effect.
Waldl, Maria; Oppel, Markus; González, Leticia
2016-07-14
Stark control of chemical reactions uses intense laser pulses to distort the potential energy surfaces of a molecule, thus opening new chemical pathways. We use the concept of Stark shifts to convert a local minimum into a local maximum of the potential energy surface, triggering constructive and destructive wave-packet interferences, which then induce different dynamics on nuclear spin isomers in the electronically excited state of a quinodimethane derivative. Model quantum-dynamical simulations on reduced dimensionality using optimized ultrashort laser pulses demonstrate a difference of the excited-state dynamics of two sets of nuclear spin isomers, which ultimately can be used to discriminate between these isomers. PMID:26840424
Enhanced non-Gaussianity from excited initial states
Holman, R; Tolley, Andrew J E-mail: atolley@perimeterinstitute.ca
2008-05-15
We use the techniques of effective field theory in an expanding universe to examine the effect of choosing an excited inflationary initial state built over the Bunch-Davies state on the CMB bi-spectrum. We find that, even for Hadamard states, there are unexpected enhancements in the bi-spectrum for certain configurations in momentum space due to interactions of modes in the early stages of inflation. These enhancements can be parametrically larger than the standard ones and are potentially observable in future data. These initial state effects have a characteristic signature in l-space which distinguishes them from the usual contributions, with the enhancement being most pronounced for configurations corresponding to flattened triangles for which two momenta are collinear.
Li, Changwei; Yang, Kun; Feng, Yan; Su, Xinyan; Yang, Junyi; Jin, Xiao; Shui, Min; Wang, Yuxiao; Zhang, Xueru; Song, Yinglin; Xu, Hongyao
2009-12-01
Two-photon absorption induced excited state absorption in the solution of a new fluorenyl-based chromophore is investigated by a time-resolved pump-probe technique using femtosecond pulses. With the help of an additional femtosecond open-aperture Z-scan technique, numerical simulations based on a three-energy level model are used to interpret the experimental results, and we determine the nonlinear optical parameters of this new chromophore uniquely. Large two-photon absorption cross section and excited state absorption cross section for singlet excited state are obtained, indicating a good candidate for optical limiting devices. Moreover, the influence of two-beam coupling induced energy transfer in neat N,N'-dimethylformamide solvent is also considered, although this effect is strongly restrained by the instantaneous two-photon absorption. PMID:19894682
2012-01-01
In the present work, we employ excited state accelerated ab initio molecular dynamics (A-AIMD) to efficiently study the excited state energy landscape and photophysical topology of a variety of molecular systems. In particular, we focus on two important challenges for the modeling of excited electronic states: (i) the identification and characterization of conical intersections and crossing seams, in order to predict different and often competing radiationless decay mechanisms, and (ii) the description of the solvent effect on the absorption and emission spectra of chemical species in solution. In particular, using as examples the Schiff bases formaldimine and salicylidenaniline, we show that A-AIMD can be readily employed to explore the conformational space around crossing seams in molecular systems with very different photochemistry. Using acetone in water as an example, we demonstrate that the enhanced configurational space sampling may be used to accurately and efficiently describe both the prominent features and line-shapes of absorption and emission spectra. PMID:22904696
Excited-State Properties of Molecular Solids from First Principles
NASA Astrophysics Data System (ADS)
Kronik, Leeor; Neaton, Jeffrey B.
2016-05-01
Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion.
Excited-State Properties of Molecular Solids from First Principles.
Kronik, Leeor; Neaton, Jeffrey B
2016-05-27
Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion. PMID:27090844
Baev, A.; Gel'mukhanov, F.; Aagren, H.; Feifel, R.; Baessler, M.; Miron, C.; Bjoerneholm, O.; Karlsson, L.; Svensson, S.; Piancastelli, M.N.; Sorensen, S.L.; Naves de Brito, A.
2003-02-01
An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s{yields}{pi}{sup *} core-excited N{sub 2} is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X {sup 2}{sigma}{sub g}{sup +} final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.
Study of intermediates from transition metal excited-state electron- transfer reactions
Hoffman, M.Z.
1993-03-31
Progress on 6 projects is reported: excited state absorption spectrum of Ru(bpy)[sub 3][sup 2+], solvent cage model for electron transfer quenching, reductive quenching of [sup *]Cr(III) complexes, solution medium effects in oxidative quenching of [sup *]Ru(II) complexes, photosensitized oxidation of phenol in aqueous solution, and quenching of Ru(II) complexes by oxygen.
Electronic Ground and Excited State Spectral Diffusion of a Photocatalyst
NASA Astrophysics Data System (ADS)
Kiefer, Laura M.; King, John T.; Kubarych, Kevin J.
2014-06-01
Re(bpy)(CO)_3Cl is a well studied CO_2 reduction catalyst, known for its ability as both a photosensitizer and a catalyst with a high quantum yield and product selectivity. The catalysis reaction is initiated by a 400 nm excitation, followed by an intersystem crossing (ISC) and re-equilibration in the lowest triplet state. We utilize the quasi-equilibrium nature of this long-lived triplet metal-to-ligand charge-transfer (3MLCT) state to completely characterize the solvent dynamics using the technique of transient two-dimensional infrared (t-2DIR) spectroscopy to extract observables such as the frequency-frequency correlation function (FFCF), an equilibrium function. The electronic ground state solvent dynamics are characterized using equilibrium two-dimensional infrared spectroscopy (2D IR). Our technique allows us to independently observe the solvent dynamics of different electronic states and compare them. In this study, three carbonyl stretching modes were utilized to probe both the intramolecular and solvent environments in each electronic state. In the electronic ground state, the totally symmetric mode exhibits pure homogeneous broadening and a lack of spectral dynamics, while the two other modes have similar FFCF decay times of ˜ 1.5 ps. In the 3MLCT, however, all three modes experience similar spectral dynamics and have a FFCF decay time of ˜ 4.5 ps, three times slower than in the electronic ground state. Our technique allows us to directly observe the differences in spectral dynamics of the ground and excited electronic states and allows us to attribute the differences to specific origins such as solvent-solute coupling and molecular flexibility.
Bellinger, Daniel; Settels, Volker; Liu, Wenlan; Fink, Reinhold F; Engels, Bernd
2016-06-30
To tune the efficiency of organic semiconductor devices it is important to understand limiting factors as trapping mechanisms for excitons or charges. An understanding of such mechanisms deserves an accurate description of the involved electronical states in the given environment. In this study, we investigate how a polarizable surrounding influences the relative positions of electronically excited states of dimers of different perylene dyes. Polarization effects are particularly interesting for these systems, because gas phase computations predict that the CT states lie slightly above the corresponding Frenkel states. A polarizable environment may change this energy order because CT states are thought to be more sensitive to a polarizable surrounding than Frenkel states. A first insight we got via a TD-HF approach in combination with a polarizable continuum model (PCM). These give limited insights because TD-HF overestimates excitation energies of CT states. However, SCS-CC2 approaches, which are sufficiently accurate, cannot easily be used in combination with continuum solvent models. Hence, we developed two approaches to combine gas phase SCS-CC2 results with solvent effects based on TD-HF computations. Their accuracies were finally checked via ADC(2)//COSMO computations. The results show that for perylene dyes a polarizable surrounding alone does not influence the energetic ordering of CT and Frenkel states. Variations in the energy order of the states only result from nuclear relaxation effects after the excitation process. © 2016 Wiley Periodicals, Inc. PMID:27030658
Yanguas-Gil, A.; Cotrino, J.; Gonzalez-Elipe, A.R.
2005-07-01
In this work the influence of the excited states on the electron-energy distribution function has been determined for an argon microwave discharge at low pressure. A collisional-radiative model of argon has been developed taking into account the most recent experimental and theoretical values of argon-electron-impact excitation cross sections. The model has been solved along with the electron Boltzmann equation in order to study the influence of the inelastic collisions from the argon excited states on the electron-energy distribution function. Results show that under certain conditions the excited states can play an important role in determining the shape of the distribution function and the mean kinetic energy of the electrons, deplecting the high-energy tail due to inelastic processes from the excited states, especially from the 4s excited configuration. It has been found that from the populations of the excited states an excitation temperature can be defined. This excitation temperature, which can be experimentally determined by optical emission spectroscopy, is lower than the electron kinetic temperature obtained from the electron-energy distribution function.
Output power of a quantum dot laser: Effects of excited states
Wu, Yuchang; Jiang, Li Asryan, Levon V.
2015-11-14
A theory of operating characteristics of quantum dot (QD) lasers is discussed in the presence of excited states in QDs. We consider three possible situations for lasing: (i) ground-state lasing only; (ii) ground-state lasing at first and then the onset of also excited-state lasing with increasing injection current; (iii) excited-state lasing only. The following characteristics are studied: occupancies of the ground-state and excited-state in QDs, free carrier density in the optical confinement layer, threshold currents for ground- and excited-state lasing, densities of photons emitted via ground- and excited-state stimulated transitions, output power, internal and external differential quantum efficiencies. Under the conditions of ground-state lasing only, the output power saturates with injection current. Under the conditions of both ground- and excited-state lasing, the output power of ground-state lasing remains pinned above the excited-state lasing threshold while the power of excited-state lasing increases. There is a kink in the light-current curve at the excited-state lasing threshold. The case of excited-state lasing only is qualitatively similar to that for single-state QDs—the role of ground-state transitions is simply reduced to increasing the threshold current.
Excited state dynamics and isomerization in ruthenium sulfoxide complexes.
King, Albert W; Wang, Lei; Rack, Jeffrey J
2015-04-21
Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect
Tuna, Deniz; Lefrancois, Daniel; Wolański, Łukasz; Gozem, Samer; Schapiro, Igor; Andruniów, Tadeusz; Dreuw, Andreas; Olivucci, Massimo
2015-12-01
As a minimal model of the chromophore of rhodopsin proteins, the penta-2,4-dieniminium cation (PSB3) poses a challenging test system for the assessment of electronic-structure methods for the exploration of ground- and excited-state potential-energy surfaces, the topography of conical intersections, and the dimensionality (topology) of the branching space. Herein, we report on the performance of the approximate linear-response coupled-cluster method of second order (CC2) and the algebraic-diagrammatic-construction scheme of the polarization propagator of second and third orders (ADC(2) and ADC(3)). For the ADC(2) method, we considered both the strict and extended variants (ADC(2)-s and ADC(2)-x). For both CC2 and ADC methods, we also tested the spin-component-scaled (SCS) and spin-opposite-scaled (SOS) variants. We have explored several ground- and excited-state reaction paths, a circular path centered around the S1/S0 surface crossing, and a 2D scan of the potential-energy surfaces along the branching space. We find that the CC2 and ADC methods yield a different dimensionality of the intersection space. While the ADC methods yield a linear intersection topology, we find a conical intersection topology for the CC2 method. We present computational evidence showing that the linear-response CC2 method yields a surface crossing between the reference state and the first response state featuring characteristics that are expected for a true conical intersection. Finally, we test the performance of these methods for the approximate geometry optimization of the S1/S0 minimum-energy conical intersection and compare the geometries with available data from multireference methods. The present study provides new insight into the performance of linear-response CC2 and polarization-propagator ADC methods for molecular electronic spectroscopy and applications in computational photochemistry. PMID:26642989
Structure of low-lying states in 140Sm studied by Coulomb excitation
NASA Astrophysics Data System (ADS)
Klintefjord, M.; Hadyńska-KlÈ©k, K.; Görgen, A.; Bauer, C.; Bello Garrote, F. L.; Bönig, S.; Bounthong, B.; Damyanova, A.; Delaroche, J.-P.; Fedosseev, V.; Fink, D. A.; Giacoppo, F.; Girod, M.; Hoff, P.; Imai, N.; Korten, W.; Larsen, A.-C.; Libert, J.; Lutter, R.; Marsh, B. A.; Molkanov, P. L.; Naïdja, H.; Napiorkowski, P.; Nowacki, F.; Pakarinen, J.; Rapisarda, E.; Reiter, P.; Renstrøm, T.; Rothe, S.; Seliverstov, M. D.; Siebeck, B.; Siem, S.; Srebrny, J.; Stora, T.; Thöle, P.; Tornyi, T. G.; Tveten, G. M.; Van Duppen, P.; Vermeulen, M. J.; Voulot, D.; Warr, N.; Wenander, F.; De Witte, H.; Zielińska, M.
2016-05-01
The electromagnetic structure of 140Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 21+ state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that 140Sm shows considerable γ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region.
Excited state dynamics of brightly fluorescent second generation epicocconone analogues.
Chatterjee, Soumit; Karuso, Peter; Boulangé, Agathe; Franck, Xavier; Datta, Anindya
2015-05-21
The natural product epicocconone, owing to its unique fluorescence properties, has been developed into a range of products used in biotechnology, especially proteomics. However, its weak green fluorescence in its native state, while advantageous for proteomics applications, is a disadvantage in other applications that require two-color readouts. Here we report the photophysical characterization of two brightly fluorescent analogues of epicocconone. These analogues, with naphthyl or pyridyl groups replacing the heptatriene chain, resulted in bright fluorescence in both the native state and the long Stokes shifted enamine. Time-resolved fluorescence studies and DFT calculations were carried out to understand the excited state processes involved in fluorescence. Results showed the p-chloro group on the pyridyl is responsible for the high fluorescence of the native fluorophore. The application of one of these compounds for staining electrophoresis gels is exemplified. PMID:25902354
Ultrafast excited-state deactivation of flavins bound to dodecin.
Staudt, Heike; Oesterhelt, Dieter; Grininger, Martin; Wachtveitl, Josef
2012-05-18
Dodecins, a group of flavin-binding proteins with a dodecameric quaternary structure, are able to incorporate two flavins within each of their six identical binding pockets building an aromatic tetrade with two tryptophan residues. Dodecin from the archaeal Halobacterium salinarum is a riboflavin storage device. We demonstrate that unwanted side reactions induced by reactive riboflavin species and degradation of riboflavin are avoided by ultrafast depopulation of the reactive excited state of riboflavin. Intriguingly, in this process, the staggered riboflavin dimers do not interact in ground and photoexcited states. Rather, within the tetrade assembly, each riboflavin is kept under the control of the respective adjacent tryptophan, which suggests that the stacked arrangement is a matter of optimizing the flavin load. We further identify an electron transfer in combination with a proton transfer as a central element of the effective excited state depopulation mechanism. Structural and functional comparisons of the archaeal dodecin with bacterial homologs reveal diverging evolution. Bacterial dodecins bind the flavin FMN instead of riboflavin and exhibit a clearly different binding pocket design with inverse incorporations of flavin dimers. The different adoption of flavin changes photochemical properties, making bacterial dodecin a comparably less efficient quencher of flavins. This supports a functional role different for bacterial and archaeal dodecins. PMID:22451648
Decay width measurements of excited states in 14C
NASA Astrophysics Data System (ADS)
Haigh, P.; Ashwood, N.; Bloxham, T.; Curtis, N.; Freer, M.; Price, D.; Ziman, V.; Bohlen, H.; Kokalova, T.; Schulz, C.; von Oertzen, W.; Weldon, C.; Catford, W.; Harlin, C.
2008-05-01
Various excited states in 14C, above the α-decay threshold, are believed to possess a geometric arrangement of three α-particles covalently bound by the two delocalised valence neutrons. The 12C(16O, 14O)14C* reaction was studied at a beam energy of 234 MeV, at the ISL facility at the Hahn-Meitner-Institut (HMI), Berlin. The 14O ejectile was detected by a Q3D spectrometer at forward angles. The energies and angles of the excited 14C recoil break-up fragments were measured in coincidence using a double sided silicon strip detector array comprised of four detectors at backwards angles. A complete kinematic reconstruction of the reaction was performed to reconstruct the 14C* → 10Be + α and 14C* → 13C + n decay channels and the branching ratios of these decays were calculated. Neutron emission was found to be favoured for the 12.96, 14.87, 16.72 and 18.6 MeV states. Evidence for α-decay was found for the 14.87, 18.6 and 21.4 MeV states; which are candidates for the three bodied molecular cluster structure of 14C.
Role of carotenoid excited states and radicals in antioxidant activities
NASA Astrophysics Data System (ADS)
Lambert, Chris R.
1995-05-01
Carotenoids are linear polyenes that occur in nature and are known to have powerful antioxidant properties. They react efficiently with the excited states of many organic molecules. In the photosynthetic apparatus of plants they quench reactive excited states that may be formed and release the energy as heat. In photodynamic therapy they may be used to ameliorate the associated skin photosensitivity that is a consequence of many photosensitizers. This protection may be either through reaction with the sensitizer triplet state or through quenching of singlet oxygen. Carotenoids also form relatively stable radical species and react efficiently with the hydroxyl radical, superoxide and the solvated electron. In cells they are associated with the lipid core of the cell membrane and are effective against lipid peroxidation. The importance of the thermodynamic properties of these compounds and their organization within biological systems is pivotal to understanding carotenoid antioxidant activity. The present paper reviews some recent work on the energy level of (beta) -carotene, electron transfer involving the one electron reduced species and the resonance Raman spectra of some carotenoids in micellar solution.
Tsirkin, S. S. Eremeev, S. V.; Chulkov, E. V.
2012-10-15
The contribution of inelastic electron-electron scattering to the decay rate of excitations in the surface states and first two image potential states at the Y-bar point on the surface is calculated in the GW approximation, and the quasi-momentum dependence of the corresponding contribution for the surface states is analyzed. The mechanisms of electron scattering in these states are studied, and the temperature dependence of the excitation lifetime is analyzed with allowance for the contribution of the electron-phonon interaction calculated earlier.
Excited State Effects in Nucleon Matrix Element Calculations
Constantia Alexandrou, Martha Constantinou, Simon Dinter, Vincent Drach, Karl Jansen, Theodoros Leontiou, Dru B Renner
2011-12-01
We perform a high-statistics precision calculation of nucleon matrix elements using an open sink method allowing us to explore a wide range of sink-source time separations. In this way the influence of excited states of nucleon matrix elements can be studied. As particular examples we present results for the nucleon axial charge g{sub A} and for the first moment of the isovector unpolarized parton distribution x{sub u-d}. In addition, we report on preliminary results using the generalized eigenvalue method for nucleon matrix elements. All calculations are performed using N{sub f} = 2+1+1 maximally twisted mass Wilson fermions.
Investigations into photo-excited state dynamics in colloidal quantum dots
NASA Astrophysics Data System (ADS)
Singh, Gaurav
Colloidal Quantum dots (QDs) have garnered considerable scientific and technological interest as a promising material for next generation solar cells, photo-detectors, lasers, bright light-emitting diodes (LEDs), and reliable biomarkers. However, for practical realization of these applications, it is crucial to understand the complex photo-physics of QDs that are very sensitive to surface chemistry and chemical surroundings. Depending on the excitation density, QDs can support single or multiple excitations. The first part of this talk addresses evolution of QD excited state dynamics in the regime of low excitation intensity. We use temperature-resolved time-resolved fluorescence spectroscopy to study exciton dynamics from picoseconds to microseconds and use kinetic modeling based on classical electron transfer to show the effect of surface trap states on dynamics of ground-state exciton manifold in core-shell CdSe/CdS QDs. We show that the thickness of CdS shell plays an important role in interaction of CdSe core exciton states with nanocrystal environment, and find that a thicker shell can minimize the mixing of QD exciton states with surface trap states. I will then present an investigation into the dynamics of multiply-excited states in QDs. One of the key challenges in QD spectroscopy is to reliably distinguish multi- from single-excited states that have similar lifetime components and spectroscopic signatures. I will describe the development of a novel multi-pulse fluorescence technique to selectively probe multi-excited states in ensemble QD samples and determine the nature of the multi-excited state contributing to the total fluorescence even in the limit of low fluorescent yields. We find that in our sample of CdSe/CdS core/shell QDs the multi-excited emission is dominated by emissive trion states rather than biexcitons. Next, I will discuss the application of this technique to probe exciton-plasmon coupling in layered hybrid films of QD/gold nanoparticles
Vura-Weis, Josh; Newton, M. D.; Wasielewski, Michael R; Subotnik, J.E.
2010-12-09
A common strategy to calculate electronic coupling matrix elements for charge or energy transfer is to take the adiabatic states generated by electronic structure computations and rotate them to form localized diabatic states. In this paper, we show that, for intermolecular transfer of singlet electronic excitation, usually we cannot fully localize the electronic excitations in this way. Instead, we calculate putative initial and final states with small excitation tails caused by weak interactions with high energy excited states in the electronic manifold. These tails do not lead to substantial changes in the total diabatic coupling between states, but they do lead to a different partitioning of the total coupling between Coulomb (Förster), exchange (Dexter), and one-electron components. The tails may be reduced by using a multistate diabatic model or eliminated entirely by truncation (denoted as “chopping”). Without more information, we are unable to conclude with certainty whether the observed diabatic tails are a physical reality or a computational artifact. This research suggests that decomposition of the diabatic coupling between chromophores into Coulomb, exchange, and one-electron components may depend strongly on the number of states considered, and such results should be treated with caution.
Hydrological excitation of polar motion by different variables of the GLDAS models
NASA Astrophysics Data System (ADS)
Wińska, Małgorzata; Nastula, Jolanta
Continental hydrological loading, by land water, snow, and ice, is an element that is strongly needed for a full understanding of the excitation of polar motion. In this study we compute different estimations of hydrological excitation functions of polar motion (Hydrological Angular Momentum - HAM) using various variables from the Global Land Data Assimilation System (GLDAS) models of land hydrosphere. The main aim of this study is to show the influence of different variables for example: total evapotranspiration, runoff, snowmelt, soil moisture to polar motion excitations in annual and short term scale. In our consideration we employ several realizations of the GLDAS model as: GLDAS Common Land Model (CLM), GLDAS Mosaic Model, GLDAS National Centers for Environmental Prediction/Oregon State University/Air Force/Hydrologic Research Lab Model (Noah), GLDAS Variable Infiltration Capacity (VIC) Model. Hydrological excitation functions of polar motion, both global and regional, are determined by using selected variables of these GLDAS realizations. First we compare a timing, spectra and phase diagrams of different regional and global HAMs with each other. Next, we estimate, the hydrological signal in geodetically observed polar motion excitation by subtracting the atmospheric -- AAM (pressure + wind) and oceanic -- OAM (bottom pressure + currents) contributions. Finally, the hydrological excitations are compared to these hydrological signal in observed polar motion excitation series. The results help us understand which variables of considered hydrological models are the most important for the polar motion excitation and how well we can close polar motion excitation budget in the seasonal and inter-annual spectral ranges.
NASA Astrophysics Data System (ADS)
Li, Zheng; Sohn, Ilyoup; Levin, Deborah A.; Modest, Michael F.
2011-05-01
The current work implemented excited levels of atomic N and corresponding electron impact excitation/de-excitation and ionization processes in DSMC. Results show that when excitation models are included, the Stardust 68.9 km re-entry flow has an observable change in the ion number densities and electron temperature. Adding in the excited levels of atoms improves the degree of ionization by providing additional intermediate steps to ionization. The extra ionization reactions consume the electron energy and reduce the electron temperature. The DSMC results of number densities of excited levels are lower than the prediction of quasi steady state calculation. Comparison of radiation calculations using electronic excited populations from DSMC and QSS indicates that, at the stagnation point, there is about 20% difference of the radiative heat flux between DSMC and QSS.
Brabec, Jiri; Bhaskaran-Nair, Kiran; Govind, Niranjan; Pittner, Jiri; Kowalski, Karol
2012-11-07
The concept of the model space underlying multireference coupled-cluster (MRCC) formulations is a powerful tool to deal with complex correlation effects for various electronic states. Here, we demonstrate that iterative state-specific MRCC methods (SS-MRCC) based on properly defined model spaces can be used to describe core-level excited states even when canonical Hartree-Fock orbitals are utilized. We show that the SS-MRCC models with single and double excitations (SSMRCCSD) are comparable in accuracy to high-level single reference equation-of-motion coupled cluster (EOMCC) formalism. We also demonstrate that the SS-MRCC methods are capable of providing high accuracy results without experiencing numerical problems of the EOMCC methods.
Thermal ground-state ordering and elementary excitations in artificial magnetic square ice
NASA Astrophysics Data System (ADS)
Morgan, Jason P.; Stein, Aaron; Langridge, Sean; Marrows, Christopher H.
2011-01-01
Recent advances in nanotechnology allow model systems to be constructed, in which frustrated interactions can be tuned at will, such as artificial spin ice. The symmetry of the square ice lattice leads to the emergence of a long-range-ordered ground state from the manifold of frustrated states. However, it is experimentally very difficult to access using the effective thermodynamics of rotating-field demagnetization protocols, because the energy barriers to thermal equilibrium are extremely large. Here we study an as-fabricated sample that approaches the ground state very closely. We identify the small localized departures from the ground state as elementary excitations of the system, at frequencies that follow a Boltzmann law. We therefore identify the state we observe as the frozen-in residue of true thermodynamics that occurred during the fabrication of the sample. The relative proportions of different excitations are suggestive of monopole interactions during thermalization.
Surface hopping investigation of benzophenone excited state dynamics.
Favero, Lucilla; Granucci, Giovanni; Persico, Maurizio
2016-04-21
We present a simulation of the photodynamics of benzophenone for the first 20 ps after n →π* excitation, performed by trajectory surface hopping calculations with on-the-fly semiempirical determination of potential energy surfaces and electronic wavefunctions. Both the dynamic and spin-orbit couplings are taken into account, and time-resolved fluorescence emission is also simulated. The computed decay time of the S1 state is in agreement with experimental observations. The direct S1→ T1 intersystem crossing (ISC) accounts for about 2/3 of the S1 decay rate. The remaining 1/3 goes through T2 or higher triplets. The nonadiabatic transitions within the triplet manifold are much faster than ISC and keep the population of T1 at about 3/4 of the total triplet population, and that of the other states (mainly T2) at 1/4. Two internal coordinates are vibrationally active immediately after n →π* excitation: one is the C[double bond, length as m-dash]O stretching and the other one is a combination of the conrotatory torsion of phenyl rings and of bending involving the carbonyl C atom. The period of the torsion-bending mode coincides with oscillations in the time-resolved photoelectron spectra of Spighi et al. and substantially confirms their assignment. PMID:27031566
Probing the Locality of Excited States with Linear Algebra.
Etienne, Thibaud
2015-04-14
This article reports a novel theoretical approach related to the analysis of molecular excited states. The strategy introduced here involves gathering two pieces of physical information, coming from Hilbert and direct space operations, into a general, unique quantum mechanical descriptor of electronic transitions' locality. Moreover, the projection of Hilbert and direct space-derived indices in an Argand plane delivers a straightforward way to visually probe the ability of a dye to undergo a long- or short-range charge-transfer. This information can be applied, for instance, to the analysis of the electronic response of families of dyes to light absorption by unveiling the trend of a given push-pull chromophore to increase the electronic cloud polarization magnitude of its main transition with respect to the size extension of its conjugated spacer. We finally demonstrate that all the quantities reported in this article can be reliably approximated by a linear algebraic derivation, based on the contraction of detachment/attachment density matrices from canonical to atomic space. This alternative derivation has the remarkable advantage of a very low computational cost with respect to the previously used numerical integrations, making fast and accurate characterization of large molecular systems' excited states easily affordable. PMID:26574379
Approximating ground and excited state energies on a quantum computer
NASA Astrophysics Data System (ADS)
Hadfield, Stuart; Papageorgiou, Anargyros
2015-04-01
Approximating ground and a fixed number of excited state energies, or equivalently low-order Hamiltonian eigenvalues, is an important but computationally hard problem. Typically, the cost of classical deterministic algorithms grows exponentially with the number of degrees of freedom. Under general conditions, and using a perturbation approach, we provide a quantum algorithm that produces estimates of a constant number of different low-order eigenvalues. The algorithm relies on a set of trial eigenvectors, whose construction depends on the particular Hamiltonian properties. We illustrate our results by considering a special case of the time-independent Schrödinger equation with degrees of freedom. Our algorithm computes estimates of a constant number of different low-order eigenvalues with error and success probability at least , with cost polynomial in and . This extends our earlier results on algorithms for estimating the ground state energy. The technique we present is sufficiently general to apply to problems beyond the application studied in this paper.
Excitation gap of fractal quantum hall states in graphene.
Luo, Wenchen; Chakraborty, Tapash
2016-01-13
In the presence of a magnetic field and an external periodic potential the Landau level spectrum of a two-dimensional electron gas exhibits a fractal pattern in the energy spectrum which is described as the Hofstadter's butterfly. In this work, we develop a Hartree-Fock theory to deal with the electron-electron interaction in the Hofstadter's butterfly state in a finite-size graphene with periodic boundary conditions, where we include both spin and valley degrees of freedom. We then treat the butterfly state as an electron crystal so that we could obtain the order parameters of the crystal in the momentum space and also in an infinite sample. A phase transition between the liquid phase and the fractal crystal phase can be observed. The excitation gaps obtained in the infinite sample is comparable to those in the finite-size study, and agree with a recent experimental observation. PMID:26657089
Excitation gap of fractal quantum hall states in graphene
NASA Astrophysics Data System (ADS)
Luo, Wenchen; Chakraborty, Tapash
2016-01-01
In the presence of a magnetic field and an external periodic potential the Landau level spectrum of a two-dimensional electron gas exhibits a fractal pattern in the energy spectrum which is described as the Hofstadter’s butterfly. In this work, we develop a Hartree-Fock theory to deal with the electron-electron interaction in the Hofstadter’s butterfly state in a finite-size graphene with periodic boundary conditions, where we include both spin and valley degrees of freedom. We then treat the butterfly state as an electron crystal so that we could obtain the order parameters of the crystal in the momentum space and also in an infinite sample. A phase transition between the liquid phase and the fractal crystal phase can be observed. The excitation gaps obtained in the infinite sample is comparable to those in the finite-size study, and agree with a recent experimental observation.
Symmetry-adapted excited states for the T1u⊗hg Jahn-Teller system
NASA Astrophysics Data System (ADS)
Qiu, Q. C.; Dunn, J. L.; Bates, C. A.
2001-08-01
Jahn-Teller (JT) systems typically contain a set of equivalent-energy wells in the lowest adiabatic potential-energy surface (APES). Quantum-mechanical tunneling between these wells (the dynamic JT effect) must be allowed for by taking appropriate symmetrized combinations of oscillator-type states associated with the wells. It is important to be able to describe the excited states of such systems for a number of reasons. One particular reason is that they are required for the calculation of second-order vibronic reduction factors, which in turn are useful for modeling experimental data using effective Hamiltonians. In this paper, projection-operator techniques are used to obtain general expressions for the symmetry-adapted excited states of the icosahedral T1u⊗hg JT system for the case of D5d minima in the APES. Analytical expressions for the states and their energies for one-phonon excitation are given explicitly. The energies of a selection of states with two-phonon excitations are also obtained and plotted. The results obtained in this paper are applicable to the C-60 molecule.
Benzonitrile: Electron affinity, excited states, and anion solvation
NASA Astrophysics Data System (ADS)
Dixon, Andrew R.; Khuseynov, Dmitry; Sanov, Andrei
2015-10-01
We report a negative-ion photoelectron imaging study of benzonitrile and several of its hydrated, oxygenated, and homo-molecularly solvated cluster anions. The photodetachment from the unsolvated benzonitrile anion to the X ˜ 1 A 1 state of the neutral peaks at 58 ± 5 meV. This value is assigned as the vertical detachment energy (VDE) of the valence anion and the upper bound of adiabatic electron affinity (EA) of benzonitrile. The EA of the lowest excited electronic state of benzonitrile, a ˜ 3 A 1 , is determined as 3.41 ± 0.01 eV, corresponding to a 3.35 eV lower bound for the singlet-triplet splitting. The next excited state, the open-shell singlet A ˜ 1 A 1 , is found about an electron-volt above the triplet, with a VDE of 4.45 ± 0.01 eV. These results are in good agreement with ab initio calculations for neutral benzonitrile and its valence anion but do not preclude the existence of a dipole-bound state of similar energy and geometry. The step-wise and cumulative solvation energies of benzonitrile anions by several types of species were determined, including homo-molecular solvation by benzonitrile, hydration by 1-3 waters, oxygenation by 1-3 oxygen molecules, and mixed solvation by various combinations of O2, H2O, and benzonitrile. The plausible structures of the dimer anion of benzonitrile were examined using density functional theory and compared to the experimental observations. It is predicted that the dimer anion favors a stacked geometry capitalizing on the π-π interactions between the two partially charged benzonitrile moieties.
Neutron decay widths of excited states of {sup 11}Be
Haigh, P. J.; Freer, M.; Ashwood, N. I.; Bloxham, T.; Curtis, N.; McEwan, P.; Bohlen, H. G.; Dorsch, T.; Kokalova, Tz.; Schulz, Ch.; Wheldon, C.
2009-01-15
The two-neutron transfer reaction {sup 9}Be({sup 16}O, {sup 14}O){sup 11}Be[{sup 10}Be +n] has been used to measure the branching ratios for the neutron decay of excited states of {sup 11}Be. The {sup 14}O ejectile was detected by a Q3D spectrometer at forward angles. The energies and angles of the {sup 10}Be fragments of the decaying {sup 11}Be* recoil were measured in coincidence with the {sup 14}O ejectile using a double-sided silicon strip detector array at backward angles. This enabled a kinematic reconstruction of the reaction to be performed. Theoretical decay branch ratios were calculated using barrier penetrability factors and were compared to the measured ratios to provide information on the relative reduced widths of the states. The decay widths have been used to link states in {sup 11}Be with a common structure and structurally to states in the daughter nucleus {sup 10}Be. The 3/2{sup -} 8.82-MeV state was identified as a candidate for a molecular band head.
Numerical computation of dynamically important excited states of many-body systems
NASA Astrophysics Data System (ADS)
Łącki, Mateusz; Delande, Dominique; Zakrzewski, Jakub
2012-07-01
We present an extension of the time-dependent density matrix renormalization group, also known as the time evolving block decimation algorithm, allowing for the computation of dynamically important excited states of one-dimensional many-body systems. We show its practical use for analyzing the dynamical properties and excitations of the Bose-Hubbard model describing ultracold atoms loaded in an optical lattice from a Bose-Einstein condensate. This allows for a deeper understanding of nonadiabaticity in experimental realizations of insulating phases.
Excited state properties of the astaxanthin radical cation: A quantum chemical study
NASA Astrophysics Data System (ADS)
Dreuw, Andreas; Starcke, Jan Hendrik; Wachtveitl, Josef
2010-07-01
Using time-dependent density functional theory, the excited electronic states of the astaxanthin radical cation (AXT rad + ) are investigated. While the optically allowed excited D 1 and D 3 states are typical ππ∗ excited states, the D 2 and D 4 states are nπ∗ states. Special emphasis is put onto the influence of the carbonyl groups onto the excited states. For this objective, the excited states of four hypothetical carotenoids and zeaxanthin have been computed. Addition of a carbonyl group to a conjugated carbon double bond system does essentially not change the vertical excitation energies of the optically allowed ππ∗ states due to two counter-acting effects: the excitation energy should increase due to the -M-effect of the carbonyl group and at the same time decrease owing to the elongation of the conjugated double bond system by the carbonyl group itself.
NASA Astrophysics Data System (ADS)
Egidi, Franco; Segado, Mireia; Koch, Henrik; Cappelli, Chiara; Barone, Vincenzo
2014-12-01
In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π*, π-π*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.
Egidi, Franco Segado, Mireia; Barone, Vincenzo; Koch, Henrik; Cappelli, Chiara
2014-12-14
In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.
NASA Astrophysics Data System (ADS)
Stavrev, K. K.; Kynev, K. D.; Nikolov, G. St.
1988-06-01
Linear Jahn-Teller coupling constants are obtained by the angular overlap model. A comparison with the data published recently [Parrot et al., J. Chem. Phys. 87, 1463 (1987)] is made in order to demonstrate the considerable improvement in the calculated Jahn-Teller coefficients when the parameters of the angular overlap model are extracted from a spectral analysis of the systems under consideration.
{beta} decay of 129Cd and excited states in 129In
Taprogge, J.; Jungclaus, A.; Grawe, H.; Nishimura, S.; Doornenbal, P.; Lorusso, G.; Simpson, G. S.; Soderstrom, P. A.; Sumikama, T.; Xu, Z. Y.; Kondev, F. G.
2015-05-26
The β decay of Cd 129 , produced in the relativistic fission of a U 238 beam, was experimentally studied at the RIBF facility at the RIKEN Nishina Center. From the γ radiation emitted after the β decays, a level scheme of In 129 was established comprising 31 excited states and 69 γ -ray transitions. The experimentally determined level energies are compared to state-of-the-art shell-model calculations. The half-lives of the two β -decaying states in Cd 129 were deduced and the β feeding to excited states in In 129 were analyzed. It is found that, as in most cases in the Z<50 , N≤82 region, both decays are dominated by the ν0g 7/2 →π0g 9/2 Gamow–Teller transition, although the contribution of first-forbidden transitions cannot be neglected.
Ultrafast electronic relaxation of excited state vitamin B 12 in the gas phase
NASA Astrophysics Data System (ADS)
Shafizadeh, Niloufar; Poisson, Lionel; Soep, Benoıˆt
2008-06-01
The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.
Marks, M; Sachs, S; Schwalb, C H; Schöll, A; Höfer, U
2013-09-28
We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate. PMID:24089789
NASA Astrophysics Data System (ADS)
Marks, M.; Sachs, S.; Schwalb, C. H.; Schöll, A.; Höfer, U.
2013-09-01
We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate.
Weiler, M.; Bartl, K.; Gerhards, M.
2012-03-21
Molecular beam investigations in combination with IR/UV spectroscopy offer the possibility to obtain structural information on isolated molecules and clusters. One of the demanding tasks is the discrimination of different isomers, e.g., by the use of isomer specific UV excitations. If this discrimination fails due to overlaying UV spectra of different isomers, IR/IR methods offer another possibility. Here, we present a new IR/UV/IR/UV quadruple resonance technique to distinguish between different isomers especially in the electronically excited state. Due to the IR spectra, structural changes and photochemical pathways in excited states can be assigned and identified. The method is applied to the dihydrated cluster of 3-hydroxyflavone which has been investigated as photochemically relevant system and proton wire model in the S{sub 1} state. By applying the new IR/UV/IR/UV technique, we are able to show experimentally that both in the electronic ground (S{sub 0}) and the electronically excited state (S{sub 1}) two isomers have to be assigned.
Initial excited-state dynamics of an N-alkylated indanylidene-pyrroline (NAIP) rhodopsin analog.
Schapiro, Igor; Fusi, Stefania; Olivucci, Massimo; Andruniów, Tadeusz; Sasidharanpillai, Swaroop; Loppnow, Glen R
2014-10-23
N-Alkylated indanylidene-pyrroline-based molecular switches mimic different aspects of the light-induced retinal chromophore isomerization in rhodopsin: the vertebrate dim-light visual pigment. In particular, they display a similar ultrashort excited-state lifetime, subpicosecond photoproduct appearance time, and photoproduct vibrational coherence. To better understand the early light-induced dynamics of such systems, we measured and modeled the resonance Raman spectra of the Z-isomer of the N-methyl-4-(5'-methoxy-2',2'-dimethyl-indan-1'-ylidene)-5-methyl-2,3-dihydro-2H-pyrrolium (NAIP) switch in methanol solution. It is shown that the data, complemented with a <70 fs excited-state trajectory computation, demonstrate initial excited-state structural dynamics dominated by double-bond expansion and single-bond contraction stretches. This mode subsequently couples with the five-membered ring inversion and double-bond torsion. These results are discussed in the context of the mechanism of the excited-state photoisomerization of NAIP switches in solution and the 11-cis retinal in rhodopsin. PMID:25255466
Modeling coherent excitation energy transfer in photosynthetic light harvesting systems
NASA Astrophysics Data System (ADS)
Huo, Pengfei
2011-12-01
Recent non-linear spectroscopy experiments suggest the excitation energy transfer in some biological light harvesting systems initially occurs coherently. Treating such processes brings significant challenge for conventional theoretical tools that usually involve different approximations. In this dissertation, the recently developed Iterative Linearized Density Matrix (ILDM) propagation scheme, which is non-perturbative and non-Markovian is extended to study coherent excitation energy transfer in various light harvesting complexes. It is demonstrated that the ILDM approach can successfully describe the coherent beating of the site populations on model systems and gives quantitative agreement with both experimental results and the results of other theoretical methods have been developed recently to going beyond the usual approximations, thus providing a new reliable theoretical tool to study this phenomenon. This approach is used to investigate the excited energy transfer dynamics in various experimentally studied bacteria light harvesting complexes, such as Fenna-Matthews-Olsen (FMO) complex, Phycocyanin 645 (PC645). In these model calculations, quantitative agreement is found between computed de-coherence times and quantum beating pattens observed in the non-linear spectroscopy. As a result of these studies, it is concluded that the stochastic resonance behavior is important in determining the optimal throughput. To begin addressing possible mechanics for observed long de-coherence time, various models which include correlation between site energy fluctuations as well as correlation between site energy and inter-site coupling are developed. The influence of both types of correlation on the coherence and transfer rate is explored using with a two state system-bath hamiltonian parametrized to model the reaction center of Rhodobacter sphaeroides bacteria. To overcome the disadvantages of a fully reduced approach or a full propagation method, a brownian dynamics
Modeling of electronic excitation and radiation in non-continuum hypersonic reentry flows
NASA Astrophysics Data System (ADS)
Li, Zheng; Ozawa, Takashi; Sohn, Ilyoup; Levin, Deborah A.
2011-06-01
The modeling of hypersonic radiation in non-equilibrium, non-continuum flows is considered in the framework of the direct simulation Monte Carlo (DSMC) approach. The study explores the influence of electronic states on the flow chemistry and degree of ionization as well as the assumption that the electronic states can be described by a steady state solution to a system of rate equations of excitation, de-excitation, and radiative transfer processes. The work implements selected excited levels of atomic nitrogen and oxygen and the corresponding electron impact excitation/de-excitation and ionization processes in DSMC. The simulations show that when excitation models are included, the degree of ionization in the Stardust transitional re-entry flow increases due to additional intermediate steps to ionization. The extra ionization reactions consume the electron energy to reduce the electron temperature. The DSMC predicted excited state level populations are lower than those predicted by a quasi steady state calculation, but the differences can be understood in terms of the flow distribution functions.
Excited-state dynamics of pentacene derivatives with stable radical substituents.
Ito, Akitaka; Shimizu, Akihiro; Kishida, Noriaki; Kawanaka, Yusuke; Kosumi, Daisuke; Hashimoto, Hideki; Teki, Yoshio
2014-06-23
The excited-state dynamics of pentacene derivatives with stable radical substituents were evaluated in detail through transient absorption measurements. The derivatives showed ultrafast formation of triplet excited state(s) in the pentacene moiety from a photoexcited singlet state through the contributions of enhanced intersystem crossing and singlet fission. Detailed kinetic analyses for the transient absorption data were conducted to quantify the excited-state characteristics of the derivatives. PMID:24788384
NASA Technical Reports Server (NTRS)
Santos, Javier; Bu, Xiu R.; Mintz, Eric A.
2001-01-01
The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.
Theoretical description of excited state dynamics in nanostructures
NASA Astrophysics Data System (ADS)
Rubio, Angel
2009-03-01
There has been much progress in the synthesis and characterization of nanostructures however, there remain immense challenges in understanding their properties and interactions with external probes in order to realize their tremendous potential for applications (molecular electronics, nanoscale opto-electronic devices, light harvesting and emitting nanostructures). We will review the recent implementations of TDDFT to study the optical absorption of biological chromophores, one-dimensional polymers and layered materials. In particular we will show the effect of electron-hole attraction in those systems. Applications to the optical properties of solvated nanostructures as well as excited state dynamics in some organic molecules will be used as text cases to illustrate the performance of the approach. Work done in collaboration with A. Castro, M. Marques, X. Andrade, J.L Alonso, Pablo Echenique, L. Wirtz, A. Marini, M. Gruning, C. Rozzi, D. Varsano and E.K.U. Gross.
Chimera states and excitation waves in networks with complex topologies
NASA Astrophysics Data System (ADS)
Schöll, Eckehard
2016-06-01
Chimera patterns, which consist of coexisting spatial domains of coherent (synchronized) and incoherent (desyn- chronized) dynamics are studied in networks of FitzHugh-Nagumo systems with complex topologies. To test the robustness of chimera patterns with respect to changes in the structure of the network, we study the following network topologies: Regular ring topology with R nearest neigbors coupled to each side, small-world topology with additional long-range random links, and a hierarchical geometry in the connectivity matrix. We find that chimera states are generally robust with respect to these perturbations, but qualitative changes of the chimera patterns in form of nested coherent and incoherent regions can be induced by a hierarchical topology. The suppression of propagating excitation waves by a small-world topology is also reviewed.
Measurement of Atomic Oscillator Strength Distribution from the Excited States
Hussain, Shahid; Saleem, M.; Baig, M. A.
2008-10-22
Saturation technique has been employed to measure the oscillator strength distribution in spectra of helium lithium using an electrical discharge cell a thermionic diode ion detector respectively. The photoabsorption cross sections in the discrete or bound region (commonly known as f-values) have been determined form the Rydberg series accessed from a particular excited state calibrating it with the absolute value of the photoionization cross section measured at the ionization threshold. The extracted discrete f-values merge into the oscillator strength densities, estimated from the measured photoionization cross sections at different photon energies above the first ionization threshold. The experimental data on helium and lithium show continuity between the discrete and the continuous oscillator strengths across the ionization threshold.
UV excited-state photoresponse of biochromophore negative ions.
Bochenkova, Anastasia V; Klærke, Benedikte; Rahbek, Dennis B; Rajput, Jyoti; Toker, Yoni; Andersen, Lars H
2014-09-01
Members of the green fluorescent protein (GFP) family may undergo irreversible phototransformation upon irradiation with UV light. This provides clear evidence for the importance of the higher-energy photophysics of the chromophore, which remains essentially unexplored. By using time-resolved action and photoelectron spectroscopy together with high-level electronic structure theory, we directly probe and identify higher electronically excited singlet states of the isolated para- and meta-chromophore anions of GFP. These molecular resonances are found to serve as a doorway for very efficient electron detachment in the gas phase. Inside the protein, this band is found to be resonant with the quasicontinuum of a solvated electron, thus enhancing electron transfer from the GFP to the solvent. This suggests a photophysical pathway for photoconversion of the protein, where GFP resonant photooxidation in solution triggers radical redox reactions inside these proteins. PMID:25044707
Theoretical study on the excited states of HCN
Nayak, Malaya K.; Chaudhuri, Rajat K.; Krishnamachari, S.N.L.G.
2005-05-08
In the flash-photolysis of oxazole, iso-oxazole, and thiozole a transient band system was observed in the region 2500-3050 A. This band system was attributed to a meta-stable form of HCN, i.e., either HNC or triplet HCN. Theoretical investigations have been carried out on the ground and excited states of HCN to characterize this and other experimentally observed transitions. The predicted geometries are compared with the experiment and earlier theoretical calculations. The present calculations show that the band system in the region 2500-3050 A corresponds to the transition 4 {sup 3}-A{sup '}<{sup -}1 {sup 3}-A{sup '} of HCN.
The mechanism of excited state proton dissociation in microhydrated hydroxylamine clusters.
Thisuwan, Jittima; Suwannakham, Parichart; Lao-ngam, Charoensak; Sagarik, Kritsana
2016-02-21
The dynamics and mechanism of excited-state proton dissociation and transfer in microhydrated hydroxylamine clusters are studied using NH2OH(H2O)n (n = 1-4) as model systems and the DFT/B3LYP/aug-cc-pVDZ and TD-DFT/B3LYP/aug-cc-pVDZ methods as model calculations. This investigation is based on the Förster acidity scheme and emphasizes the photoacid dissociation in the ground (S0) and lowest singlet-excited states (S1) and the interplay between the photo and thermal excitations. The quantum chemical results suggest that the intermediate complexes are formed only in the S1 state in a low local-dielectric environment (e.g., ε = 1) and that upon the S0→ S1 transition, the photon energy excites mostly NH2OH, which leads to a homolytic cleavage of the O-H bond and to dynamically stable charge-separated Rydberg-like H-bond complexes (e.g., NH2O˙-H3O(+)˙). The potential energy surfaces for proton displacement in the smallest Rydberg-like H-bond complex support the intersection of the S0 and S1 states in low local-dielectric environments, whereas in a high local-dielectric environment (e.g., ε = 78), these two states are completely separated. Based on the static results, a photoacid-dissociation mechanism that involves Rydberg-like H-bond complex formation, an H-bond chain extension and fluctuations in the local-dielectric environment is proposed. NVT-BOMD simulations confirm the static results and show that the dynamic behavior of the dissociating proton in the S1 state is not different from that of the protonated H-bond systems in the ground state, which consists of the oscillatory shuttling and structural diffusion motions. These findings allow our theoretical methods, which have been used successfully in protonated H-bond systems in the ground state, to be applied in the study of the photoacid-dissociation processes. The current theoretical study suggests effective steps as well as guidelines for the investigation of the dynamics of the photoacid-dissociation and
Suppression of excited-state contributions to stellar reaction rates
NASA Astrophysics Data System (ADS)
Rauscher, T.
2013-09-01
It has been shown in previous work [Kiss , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.191101 101, 191101 (2008); Rauscher , Phys. Rev. C10.1103/PhysRevC.80.035801 80, 035801 (2009)] that a suppression of the stellar enhancement factor (SEF) occurs in some endothermic reactions at and far from stability. This effect is re-evaluated using the ground-state contributions to the stellar reaction rates, which were shown to be better suited to judging the importance of excited-state contributions than the previously applied SEFs. An update of the tables shown in the latter work is given. The new evaluation finds 2350 cases (out of a full set of 57 513 reactions) for which the ground-state contribution is larger in the reaction direction with a negative reaction Q value than in the exothermic direction, thus providing exceptions to the commonly applied Q value rule. The results confirm the Coulomb suppression effect but lead to a larger number of exceptions than previously found. This is due to the fact that often a large variation in the g.s. contribution does not lead to a sizable change in the SEF. On the other hand, several previously identified cases do not appear anymore because it is found that their g.s. contribution is smaller than inferred from the SEF.
Ultrafast dynamics of excited state of phenoxy-phthalocyanines in solution
NASA Astrophysics Data System (ADS)
Yao, Cheng-Bao; Yan, Xiao-Yan; Sun, Da-Wei; Sui, Yan-Li; Li, Jin; Sun, Wen-Jun; Li, Qiang-Hua; Yang, Shou-Bin
2016-01-01
Ultrafast dynamics of the excited state of 2,9,16,23-phenoxy-phthalocyanine (Pc1) and 2,9,16,23-phenoxy-phthalocyanine-zinc (Pc2) has been investigated using femtosecond transient absorption (TA) and time-resolved fluorescence (TRFL) techniques. The observed dynamics of femtosecond TA and TRFL experiments are similar, which demonstrated the intrinsic properties of the excitation and the relaxation processes in both kinds of phthalocyanines with two decay components. A multi level model has been proposed to explain the photophysical processes after Soret-band excitation. The results show that the fast decay component dynamics comes from the intramolecular vibrational relaxation, the slower ones from the internal conversion. The samples are expected to be a potential candidate for optical applications and photodynamic therapy.
Fujiwara, Y.; Kohno, M.; Miyagawa, K.; Suzuki, Y.
2004-10-01
The previous Faddeev calculation of the two-alpha plus {lambda} system for {sub {lambda}}{sup 9}Be is extended to incorporate the spin-orbit components of the SU{sub 6} quark-model (QM) baryon-baryon interactions. We employ the Born kernel of the QM {lambda}N LS interaction and generate the spin-orbit component of the {lambda}{alpha} potential by {alpha}-cluster folding. The Faddeev calculation in the jj-coupling scheme implies that the direct use of the QM Born kernel for the {lambda}N LS component is not good enough to reproduce the small experimental value {delta}E{sub ls}{sup expt}=43{+-}5 keV for the 5/2{sup +}-3/2{sup +} splitting. This procedure predicts 3-5 times larger values in the models FSS and fss2. The spin-orbit contribution from the effective meson-exchange potentials in fss2 is argued to be unfavorable to the small ls splitting, through the analysis of the Scheerbaum factors for the single-particle spin-orbit potentials calculated in the G-matrix formalism.
Stability of quantum-dot excited-state laser emission under simultaneous ground-state perturbation
Kaptan, Y. Herzog, B.; Schöps, O.; Kolarczik, M.; Woggon, U.; Owschimikow, N.; Röhm, A.; Lingnau, B.; Lüdge, K.; Schmeckebier, H.; Arsenijević, D.; Bimberg, D.; Mikhelashvili, V.; Eisenstein, G.
2014-11-10
The impact of ground state amplification on the laser emission of In(Ga)As quantum dot excited state lasers is studied in time-resolved experiments. We find that a depopulation of the quantum dot ground state is followed by a drop in excited state lasing intensity. The magnitude of the drop is strongly dependent on the wavelength of the depletion pulse and the applied injection current. Numerical simulations based on laser rate equations reproduce the experimental results and explain the wavelength dependence by the different dynamics in lasing and non-lasing sub-ensembles within the inhomogeneously broadened quantum dots. At high injection levels, the observed response even upon perturbation of the lasing sub-ensemble is small and followed by a fast recovery, thus supporting the capacity of fast modulation in dual-state devices.
Neves, R F C; Jones, D B; Lopes, M C A; Blanco, F; García, G; Ratnavelu, K; Brunger, M J
2015-05-21
We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of composite vibrational modes and electronic-states in phenol, where the energy range of those experiments was 15-250 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely, for the inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. In addition, for the relevant dipole-allowed excited electronic states, we also report f-scaled Born-level and energy-corrected and f-scaled Born-level (BEf-scaled) ICS. Where possible, our measured and calculated ICSs are compared against one another with the general level of accord between them being satisfactory to within the measurement uncertainties. PMID:26001459
Charge state dynamics of the nitrogen vacancy center in diamond under 1064-nm laser excitation
NASA Astrophysics Data System (ADS)
Ji, Peng; Dutt, M. V. Gurudev
2016-07-01
The photophysics and charge state dynamics of the nitrogen vacancy (NV) center in diamond has been extensively investigated, but is still not fully understood. In contrast to previous work, we find that NV0 converts to NV- under excitation with low power near-infrared (1064-nm) light, resulting in increased photoluminescence from the NV- state. We used a combination of spectral and time-resolved photoluminescence experiments and rate-equation modeling to conclude that NV0 converts to NV- via absorption of 1064-nm photons from the valence band of diamond. We report fast quenching and recovery of the photoluminescence from both charge states of the NV center under low power 1064-nm laser excitation, which has not been previously observed. We also find, using optically detected magnetic resonance experiments, that the charge transfer process mediated by the 1064-nm laser is spin dependent.
Neves, R. F. C.; Jones, D. B.; Lopes, M. C. A.; Blanco, F.; García, G.; Ratnavelu, K.; Brunger, M. J.
2015-05-21
We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of composite vibrational modes and electronic-states in phenol, where the energy range of those experiments was 15–250 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely, for the inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. In addition, for the relevant dipole-allowed excited electronic states, we also report f-scaled Born-level and energy-corrected and f-scaled Born-level (BEf-scaled) ICS. Where possible, our measured and calculated ICSs are compared against one another with the general level of accord between them being satisfactory to within the measurement uncertainties.
The End of Superdeformation: De-excitation to Spherical States in Lead Isotopes
NASA Astrophysics Data System (ADS)
Cizewski, Jolie A.
1997-04-01
Numerous examples of superdeformed rotational bands at high angular momenta have been observed in medium and heavy mass nuclei. The A ~190 region has been especially rich - superdeformed (SD) excitations have been identified in at least 22 isotopes and a large fraction of these bands have γ-ray energies which are simply related. However, the fundamental properties of excitation energy and spin-parity have only recently between determined. The first candidate for a discrete transition which links the SD band to ``normal" deformed (ND) excitations was observed in ^194Pb.(M. J. Brinkman, et al., Phys. Rev. C53), R1461 (1996). Subsequently, many transitions which connect SD and ND excitations in ^194Hg were observed, which allowed the determination of the excitation energy and spin.footnote T. L. Khoo, et al., Phys. Rev. Lett. 76, 1583 (1996). In ^194Pb as many as 12 discrete transitionsfootnote A. Lopez-Martens, et al., Phys. Lett. B380, 18 (1996) and K. Hauschild, et al., Phys. Rev. C (1996). have now been identified with the Eurogam or Gammasphere arrays of γ-ray detectors. This has allowed model-independent determinations of the excitation energy, spin, and parity of these states. The decay of the SD to ND states has been suggested to proceed via mixing between SD and ND excitations with similar excitation energies and angular momenta,(E. Vigezzi, et al., Phys. Lett. B249), 163 (1990). and allows a probe of the complex character of excitations at moderate temperatures in the ND well. In addition, the quasi-continuous spectrum of transitions which link SD and ND excitations can be used to probe level density and pairing degrees of freedom in hot, ND nuclei.footnote T. Dossing, et al., Phys. Rev. Lett. 75, 1276 (1995); A. Lopez-Martens, et al., PRL 77, 1707 (1996); and D.P. McNabb, et al., BAPS 41, 1237 (1996). Studies of the deexcitation of SD bands will be reviewed with a focus on the Pb isotopes.
Watching ultrafast barrierless excited-state isomerization of pseudocyanine in real time.
Dietzek, Benjamin; Yartsev, Arkady; Tarnovsky, Alexander N
2007-05-01
The photoinduced excited-state processes in 1,1'-diethyl-2,2'-cyanine iodine are investigated using femtosecond time-resolved pump-probe spectroscopy. Using a broad range of probe wavelengths, the relaxation of the initially prepared excited-state wavepacket can be followed down to the sink region. The data directly visualize the directed downhill motion along the torsional reaction coordinate and suggest a barrierless excited-state isomerization in the short chain cyanine dye. Additionally, ultrafast ground-state hole and excited-state hole replica broadening is observed. While the narrow excited-state wavepacket broadens during pump-probe overlap, the ground-state hole burning dynamics takes place on a significantly longer time-scale. The experiment reported can be considered as a direct monitoring of the shape and the position of the photoprepared wavepacket on the excited-state potential energy surface. PMID:17417893
Excited state polarizabilities for CC2 using the resolution-of-the-identity approximation.
Graf, Nora K; Friese, Daniel H; Winter, Nina O C; Hättig, Christof
2015-12-28
We report an implementation of static and frequency-dependent excited state polarizabilities for the approximate coupled cluster single and doubles model CC2 as analytic second derivatives of an excited state quasienergy Lagrangian. By including appropriate conditions for the normalization and the phase of the eigenvectors, divergent secular terms are avoided. This leads to response equations in a subspace orthogonal to the unperturbed eigenvectors. It is shown how these projected equations can be solved without storage of the double excitation part of the eigenvectors. By exploiting the resolution-of-the-identity approximation and a numerical Laplace transformation, the quadratic scaling of the main memory demands of RI-CC2 with the system size could be preserved. This enables calculations of excited state polarizabilities for large molecules, e.g., linear polyacenes up to decacene with almost 2500 basis functions on a single compute node within a few days. For a test set of molecules where measurements are available as reference data, we compare the orbital-relaxed and unrelaxed CC2 approaches with experiment to validate its accuracy. The approach can be easily extended to other response methods, in particular CIS(D∞). The latter gives results which, in the orbital-relaxed case, are within a few percent of the CC2 values, while coupled cluster singles results deviate typically by about 20% from orbital-relaxed CC2 and experimental reference data. PMID:26723652
Observation of excited state charge transfer with fs/ps-CARS
Blom, Alex Jason
2009-01-01
Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4'-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.
Dobryakov, A. L.; Quick, M.; Ioffe, I. N.; Granovsky, A. A.; Ernsting, N. P.; Kovalenko, S. A.
2014-05-14
We show that femtosecond stimulated Raman spectroscopy can record excited-state spectra in the absence of actinic excitation, if the Raman pump is in resonance with an electronic transition. The approach is illustrated by recording S{sub 1} and S{sub 0} spectra of trans-azobenzene in n-hexane. The S{sub 1} spectra were also measured conventionally, upon nπ* (S{sub 0} → S{sub 1}) actinic excitation. The results are discussed and compared to earlier reports.
NASA Astrophysics Data System (ADS)
Peng, Hsuan Tung; Ho, Yew Kam
2015-10-01
We have investigated quantum entanglement for two interacting ultracold bosonic atoms in one-dimensional harmonic traps. The effective potential is modeled by delta interaction. For this two-atom system, we have investigated quantum entanglement properties, such as von Neumann entropy and linear entropy for its ground state and excited states. Using a computational scheme that is different from previously employed, a total of the lowest 16 states are studied. Here we show the dependencies of entanglement properties under various interacting strengths. Comparisons for the ground state entanglement are made with earlier results in the literature. New results for the other 15 excited states are reported here.
Herbert, John M; Zhang, Xing; Morrison, Adrian F; Liu, Jie
2016-05-17
Franck-Condon region, but we describe a "spin-complete" version of the theory in which proper spin eigenstates are obtained by construction. For systems of coupled chromophores, we have developed an ab initio version of the Frenkel-Davydov exciton model in which collective excitations of the system are expanded in a basis of excited states computed for individual chromophores. The monomer calculations are trivially parallelizable, as is computation of the coupling matrix elements needed to construct the exciton Hamiltonian, and systems containing hundreds of chromophores can be tackled on commodity hardware. This enables calculations on organic semiconductors, where even small model systems exhibit a semicontinuum of excited states that renders traditional TDDFT computationally challenging. Despite including only single excitations on each monomer, the exciton model can describe entangled spins on two or more monomers, an effect that is responsible for excitation energy transfer between chromophores, for example, in singlet fission. Excitonic approximations can also be applied to the TDDFT equations themselves, and a particularly promising application is to describe the effects of environment on an excitation that is localized on a single chromophore. This "local excitation approximation" to TDDFT allows an essentially arbitrary number of solvent molecules to be included in the calculation in a highly parallelizable way such that the time-to-solution increases only very slowly as additional solvent molecules are added. It is therefore possible to converge the calculation with respect to describing an ever-larger portion of the environment at a quantum-mechanical level. PMID:27100899
NASA Astrophysics Data System (ADS)
Kosumi, Daisuke; Yanagi, Kazuhiro; Nishio, Tomohiro; Hashimoto, Hideki; Yoshizawa, Masayuki
2005-06-01
Ultrafast relaxation kinetics in β-carotene and lycopene has been investigated by femtosecond absorption and fluorescence spectroscopies using tunable excitation pulses. The transient signals induced by the photoexcitation with larger excess energy have broader bands and longer lifetimes both in the 11Bu+and21Ag- excited states. The excess vibrational energy remains longer than several picoseconds and slows the relaxation kinetics in carotenoids.
NASA Astrophysics Data System (ADS)
Bohr, Henrik G.; Malik, F. Bary
2013-11-01
The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin-chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used Förster-Dexter theory, which does not allow for charge transfer, is a special case of B-A theory. The latter could, under appropriate circumstances, lead to excimers.
First identification of excited states in the N=Z+1 nucleus {sup 89}Ru
Marginean, N.; Rusu, C.; Bucurescu, D.; Ionescu-Bujor, M.; Iordachescu, A.; Alvarez, C. Rossi; Bazzacco, D.; Lunardi, S.; Pavan, P.; Farnea, E.; Lenzi, S.M.; Menegazzo, R.; Ur, C.A.; De Angelis, G.; Axiotis, M.; Gadea, A.; Kroell, Th.; Martinez, T.; Napoli, D.R.; Spolaore, P.
2004-10-01
High-spin excited states have been identified for the first time in the N=Z+1 nucleus {sup 89}Ru with the reaction {sup 54}Fe({sup 40}Ca,{alpha}n{gamma}) at 130 MeV, using the GASP array, the ISIS Silicon array, and the n-Ring detector system. The observed structure is discussed within systematics of the N=45 isotones and is compared with shell model calculations.
Charge state dynamics of the nitrogen vacancy center in diamond under near-infrared excitation
NASA Astrophysics Data System (ADS)
Ji, Peng; Dutt, M. V. Gurudev
2016-05-01
The negatively charged NV defect center (NV-) in diamond has become prominent for applications in quantum information, nanoscale magnetic and electric field sensing, and fluorescent biological markers. Switching between NV- and neutral charge states (NV0) have been extensively studied and modeled using exciting laser wavelengths that are shorter than the NV- zero-phonon line (ZPL), and typically result in decreased fluorescence from the NV- state. In this work, we report on the experimental observation that NV0 converts to NV- under excitation with near-infrared (1064 nm) light, resulting in increased fluorescence from the NV- state. We have observed this effect in both ensembles of NVs in bulk diamond, and in diamond nanocrystals, and find that it is robust both at room and low temperature. We carried out microwave and two-color excitation combined with spectral and time-resolved experimental studies. We used rate-equation modeling and find evidence for competition between one-photon and two-photon processes for hole and electron ionization. This finding may help elucidate the study of the NV energy level structure, and impact recently emerging research in single-shot measurement of the NV- spin state via spin-to-charge conversion.
Excited State Dynamics of 7-AZAINDOLE Homodimer in Frozen Nitrogen Matrix
NASA Astrophysics Data System (ADS)
Mukherjee, Moitrayee; Bandyopadhyay, Biman; Karmakar, Shreetama; Chakraborty, Tapas
2011-06-01
In a fluid medium (liquid or gas), the doubly hydrogen bonded dimer of 7-azaindole (7AI) undergoes tautomerization via simultaneous exchange of two H-atoms/protons between the two moieties upon UV excitation to lowest excited singlet state. The excited dimer emits exclusively visible fluorescence from tautomeric configuration, and no UV fluorescence is detected from the locally excited state. We show here for the first time that this generic excited state dynamics of 7AI dimer is totally altered if the species is synthesized and confined in frozen nitrogen at 8 K. The dimer has been found to emit only from the locally excited state, and the photophysical channel leading to excited state tautomerization is completely blocked. The formation of the centrosymmetric dimer in nitrogen matrix is ensured by recording the FTIR spectrum of the dimer before initiating the photophysical measurements. The details of our findings and interpretation of the measured data will be presented in the talk.
Two-Component Structure in the Entanglement Spectrum of Highly Excited States.
Yang, Zhi-Cheng; Chamon, Claudio; Hamma, Alioscia; Mucciolo, Eduardo R
2015-12-31
We study the entanglement spectrum of highly excited eigenstates of two known models that exhibit a many-body localization transition, namely the one-dimensional random-field Heisenberg model and the quantum random energy model. Our results indicate that the entanglement spectrum shows a "two-component" structure: a universal part that is associated with random matrix theory, and a nonuniversal part that is model dependent. The nonuniversal part manifests the deviation of the highly excited eigenstate from a true random state even in the thermalized phase where the eigenstate thermalization hypothesis holds. The fraction of the spectrum containing the universal part decreases as one approaches the critical point and vanishes in the localized phase in the thermodynamic limit. We use the universal part fraction to construct an order parameter for measuring the degree of randomness of a generic highly excited state, which is also a promising candidate for studying the many-body localization transition. Two toy models based on Rokhsar-Kivelson type wave functions are constructed and their entanglement spectra are shown to exhibit the same structure. PMID:26765022
Excited triplet states as photooxidants in surface waters
NASA Astrophysics Data System (ADS)
Canonica, S.
2012-12-01
The chromophoric components of dissolved organic matter (DOM) are generally the main absorbers of sunlight in surface waters and therefore a source of transient reactants under irradiation. Such short-lived species can be relevant for the fate of various classes of chemical contaminants in the aquatic environment. The present contribution focuses on the role of excited triplet states of chromophoric DOM, 3CDOM*, as transient photooxidants initiating the transformation and degradation of organic chemical contaminants. An early study [1] indicated that 3CDOM* may play a dominant role in the photo-induced transformation of electron-rich phenols, a conclusion which was later fortified by the results of transient absorption investigations using aromatic ketones as model photosensitizers [2] and by a recent careful analysis of the effect of oxygen concentration on transformation rates [3]. The variety of aquatic contaminants shown to be affected by triplet-induced oxidation has kept increasing, phenylurea herbicides [4], sulfonamide antibiotics [5] and some phytoestrogens [6] being prominent examples. Recent research has shown that the triplet-induced transformation of specific contaminants, especially aromatic nitrogen compounds, could be inhibited by the presence of DOM, very probably due to its antioxidant moieties [7]. While such moieties are not relevant for the quenching of 3CDOM*, they are expected to react with it in a similar way as the studied contaminants. Analogous reactions can be postulated to occur in liquid or solid phases of the atmospheric environment, as demonstrated in the case of HONO formation [8]. References 1. Canonica, S.; Jans, U.; Stemmler, K.; Hoigné, J. Transformation kinetics of phenols in water: Photosensitization by dissolved natural organic material and aromatic ketones. Environ. Sci. Technol. 1995, 29 (7), 1822-1831. 2. Canonica, S.; Hellrung, B.; Wirz, J. Oxidation of phenols by triplet aromatic ketones in aqueous solution. J. Phys
Excited-State Dynamics in Colloidal Semiconductor Nanocrystals.
Rabouw, Freddy T; de Mello Donega, Celso
2016-10-01
Colloidal semiconductor nanocrystals have attracted continuous worldwide interest over the last three decades owing to their remarkable and unique size- and shape-, dependent properties. The colloidal nature of these nanomaterials allows one to take full advantage of nanoscale effects to tailor their optoelectronic and physical-chemical properties, yielding materials that combine size-, shape-, and composition-dependent properties with easy surface manipulation and solution processing. These features have turned the study of colloidal semiconductor nanocrystals into a dynamic and multidisciplinary research field, with fascinating fundamental challenges and dazzling application prospects. This review focuses on the excited-state dynamics in these intriguing nanomaterials, covering a range of different relaxation mechanisms that span over 15 orders of magnitude, from a few femtoseconds to a few seconds after photoexcitation. In addition to reviewing the state of the art and highlighting the essential concepts in the field, we also discuss the relevance of the different relaxation processes to a number of potential applications, such as photovoltaics and LEDs. The fundamental physical and chemical principles needed to control and understand the properties of colloidal semiconductor nanocrystals are also addressed. PMID:27573500
Excited-state properties from ground-state DFT descriptors: A QSPR approach for dyes.
Fayet, Guillaume; Jacquemin, Denis; Wathelet, Valérie; Perpète, Eric A; Rotureau, Patricia; Adamo, Carlo
2010-02-26
This work presents a quantitative structure-property relationship (QSPR)-based approach allowing an accurate prediction of the excited-state properties of organic dyes (anthraquinones and azobenzenes) from ground-state molecular descriptors, obtained within the (conceptual) density functional theory (DFT) framework. The ab initio computation of the descriptors was achieved at several levels of theory, so that the influence of the basis set size as well as of the modeling of environmental effects could be statistically quantified. It turns out that, for the entire data set, a statistically-robust four-variable multiple linear regression based on PCM-PBE0/6-31G calculations delivers a R(adj)(2) of 0.93 associated to predictive errors allowing for rapid and efficient dye design. All the selected descriptors are independent of the dye's family, an advantage over previously designed QSPR schemes. On top of that, the obtained accuracy is comparable to the one of the today's reference methods while exceeding the one of hardness-based fittings. QSPR relationships specific to both families of dyes have also been built up. This work paves the way towards reliable and computationally affordable color design for organic dyes. PMID:20036173
Investigation of excited 0+ states populated in the 162 Er (p,t) reaction
NASA Astrophysics Data System (ADS)
Burbadge, C.; Bildstein, V.; Diaz Varela, A.; Dunlop, M.; Dunlop, R.; Garrett, P. E.; Jamieson, D. S.; Kisliuk, D.; Leach, K. G.; Loranger, J.; Maclean, A.; Radich, A.; Rand, E.; Svensson, C. E.; Ball, G. C.; Triambak, S.; Faestermann, T.; Hertenberger, R.; Wirth, H.-F.
2015-10-01
A continuing challenge in nuclear structure physics is the determination of the nature of low-lying excited 0+ states. Various approaches have been implemented to interpret the occurence of these states, such as vibrational excitations in β and γ phonons or pairing excitations. One of the difficulties, however, in resolving the nature of these states is that there is a paucity of data; even the first excited state, 02+,is not always known. Direct two-neutron transfer reactions are a useful tool for locating and investigating the nature of excited 0+ states in well-deformed nuclei. Using the Q3D spectrograph at the Maier-Leibnitz Laboratory, the N = 92 nucleus 160Er was studied via (p , t) reactions with a highly-enriched 162Er target. Strong population of the 02+state was observed with large cross sections greater than any other excited 0+ state. Preliminary results will be presented.
Pritchett, Timothy M; Sun, Wenfang; Zhang, Bingguang; Ferry, Michael J; Li, Yunjing; Haley, Joy E; Mackie, David M; Shensky, William; Mott, Andrew G
2010-05-01
The singlet excited-state lifetime of a bipyridyl platinum(II) complex containing two alkynyl-benzothiazolylfluorene units was determined to be 145+/-105 ps by fitting femtosecond transient difference absorption data, and the triplet quantum yield was measured to be 0.14. A ground-state absorption cross section of 6.1 x 10(-19) cm(2) at 532 nm was deduced from UV-visible absorption data. Excited-state absorption cross sections of (6.7+/-0.1) x 10(-17) cm(2) (singlet) and (4.6+/-0.1) x 10(-16) cm(2) (triplet) were obtained by using a five-level dynamic model to fit open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies. For this complex, the ratio of the triplet excited-state absorption cross section to the ground-state absorption cross section--long used as a figure of merit for reverse saturable absorbers--thus stands at 754, to our knowledge the largest ever reported at 532 nm wavelength. PMID:20436550
NASA Astrophysics Data System (ADS)
López, Alicia; Tercero, Belén; Cernicharo, Jose; Kisiel, Zbigniew; Pszczółkowski, Lech; Bermúdez, Celina; Alonso, José L.; Medvedev, Ivan; Neese, Christopher F.; Drouin, Brian; Daly, Adam M.; Marcelino, Nuria; Viti, Serena; Calcutt, Hannah
2014-06-01
Vinyl cyanide (acrylonitrile, H_2C=CHC≡N) is an interstellar molecule that was classified as a 'weed' since transitions in its isotopic species and vibrationally excited states have already been detected and need to be accounted for in searches for complex organic molecules. Presently we extend the systematic analysis of the laboratory rotational spectrum of vinyl cyanide to 9 new excited vibrational states with vibrational energies above 550 cm-1 (785K). The spectroscopic analysis is based on the broadband 50-1900 GHz spectrum combined from results from the participating spectroscopic laboratories and covering a total of 1235 GHz. The studied states come in the form of polyads of perturbing vibrational states, and such perturbations also affect the strong, low-K_a transitions used for astrophysical detection. It is therefore crucial to account for such effects in order to produce reliable linelists. The experimental data for three new polyads were fitted to experimental accuracy using Coriolis and Fermi perturbation models. Multiple transitions in the lowest of these polyads (and in other excited vibrational states and isotopic species of vinyl cyanide) were detected in the millimetre survey of the Orion-KL Nebula made with the IRAM 30-m radiotelescope.
Open-shell nuclei and excited states from multireference normal-ordered Hamiltonians
NASA Astrophysics Data System (ADS)
Gebrerufael, Eskendr; Calci, Angelo; Roth, Robert
2016-03-01
We discuss the approximate inclusion of three-nucleon (3 N ) interactions into ab initio nuclear structure calculations using a multireference formulation of normal ordering and Wick's theorem. Following the successful application of single-reference normal ordering for the study of ground states of closed-shell nuclei, e.g., in coupled-cluster theory, multireference normal ordering opens a path to open-shell nuclei and excited states. Based on different multideterminantal reference states we benchmark the truncation of the normal-ordered Hamiltonian at the two-body level in no-core shell-model calculations for p -shell nuclei, including 6Li,12C, and 10B. We find that this multireference normal-ordered two-body approximation is able to capture the effects of the 3 N interaction with sufficient accuracy, both for ground-state and excitation energies, at the computational cost of a two-body Hamiltonian. It is robust with respect to the choice of reference states and has a multitude of applications in ab initio nuclear structure calculations of open-shell nuclei and their excitations as well as in nuclear reaction studies.
Spectroscopy of ground and excited states of pseudoscalar and vector charmonium and bottomonium
NASA Astrophysics Data System (ADS)
Negash, Hluf; Bhatnagar, Shashank
2016-07-01
In this paper, we calculate the mass spectrum, weak decay constants, two photon decay widths, and two-gluon decay widths of ground (1S) and radially excited (2S, 3S,…) states of pseudoscalar charmoniuum and bottomonium such as ηc and ηb, as well as the mass spectrum and leptonic decay constants of ground state (1S), excited (2S, 1D, 3S, 2D, 4S,…, 5D) states of vector charmonium and bottomonium such as J/ψ, and Υ, using the formulation of Bethe-Salpeter equation under covariant instantaneous ansatz (CIA). Our results are in good agreement with data (where ever available) and other models. In this framework, from the beginning, we employ a 4 × 4 representation for two-body (qq¯) BS amplitude for calculating both the mass spectra as well as the transition amplitudes. However, the price we have to pay is to solve a coupled set of equations for both pseudoscalar and vector quarkonia, which we have explicitly shown get decoupled in the heavy-quark approximation, leading to mass spectral equation with analytical solutions for both masses, as well as eigenfunctions for all the above states, in an approximate harmonic oscillator basis. The analytical forms of eigenfunctions for ground and excited states so obtained are used to evaluate the decay constants and decay widths for different processes.
Scaling of collision strengths for highly-excited states of ions of the H- and He-like sequences
NASA Astrophysics Data System (ADS)
Fernández-Menchero, L.; Del Zanna, G.; Badnell, N. R.
2016-08-01
Emission lines from highly-excited states (n ≥ 5) of H- and He-like ions have been detected in astrophysical sources and fusion plasmas. For such excited states, R-matrix or distorted wave calculations for electron-impact excitation are very limited, due to the large size of the atomic basis set needed to describe them. Calculations for n ≥ 6 are also not generally available. We study the behaviour of the electron-impact excitation collision strengths and effective collision strengths for the most important transitions used to model electron collision dominated astrophysical plasmas, solar, for example. We investigate the dependence on the relevant parameters: the principal quantum number n or the nuclear charge Z. We also estimate the importance of coupling to highly-excited states and the continuum by comparing the results of different sized calculations. We provide analytic formulae to calculate the electron-impact excitation collision strengths and effective collision strengths to highly-excited states (n ≥ 8) of H- and He-like ions. These extrapolated effective collision strengths can be used to interpret astrophysical and fusion plasma via collisional-radiative modelling. Tables of atomic data for Si xiii and S xv are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A135
Zeng, Qiao; Liang, WanZhen
2015-10-07
The time-dependent density functional theory (TDDFT) has become the most popular method to calculate the electronic excitation energies, describe the excited-state properties, and perform the excited-state geometric optimization of medium and large-size molecules due to the implementation of analytic excited-state energy gradient and Hessian in many electronic structure software packages. To describe the molecules in condensed phase, one usually adopts the computationally efficient hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) models. Here, we extend our previous work on the energy gradient of TDDFT/MM excited state to account for the mutual polarization effects between QM and MM regions, which is believed to hold a crucial position in the potential energy surface of molecular systems when the photoexcitation-induced charge rearrangement in the QM region is drastic. The implementation of a simple polarizable TDDFT/MM (TDDFT/MMpol) model in Q-Chem/CHARMM interface with both the linear response and the state-specific features has been realized. Several benchmark tests and preliminary applications are exhibited to confirm our implementation and assess the effects of different treatment of environmental polarization on the excited-state properties, and the efficiency of parallel implementation is demonstrated as well.
Zeng, Qiao; Liang, WanZhen
2015-10-01
The time-dependent density functional theory (TDDFT) has become the most popular method to calculate the electronic excitation energies, describe the excited-state properties, and perform the excited-state geometric optimization of medium and large-size molecules due to the implementation of analytic excited-state energy gradient and Hessian in many electronic structure software packages. To describe the molecules in condensed phase, one usually adopts the computationally efficient hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) models. Here, we extend our previous work on the energy gradient of TDDFT/MM excited state to account for the mutual polarization effects between QM and MM regions, which is believed to hold a crucial position in the potential energy surface of molecular systems when the photoexcitation-induced charge rearrangement in the QM region is drastic. The implementation of a simple polarizable TDDFT/MM (TDDFT/MMpol) model in Q-Chem/CHARMM interface with both the linear response and the state-specific features has been realized. Several benchmark tests and preliminary applications are exhibited to confirm our implementation and assess the effects of different treatment of environmental polarization on the excited-state properties, and the efficiency of parallel implementation is demonstrated as well. PMID:26450289
NASA Astrophysics Data System (ADS)
Prabhumirashi, L. S.; Satpute, R. S.
The dipole moments of isomeric o-, m- and p-chloroanilines and chlorophenols in electronically excited L a and L b states are estimated from solvent induced polarization shifts in electronic absorption spectra. It is observed that μ e( L a) > μ e( L b) > μ g, which is consistent with the general theory of polarization red shift. The μ es are found to be approximately co-linear with the corresponding μ gs. The concept of group moments is extended to aromatic molecules in excited states. This approach is found to be useful in understanding correlations among the excited states of mono- and disubstituted benzenes.
Self-Exciting Point Process Modeling of Conversation Event Sequences
NASA Astrophysics Data System (ADS)
Masuda, Naoki; Takaguchi, Taro; Sato, Nobuo; Yano, Kazuo
Self-exciting processes of Hawkes type have been used to model various phenomena including earthquakes, neural activities, and views of online videos. Studies of temporal networks have revealed that sequences of social interevent times for individuals are highly bursty. We examine some basic properties of event sequences generated by the Hawkes self-exciting process to show that it generates bursty interevent times for a wide parameter range. Then, we fit the model to the data of conversation sequences recorded in company offices in Japan. In this way, we can estimate relative magnitudes of the self excitement, its temporal decay, and the base event rate independent of the self excitation. These variables highly depend on individuals. We also point out that the Hawkes model has an important limitation that the correlation in the interevent times and the burstiness cannot be independently modulated.
Unbound Excited States of the N = 16 Closed Shell Nucleus 24O
NASA Astrophysics Data System (ADS)
Rogers, W. F.; MoNA Collaboration
2015-10-01
The energies of two low-lying neutron-unbound excited states of 24O, which were populated by proton-knockout reactions on 26F, have been measured using the MoNA and LISA arrays in combination with the Sweeper Magnet at the Coupled Cyclotron Facility at the NSCL using invariant mass spectroscopy. The current measurement confirms for the first time the separate identity of 2+ and (1+) neutron-unbound excited states in 24O with decay energies 0.51(5) MeV state and 1.20(7) MeV, respectively, to the 23O ground state. These measured decay energies are consistent with two previous lower resolution measurements to within 2 σ. The level energies for the two states are computed using the decay energies and the 1-neutron separation energy for 24O, resulting in 4.70(15) MeV for the 2+ state and 5.39(16) MeV for the (1+) state. Errors in the level energies are dominated by uncertainty in the 24O neutron separation energy, underscoring the need for a higher resolution 24O ground state mass measurement. Results will be compared with 3 phenomenological and 2 ab initio model calculations. Work Supported by NSF Grants PHY-0922335, PHY-0922409, PHY-0922446, PHY-0922462, PHY-0922473, PHY-0922537, PHY-0922559, PHY-0922622, PHY-0922794, PHY-0969173, PHY-1101745, PHY-1205357, PHY- 1205537.
NASA Astrophysics Data System (ADS)
Lan, Sheng-Cheng; Liu, Yu-Hui
2015-03-01
Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.
NASA Astrophysics Data System (ADS)
Chong, C.; Kim, E.; Charalampidis, E. G.; Kim, H.; Li, F.; Kevrekidis, P. G.; Lydon, J.; Daraio, C.; Yang, J.
2016-05-01
This article explores the excitation of different vibrational states in a spatially extended dynamical system through theory and experiment. As a prototypical example, we consider a one-dimensional packing of spherical particles (a so-called granular chain) that is subject to harmonic boundary excitation. The combination of the multimodal nature of the system and the strong coupling between the particles due to the nonlinear Hertzian contact force leads to broad regions in frequency where different vibrational states are possible. In certain parametric regions, we demonstrate that the nonlinear Schrödinger equation predicts the corresponding modes fairly well. The electromechanical model we apply predicts accurately the conversion from the obtained mechanical energy to the electrical energy observed in experiments.
Dynamic modification of the fragmentation of COq+ excited states generated with high-order harmonics
NASA Astrophysics Data System (ADS)
Cao, W.; de, S.; Singh, K. P.; Chen, S.; Schöffler, M. S.; Alnaser, A. S.; Bocharova, I. A.; Laurent, G.; Ray, D.; Zherebtsov, S.; Kling, M. F.; Ben-Itzhak, I.; Litvinyuk, I. V.; Belkacem, A.; Osipov, T.; Rescigno, T.; Cocke, C. L.
2010-10-01
The dynamic process of fragmentation of COq+ excited states is investigated using a pump-probe approach. EUV radiation (32-48 eV) generated by high-order harmonics was used to ionize and excite CO molecules and a time-delayed infrared (IR) pulse (800 nm) was used to influence the evolution of the dissociating multichannel wave packet. Two groups of states, separable experimentally by their kinetic-energy release (KER), are populated by the EUV and lead to C+-O+ fragmentation: direct double ionization of the neutral molecule and fragmentation of the cation leading to C+-O*, followed by autoionization of O*. The IR pulse was found to modify the KER of the latter group in a delay-dependent way which is explained with a model calculation.
The repopulation of electronic states upon vibrational excitation of niobium carbide clusters.
Chernyy, V; Logemann, R; Bakker, J M; Kirilyuk, A
2016-07-14
We study the infrared (IR) resonant heating of neutral niobium carbide clusters probed through ultraviolet photoionization spectroscopy. The IR excitation not only changes the photoionization spectra for the photon energies above the ionization threshold, but also modulates ion yield for energies significantly below it. An attempt to describe the experimental spectra using either Fowler's theory or thermally populated vibrational states was not successful. However, the data can be fully modeled by vibrationally and rotationally broadened discrete electronic levels obtained from Density Functional Theory (DFT) calculations. The application of this method to spectra with different IR pulse energies not only yields information about the excited electronic states in the vicinity of the HOMO level, populated by manipulation of the vibrational coordinates of a cluster, but also can serve as an extra indicator for the cluster isomeric structure and corresponding DFT-calculated electronic levels. PMID:27421411
Chong, C; Kim, E; Charalampidis, E G; Kim, H; Li, F; Kevrekidis, P G; Lydon, J; Daraio, C; Yang, J
2016-05-01
This article explores the excitation of different vibrational states in a spatially extended dynamical system through theory and experiment. As a prototypical example, we consider a one-dimensional packing of spherical particles (a so-called granular chain) that is subject to harmonic boundary excitation. The combination of the multimodal nature of the system and the strong coupling between the particles due to the nonlinear Hertzian contact force leads to broad regions in frequency where different vibrational states are possible. In certain parametric regions, we demonstrate that the nonlinear Schrödinger equation predicts the corresponding modes fairly well. The electromechanical model we apply predicts accurately the conversion from the obtained mechanical energy to the electrical energy observed in experiments. PMID:27300876
The repopulation of electronic states upon vibrational excitation of niobium carbide clusters
NASA Astrophysics Data System (ADS)
Chernyy, V.; Logemann, R.; Bakker, J. M.; Kirilyuk, A.
2016-07-01
We study the infrared (IR) resonant heating of neutral niobium carbide clusters probed through ultraviolet photoionization spectroscopy. The IR excitation not only changes the photoionization spectra for the photon energies above the ionization threshold, but also modulates ion yield for energies significantly below it. An attempt to describe the experimental spectra using either Fowler's theory or thermally populated vibrational states was not successful. However, the data can be fully modeled by vibrationally and rotationally broadened discrete electronic levels obtained from Density Functional Theory (DFT) calculations. The application of this method to spectra with different IR pulse energies not only yields information about the excited electronic states in the vicinity of the HOMO level, populated by manipulation of the vibrational coordinates of a cluster, but also can serve as an extra indicator for the cluster isomeric structure and corresponding DFT-calculated electronic levels.
Exotic and excited-state radiative transitions in charmonium from lattice QCD
Dudek, Jozef J.; Edwards, Robert G.; Thomas, Christopher E.
2009-05-01
We compute, for the first time using lattice QCD methods, radiative transition rates involving excited charmonium states, states of high spin and exotics. Utilizing a large basis of interpolating fields we are able to project out various excited state contributions to three-point correlators computed on quenched anisotropic lattices. In the first lattice QCD calculation of the exoticmore » $$1^{-+}$$ $$\\eta_{c1}$$ radiative decay, we find a large partial width $$\\Gamma(\\eta_{c1} \\to J/\\psi \\gamma) \\sim 100 \\,\\mathrm{keV}$$. We find clear signals for electric dipole and magnetic quadrupole transition form factors in $$\\chi_{c2} \\to J/\\psi \\gamma$$, calculated for the first time in this framework, and study transitions involving excited $$\\psi$$ and $$\\chi_{c1,2}$$ states. We calculate hindered magnetic dipole transition widths without the sensitivity to assumptions made in model studies and find statistically significant signals, including a non-exotic vector hybrid candidate $Y_{\\mathrm{hyb?}} \\to \\et« less
Jiménez-Hoyos, Carlos A.; Rodríguez-Guzmán, R.; Scuseria, Gustavo E.
2013-12-14
Recent work from our research group has demonstrated that symmetry-projected Hartree–Fock (HF) methods provide a compact representation of molecular ground state wavefunctions based on a superposition of non-orthogonal Slater determinants. The symmetry-projected ansatz can account for static correlations in a computationally efficient way. Here we present a variational extension of this methodology applicable to excited states of the same symmetry as the ground state. Benchmark calculations on the C{sub 2} dimer with a modest basis set, which allows comparison with full configuration interaction results, indicate that this extension provides a high quality description of the low-lying spectrum for the entire dissociation profile. We apply the same methodology to obtain the full low-lying vertical excitation spectrum of formaldehyde, in good agreement with available theoretical and experimental data, as well as to a challenging model C{sub 2v} insertion pathway for BeH{sub 2}. The variational excited state methodology developed in this work has two remarkable traits: it is fully black-box and will be applicable to fairly large systems thanks to its mean-field computational cost.
Exotic and excited-state radiative transitions in charmonium from lattice QCD
Dudek, Jozef J.; Edwards, Robert G.; Thomas, Christopher E.
2009-05-01
We compute, for the first time using lattice QCD methods, radiative transition rates involving excited charmonium states, states of high spin and exotics. Utilizing a large basis of interpolating fields we are able to project out various excited state contributions to three-point correlators computed on quenched anisotropic lattices. In the first lattice QCD calculation of the exotic $1^{-+}$ $\\eta_{c1}$ radiative decay, we find a large partial width $\\Gamma(\\eta_{c1} \\to J/\\psi \\gamma) \\sim 100 \\,\\mathrm{keV}$. We find clear signals for electric dipole and magnetic quadrupole transition form factors in $\\chi_{c2} \\to J/\\psi \\gamma$, calculated for the first time in this framework, and study transitions involving excited $\\psi$ and $\\chi_{c1,2}$ states. We calculate hindered magnetic dipole transition widths without the sensitivity to assumptions made in model studies and find statistically significant signals, including a non-exotic vector hybrid candidate $Y_{\\mathrm{hyb?}} \\to \\et
NASA Astrophysics Data System (ADS)
Jiménez-Hoyos, Carlos A.; Rodríguez-Guzmán, R.; Scuseria, Gustavo E.
2013-12-01
Recent work from our research group has demonstrated that symmetry-projected Hartree-Fock (HF) methods provide a compact representation of molecular ground state wavefunctions based on a superposition of non-orthogonal Slater determinants. The symmetry-projected ansatz can account for static correlations in a computationally efficient way. Here we present a variational extension of this methodology applicable to excited states of the same symmetry as the ground state. Benchmark calculations on the C2 dimer with a modest basis set, which allows comparison with full configuration interaction results, indicate that this extension provides a high quality description of the low-lying spectrum for the entire dissociation profile. We apply the same methodology to obtain the full low-lying vertical excitation spectrum of formaldehyde, in good agreement with available theoretical and experimental data, as well as to a challenging model C2v insertion pathway for BeH2. The variational excited state methodology developed in this work has two remarkable traits: it is fully black-box and will be applicable to fairly large systems thanks to its mean-field computational cost.
Wave packet dynamics in doubly excited states of He
NASA Astrophysics Data System (ADS)
Feist, Johannes; Nagele, Stefan; Persson, Emil; Burgdörfer, Joachim; Schneider, Barry
2007-06-01
We have developed a method for the ab initio simulation of the interaction of ultrashort laser pulses with helium atoms. We expand the two-electron Schr"odinger equation in coupled spherical harmonics and perform direct time integration utilizing either the Arnoldi-Lanczos or the Leapfrog method. The spatial discretization is performed in an FEDVR basis [1]. This allows for a numerically accurate description while possessing desirable computational features, e.g. a block-diagonal form of the kinetic energy matrix. We will present results on electron-electron correlation and wave packet dynamics in He. By using a suitable combination of attosecond XUV/EUV pulses, we prepare a wave packet in the doubly excited states of helium. The motion of this wave packet can be observed by using a probe pulse to induce ionization. We aim for a detailed understanding of the process by a careful study of the ionized electrons, e.g. by investigating doubly differential momentum spectra. [enumi] *B. I. Schneider and L. A. Collins. J. Non-Cryst. Solids 351, 1551.
State-averaged Monte Carlo configuration interaction applied to electronically excited states
NASA Astrophysics Data System (ADS)
Coe, J. P.; Paterson, M. J.
2013-10-01
We introduce state-averaging into the method of Monte Carlo configuration interaction (SA-MCCI) to allow the stable and efficient calculation of excited states. We show that excited potential curves for H3, including a crossing with the ground state, can be accurately reproduced using a small fraction of the full configuration interaction (FCI) space. A recently introduced error measure for potential curves [J. P. Coe and M. J. Paterson, J. Chem. Phys. 137, 204108 (2012)] is also shown to be a fair approach when considering potential curves for multiple states. We demonstrate that potential curves for LiF using SA-MCCI agree well with the FCI results and the avoided crossing occurs correctly. The seam of conical intersections for CH2 found by Yarkony [J. Chem. Phys. 104, 2932 (1996)] is used as a test for SA-MCCI and we compare potential curves from SA-MCCI with FCI results for this system for the first three triplet states. We then demonstrate the improvement from using SA-MCCI on the dipole of the 2 1A1 state of carbon monoxide. We then look at vertical excitations for small organic molecules up to the size of butadiene where the SA-MCCI energies and oscillator strengths are compared with CASPT2 values [M. Schreiber, M. R. Silva-Junior, S. P. A. Sauer, and W. Thiel, J. Chem. Phys. 128, 134110 (2008)]. We finally see if the SA-MCCI results for these excitation energies can be improved by using MCCIPT2 with approximate natural orbitals when the PT2 space is not onerously large.
Soliton excitations and stability in a square lattice model of ferromagnetic spin system
NASA Astrophysics Data System (ADS)
Latha, M. M.; Anitha, T.
2015-12-01
We investigate the nature of nonlinear spin excitations in a square lattice model of ferromagnetic (FM) spin system with bilinear and biquadratic interactions. Using the coherent state ansatz combined with the Holstein-Primakoff (HP) bosonic representation of spin operators, the dynamics is found to be governed by a discrete nonlinear equation which possesses soliton solution. The modulational instability aspects of the soliton excitations are analysed for small perturbations in wave vectors.
Takaya, Tomohisa; Su, Charlene; de La Harpe, Kimberly; Crespo-Hernández, Carlos E.; Kohler, Bern
2008-01-01
Excited electronic states created by UV excitation of the diribonucleoside monophosphates ApA, ApG, ApC, ApU, and CpG were studied by the femtosecond transient-absorption technique. Bleach recovery signals recorded at 252 nm show that long-lived excited states are formed in all five dinucleosides. The lifetimes of these states exceed those measured in equimolar mixtures of the constituent mononucleotides by one to two orders of magnitude, indicating that electronic coupling between proximal nucleobases dramatically slows the relaxation of excess electronic energy. The decay rates of the long-lived states decrease with increasing energy of the charge-transfer state produced by transferring an electron from one base to another. The charge-transfer character of the long-lived states revealed by this analysis supports their assignment to excimer or exciplex states. Identical bleach recovery signals were seen for ApA, (A)4, and poly(A) at delay times >10 ps after photoexcitation. This indicates that excited states localized on a stack of just two bases are the common trap states independent of the number of stacked nucleotides. The fraction of initial excitations that decay to long-lived exciplex states is approximately equal to the fraction of stacked bases determined by NMR measurements. This supports a model in which excitations associated with two stacked bases decay to exciplex states, whereas excitations in unstacked bases decay via ultrafast internal conversion. These results establish the importance of charge transfer-quenching pathways for UV-irradiated RNA and DNA in room-temperature solution. PMID:18647840
Takaya, Tomohisa; Su, Charlene; de La Harpe, Kimberly; Crespo-Hernández, Carlos E; Kohler, Bern
2008-07-29
Excited electronic states created by UV excitation of the diribonucleoside monophosphates ApA, ApG, ApC, ApU, and CpG were studied by the femtosecond transient-absorption technique. Bleach recovery signals recorded at 252 nm show that long-lived excited states are formed in all five dinucleosides. The lifetimes of these states exceed those measured in equimolar mixtures of the constituent mononucleotides by one to two orders of magnitude, indicating that electronic coupling between proximal nucleobases dramatically slows the relaxation of excess electronic energy. The decay rates of the long-lived states decrease with increasing energy of the charge-transfer state produced by transferring an electron from one base to another. The charge-transfer character of the long-lived states revealed by this analysis supports their assignment to excimer or exciplex states. Identical bleach recovery signals were seen for ApA, (A)(4), and poly(A) at delay times >10 ps after photoexcitation. This indicates that excited states localized on a stack of just two bases are the common trap states independent of the number of stacked nucleotides. The fraction of initial excitations that decay to long-lived exciplex states is approximately equal to the fraction of stacked bases determined by NMR measurements. This supports a model in which excitations associated with two stacked bases decay to exciplex states, whereas excitations in unstacked bases decay via ultrafast internal conversion. These results establish the importance of charge transfer-quenching pathways for UV-irradiated RNA and DNA in room-temperature solution. PMID:18647840
The Structure of the Nucleon and it's Excited States
1995-02-20
The past year has been an exciting and productive one for particle physics research at Abilene Christian University. The thrust of our experimental investigations is the study of the nucleon and its excited states. Laboratories where these investigations are presently being conducted are the AGS at Brookhaven, Fermilab and LAMPF. Some analysis of the data for experiments at the Petersburg Nuclear Physics Institute (Gatchina, Russia) is still in progress. Scheduling of activities at different laboratories inevitably leads to occasional conflicts. This likelihood is increased by the present budget uncertainties at the laboratories that make long-term scheduling difficult. For the most part, the investigators have been able to avoid such conflicts. Only one experiment received beam time in 1994 (E890 at the AGS). The situation for 1995-1996 also appears manageable at this point. E890 and another AGS experiment (E909) will run through May, 1995. El 178 at LAMPF is presently scheduled for August/September 1995. E866 at Fermilab is scheduled to start in Spring/Summer 1996. Undergraduate student involvement has been a key element in this research contract since its inception. Summer students participated at all of the above laboratories in 1994 and the same is planned in 1995. A transition to greater involvement by graduate students will provide cohesiveness to ACU involvement at a given laboratory and full-time on-site involvement in the longer running experiments at FNAL and BNL. Funds to support a full-time graduate student are requested this year. Finally, collaboration by Russian, Croatian and Bosnian scientists has proven to be mutually beneficial to these experimental programs and to the overall programs at the institutions involved. Past support has been augmented by other grants from government agencies and from the Research Council at Abilene Christian University. Additional funds are requested in this renewal to enable more programmatic support for these
Electronic excitation of ground state atoms by collision with heavy gas particles
NASA Technical Reports Server (NTRS)
Hansen, C. Frederick
1993-01-01
point where the initial and final potentials cross, or at least come very close. Therefore, this mechanism would be applicable to the case where a gas is initially at very low temperature suddenly subjected to high energy heavy particle bombardment. This situation would model the measurement of excitation cross section by molecular beam techniques, for example. The purpose is to report values of cross sections and rate coefficients for collision excitation of ground state atoms estimated with the Landau-Zener transition theory and to compare results with measurement of excitation cross sections for a beam of Hydrogen atoms impacting Argon atom targets. Some very dubious approximations are used, and the comparison with measurement is found less than ideal, but results are at least consistent within order of magnitude. The same model is then applied to the case of N-N atom collisions, even though the approximations then become even more doubtful. Still the rate coefficients obtained are at least plausible in both magnitude and functional form, and as far as I am aware these are the only estimates available for such rate coefficients.
Vibrational dynamics of aniline (N2)1 clusters in their first excited singlet state
NASA Astrophysics Data System (ADS)
Hineman, M. F.; Kim, S. K.; Bernstein, E. R.; Kelley, D. F.
1992-04-01
The first excited singlet state S1 vibrational dynamics of aniline(N2)1 clusters are studied and compared to previous results on aniline(CH4)1 and aniline(Ar)1. Intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) rates fall between the two extremes of the CH4 (fast IVR, slow VP) and Ar (slow IVR, fast VP) cluster results as is predicted by a serial IVR/VP model using Fermi's golden rule to describe IVR processes and a restricted Rice-Ramsperger-Kassel-Marcus (RRKM) theory to describe unimolecular VP rates. The density of states is the most important factor determining the rates. Two product states, 00 and 10b1, of bare aniline and one intermediate state ˜(00) in the overall IVR/VP process are observed and time resolved measurements are obtained for the 000 and ˜(000) transitions. The results are modeled with the serial mechanism described above.
Structure of excited states in {sup 21}Mg studied in one-neutron knockout
Diget, C. A.; Adrich, P.; Bazin, D.; Campbell, C. M.; Obertelli, A.; Weisshaar, D.; Bowen, M. D.; Brown, B. A.; Cook, J. M.; Gade, A.; Glasmacher, T.; McDaniel, S.; Siwek, K.; Terry, J. R.; Hosier, K.; McGlinchery, D.; Riley, L. A.; Tostevin, J. A.
2008-06-15
Bound excited states in the neutron-deficient nucleus {sup 21}Mg were probed in the one-neutron knockout reaction {sup 9}Be({sup 22}Mg,{sup 21}Mg+{gamma})X at 74 MeV/nucleon projectile energy. The low-lying level scheme of {sup 21}Mg was investigated for the first time with {gamma}-ray spectroscopy. Contrary to the interpretation of previous particle spectroscopy data, our proposed excitation scheme is in agreement with the mirror nucleus and shell-model calculations in the p-sd shell. Spectroscopic factors for the one-neutron removal from {sup 22}Mg to {sup 21}Mg are extracted and compared to shell-model calculations using the WBP effective interaction.
Lake, M.L.
1981-08-01
Experiments were undertaken to determine electron impact cross sections of atoms in metastable states. One or two electron guns were used to first produce atoms in metastable states, then further excite these atoms to other levels. Limits on certain cross sections of helium atoms were obtained, but the detection limits of the apparatus prevented exhaustive study. Excitation functions and cross sections of xenon were obtained in the wavelength range from 3000 A to 9000 A.
NASA Astrophysics Data System (ADS)
Yamaguchi, Maiku; Nobusada, Katsuyuki
2016-02-01
In this paper, effects of the spatial nonuniformity of an optical near field (ONF) on the molecular photodissociation process are presented. The dissociation dynamics of H2 + was theoretically investigated by solving a non-Born-Oppenheimer Schrödinger equation. It was found that in addition to two dissociation mechanisms, which are one-photon and three-photon processes induced by uniform laser light excitation, the nonuniform ONF opens another dissociation path: two-step excitation mediated by vibrationally excited states. The nonuniformity of the ONF causes a transition between vibrational states that is forbidden according to conventional selection rules, leading to the dissociation path. The dependences of photodissociation on the intensity and nonuniformity of the ONF were calculated and the results validated the two-step dissociation mechanism.
Hybrid automata as a unifying framework for modeling excitable cells.
Ye, P; Entcheva, E; Smolka, S A; True, M R; Grosu, R
2006-01-01
We propose hybrid automata (HA) as a unifying framework for computational models of excitable cells. HA, which combine discrete transition graphs with continuous dynamics, can be naturally used to obtain a piecewise, possibly linear, approximation of a nonlinear excitable-cell model. We first show how HA can be used to efficiently capture the action-potential morphology--as well as reproduce typical excitable-cell characteristics such as refractoriness and restitution--of the dynamic Luo-Rudy model of a guinea-pig ventricular myocyte. We then recast two well-known computational models, Biktashev's and Fenton-Karma, as HA without any loss of expressiveness. Given that HA possess an intuitive graphical representation and are supported by a rich mathematical theory and numerous analysis tools, we argue that they are well positioned as a computational model for biological processes. PMID:17947070
Properties of Shell-Model Wavefunctions at High Excitation Energies
NASA Astrophysics Data System (ADS)
Frazier, Njema Jioni
Within the framework of the nuclear shell model with a realistic residual hamiltonian one can obtain the exact solution of the many-body problem. This makes it possible to study the interrelation between regular and chaotic features of dynamics in a generic many-body system with strong interaction. As an important application, we analyse the fragmentation of simple configurations as a function of excitation energy and interaction strength and examine the transition strengths induced by simple operators as a function of excitation energy. The analysis is performed for two systems; that of 12 valence particles in the sd-shell, or 28Si, and that of 8 valence particles in the sd-shell, or 24Mg. For the system of 12 valence particles in the sd-shell, we examine the fragmentation of shell-model basis states. For the system of 8 valence nucleons in the sd-shell, we examine the fragmentation associated with single-nucleon transfer and Gamow-Teller transitions. For the fragmentation of basis states, we use our statistics to establish the generic shape of the strength function distribution in the region of strong mixing. For the realistic interaction, the strength function distribution is close to Gaussian in the central part of the energy spectra. The width of the distribution is larger than predicted by Fermi's golden rule (4). We then take this one step further and examine the strength distributions associated with the one-nucleon transfer operator, aλ†, and the Gamow-Teller (GT) operator, Σλλ'(σμ τ±) λλ'aλ†a λ'. The spectroscopic factor, which is proportional to the square of the matrix element for the aλ† operator, is the simplest quantity used in predicting experimental observables. In our discussion of Gamow-Teller transitions, we examine both the GT strength function distribution and the values of total strength B(GT). For all the cases we examine, we take advantage of the reliability of our model for low-lying levels and our statistics to explore
Effect of Turbulence Modeling on an Excited Jet
NASA Technical Reports Server (NTRS)
Brown, Clifford A.; Hixon, Ray
2010-01-01
The flow dynamics in a high-speed jet are dominated by unsteady turbulent flow structures in the plume. Jet excitation seeks to control these flow structures through the natural instabilities present in the initial shear layer of the jet. Understanding and optimizing the excitation input, for jet noise reduction or plume mixing enhancement, requires many trials that may be done experimentally or computationally at a significant cost savings. Numerical simulations, which model various parts of the unsteady dynamics to reduce the computational expense of the simulation, must adequately capture the unsteady flow dynamics in the excited jet for the results are to be used. Four CFD methods are considered for use in an excited jet problem, including two turbulence models with an Unsteady Reynolds Averaged Navier-Stokes (URANS) solver, one Large Eddy Simulation (LES) solver, and one URANS/LES hybrid method. Each method is used to simulate a simplified excited jet and the results are evaluated based on the flow data, computation time, and numerical stability. The knowledge gained about the effect of turbulence modeling and CFD methods from these basic simulations will guide and assist future three-dimensional (3-D) simulations that will be used to understand and optimize a realistic excited jet for a particular application.
Direct Electron Impact Excitation of Rydberg-Valence States of Molecular Nitrogen
NASA Astrophysics Data System (ADS)
Malone, C. P.; Johnson, P. V.; Liu, X.; Ajdari, B.; Muleady, S.; Kanik, I.; Khakoo, M. A.
2012-12-01
Collisions between electrons and neutral N2 molecules result in emissions that provide an important diagnostic probe for understanding the ionospheric energy balance and the effects of space weather in upper atmospheres. Also, transitions to singlet ungerade states cause N2 to be a strong absorber of solar radiation in the EUV spectral range where many ro-vibrational levels of these Rydberg-valence (RV) states are predissociative. Thus, their respective excitation and emission cross sections are important parameters for understanding the [N]/[N2] ratio in the thermosphere of nitrogen dominated atmospheres. The following work provides improved constraints on absolute and relative excitation cross sections of numerous RV states of N2, enabling more physically accurate atmospheric modeling. Here, we present recent integral cross sections (ICSs) for electron impact excitation of RV states of N2 [6], which were based on the differential cross sections (DCSs) derived from electron energy-loss (EEL) spectra of [5]. This work resulted in electronic excitation cross sections over the following measured vibrational levels: b 1Πu (v‧=0-14), c3 1Πu (v‧=0-3), o3 1Πu (v‧=0-3), b‧ 1Σu+ (v‧=0-10), c‧4 1Σu+ (v‧=0-3), G 3Πu (v‧=0-3), and F 3Πu (v‧=0-3). We further adjusted the cross sections of the RV states by extending the vibronic contributions to unmeasured v‧-levels via the relative excitation probabilities (REPs) as discussed in [6]. This resulted in REP-scaled ICSs over the following vibrational levels for the singlet ungerade states: b(0-19), c3(0-4), o3(0-4), b‧(0-16), and c‧4(0-8). Comparison of the ICSs of [6] with available EEL based measurements, theoretical calculations, and emission based work generally shows good agreement within error estimations, except with the recent reevaluation provided by [1]. Further, we have extended these results, using the recent EEL data of [3], to include the unfolding of better resolved features above ~13
Haloalkane- Aromatic Complexes in the Ground and Excited States. Molecular Orbital Calculation
NASA Astrophysics Data System (ADS)
Brinn, I. M.
1980-04-01
CNDO/2 calculations have been carried out on a series of haloalkane-aromatic 1: 1 complexes in the ground and first excited singlet states and one 2 : 1 complex in the ground state. Calculated stabilities agree very well with reported experimental results for the ground state. Our calculations indicate that the substituent effect on complex stability in excited states will be the opposite of that found for the ground state.
Modeling K,ATP-Dependent Excitability in Pancreatic Islets
Silva, Jonathan R.; Cooper, Paige; Nichols, Colin G.
2014-01-01
In pancreatic β-cells, K,ATP channels respond to changes in glucose to regulate cell excitability and insulin release. Confirming a high sensitivity of electrical activity to K,ATP activity, mutations that cause gain of K,ATP function cause neonatal diabetes. Our aim was to quantitatively assess the contribution of K,ATP current to the regulation of glucose-dependent bursting by reproducing experimentally observed changes in excitability when K,ATP conductance is altered by genetic manipulation. A recent detailed computational model of single cell pancreatic β-cell excitability reproduces the β-cell response to varying glucose concentrations. However, initial simulations showed that the model underrepresents the significance of K,ATP activity and was unable to reproduce K,ATP conductance-dependent changes in excitability. By altering the ATP and glucose dependence of the L-type Ca2+ channel and the Na-K ATPase to better fit experiment, appropriate dependence of excitability on K,ATP conductance was reproduced. Because experiments were conducted in islets, which contain cell-to-cell variability, we extended the model from a single cell to a three-dimensional model (10×10×10 cell) islet with 1000 cells. For each cell, the conductance of the major currents was allowed to vary as was the gap junction conductance between cells. This showed that single cell glucose-dependent behavior was then highly variable, but was uniform in coupled islets. The study highlights the importance of parameterization of detailed models of β-cell excitability and suggests future experiments that will lead to improved characterization of β-cell excitability and the control of insulin secretion. PMID:25418087
NASA Astrophysics Data System (ADS)
Poga, C.; Brown, T. M.; Kuzyk, M. G.; Dirk, Carl W.
1995-04-01
We apply quadratic electroabsorption spectroscopy (QES) to thin-film solid solutions of squarylium dye molecules in poly(methyl methacrylate) polymer to study the dye's electronic excited states and to investigate the importance of these states with regard to their contribution to the third-order nonlinear-optical susceptibility. We first show that the room-temperature tensor ratio a= chi (3)3333/ chi (3)1133 \\approximately 3 throughout most of the visible region to establish that the electronic mechanism dominates. Because QES is a third-order nonlinear-optical susceptibility measurement, it can be used to identify two photon states. By obtaining good agreement between the quadratic electroabsorption spectrum and a three level model, we conclude that there are two dominant states that contribute to the near-resonant and a two-photon state that are separated by less than 0.2 eV in energy. QES is thus shown to be a versatile tool for measuring the nature of excited states in a molecule. Furthermore, by applying a Kramers-Kronig transformation to determine the real part of the response, we are able to assess the two-photon all-optical device figure of merit of these materials. Such an
Bokhan, Denis; Ten-No, Seiichiro
2010-11-28
Based on the linearly approximated F12 coupled cluster singles and doubles [CCSD(F12)] model, equation-of-motion [EOM-CCSD(F12)] methods for electron affinities (EAs) and excitation energies (EEs) have been formulated and implemented. Extended electron-attachment and excitation operators are introduced for balanced descriptions of both neutral and electron-attached (or excited) states. In our implementation the cusp conditions are used for the definition of extended electron-attachment (excitation) operators. It is shown that EA-EOM-CCSD(F12) provides vertical electron affinities accurate to 0.1 eV compared to those in the complete basis set limit. Numerical tests conducted on a selection of small molecules have also shown notable improvement in Rydberg excitation energies compared to valence ones by the use of correlation factors. PMID:21133437
Ab Initio Calculations of Singlet and Triplet Excited States of Chlorine Nitrate and Nitric Acid
NASA Technical Reports Server (NTRS)
Grana, Ana M.; Lee, Timothy J.; Head-Gordon, Martin; Langhoff, Stephen R. (Technical Monitor)
1994-01-01
Ab initio calculations of vertical excitations to singlet and triplet excited states of chlorine nitrate and nitric acid are reported. The nature of the electronic transitions are examined by decomposing the difference density into the sum of detachment and attachment densities. Counterparts for the three lowest singlet excited states of nitric acid survive relatively unperturbed in chlorine nitrate, while other low-lying singlet states of chlorine nitrate appear to be directly dissociative in the ClO chromophore. These results suggest an assignment of the two main peaks in the experimental chlorine nitrate absorption spectrum. In addition, triplet vertical excitations and the lowest optimized triplet geometries of both molecules are studied.
Banyasz, Akos; Gustavsson, Thomas; Onidas, Delphine; Changenet-Barret, Pascale; Markovitsi, Dimitra; Improta, Roberto
2013-03-11
The singlet excited states of adenine oligomers, model systems widely used for the understanding of the interaction of ultraviolet radiation with DNA, are investigated by fluorescence spectroscopy and time-dependent (TD) DFT calculations. Fluorescence decays, fluorescence anisotropy decays, and time-resolved fluorescence spectra are recorded from the femtosecond to the nanosecond timescales for single strand (dA)20 in aqueous solution. These experimental observations and, in particular, the comparison of the fluorescence behavior upon UVC and UVA excitation allow the identification of various types of electronic transitions with different energy and polarization. Calculations performed for up to five stacked 9-methyladenines, taking into account the solvent, show that different excited states are responsible for the absorption in the UVC and UVA spectral domains. Independently of the number of bases, bright excitons may evolve toward two types of excited dimers having π-π* or charge-transfer character, each one distinguished by its own geometry and spectroscopic signature. According to the picture arising from the joint experimental and theoretical investigation, UVC-induced fluorescence contains contribution from 1) exciton states with a different degree of localization, decaying within a few ps, 2) "neutral" excited dimers decaying on the sub-nanosecond timescale, being the dominant species, and 3) charge-transfer states decaying on the nanosecond timescale. The majority of the photons emitted upon UVA excitation are related to charge-transfer states. PMID:23335234
Instability of insulating states in optical lattices due to collective phonon excitations
NASA Astrophysics Data System (ADS)
Yukalov, V. I.; Ziegler, K.
2015-02-01
The effect of collective phonon excitations on the properties of cold atoms in optical lattices is investigated. These phonon excitations are collective excitations, whose appearance is caused by intersite atomic interactions correlating the atoms, and they do not arise without such interactions. These collective excitations should not be confused with lattice vibrations produced by an external force. No such force is assumed. But the considered phonons are purely self-organized collective excitations, characterizing atomic oscillations around lattice sites, due to intersite atomic interactions. It is shown that these excitations can essentially influence the possibility of atoms' being localized. The states that would be insulating in the absence of phonon excitations can become delocalized when these excitations are taken into account. This concerns long-range as well as local atomic interactions. To characterize the region of stability, the Lindemann criterion is used.
NASA Astrophysics Data System (ADS)
Bruno, D.; Colonna, G.; Laricchiuta, A.; Capitelli, M.
2012-12-01
Internal and reactive contributions to the thermal conductivity of a local thermodynamic equilibrium nitrogen plasma have been calculated using the Chapman-Enskog method. Low-lying (LL) electronically excited states (i.e., states with the same principal quantum number of the ground state) and high-lying (HL) ones (i.e., states with principal quantum number n > 2) have been considered. Several models have been developed, the most accurate being a model that treats the LL states as separate species while disregarding the presence of HL states, on account of their enormous transport cross sections.
Bruno, D.; Colonna, G.; Laricchiuta, A.; Capitelli, M.
2012-12-15
Internal and reactive contributions to the thermal conductivity of a local thermodynamic equilibrium nitrogen plasma have been calculated using the Chapman-Enskog method. Low-lying (LL) electronically excited states (i.e., states with the same principal quantum number of the ground state) and high-lying (HL) ones (i.e., states with principal quantum number n> 2) have been considered. Several models have been developed, the most accurate being a model that treats the LL states as separate species while disregarding the presence of HL states, on account of their enormous transport cross sections.
Tuna, Deniz; Lu, You; Koslowski, Axel; Thiel, Walter
2016-09-13
The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states. The present benchmarks cover vertical excitation energies, excited-state equilibrium geometries (including an analysis of significant changes between ground- and excited-state geometries), minimum-energy conical intersections, ground- and excited-state zero-point vibrational energies, and 0-0 transition energies for a total of 520 molecular structures and 412 excited states. For comparison, we evaluate the TDDFT/B3LYP method for all benchmark sets, and the CC2, MRCISD, and CASPT2 methods for some of them. We find that the current OMx/MRCI methods perform reasonably well for many of the excited-state properties. However, in comparison to the first-principles methods, there are also a number of shortcomings that should be addressed in future developments. PMID:27380455
Modeling the acoustic excitation of a resonator
NASA Astrophysics Data System (ADS)
Mandre, Shreyas; Mahadevan, Lakshminarayanan
2007-11-01
The sounding of a beverage bottle when blown on is a familiar but very little understood phenomenon. A very similar mechanism is used by musical wind instruments, like organ pipes and flutes, for sound production. This phenomenon falls under the general umbrella of flow induced oscillations and is representative of a more generic mechanism. The modeling of this phenomenon essentially involves two components. The first is the resonator, which bears the oscillations and this component is very well understood. The resonator, however, needs an external energy input to sustain the oscillations, which is provided by the jet of air blown. The dynamics of the jet and its interaction with the resonator is the primary focus of this talk. In particular, we provide a linearized model based on first principles to explain the feedback of energy from the jet to the resonator and compare the predictions with experimental results.
Explicit calculation of the excited electronic states of the photosystem II reaction centre.
Frankcombe, Terry J
2015-02-01
The excited states of sets of the cofactors found in the photosystem II reaction centre have been calculated directly as a multi-monomer supermolecule for the first time. Time-dependent density functional theory was used with the CAM-B3LYP functional. Multiple excited states for each cofactor were found at lower energies than the lowest energy state corresponding to charge transfer states (in which an electron is shifted from one cofactor to another). The electrostatic environment was found to have a dramatic impact on the excited state energies, with the effect of a surrounding dielectric medium being less significant. PMID:25523136
NASA Astrophysics Data System (ADS)
Liang, Xian-Ting; Zhang, Wei-Min; Zhuo, Yi-Zhong
2010-01-01
In this paper, we present a theoretical description to the quantum coherence and decoherence phenomena of energy transfer in photosynthesis observed in a recent experiment [Science 316, 1462 (2007)]. As a successive two-color laser pulses with selected frequencies cast on a sample of the photosynthetic purple bacterium Rb. sphaeroides two resonant excitations of electrons in chromophores can be generated. However, this effective two-level subsystem will interact with its protein environment and decoherence is inevitable. We describe this subsystem coupled with its environment as a dynamical spin-boson model. The non-Markovian decoherence dynamics is described using a quasiadiabatic propagator path integral (QUAPI) approach. With the photon-induced effective time-dependent level splitting energy and level flip coupling coefficient between the two excited states and the environment-induced non-Markovian decoherence dynamics, our theoretical result is in good agreement with the experimental data.
NASA Astrophysics Data System (ADS)
Haag, M.; van den Brandt, B.; Eichhorn, T. R.; Hautle, P.; Wenckebach, W. Th.
2012-06-01
In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks. The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ˜0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.
NASA Technical Reports Server (NTRS)
Erdman, P. W.; Zipf, E. C.
1986-01-01
Metastable N(+)(5S) ions were produced in the laboratory by dissociative excitation of N2 with energetic electrons. The resulting radiative decay of the N(+)(5S) state was observed with sufficient resolution to completely resolve the doublet from the nearby N2 molecular radiation. The excitation function was measured from threshold to 500 eV. The cross section peaks at a high electron energy and also exhibits a high threshold energy both of which are typical of dissociative excitation-ionization processes. This finding complicates the explanation of electron impact on N2 as the mechanism for the source of the 2145 A 'auroral mystery feature' by further increasing the required peak cross section. It is suggested that the apparent N(+)(5S) quenching in auroras may be an artifact due to the softening of the electron energy spectrum in the auroral E region.
NASA Technical Reports Server (NTRS)
Salter, Latasha M.; Chaban, Galina M.; Kwak, Dochan (Technical Monitor)
2002-01-01
Geometrical structures and energetic properties for different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest singlet excited state potential energy surfaces are studied. Four tautomeric forms are considered, and their energetic order is found to be different on the ground and the excited state potential energy surfaces. Minimum energy reaction paths are obtained for hydrogen atom transfer (tautomerization) reactions in the ground and the lowest excited electronic states. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic states, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. This tautomerization process should become possible in the presence of water or other polar solvent molecules and should play an important role in the photochemistry of adenine.
S1 and S2 Excited States of Gas-Phase Schiff-Base Retinal Chromophores
NASA Astrophysics Data System (ADS)
Nielsen, I. B.; Lammich, L.; Andersen, L. H.
2006-01-01
Photoabsorption studies of 11-cis and all-trans Schiff-base retinal chromophore cations in the gas phase have been performed at the electrostatic ion storage ring in Aarhus. A broad absorption band due to the optically allowed excitation to the first electronically excited singlet state (S1) is observed at around 600 nm. A second “dark” excited state (S2) just below 400 nm is reported for the first time. It is located ˜1.2eV above S1 for both chromophores. The S2 state was not visible in a solution measurement where only one highly blueshifted absorption band corresponding to the first excited state was visible. Knowledge of the position of the excited states in retinal is essential for the understanding of the fast photoisomerization in, for example, visual pigments.
NASA Technical Reports Server (NTRS)
Head-Gordon, Martin; Rico, Rudolph J.; Lee, Timothy J.; Oumi, Manabu
1994-01-01
A perturbative correction to the method of configuration interaction with single substitutions (CIS) is presented. This CIS(D) correction approximately introduces the effect of double substitutions which are absent in CIS excited states. CIS(D) is a second-order perturbation expansion of the coupled-cluster excited state method, restricted to single and double substitutions, in a series in which CIS is zeroth order, and the first-order correction vanishes. CIS (D) excitation energies are size consistent and the calculational complexity scales with the fifth power of molecular size, akin to second-order Moller-Plesset theory for the ground state. Calculations on singlet excited states of ethylene, formaldehyde, acetaldehyde, butadiene and benzene show that CIS (D) is a uniform improvement over CIS. CIS(D) appears to be a promising method for examining excited states of large molecules, where more accurate methods are not feasible.
Steady-state responses of a belt-drive dynamical system under dual excitations
NASA Astrophysics Data System (ADS)
Ding, Hu
2016-02-01
The stable steady-state periodic responses of a belt-drive system with a one-way clutch are studied. For the first time, the dynamical system is investigated under dual excitations. The system is simultaneously excited by the firing pulsations of the engine and the harmonic motion of the foundation. Nonlinear discrete-continuous equations are derived for coupling the transverse vibration of the belt spans and the rotations of the driving and driven pulleys and the accessory pulley. The nonlinear dynamics is studied under equal and multiple relations between the frequency of the firing pulsations and the frequency of the foundation motion. Furthermore, translating belt spans are modeled as axially moving strings. A set of nonlinear piecewise ordinary differential equations is achieved by using the Galerkin truncation. Under various relations between the excitation frequencies, the time histories of the dynamical system are numerically simulated based on the time discretization method. Furthermore, the stable steady-state periodic response curves are calculated based on the frequency sweep. Moreover, the convergence of the Galerkin truncation is examined. Numerical results demonstrate that the one-way clutch reduces the resonance amplitude of the rotations of the driven pulley and the accessory pulley. On the other hand, numerical examples prove that the resonance areas of the belt spans are decreased by eliminating the torque-transmitting in the opposite direction. With the increasing amplitude of the foundation excitation, the damping effect of the one-way clutch will be reduced. Furthermore, as the amplitude of the firing pulsations of the engine increases, the jumping phenomena in steady-state response curves of the belt-drive system with or without a one-way clutch both occur.
NASA Astrophysics Data System (ADS)
Huang, Cheng; Guo, Wenliang; Zhou, Yueming; Wu, Zhengmao
2016-01-01
With the classical ensemble model, we investigate nonsequential double ionization of aligned molecules by few-cycle laser pulses at low intensity, where the two electrons finally are ionized through a transition doubly excited state induced by recollision. The correlated electron momentum distribution of parallel molecules exhibits the line-shaped structure parallel to the diagonal. Our analysis indicates that besides the ionization time difference of two electrons from the doubly excited state, the final-state e-e Coulomb repulsion plays a vital role in the formation of the line-shaped structural momentum distribution. For perpendicular molecules, due to the prominent near half-cycle ionization time difference between the two electrons from the doubly excited state, the momentum distribution shows clear anticorrelation behavior.
Vibrations of acrylonitrile in N 1s excited states
NASA Astrophysics Data System (ADS)
Ilakovac, V.; Carniato, S.; Gallet, J.-J.; Kukk, E.; Horvatić, D.; Ilakovac, A.
2008-01-01
The N 1s near edge x-ray absorption fine structure spectra of acrylonitrile gas are accurately reproduced by a complete ab initio multidimensional vibrational analysis. The role of π∗ -orbital localization and hybridization on vibrations accompanying core excitation is discussed. Transition to the π⊥∗(C=C-C≡N) delocalized orbital excites mostly stretching vibrations of the whole spinal column of the molecule. Promoting a core electron to the localized π∥∗(C≡N) produces C≡N stretching vibration combined with two strong bending modes of the C-C≡N end of the molecule, related to the change of carbon hybridization.
2νββ decay of 76Ge into excited states with GERDA phase I
NASA Astrophysics Data System (ADS)
GERDA Collaboration; Agostini, M.; Allardt, M.; Bakalyarov, A. M.; Balata, M.; Barabanov, I.; Barros, N.; Baudis, L.; Bauer, C.; Becerici-Schmidt, N.; Bellotti, E.; Belogurov, S.; Belyaev, S. T.; Benato, G.; Bettini, A.; Bezrukov, L.; Bode, T.; Borowicz, D.; Brudanin, V.; Brugnera, R.; Budjáš, D.; Caldwell, A.; Cattadori, C.; Chernogorov, A.; D'Andrea, V.; Demidova, E. V.; di Vacri, A.; Domula, A.; Doroshkevich, E.; Egorov, V.; Falkenstein, R.; Fedorova, O.; Freund, K.; Frodyma, N.; Gangapshev, A.; Garfagnini, A.; Gooch, C.; Grabmayr, P.; Gurentsov, V.; Gusev, K.; Hegai, A.; Heisel, M.; Hemmer, S.; Heusser, G.; Hofmann, W.; Hult, M.; Inzhechik, L. V.; Janicskó Csáthy, J.; Jochum, J.; Junker, M.; Kazalov, V.; Kihm, T.; Kirpichnikov, I. V.; Kirsch, A.; Klimenko, A.; Knöpfle, K. T.; Kochetov, O.; Kornoukhov, V. N.; Kuzminov, V. V.; Laubenstein, M.; Lazzaro, A.; Lebedev, V. I.; Lehnert, B.; Liao, H. Y.; Lindner, M.; Lippi, I.; Lubashevskiy, A.; Lubsandorzhiev, B.; Lutter, G.; Macolino, C.; Majorovits, B.; Maneschg, W.; Medinaceli, E.; Mi, Y.; Misiaszek, M.; Moseev, P.; Nemchenok, I.; Palioselitis, D.; Panas, K.; Pandola, L.; Pelczar, K.; Pullia, A.; Riboldi, S.; Rumyantseva, N.; Sada, C.; Salathe, M.; Schmitt, C.; Schneider, B.; Schreiner, J.; Schulz, O.; Schwingenheuer, B.; Schönert, S.; Schütz, A.-K.; Selivanenko, O.; Shirchenko, M.; Simgen, H.; Smolnikov, A.; Stanco, L.; Stepaniuk, M.; Ur, C. A.; Vanhoefer, L.; Vasenko, A. A.; Veresnikova, A.; von Sturm, K.; Wagner, V.; Walter, M.; Wegmann, A.; Wester, T.; Wilsenach, H.; Wojcik, M.; Yanovich, E.; Zavarise, P.; Zhitnikov, I.; Zhukov, S. V.; Zinatulina, D.; Zuber, K.; Zuzel, G.
2015-11-01
Two neutrino double beta decay of {}76{Ge} to excited states of {}76{Se} has been studied using data from Phase I of the GERDA experiment. An array composed of up to 14 germanium detectors including detectors that have been isotopically enriched in {}76{Ge} was deployed in liquid argon. The analysis of various possible transitions to excited final states is based on coincidence events between pairs of detectors where a de-excitation γ ray is detected in one detector and the two electrons in the other. No signal has been observed and an event counting profile likelihood analysis has been used to determine Frequentist 90% C.L. bounds for three transitions: {0}{{g}.{{s}}.}+-{2}1+: {T}1/22ν \\gt 1.6× {10}23 yr, {0}{{g}.{{s}}.}+-{0}1+: {T}1/22ν \\gt 3.7× {10}23 yr and {0}{{g}.{{s}}.}+-{2}2+: {T}1/22ν \\gt 2.3× {10}23 yr. These bounds are more than two orders of magnitude larger than those reported previously. Bayesian 90% credibility bounds were extracted and used to exclude several models for the {0}{{g}.{{s}}.}+-{0}1+ transition.
Molecular dynamics of excited state intramolecular proton transfer: 3-hydroxyflavone in solution
Bellucci, Michael A.; Coker, David F.
2012-05-21
The ultrafast enol-keto photoisomerization in the lowest singlet excited state of 3-hydroxyflavone is investigated using classical molecular dynamics in conjunction with empirical valence bond (EVB) potentials for the description of intramolecular interactions, and a molecular mechanics and variable partial charge model, dependent on transferring proton position, for the description of solute-solvent interactions. A parallel multi-level genetic program was used to accurately fit the EVB potential energy surfaces to high level ab initio data. We have studied the excited state intramolecular proton transfer (ESIPT) reaction in three different solvent environments: methylcyclohexane, acetonitrile, and methanol. The effects of the environment on the proton transfer time and the underlying mechanisms responsible for the varied time scales of the ESIPT reaction rates are analyzed. We find that simulations with our EVB potential energy surfaces accurately reproduce experimentally determined reaction rates, fluorescence spectra, and vibrational frequency spectra in all three solvents. Furthermore, we find that the ultrafast ESIPT process results from a combination of ballistic transfer, and intramolecular vibrational redistribution, which leads to the excitation of a set of low frequency promoting vibrational modes. From this set of promoting modes, we find that an O-O in plane bend and a C-H out of plane bend are present in all three solvents, indicating that they are fundamental to the ultrafast proton transfer. Analysis of the slow proton transfer trajectories reveals a solvent mediated proton transfer mechanism, which is diffusion limited.
Khanduri, Deepti; Adhikary, Amitava; Sevilla, Michael D.
2011-01-01
Excited states of one-electron oxidized guanine in DNA are known to induce hole transfer to the sugar moiety and on deprotonation result in neutral sugar radicals that are precursors of DNA-strand breaks. This work carried out in homogeneous aqueous glass (7.5 M LiCl) at low temperatures (77 to 175 K) shows the extent of photoconversion of one-electron oxidized guanine and the associated yields of individual sugar radicals and are crucially controlled by photon energy, protonation state, and strandedness of the oligomer. In addition to forming sugar radicals, highly oxidizing excited states of one-electron oxidized guanine are produced with 405 nm light at pH 5 and below that are able to oxidize chloride ion in the surrounding solution to form Cl2•− via an excited state hole transfer process. Among the various DNA model systems studied in this work, the maximum amount of Cl2•− is produced with ds (double stranded) DNA where the one-electron oxidized guanine exists in its cation radical (G•+:C) form. Thus, via excited state hole transfer, the dsDNA is apparently able to protect itself from cation radical excited states by transfer of damage to the surrounding environment. PMID:21381665
NASA Astrophysics Data System (ADS)
Shi, Jichun
The photochemistry of O_3 has matured through the extensive research efforts of the last two decades, but its completeness has been questioned by several laboratory and atmospheric observations, including the unusually complex kinetics for the ozone three-body recombination reaction at high pressures, the unexplained heavy ozone isotope enhancement in the stratosphere, and the deficiencies of current chemical models at 90-120 km. The model deficiencies may be related to several of the excited states of O_3 and O_2 . In this dissertation, the photochemical kinetics of these excited species have been studied in a series of laboratory measurements, which are divided into two groups: (1) the study of the excited intermediates formed in the ozone recombination reaction, and (2) the investigation of the unusual odd oxygen formation in O_2 under laser irradiation at 248 nm. The ozone recombination reaction has been investigated at room temperature by monitoring the time-resolved infrared chemiluminescence of ozone at 9.6 mum, 4.7 mum, and 3.4 mu m. These studies have indicated that the recombination reaction (O+O_2+M) apparently proceeds through an intermediate complex OM, and, for M=O _2, the recombination also involves the participation of a metastable electronic state, O_3(E). The three infrared emissions have also been used to analyze the deactivation of vibrationally excited O_3 (v). The unusual odd oxygen formation in O _2 at 248 nm has been studied in both pure O_2 and O_2+N _2 and O_2+Ar mixtures at pressures between 200 and 1600 torr and at temperatures between 298 and 370^circ K. The results have indicated that this odd oxygen formation is initiated by O_2 absorption in the Herzberg continuum, and it is autocatalytically accelerated by the photodissociation of vibrationally excited O_2(v) at 248 nm. These kinetics results have been used to study the possible roles of excited O_3 and O_2 species in the sources and sinks of odd oxygen at 90-120 km, and in the
Exotic and excited-state meson spectroscopy and radiative transitions from lattice QCD
Christopher Thomas
2010-09-01
We discuss recent progress in extracting the excited meson spectrum and radiative transition form factors using lattice QCD. We mention results in the charmonium sector, including the first lattice QCD calculation of radiative transition rates involving excited charmonium states, highlighting results for high spin and exotic states. We present recent results on a highly excited isovector meson spectrum from dynamical anisotropic lattices. Using carefully constructed operators we show how the continuum spin of extracted states can be reliably identified and confidently extract excited states, states with exotic quantum numbers and states of high spin. This spectrum includes the first spin-four state extracted from lattice QCD. We conclude with some comments on future prospects.
ERIC Educational Resources Information Center
Morgan, Gwen
Models of state involvement in training child care providers are briefly discussed and the employers' role in training is explored. Six criteria for states that are taken as models are identified, and four are described. Various state activities are described for each criterion. It is noted that little is known about employer and other private…
Lifetime measurement of excited states in 105Ag
NASA Astrophysics Data System (ADS)
Mittal, V. K.; Govil, I. M.
1986-11-01
The levels up to about 2.1 MeV in 105Ag were excited via 105Pd(p,nγ) reaction. For the first time, lifetimes of energy levels at 1023, 1042, 1097, 1166, 1243, 1295, 1328, 1386, 1442, 1543, 1558, 1587, 1719, 1923, and 2081 keV have been measured using the Doppler shift attenuation technique.
Lifetime measurement of excited states in /sup 105/Ag
Mittal, V.K.; Govil, I.M.
1986-11-01
The levels up to about 2.1 MeV in /sup 105/Ag were excited via /sup 105/Pd(p,n..gamma..) reaction. For the first time, lifetimes of energy levels at 1023, 1042, 1097, 1166, 1243, 1295, 1328, 1386, 1442, 1543, 1558, 1587, 1719, 1923, and 2081 keV have been measured using the Doppler shift attenuation technique.
Bjorgaard, J. A.; Nelson, T.; Kalinin, K.; Kuzmenko, V.; Velizhanin, K. A.; Tretiak, S.
2015-04-28
In this study, an efficient method of treating solvent effects in excited state molecular dynamics (ESMD) is implemented and tested by exploring the solvatochromic effects in substituted p-phenylene vinylene oligomers. A continuum solvent model is used which has very little computational overhead. This allows simulations of ESMD with solvent effects on the scale of hundreds of picoseconds for systems of up to hundreds of atoms. At these time scales, solvatochromic shifts in fluoresence spectra can be described. Solvatochromic shifts in absorption and fluorescence spectra from ESMD are compared with time-dependent density functional theory calculations and experiments.
CHEMI-IONIZATION IN SOLAR PHOTOSPHERE: INFLUENCE ON THE HYDROGEN ATOM EXCITED STATES POPULATION
Mihajlov, Anatolij A.; Ignjatovic, Ljubinko M.; Sreckovic, Vladimir A.; Dimitrijevic, Milan S. E-mail: mihajlov@ipb.ac.rs
2011-03-15
In this paper, the influence of chemi-ionization processes in H*(n {>=} 2) + H(1s) collisions, as well as the influence of inverse chemi-recombination processes on hydrogen atom excited-state populations in solar photosphere, are compared with the influence of concurrent electron-atom and electron-ion ionization and recombination processes. It has been found that the considered chemi-ionization/recombination processes dominate over the relevant concurrent processes in almost the whole solar photosphere. Thus, it is shown that these processes and their importance for the non-local thermodynamic equilibrium modeling of the solar atmosphere should be investigated further.
Self-Consistent Optimization of Excited States within Density-Functional Tight-Binding.
Kowalczyk, Tim; Le, Khoa; Irle, Stephan
2016-01-12
We present an implementation of energies and gradients for the ΔDFTB method, an analogue of Δ-self-consistent-field density functional theory (ΔSCF) within density-functional tight-binding, for the lowest singlet excited state of closed-shell molecules. Benchmarks of ΔDFTB excitation energies, optimized geometries, Stokes shifts, and vibrational frequencies reveal that ΔDFTB provides a qualitatively correct description of changes in molecular geometries and vibrational frequencies due to excited-state relaxation. The accuracy of ΔDFTB Stokes shifts is comparable to that of ΔSCF-DFT, and ΔDFTB performs similarly to ΔSCF with the PBE functional for vertical excitation energies of larger chromophores where the need for efficient excited-state methods is most urgent. We provide some justification for the use of an excited-state reference density in the DFTB expansion of the electronic energy and demonstrate that ΔDFTB preserves many of the properties of its parent ΔSCF approach. This implementation fills an important gap in the extended framework of DFTB, where access to excited states has been limited to the time-dependent linear-response approach, and affords access to rapid exploration of a valuable class of excited-state potential energy surfaces. PMID:26587877
Structures and Binding Energies of the Naphthalene Dimer in Its Ground and Excited States.
Dubinets, N O; Safonov, A A; Bagaturyants, A A
2016-05-01
Possible structures of the naphthalene dimer corresponding to local energy minima in the ground and excited (excimer) electronic states are comprehensively investigated using DFT-D and TDDFT-D methods with a special accent on the excimer structures. The corresponding binding and electronic transition energies are calculated, and the nature of the electronic states in different structures is analyzed. Several parallel (stacked) and T-shaped structures were found in both the ground and excited (excimer) states in a rather narrow energy range. The T-shaped structure with the lowest energy in the excited state exhibits a marked charge transfer from the upright molecule to the base one. PMID:27080987
NASA Astrophysics Data System (ADS)
Szczepanik, Beata
2015-11-01
The excited state proton transfer (ESPT) has been extensively studied for hydroxyarenes, phenols, naphthols, hydroxystilbenes, etc., which undergo large enhancement of acidity upon electronic excitation, thus classified as photoacids. The changes of acidic character in the excited state of cyano-substituted derivatives of phenol, hydroxybiphenyl and naphthol are reviewed in this paper. The acidity constants pKa in the ground state (S0), pKa∗ in the first singlet excited state (S1) and the change of the acidity constant in the excited state ΔpKa for the discussed compounds are summarized and compared. The results of the acidity studies show, that the "electro-withdrawing" CN group in the molecules of naphthol, hydroxybiphenyl and phenol causes dramatic increase of their acidity in the excited state in comparison to the ground state. This effect is greatest for the cyanonaphthols (the doubly substituted CN derivatives are almost as strong as a mineral acid in the excited state), comparable for cyanobiphenyls, and smaller for phenol derivatives. The increase of acidity enables proton transfer to various organic solvents, and the investigation of ESPT can be extended to a variety of solvents besides water. The results of theoretical investigations were also presented and used for understanding the protolytic equilibria of cyano derivatives of naphthol, hydroxybiphenyl and phenol.
Comparative study of multireference perturbative theories for ground and excited states
NASA Astrophysics Data System (ADS)
Hoffmann, Mark R.; Datta, Dipayan; Das, Sanghamitra; Mukherjee, Debashis; Szabados, Ágnes; Rolik, Zoltán; Surján, Péter R.
2009-11-01
Three recently developed multireference perturbation theories (PTs)—generalized Van Vleck PT (GVVPT), state-specific multireference PT (SS-MRPT), and multiconfiguration PT (MCPT)-are briefly reviewed and compared numerically on representative examples, at the second order of approximations. We compute the dissociation potential curve of the LiH molecule and the BeH2 system at various geometries, both in the ground and in the first excited singlet state. Furthermore, the ethylene twisting process is studied. Both Møller-Plesset (MP) and Epstein-Nesbet partition are used for MCPT and SS-MRPT, while GVVPT uses MP partitioning. An important thrust in our comparative study is to ascertain the degree of interplay of dynamical and nondynamical correlation for both ground and excited states. The same basis set and the same set of orbitals are used in all calculations to keep artifactual differences away when comparing the results. Nonparallelity error is used as a measure of the performance of the respective theories. Significant differences among the three methods appear when an intruder state is present. Additionally, difficulties arise (a) in MCPT when the choice of a pivot determinant becomes problematic, and (b) in SS-MRPT when there are small coefficients of the model function and there is implicit division by these coefficients, which generates a potential instability of the solutions. Ways to alleviate these latter shortcomings are suggested.
Pina, J; Queiroz, M-J R P; Seixas de Melo, J
2016-08-01
A complete and systematic study of the spectroscopic and photophysical properties of five novel diarylamines in the benzo[b]thiophene series (oligoanilines) was performed in solution at room (293 K) and low (77 K) temperature. The title compounds resulting from the link between one aniline unit with a benzo[b]thiophene unit (with two different methyl and methoxy substitution) were characterized using steady-state absorption, fluorescence and phosphorescence spectroscopy, as well as femto- to nano-second time resolved spectroscopies. The study involved the determination of the absorption, emission and triplet-triplet absorption together with all relevant quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion and singlet oxygen yields), excited state lifetimes and the overall set of deactivation rate constants (kF, kIC and kISC). This study was further complemented with theoretical calculations, namely with the determination of the optimized ground-state molecular geometries for the diarylamines together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours using DFT calculations. The DFT results were found to corroborate the observed charge-transfer character of the singlet excited state. The experimental results showed that the radiationless decay processes (internal conversion and intersystem-crossing) constitute the main excited state deactivation pathways and that substitution with methyl and methoxy groups induces significant changes in the spectroscopic and photophysical behaviour of these compounds. This was also corroborated by the femtosecond transient absorption study, where it was found that the ultrafast dynamics of the diarylamines was best described by a sequential model featuring fast solvent relaxation followed by conformational relaxation to a more planar excited state, from where singlet excited state deactivation occurs through internal conversion and
Electron-impact excitation of the low-lying electronic states of formaldehyde
NASA Technical Reports Server (NTRS)
Chutjian, A.
1974-01-01
Electron-impact excitation has been observed at incident electron energies of 10.1 and 20.1 eV to the first five excited electronic states of formaldehyde lying at and below the 1B2 state at 7.10 eV. These excitations include two new transitions in the energy-loss range 5.6-6.2 eV and 6.7-7.0 eV which have been detected for the first time, either through electron-impact excitation or photon absorption. The differential cross sections of these new excitations are given at scattering angles between 15 and 135 deg. These cross-section ratios peak at large scattering angles - a characteristic of triplet - singlet excitations. The design and performance of the electron-impact spectrometer used in the above observations is outlined and discussed.
Excited-state absorption of pump radiation as a loss mechanism in solid-state lasers
Kliewer, M.L.; Powell, R.C.
1989-08-01
The characteristics of optical pumping dynamics occuring in laser-pumped rare earth-doped, solid-state laser materials were investigated by using a tunable alexandrite laser to pump Y3Al5O12:Nd(3+) in an optical cavity. It was found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelength resulting in low slope efficiencies, intense fluorescence emission is observed form the sample in the blue-green spectral region. This is attributed to the excited state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process will be an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths.
Excited state absorption of pump radiation as a loss mechanism in solid-state lasers
NASA Technical Reports Server (NTRS)
Kliewer, Michael L.; Powell, Richard C.
1989-01-01
The characteristics of optical pumping dynamics in laser-pumped, rare-earth-doped, solid-state laser materials are investigated by using a tunable alexandrite laser to pump Y3Al5O12:Nd(3+) in an optical cavity. It is found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelengths resulting in low slope efficiencies, intense fluorescence emission is observed from the sample in the blue-green spectral region. This is attributed to the excited-state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process is an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths.
Excited state absorption of pump radiation as a loss mechanism in solid-state lasers
Kliewer, M.L.; Powell, R.C.
1989-08-01
The characteristics of optical pumping dynamics occurring in laser-pumped rare earth-doped, solid-state laser materials were investigated by using a tunable alexandrite laser to pump Y/sub 3/Al/sub 5/O/sub 12/:Nd/sup 3+/ in an optical cavity. It was found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelengths resulting in low slope efficiencies, intense fluorescence emission is observed from the sample in the blue-green spectral region. This is attributed to the excited state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process will be an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths.
Multireference coupled-cluster approaches to excited states
NASA Astrophysics Data System (ADS)
Paldus, Josef; Li, Xiangzhu
2015-01-01
We review our recent work on multireference (MR) coupled-cluster (CC) methodology, namely (i) the idea of external corrections that are essential for the so-called reduced MR (RMR) CCSD and RMR-CCSD(T) methods at the single-reference (SR) level and for (N,M)-CCSD at the MR level, and (ii) the concept of the so-called C-conditions for the internal cluster amplitudes at the genuine MR CC state universal (SU) level. The latter concept enables the use of general model spaces (GMSs) while preserving the intermediate normalization and can be employed in any MR CC method that is based on the SU cluster Ansatz of Jeziorski and Monkhorst, including state-selective (SS) approaches, such as the Mukherjee MkCCSD and Brillouin-Wigner BW-CC methods. The performance of the RMR-CCSD(T), GMS-SU-CCSD, GMS-MkCCSD, and (N,M)-CCSD approaches is illustrated on a few typical examples.
Van der Waals Dispersion Interactions and Excited States of Oligoacene Molecular Crystals
NASA Astrophysics Data System (ADS)
Rangel Gordillo, Tonatiuh; Sharifzadeh, Sahar; Berland, Kristian; Altvater, Florian; Lee, Kyuho; Hyldgaard, Per; Kronik, Leeor; Neaton, Jeffrey B.
2015-03-01
Molecular crystals are a prototypical class of van der Waals (vdWs)-bound organic materials with novel excited state properties relevant for photovoltaics applications. Predicting the structure and excited state properties of oligoacene crystals presents a challenge for standard density functional theory (DFT), as standard functionals do not have long-range dispersion, and DFT does not yield excited-state properties. In this work, we use a combination of vdW-corrected DFT - both pair-wise correction methods and correlation functionals - and many-body perturbation theory to study the geometry and excited states of oligoacene crystals. We find that vdWs methods can predict lattice constants up to 1% of the experimental measurements. Low lying excited states computed with MBPT compare well with experiments, and are found to be quite sensitive to geometry. Our study reveals the importance of vdWs dispersion interactions to the determination of excited states; moreover, our work suggests routes for predictive calculations, in which both structures and excited states are calculated entirely from first-principles. We thank DOE for external funds, and NERSC for computational resources.
Ultrafast excited-state proton transfer from dicyano-naphthol
NASA Astrophysics Data System (ADS)
Carmeli, I.; Huppert, D.; Tolbert, L. M.; Haubrich, J. E.
1996-09-01
The rate of proton transfer from electronically excited 5,8-dicyano-2-naphthol (DCN2) to the solvent is studied by time-resolved fluorescence. Unlike most naphthol derivatives, excited DCN2 is a strong acid ( pK ∗ 2≈ -4.5 ) and therefore is capable of transferring protons to alcohols and other moderate proton acceptor solvents. The rate constant of proton transfer, κd, at low temperatures (< 250 K) is slightly larger than the inverse dielectric relaxation time, 1/τ D and has the same activation energy of the dielectric relaxation. On the other hand, at temperatures above 250 K the temperature dependence of the proton transfer rate decreases monotonically with increasing temperature, while the dielectric relaxation activation energy maintains the low temperature value.
On the 2 s-like relaxed excited state of the F center in alkali halide crystals
NASA Astrophysics Data System (ADS)
Panov, V. G.; Varaksin, A. N.; Sobolev, A. B.
2008-06-01
The energy and spectroscopic characteristics of the first excited 2 s-like electron state of the F center are presented according to the calculations performed in the framework of the variational model proposed by Gourary and Adrian. The relaxation of the crystal lattice in the vicinity of the excited F center is described. The problem of the spatial propagation of the F center is discussed. The results obtained for the 2 p and 2 s states of the F center are compared with each other and with the relevant experimental data.
Excited states in the active media of oxygen - iodine lasers
Azyazov, V N
2009-11-30
A review of investigations of kinetic processes in active media oxygen - iodine lasers (OILs) performed in the last decade is presented. The mechanisms of pumping and quenching of electronically and vibrationally excited O{sub 2} and I{sub 2} molecules are considered, and dissociation mechanisms of I{sub 2} in the active medium of the OIL are analysed. The values of kinetic constants of processes proceeding in the active media of OILs are recommended. (review)
Excited State Electronic Properties of Sodium Iodide and Cesium Iodide
Campbell, Luke W.; Gao, Fei
2013-05-01
We compute from first principles the dielectric function, loss function, lifetime and scattering rate of quasiparticles due to electronic losses, and secondary particle spectrum due to plasmon decay in two scintillating alkali halides, sodium iodide and cesium iodide. Particular emphasis is placed on quasiparticles within several multiples of the band gap from the band edges. A theory for the decay spectra of plasmons and other electronic excitations in crystals is presented. Applications to Monte Carlo radiation transport codes are discussed.
Comparison of ground- and excited-state raman transitions using resonant coherent stokes generation
NASA Astrophysics Data System (ADS)
Andrews, J. R.; Hochstrasser, R. M.
1981-11-01
Coherent Stokes generation was explored as a means to investigate vibrational dephasing in both the ground state and first excited singlet state of pentacene in benzoic acid. The dephasing-induced coherent emission (DICE) was used to obtain the ground- and excited-state Ramon linewidths between 1.6 K and 200 K. The broadening for both modes displayed an Arrhenius energy of ≈100 cm -1.
Two-component Structure in the Entanglement Spectrum of Highly Excited States
NASA Astrophysics Data System (ADS)
Yang, Zhi-Cheng; Chamon, Claudio; Hamma, Alioscia; Mucciolo, Eduardo
We study the entanglement spectrum of highly excited eigenstates of two known models which exhibit a many-body localization transition, namely the one-dimensional random-field Heisenberg model and the quantum random energy model. Our results indicate that the entanglement spectrum shows a ``two-component'' structure: a universal part that is associated to Random Matrix Theory, and a non-universal part that is model dependent. The non-universal part manifests the deviation of the highly excited eigenstate from a true random state even in the thermalized phase where the Eigenstate Thermalization Hypothesis holds. The fraction of the spectrum containing the universal part decreases continuously as one approaches the critical point and vanishes in the localized phase in the thermodynamic limit. We use the universal part fraction to construct a new order parameter for the many-body delocalized-to-localized transition. Two toy models based on Rokhsar-Kivelson type wavefunctions are constructed and their entanglement spectra are shown to exhibit the same structure.
Ehrler, Oli T.; Yang Jiping; Sugiharto, Albert B.; Unterreiner, Andreas N.; Kappes, Manfred M.
2007-11-14
Femtosecond time-resolved pump-probe photoelectron spectroscopy was used to study elementary relaxation processes occurring in isolated phthalocyanine-tetrasulfonate tetra-anions ([MPc(SO{sub 3}){sub 4}]{sup 4-}, M=Cu,Ni, and ''free-base'' [H{sub 2}Pc(SO{sub 3}){sub 4}]{sup 4-}) following Q band excitation by one-photon absorption at 775 nm. Whereas the Cu and Ni systems decay rapidly by means of internal conversion without electron loss, the free-base phthalocyanine primarily undergoes excited state tunneling electron emission. This reflects less efficient coupling to lower lying states within the corresponding spin manifold. Results are interpreted in terms of (time-dependent) density functional theory calculations of ground and electronically excited states and kinetically modeled to yield the associated rates.
Hoffman, M.Z.
1993-03-31
Progress on 6 projects is reported: excited state absorption spectrum of Ru(bpy){sub 3}{sup 2+}, solvent cage model for electron transfer quenching, reductive quenching of {sup *}Cr(III) complexes, solution medium effects in oxidative quenching of {sup *}Ru(II) complexes, photosensitized oxidation of phenol in aqueous solution, and quenching of Ru(II) complexes by oxygen.
NASA Astrophysics Data System (ADS)
Joshi, Sunita; Pant, Debi D.
2012-06-01
Ground and excited state dipole moments of probe quinine sulphate (QS) was obtained using Solvatochromic shift method. Higher dipole moment is observed for excited state as compared to the ground state which is attributed to the higher polarity of excited state.
Li, Zhendong; Liu, Wenjian
2016-01-12
A benchmark set of 11 small radicals is set up to assess the performance of time-dependent density functional theory (TD-DFT) for the excited states of open-shell systems. Both the unrestricted (U-TD-DFT) and spin-adapted (X-TD-DFT) formulations of TD-DFT are considered. For comparison, the well-established EOM-CCSD (equation-of-motion coupled-cluster with singles and doubles) is also used. In total, 111 low-lying singly excited doublet states are accessed by all the three approaches. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as the benchmark, it is found that both U-TD-DFT and EOM-CCSD perform well for those states dominated by singlet-coupled single excitations (SCSE) from closed-shell to open-shell, open-shell to vacant-shell, or closed-shell to vacant-shell orbitals. However, for those states dominated by triplet-coupled single excitations (TCSE) from closed-shell to vacant-shell orbitals, both U-TD-DFT and EOM-CCSD fail miserably due to severe spin contaminations. In contrast, X-TD-DFT provides balanced descriptions of both SCSE and TCSE. As far as the functional dependence is concerned, it is found that, when the Hartree-Fock ground state does not suffer from the instability problem, both global hybrid (GH) and range-separated hybrid (RSH) functionals perform grossly better than pure density functionals, especially for Rydberg and charge-transfer excitations. However, if the Hartree-Fock ground state is instable or nearly instable, GH and RSH tend to underestimate severely the excitation energies. The SAOP (statistically averaging of model orbital potentials) performs more uniformly than any other density functionals, although it generally overestimates the excitation energies of valence excitations. Not surprisingly, both EOM-CCSD and adiabatic TD-DFT are incapable of describing excited states with substantial double excitation characters. PMID:26672389
NASA Astrophysics Data System (ADS)
Cheng, Yan; Chini, Michael; Wang, Xiaowei; González-Castrillo, Alberto; Palacios, Alicia; Argenti, Luca; Martín, Fernando; Chang, Zenghu
2016-08-01
Attosecond science promises to allow new forms of quantum control in which a broadband isolated attosecond pulse excites a molecular wave packet consisting of a coherent superposition of multiple excited electronic states. This electronic excitation triggers nuclear motion on the molecular manifold of potential energy surfaces and can result in permanent rearrangement of the constituent atoms. Here, we demonstrate attosecond transient absorption spectroscopy (ATAS) as a viable probe of the electronic and nuclear dynamics initiated in excited states of a neutral molecule by a broadband vacuum ultraviolet pulse. Owing to the high spectral and temporal resolution of ATAS, we are able to reconstruct the time evolution of a vibrational wave packet within the excited B'Σ1u+ electronic state of H2 via the laser-perturbed transient absorption spectrum.
(e,2e) Reactions for He+ and Li2+ Ions from their Excited States. Scaling Law
NASA Astrophysics Data System (ADS)
Stia, C. R.; Fojón, O. A.; Rivarola, R. D.
In this work, theoretical triply differential cross sections for ionization of several hydrogenic atoms from excited states by fast electron impact are computed'in the case of asymmetric coplanar geometry. The final wavefunction is chosen as an approximate solution to the three-body scattering problem with correct asymptotic conditions. The initial wavefunction also satisfies correct boundary conditions. Results for Li2+ ions in their 2s and 2p excited states are presented. In addition, it is shown that a simple scaling law for the triply differential cross sections obtained for ionization of hydrogenic targets from their ground state is also satisfied by excited hydrogenic targets.
NASA Astrophysics Data System (ADS)
Bjorgaard, J. A.; Velizhanin, K. A.; Tretiak, S.
2016-04-01
The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited state molecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited state molecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission.
2016-01-01
The chemical locking of the central single bond in core chromophores of green fluorescent proteins (GFPs) influences their excited-state behavior in a distinct manner. Experimentally, it significantly enhances the fluorescence quantum yield of GFP chromophores with an ortho-hydroxyl group, while it has almost no effect on the photophysics of GFP chromophores with a para-hydroxyl group. To unravel the underlying physical reasons for this different behavior, we report static electronic structure calculations and nonadiabatic dynamics simulations on excited-state intramolecular proton transfer, cis–trans isomerization, and excited-state deactivation in a locked ortho-substituted GFP model chromophore (o-LHBI). On the basis of our previous and present results, we find that the S1 keto species is responsible for the fluorescence emission of the unlocked o-HBI and the locked o-LHBI species. Chemical locking does not change the parts of the S1 and S0 potential energy surfaces relevant to enol–keto tautomerization; hence, in both chromophores, there is an ultrafast excited-state intramolecular proton transfer that takes only 35 fs on average. However, the locking effectively hinders the S1 keto species from approaching the keto S1/S0 conical intersections so that most of trajectories are trapped in the S1 keto region for the entire 2 ps simulation time. Therefore, the fluorescence quantum yield of o-LHBI is enhanced compared with that of unlocked o-HBI, in which the S1 excited-state decay is efficient and ultrafast. In the case of the para-substituted GFP model chromophores p-HBI and p-LHBI, chemical locking hardly affects their efficient excited-state deactivation via cis–trans isomerization; thus, the fluorescence quantum yields in these chromophores remain very low. The insights gained from the present work may help to guide the design of new GFP chromophores with improved fluorescence emission and brightness. PMID:26744782
Systematic study of excited 0+ states in the Er isotopes populated in the (p , t) reaction
NASA Astrophysics Data System (ADS)
Garrett, P. E.; Finlay, A.; Kisliuk, D.; Chagnon-Lessard, S.; Diaz Varela, A.; Dunlop, R.; Jamieson, D. S.; Leach, K. G.; Svensson, C. E.; Ball, G. C.; Triambak, S.; Faestermann, T.; Hertenberger, R.; Wirth, H.-F.
2014-09-01
The nature of excited 0+ states in well-deformed nuclei continue to pose a challenge in nuclear structure. Often, even the nature of the first excited 0+ state, 02+, is unclear and interpretations involving β vibrations, pairing excitations, two-phonon γ vibrations, etc., have been advanced with different degrees of success. A major issue historically has been lack of data on excited 0+ states. In light of this, the study of the Er isotopes has been extended via the 162Er and 164Er (p , t) reactions. The experiments were performed at the Maier-Leibnitz Laboratory using 22 MeV proton beams on highly-enriched targets of 162,164Er, and the reaction products were analyzed with the Q3D spectrograph. Strong populations of the 02+ states have been observed. The systematics of the strong population of the 0+ states in the Er (p , t) reactions sheds light on the underlying nature of these levels.
Excited-state positronium formation in positron–hydrogen collisions under weakly coupled plasmas
NASA Astrophysics Data System (ADS)
Rej, Pramit; Ghoshal, Arijit
2016-06-01
The effect of screening of weakly coupled plasma on positronium (Ps) formation in excited states in the scattering of a positron from the ground state of a hydrogen atom has been investigated using a distorted wave theory which includes screened dipole polarization potential. The effect of external plasma has been incorporated by using the Debye–Hückel screening model of the interacting charge particles. Variationally determined simple hydrogenic wave functions have been used to obtain the distorted wave scattering amplitude in a closed form. Effects of plasma screening on the differential and total cross sections have been studied in detail in the energy range 20–300 eV of incident positron. For the free atomic case, our results agree nicely with some of the most accurate results available in the literature. To the best of our knowledge, such a study on the differential and total cross sections for Ps formation in highly excited states in positron–hydrogen collisions under weakly coupled plasma is reported first time in the literature.
Exploring Photoinduced Excited State Evolution in Heterobimetallic Ru(II)-Co(III) Complexes.
Kuhar, Korina; Fredin, Lisa A; Persson, Petter
2015-06-18
Quantum chemical calculations provide detailed theoretical information concerning key aspects of photoinduced electron and excitation transfer processes in supramolecular donor-acceptor systems, which are particularly relevant to fundamental charge separation in emerging molecular approaches for solar energy conversion. Here we use density functional theory (DFT) calculations to explore the excited state landscape of heterobimetallic Ru-Co systems with varying degrees of interaction between the two metal centers, unbound, weakly bound, and tightly bound systems. The interplay between structural and electronic factors involved in various excited state relaxation processes is examined through full optimizations of multiple charge/spin states of each of the investigated systems. Low-energy relaxed heterobimetallic states of energy transfer and excitation transfer character are characterized in terms of energy, structure, and electronic properties. These findings support the notion of efficient photoinduced charge separation from a Ru(II)-Co(III) ground state, via initial optical excitation of the Ru-center, to low-energy Ru(III)-Co(II) states. The strongly coupled system has significant involvement of the conjugated bridge, qualitatively distinguishing it from the other two weakly coupled systems. Finally, by constructing potential energy surfaces for the three systems where all charge/spin state combinations are projected onto relevant reaction coordinates, excited state decay pathways are explored. PMID:25719556
NASA Astrophysics Data System (ADS)
Johnson, Matthew P.; Zia, Ahmad; Horton, Peter; Ruban, Alexander V.
2010-07-01
Xanthophyll excited states have been implicated by transient absorption and two-photon excitation studies in playing a key role in the regulation of photosynthetic light harvesting via photoprotective energy dissipation. For any proposed quenching mechanism to be effective it must reduce the chlorophyll excited state lifetime from 2 ns to ˜0.5-0.4 ns. In the presented study the effect of xanthophyll composition on the chlorophyll excited state lifetime in Arabidopsis leaves in the light harvesting ( F m) and photoprotective (NPQ) states was determined. The data was compared to the chlorophyll excited state lifetime of native isolated LHCII and CP26 in detergent micelles with varying xanthophyll composition. It was found that although the differences in xanthophyll composition between LHC complexes from various Arabidopsis mutants were sufficient to explain the varying F m lifetime (and varying PSII efficiency), they were not of a sufficient scale to fully explain the observed differences in the NPQ lifetimes. Only when the LHC complexes were exposed to a low detergent/low pH media, a condition known to mimic the conformational state of LHCII associated with NPQ in vivo, were variations in excited state lifetime large enough to explain the differences observed in leaves. Furthermore, the data reveal that the replacement of lutein by either zeaxanthin or violaxanthin in the internal xanthophyll binding sites of LHCII and CP26 reduces the efficiency of energy dissipation in the photoprotective state in leaves and isolated complexes.
Slow Intramolecular Vibrational Relaxation Leads to Long-Lived Excited-State Wavepackets.
Rafiq, Shahnawaz; Scholes, Gregory D
2016-09-01
Broadband optical pump and compressed white light continuum probe were used to measure the transient excited-state absorption, ground-state bleach, and stimulated emission signals of cresyl violet solution in methanol. Amplitude oscillations caused by wavepacket motion in the ground and excited electronic states were analyzed. It was found that vibrational coherences in the excited state persist for more than the experimental waiting time window of 6 ps, and the strongest mode had a dephasing time constant of 2.4 ps. We hypothesize the dephasing of the wavepacket in the excited state is predominantly caused by intramolecular vibrational relaxation (IVR). Slow IVR indicates weak mode-mode coupling and therefore weak anharmonicity of the potential of this vibration. Thus, the initially prepared vibrational wavepacket in the excited state is not significantly perturbed by nonadiabatic coupling to other electronic states, and hence the diabatic and adiabatic representations of the system are essentially identical within the Born-Oppenheimer approximation. The wavepacket therefore evolves with time in an almost harmonic potential, slowly dephased by IVR and the pure vibrational decoherence. The consistency in the position of node (phase change in the wavepacket) in the excited-state absorption and stimulated emission signals without undergoing any frequency shift until the wavepacket is completely dephased conforms to the absence of any reactive internal conversion. PMID:27510098
Shelby, Megan L; Lestrange, Patrick J; Jackson, Nicholas E; Haldrup, Kristoffer; Mara, Michael W; Stickrath, Andrew B; Zhu, Diling; Lemke, Henrik T; Chollet, Matthieu; Hoffman, Brian M; Li, Xiaosong; Chen, Lin X
2016-07-20
Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the ∼100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance. PMID:27286410
Reichardt, Christian; Vogt, R. Aaron; Crespo-Hernandez, Carlos E.
2009-12-14
The electronic energy relaxation of 1-nitronaphthalene was studied in nonpolar, aprotic, and protic solvents in the time window from femtoseconds to microseconds. Excitation at 340 or 360 nm populates the Franck-Condon S{sub 1}({pi}{pi}{sup *}) state, which is proposed to bifurcate into two essentially barrierless nonradiative decay channels with sub-200 fs lifetimes. The first main decay channel connects the S{sub 1} state with a receiver T{sub n} state that has considerable n{pi}{sup *} character. The receiver T{sub n} state undergoes internal conversion to populate the vibrationally excited T{sub 1}({pi}{pi}{sup *}) state in 2-4 ps. It is shown that vibrational cooling dynamics in the T{sub 1} state depends on the solvent used, with average lifetimes in the range from 6 to 12 ps. Furthermore, solvation dynamics competes effectively with vibrational cooling in the triplet manifold in primary alcohols. The relaxed T{sub 1} state undergoes intersystem crossing back to the ground state within a few microseconds in N{sub 2}-saturated solutions in all the solvents studied. The second minor channel involves conformational relaxation of the bright S{sub 1} state (primarily rotation of the NO{sub 2}-group) to populate a dissociative singlet state with significant charge-transfer character and negligible oscillator strength. This dissociative channel is proposed to be responsible for the observed photochemistry in 1-nitronaphthalene. Ground- and excited-state calculations at the density functional level of theory that include bulk and explicit solvent effects lend support to the proposed mechanism where the fluorescent S{sub 1} state decays rapidly and irreversibly to dark excited states. A four-state kinetic model is proposed that satisfactorily explains the origin of the nonradiative electronic relaxation pathways in 1-nitronaphthalene.
Populating excited states of incoherent atoms using coherent light.
NASA Technical Reports Server (NTRS)
Mcilrath, T. J.; Carlsten, J. L.
1972-01-01
Study of the influence of various experimental parameters on the interaction between a multimode high-intensity laser light and the absorbing atoms of an atomic gas. Using a simplified treatment of line broadening which does not include correlations between momentum-changing collisions and pressure-broadening collisions, expressions are obtained that show the effect of pressure, laser-pulse length, and intensity on the excitation. It is found that, as long as the dephasing time of the atomic system is sufficiently short, the interaction reduces to a two-body collision between the atoms and photons, where coherence effects do not occur.
Thermodynamical property of entanglement entropy for excited states.
Bhattacharya, Jyotirmoy; Nozaki, Masahiro; Takayanagi, Tadashi; Ugajin, Tomonori
2013-03-01
We argue that the entanglement entropy for a very small subsystem obeys a property which is analogous to the first law of thermodynamics when we excite the system. In relativistic setups, its effective temperature is proportional to the inverse of the subsystem size. This provides a universal relationship between the energy and the amount of quantum information. We derive the results using holography and confirm them in two-dimensional field theories. We will also comment on an example with negative specific heat and suggest a connection between the second law of thermodynamics and the strong subadditivity of entanglement entropy. PMID:23496702
Noncollisional excitation of low-lying states in gaseous nebulae
NASA Technical Reports Server (NTRS)
Rubin, Robert H.
1986-01-01
Consideration is given to the effects of processes other than electron collisional excitation on the energy level populations of species of C, N, and O. It is found that dielectronic as well as direct-radiative recombination may contribute significantly and in some cases be the major input to populating the low-lying metastable levels. It is concluded that the most pronounced changes occur when there is a large effective recombination coefficient to a level and when T(e) is low. The most dramatic change among the forbidden lines occurs for the O II forbidden lines.
Dietzek, Benjamin; Kiefer, Wolfgang; Blumhoff, Jörg; Böttcher, Lars; Rau, Sven; Walther, Dirk; Uhlemann, Ute; Schmitt, Michael; Popp, Jürgen
2006-06-23
A detailed study on the excited-state-excitation migration taking place within the tetranuclear complex [{(tbbpy)(2)Ru(tmbi)}(2){Pd(allyl)}(2)](PF(6))(2) (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine and tmbi = 5,6,5',6'-tetramethyl-2,2'-bibenzimidazolate) is presented. The charge transfer is initiated by the photoexcitation into the lowest metal-to-ligand charge-transfer (MLCT) band of one of the peripheral ruthenium(II) chromophores and terminates on the central structurally complex Pd(2) (II)(allyl)(2) subunit. Thus, the system under investigation can be thought of as a functional model for the photosynthesis reaction center in plants. The kinetic steps involved in the overall process are inferred from femtosecond time-resolved transient-grating kinetics recorded at spectral positions within the regions of ground-state bleach and transient absorption. The kinetics features a complex non-exponential time behavior and can be fitted to a bi-exponential rise (tau(1)> or =200 fs, tau(2) approximately 1.5 ps) and a mono- or bi-exponential decay, depending on the experimental situation. The data leads to the formulation of a model for the intramolecular excitation-hopping ascribing intersystem crossing and subsequent cooling as the two fastest observed processes. Following these initial steps, charge transfer from the ruthenium to the central complex Pd(2)(allyl)(2) moiety is observed with a characteristic time constant of 50 ps. A 220-ps component that is observed in the ground-state recovery only is attributed to excitation equilibration between the two identical Pd(allyl) chromophores. PMID:16628758
Kowalski, Karol
2009-05-21
In this article we discuss a problem of proper balancing of the non-iterative corrections to the ground- and excited-state energies obtained with approximate coupled cluster (CC) and Equation-of-Motion CC (EOMCC) approaches. It is demonstrated that for a class of excited states dominated by single excitations and for states with medium doubly excited component the newly introduced embedded variant of the Method of Moments of Coupled Cluster equations provides mathematically rigorous way of balancing the ground- and excited-state correlation effects. The resulting noniterative methodology accounting for the effect of triples (Em-EOMCCSD(T)) is tested using its parallel implementation on the systems for which iterative CC/EOMCC calculations with full inclusion of triply excited configurations or their most important subset is numerically feasible.
Dixon, David A; Gole, James L
2005-08-11
Time-dependent density functional theory calculations with a proper treatment of the asymptotic form of the exchange-correlation potential have been performed on R(R')Si=O to predict vertical excitation energies. The species R(R')Si=O is used as a model for the binding of the -(R)Si=O chromophore to a porous silicon surface. The calculated vertical excitation energies are substantially lower than those determined previously and show that vertical excitation of the lone chromophore is possible for all types of substituents including electronegative ones with KrF laser excitation in contrast to other predictions. If the substituents are electropositive, the chromophore can also be excited by a nitrogen laser. These results, in concert with the effect of the porous silicon surface on the R(R')Si=O excited states, confirm our previous explanation of the photoluminescence of porous silicon as being due to the presence of Si=O chromophores and provide new insights into the photoexcitation process. The results show that the differences in the vertical and adiabatic excitation energies are strongly dependent on whether the substituents are electronegative or electropositive with the former leading to larger differences and the latter leading to smaller differences. The results for the energy differences are explained in terms of the changes in the Si=O bond length on vertical excitation and on the changes in bond angles, which are related to the ability of the Si center in the excited state to undergo an inversion process. PMID:16852877
Structural and excited-state properties of oligoacene crystals from first principles
NASA Astrophysics Data System (ADS)
Rangel, Tonatiuh; Berland, Kristian; Sharifzadeh, Sahar; Brown-Altvater, Florian; Lee, Kyuho; Hyldgaard, Per; Kronik, Leeor; Neaton, Jeffrey B.
2016-03-01
Molecular crystals are a prototypical class of van der Waals (vdW) bound organic materials with excited-state properties relevant for optoelectronics applications. Predicting the structure and excited-state properties of molecular crystals presents a challenge for electronic structure theory, as standard approximations to density functional theory (DFT) do not capture long-range vdW dispersion interactions and do not yield excited-state properties. In this work, we use a combination of DFT including vdW forces, using both nonlocal correlation functionals and pairwise correction methods, together with many-body perturbation theory (MBPT) to study the geometry and excited states, respectively, of the entire series of oligoacene crystals, from benzene to hexacene. We find that vdW methods can predict lattice constants within 1% of the experimental measurements, on par with the previously reported accuracy of pairwise approximations for the same systems. We further find that excitation energies are sensitive to geometry, but if optimized geometries are used MBPT can yield excited-state properties within a few tenths of an eV from experiment. We elucidate trends in MBPT-computed charged and neutral excitation energies across the acene series and discuss the role of common approximations used in MBPT.
Datz, S.; Dittner, P.F.; Gomez del Campo, J.; Krause, H.F.; Rosseel, T.M.; Vane, C.R. ); Iwata, I.; Komaki, I.; Kimura, M.; Yamazaki, Y. ); Fujimoto, F.; Honda, F. )
1990-01-01
Hydrogenic ions passing through axial and planar channels can be excited from n = 1 to n = 2 when the frequency of perturbation by the atoms in the crystal spaced a distance d apart comes into resonance with the spacing between eigenstates i and j {Delta}E{sub ij} = hK(v{sub i}/d) where K is a harmonic 1,2,3{hor ellipsis} of the (v{sub i}/d) frequency. The degeneracy in the n = 2 levels is removed; first by the assymetry in the crystal field and second by Stark mixing of 2s with 2p{sub x} which is caused by the wake field. Thus, the resonant frequency, and hence velocity, for excitation to 2p{sub x,y} is different than that for 2p{sub x} and they can be excited selectively. In the present work we used Mg{sup 11+}, where the n = 2 ionization cross section is small enough to permit escape of some of the excited ions from the crystal without being ionized by subsequent collisions and with the subsequent emission of radiation. Since we can excite different orientations of the ion selectively by varying the velocity we can measure the separate ionization cross sections for these states by determining the yields of totally stripped ions compared to those which emit a Ly {alpha} x-ray. A comparison of the two channels shows that the probability of escape from the crystal without ionizations is greater for ions in the 2p{sub x} state than those in the 2p{sub x,y} state. These RCE data and are presented as proof of principal for experiments which measure electron bombardment ionization cross sections for short lived excited states with specific polarization.
S-wave triplet doubly-excited states 3Se of Li+ below the N=2 excitation threshold of Li2+
NASA Astrophysics Data System (ADS)
Gien, T. T.
2009-11-01
The Harris-Nesbet variational method was considered for the determination of the series a and b of S-wave triplet doubly-excited-state resonances 3Se of Li+ below the N=2 excitation threshold of Li2+. Because of the high accuracy of our numerical method, we succeeded in determining a greatest number of these doubly-excited states below this threshold, including those lying very close to the threshold. Five of these high-lying doubly excited states were determined by us for the first time.
Sharipov, Sh.; Ermamatov, M. J. Bayimbetova, J. K.
2008-02-15
The properties of excited states of two deformable odd nuclei are investigated within the nonadiabatic model previously developed by the present authors. The results of relevant calculations are compared with available experimental data.
Carotenoid Excited State Kinetics in Bacterial RCs with the Primary Electron Donor Oxidized
NASA Astrophysics Data System (ADS)
Lin, Su; Katilius, Evaldas; Woodbury, Neal W.
Carotenoid singlet excited state kinetics in wild type reaction centers from Rhodobacter sphaeroides was investigated using ultrafast laser spectroscopy under conditions where the primary electron donor is either neutral or oxidized.
Newton, M.D.; Vura-Weis, J.; Wasielewski, M.R.; Subotnik, J.E.
2010-10-19
A common strategy to calculate electronic coupling matrix elements for charge or energy transfer is to take the adiabatic states generated by electronic structure computations and rotate them to form localized diabatic states. In this paper, we show that, for intermolecular transfer of singlet electronic excitation, usually we cannot fully localize the electronic excitations in this way. Instead, we calculate putative initial and final states with small excitation tails caused by weak interactions with high energy excited states in the electronic manifold. These tails do not lead to substantial changes in the total diabatic coupling between states, but they do lead to a different partitioning of the total coupling between Coulomb (Forster), exchange (Dexter), and one-electron components. The tails may be reduced by using a multistate diabatic model or eliminated entirely by truncation (denoted as 'chopping'). Without more information, we are unable to conclude with certainty whether the observed diabatic tails are a physical reality or a computational artifact. This research suggests that decomposition of the diabatic coupling between chromophores into Coulomb, exchange, and one-electron components may depend strongly on the number of states considered, and such results should be treated with caution.
Contribution of excited states to stellar weak-interaction rates in odd-A nuclei
NASA Astrophysics Data System (ADS)
Sarriguren, P.
2016-05-01
Weak-interaction rates, including β decay and electron capture, are studied in several odd-A nuclei in the p f -shell region at various densities and temperatures of astrophysical interest. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus. The nuclear structure involved in the weak processes is studied within a quasiparticle random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree-Fock mean field with pairing correlations. In the range of densities and temperatures considered, it is found that the total rates do not differ much from the rates of the ground state fully populated. In any case, the changes are not larger than the uncertainties due to the nuclear-model dependence of the rates.
NASA Astrophysics Data System (ADS)
Almeida, Nuno M. S.; McKinlay, Russell G.; Paterson, Martin J.
2015-01-01
The lowest excited electronic states of the permanganate ion MnO4- are calculated using a hierarchy of coupled cluster response approaches, as well as time-dependent density functional theory. It is shown that while full linear response coupled cluster with singles and doubles (or higher) performs well, that permanganate represents a stern test for approximate coupled cluster response models, and that problems can be traced to very large orbital relaxation effects. TD-DFT is reasonably robust although errors around 0.6 eV are still observed. In order to further investigate the strong correlations prevalent in the electronic ground state large-scale RASSCF calculations were also performed. Again very large orbital relaxation in the correlated wavefunction is observed. Although the system can qualitatively be described by a single configuration, multi-reference diagnostic values show that care must be taken in this and similar metal complexes.
Excitation of Helium to the n=2 States in Intermediate Energy H^- + He Collisions.
NASA Astrophysics Data System (ADS)
Kvale, T. J.; Lu, C. E.; Theodosiou, D. G.; Seely
1996-05-01
The first measurements and calculations of excitation of helium to the n=2 states by H^- impact are reported. The experimental method that was employed in these measurements was Ion Energy-Loss Spectroscopy which resulted in absolute cross section determinations. A H^- ion beam was accelerated into a gas target cell containing helium and the scattered H^- beam was magnetically separated from the other charge state components of the emerging projectile beam and directed into an energy analyzer in the decelerator terminal. The potential placed on the accelerator was varied to produce the energy-loss spectra. These spectra were analyzed in order to deduce the cross section values. Cross section predictions using the VPSA model, with explicit allowance for the internal structure of H^-, are also reported and will be compared to the experimentally determined cross sections.
Relative entropy of excited states in two dimensional conformal field theories
NASA Astrophysics Data System (ADS)
Sárosi, Gábor; Ugajin, Tomonori
2016-07-01
We study the relative entropy and the trace square distance, both of which measure the distance between reduced density matrices of two excited states in two dimensional conformal field theories. We find a general formula for the relative entropy between two primary states with the same conformal dimension in the limit of a single small interval and find that in this case the relative entropy is proportional to the trace square distance. We check our general formulae by calculating the relative entropy between two generalized free fields and the trace square distance between the spin and disorder operators of the critical Ising model. We also give the leading term of the relative entropy in the small interval expansion when the two operators have different conformal dimensions. This turns out to be universal when the CFT has no primaires lighter than the stress tensor. The result reproduces the previously known special cases.
Study of the Excited State of Double-Λ Hypernuclei by Hyperspherical Supersymmetric Approach
NASA Astrophysics Data System (ADS)
Khan, Md. Abdul; Das, Tapan Kumar; Chakrabarti, Barnali
Hyperspherical harmonics expansion (HHE) method has been applied to study the structure and ΛΛ dynamics for the ground and first excited states of low and medium mass double-Λ hypernuclei in the framework of core+Λ+Λ three-body model. The ΛΛ potential is chosen phenomenologically while core-Λ potential is obtained by folding the phenomenological Λ N interaction into the density distribution of the core. The parameters of this effective Λ N potential is obtained by the condition that they reproduce the experimental (or empirical) data for core-Λ subsystem. The three-body (core+Λ+Λ) Schrödinger equation is solved by hyperspherical adiabatic approximation (HAA) to get the ground state energy and wave function. This ground state energy and wave function are used to construct a partner potential. The three-body Schrödinger equation is solved once again for this partner potential. According to supersymmetric quantum mechanics, the ground state energy of this potential is exactly the same as that of the first excited state of the potential used in the first step. In addition to the two-Λ separation energy for the ground and first excited state, some geometrical quantities for the ground state of double-Λ hypernuclei $_{\\Lambda\\Lambda}^{6}He, _{\\Lambda\\Lambda}^{10}Be, _{\\Lambda\\Lambda}^{14}C, _{\\Lambda\\Lambda}^{18}O, _{\\Lambda\\Lambda}^{22}Ne, _{\\Lambda\\Lambda}^{26}Mg, _{\\Lambda\\Lambda}^{30}Si, _{\\Lambda\\Lambda}^{34}S, _{\\Lambda\\Lambda}^{38}Ar, _{\\Lambda\\Lambda}^{42}Ca, _{\\Lambda\\Lambda}^{46}Ti, _{\\Lambda\\Lambda}^{50}Cr, _{\\Lambda\\Lambda}^{54}Fe, _{\\Lambda\\Lambda}^{58}Ni, _{\\Lambda\\Lambda}^{62}Zn, _{\\Lambda\\Lambda}^{66}Ge, _{\\Lambda\\Lambda}^{70}Se, _{\\Lambda\\Lambda}^{74}Kr, _{\\Lambda\\Lambda}^{78}Sr, _{\\Lambda\\Lambda}^{82}Zr, _{\\Lambda\\Lambda}^{86}Mo, _{\\Lambda\\Lambda}^{90}Ru, _{\\Lambda\\Lambda}^{94}Pd, _{\\Lambda\\Lambda}^{98}Pd, _{\\Lambda\\Lambda}^{102}Cd, _{\\Lambda\\Lambda}^{106}Sn, _{\\Lambda\\Lambda}^{132
Switching between ground and excited states by optical feedback in a quantum dot laser diode
Virte, Martin; Breuer, Stefan; Sciamanna, Marc; Panajotov, Krassimir
2014-09-22
We demonstrate switching between ground state and excited state emission in a quantum-dot laser subject to optical feedback. Even though the solitary laser emits only from the excited state, we can trigger the emission of the ground state by optical feedback. We observe recurrent but incomplete switching between the two emission states by variation of the external cavity length in the sub-micrometer scale. We obtain a good qualitative agreement of experimental results with simulation results obtained by a rate equation that accounts for the variations of the feedback phase.
Role of the low-energy excited states in the radiolysis of aromatic liquids.
Baidak, Aliaksandr; Badali, Matthew; LaVerne, Jay A
2011-07-01
The contribution of the low-energy excited states to the overall product formation in the radiolysis of simple aromatic liquids--benzene, pyridine, toluene, and aniline--has been examined by comparison of product yields obtained in UV-photolysis and in γ-radiolysis. In photolysis, these electronic excited states were selectively populated using UV-light excitation sources with various energies. Yields of molecular hydrogen and of "dimers" (biphenyl, bibenzyl, dipyridyl for benzene, toluene, pyridine, respectively, and of ammonia and diphenylamine for aniline) have been determined, since they are the most abundant radiolytic products. Negligibly small production of molecular hydrogen in the UV-photolysis of aromatic liquids with excitation to energies of 4.88, 5.41, 5.79, and 6.70 eV and the lack of a scavenger effect suggest that this product originates from short-lived high-energy singlet states. A significant reduction in "dimer" radiation-chemical yields in the presence of scavengers such as anthracene or naphthalene indicates that the triplet excited states are important precursors to these products. The results for toluene and aniline suggest that efficient dissociation from the lowest-energy excited triplet state leads to noticeable "dimer" production. For benzene and pyridine, the lowest-energy triplet excited states are not likely to fragment into radicals because of the relatively large energy gap between the excited state level and corresponding bond dissociation energy. The "dimer" formation in the radiolysis of benzene and pyridine is likely to involve short-lived high-energy triplet states. PMID:21634362
Excited states of 26Al studied via the reaction 27Al(d,t)
NASA Astrophysics Data System (ADS)
Srivastava, Vishal; Bhattacharya, C.; Rana, T. K.; Manna, S.; Kundu, S.; Bhattacharya, S.; Banerjee, K.; Roy, P.; Pandey, R.; Mukherjee, G.; Ghosh, T. K.; Meena, J. K.; Roy, T.; Chaudhuri, A.; Sinha, M.; Saha, A. K.; Asgar, Md. A.; Dey, A.; Roy, Subinit; Moin Shaikh, Md.
2016-05-01
The reaction 27Al(d,t) at 25 MeV was utilized to study the excited states of 26Al. The angular distributions of the observed excited states of 26Al were analyzed with zero range distorted wave Born approximation as well as by incorporating finite range correction parameters to extract spectroscopic factors. The two sets of extracted spectroscopic factors were compared with each other to see the effect of using finite range correction in the transfer form factor.
An Efficient Variational Principle for the Direct Optimization of Excited States.
Zhao, Luning; Neuscamman, Eric
2016-08-01
We present a variational principle that enables systematically improvable predictions for individual excited states through an efficient Monte Carlo evaluation. We demonstrate its compatibility with different ansatzes and with both real space and Fock space sampling and discuss its potential for use in the solid state. In numerical demonstrations for challenging molecular excitations, the method rivals or surpasses the accuracy of very high level methods using drastically more compact wave function approximations. PMID:27379468
Measurement of the lifetime of excited-state electron bubbles in superfluid helium
Ghosh, Ambarish; Maris, Humphrey J.
2005-08-01
We report on the measurement of the lifetime of bubbles in superfluid helium that contain an electron in the 1P state. The 1P bubbles are produced by laser excitation of ground-state bubbles, and are detected by ultrasonic cavitation. Our measurements show that the lifetime of these excited bubbles is much less than the calculated lifetime for radiative decay and, hence, is determined by a nonradiative mechanism.
Excited state dynamics in pyrrole water clusters: First-principles simulation
NASA Astrophysics Data System (ADS)
Frank, Irmgard; Damianos, Konstantina
2008-01-01
The excited state dynamics in pyrrole-water clusters is investigated using restricted open-shell Kohn-Sham theory. While the isolated pyrrole molecule dissociates in the excited state, no dissociation is observed in the presence of water molecules. Instead an electron is transferred to water and moves as solvated electron between the water molecules. The results are compared to data obtained from other first-principles and ab initio calculations.
Highly excited {Sigma}{sup -} states of molecular hydrogen
Argoubi, F.; Bezzaouia, S.; Oueslati, H.; Telmini, M.; Jungen, Ch.
2011-05-15
We report calculations of H{sub 2} {Sigma}{sup -} states using a variational R-matrix approach combined with multichannel quantum defect theory. Several Rydberg series converging to the 2p{pi} state of the H{sub 2}{sup +} ion core are established and their mutual channel interactions characterized. The influence of the external electron on the chemical bond is found to be particularly strong in these electronically and chemically weakly bound states.
Relativistic Hartree-Fock-Bogoliubov theory: ground states and excitations
NASA Astrophysics Data System (ADS)
Long, Wen Hui; Meng, Jie; Giai, Nguyen Van
The covariant density functional (CDF) theory with the Fock diagrams, the indivisible part of the effective nuclear interaction, is introduced, including both the relativistic Hartree-Fock and its extension -- the relativistic Hartree-Fock-Bogoliubov methods. The specific roles played by Fock diagrams, particularly for the new degrees of freedom associated with the π and ρ-tensor fields and the non-local mean fields, are discussed in determining the nuclear energy functional, the shell structure and the evolution, and nuclear isospin excitations. The existing problems and limits of the CDF theory with Fock terms are also discussed, and the perspective on a new algorithm of dealing with the non-local Fock terms is given.
Steady-state photoluminescent excitation characterization of semiconductor carrier recombination.
Bhosale, J S; Moore, J E; Wang, X; Bermel, P; Lundstrom, M S
2016-01-01
Photoluminescence excitation spectroscopy is a contactless characterization technique that can provide valuable information about the surface and bulk recombination parameters of a semiconductor device, distinct from other sorts of photoluminescent measurements. For this technique, a temperature-tuned light emitting diode (LED) has several advantages over other light sources. The large radiation density offered by LEDs from near-infrared to ultraviolet region at a low cost enables efficient and fast photoluminescence measurements. A simple and inexpensive LED-based setup facilitates measurement of surface recombination velocity and bulk Shockley-Read-Hall lifetime, which are key parameters to assess device performance. Under the right conditions, this technique can also provide a contactless way to measure the external quantum efficiency of a solar cell. PMID:26827306
Steady-state photoluminescent excitation characterization of semiconductor carrier recombination
NASA Astrophysics Data System (ADS)
Bhosale, J. S.; Moore, J. E.; Wang, X.; Bermel, P.; Lundstrom, M. S.
2016-01-01
Photoluminescence excitation spectroscopy is a contactless characterization technique that can provide valuable information about the surface and bulk recombination parameters of a semiconductor device, distinct from other sorts of photoluminescent measurements. For this technique, a temperature-tuned light emitting diode (LED) has several advantages over other light sources. The large radiation density offered by LEDs from near-infrared to ultraviolet region at a low cost enables efficient and fast photoluminescence measurements. A simple and inexpensive LED-based setup facilitates measurement of surface recombination velocity and bulk Shockley-Read-Hall lifetime, which are key parameters to assess device performance. Under the right conditions, this technique can also provide a contactless way to measure the external quantum efficiency of a solar cell.
Intersystem crossing from highly excited states. rhodamine 6G
Ryl'kov, V.V.; Cheshev, E.A.
1985-09-01
The authors carried out an investigation of ethanolic solutions of Rhodamine 6G (R6G) at 20 C by laser flash photolysis. The excitation of dilute (3 /SUP ./ 10/sup -5/ M) solutions of R6G with an initial optical density of 1.5 up to an intensity of 100 MW/cm/sup 2/ resulted in only weak triplet-triplet absorption. The introduction of additions of lithium chloride or lithium bromide in 0.1 M concentrations into a solution of R6G (3.10/sup -5/ M) resulted in the appearance of induced absorption and the introduction of an addition of lithium nitrate in the same concentration into the solution did not result in enhancement of triplet-triplet absorption.
NASA Astrophysics Data System (ADS)
Feng, Qiang; Xu, Yun-Feng; Sun, Jin-Da; Tian, Shan-Xi; Shan, Xiao-Bin; Liu, Fu-Yi; Sheng, Liu-Si
2009-10-01
Photodissociation efficiency spectrum of anionic oxygen atom produced via ion-pair dissociations of carbon dioxide is recorded by means of the synchrotron radiation excitation (XUV photon energy 17.40-20.00 eV). The present spectrum is assigned as the Rydberg-like excited ion-pair states, i.e., Tanaka-Ogawa and Henning series, tilde C2Σg+ (CO+2) vibrational ground-state and excitation series. Three Rydberg series, npσu, npπu, and nfu, converging to tilde C2Σg+ (0, 0, 0), show the higher cross sections.
State-resolved collisional relaxation of highly vibrationally excited CsH by CO2
NASA Astrophysics Data System (ADS)
Mu, Baoxia; Cui, Xiuhua; Shen, Yifan; Dai, Kang
2015-09-01
Quenching of highly vibrationally excited CsH(X1Σ+, v = 15-23) by collisions with CO2 was investigated. A significant fraction of the initial population of highly vibrationally excited CsH(v = 22) was relaxed to a low vibrational level (Δv = -5). The near-resonant 5-1 vibration-to-vibration (V-V) energy was efficiently exchanged. The rate constants for the rotational levels of CO2(0000) [J = 36-60] and CO2(0001) [J = 5-31] from the collisions with excited CsH were determined. The experiments revealed that the collisions resulting in CO2(0000) were accompanied by substantial excitation in rotation and translation. The vibrationally excited CO2(0001) state exhibited rotational and translational energy distributions near those of the initial state. The total quenching rates relative to the probed state of excited CsH were determined for both CO2 states. The corresponding data indicated that the gains in the rotational and translational energies in CO2 were sensitive to the collisional depletion of excited CsH.
Measurement of the Magnetic Moment of the First Excited State in 93Sr Using on-line TDPAC technique
NASA Astrophysics Data System (ADS)
Sasanuma, T.; Taniguchi, A.; Tanigaki, M.; Ohkubo, Y.; Kawase, Y.
2004-12-01
The g-factor of the first excited state of 93Sr ( E = 213 keV, T 1/2 = 4.6 ns) was measured by an on-line TDPAC technique with use of the strong hyperfine field in Fe metal. The Larmor frequency ω L = (2.60 ± 0.15) × 108 rad/s was obtained. The g-factor is derived as g = -0.227 ± 0.013 from g = - ℏω L/ B hf μ N. If the spin of the first excited state of 93Sr is assumed to be 3/2, the g-factor is predicted by a simple core-excitation model as g = -0.22, which is in good agreement with the present experimental result.
Excited-State Energies and Electronic Couplings of DNA Base Dimers
Kozak, Christopher R.; Kistler, Kurt A.; Lu, Zhen; Matsika, Spiridoula
2010-02-04
The singlet excited electronic states of two π-stacked thymine molecules and their splittings due to electronic coupling have been investigated with a variety of computational methods. Focus has been given on the effect of intermolecular distance on these energies and couplings. Single-reference methods, CIS, CIS(2), EOMCCSD, TDDFT, and the multireference method CASSCF, have been used, and their performance has been compared. It is found that the excited-state energies are very sensitive to the applied method but the couplings are not as sensitive. Inclusion of diffuse functions in the basis set also affects the excitation energies significantly but not the couplings. TDDFT is inadequate in describing the states and their coupling, while CIS(2) gives results very similar to EOM-CCSD. Excited states of cytosine and adenine π-stacked dimers were also obtained and compared with those of thymine dimers to gain a more general picture of excited states in π-stacked DNA base dimers. The coupling is very sensitive to the relative position and orientation of the bases, indicating great variation in the degree of delocalization of the excited states between stacked bases in natural DNA as it fluctuates.
Yan, Bokai; Caflisch, Russel E.; Barekat, Farzin; Cambier, Jean-Luc
2015-10-15
This paper describes a kinetic model and a corresponding Monte Carlo simulation method for excitation/deexcitation and ionization/recombination by electron impact in a plasma free of external fields. The atoms and ions in the plasma are represented by continuum densities and the electrons by a particle distribution. A Boltzmann-type equation is formulated and a corresponding H-theorem is formally derived. An efficient Monte Carlo method is developed for an idealized analytic model of the excitation and ionization collision cross sections. To accelerate the simulation, the reduced rejection method and binary search method are used to overcome the singular rate in the recombination process. Numerical results are presented to demonstrate the efficiency of the method on spatially homogeneous problems. The evolution of the electron distribution function and atomic states is studied, revealing the possibility under certain circumstances of system relaxation towards stationary states that are not the equilibrium states, a potential non-ergodic behavior.
Excitation model of pacemaker cardiomyocytes of cardiac conduction system
NASA Astrophysics Data System (ADS)
Grigoriev, M.; Babich, L.
2015-11-01
Myocardium includes typical and atypical cardiomyocytes - pacemakers, which form the cardiac conduction system. Excitation from the atrioventricular node in normal conditions is possible only in one direction. Retrograde direction of pulses is impossible. The most important prerequisite for the work of cardiomyocytes is the anatomical integrity of the conduction system. Changes in contractile force of the cardiomyocytes, which appear periodically, are due to two mechanisms of self-regulation - heterometric and homeometric. Graphic course of the excitation pulse propagation along the heart muscle more accurately reveals the understanding of the arrhythmia mechanism. These models have the ability to visualize the essence of excitation dynamics. However, they do not have the proper forecasting function for result estimation. Integrative mathematical model enables further investigation of general laws of the myocardium active behavior, allows for determination of the violation mechanism of electrical and contractile function of cardiomyocytes. Currently, there is no full understanding of the topography of pacemakers and ionic mechanisms. There is a need for the development of direction of mathematical modeling and comparative studies of the electrophysiological arrangement of cells of atrioventricular connection and ventricular conduction system.
Introducing QMC/MMpol: Quantum Monte Carlo in Polarizable Force Fields for Excited States.
Guareschi, Riccardo; Zulfikri, Habiburrahman; Daday, Csaba; Floris, Franca Maria; Amovilli, Claudio; Mennucci, Benedetta; Filippi, Claudia
2016-04-12
We present for the first time a quantum mechanics/molecular mechanics scheme which combines quantum Monte Carlo with the reaction field of classical polarizable dipoles (QMC/MMpol). In our approach, the optimal dipoles are self-consistently generated at the variational Monte Carlo level and then used to include environmental effects in diffusion Monte Carlo. We investigate the performance of this hybrid model in describing the vertical excitation energies of prototypical small molecules solvated in water, namely, methylenecyclopropene and s-trans acrolein. Two polarization regimes are explored where either the dipoles are optimized with respect to the ground-state solute density (polGS) or different sets of dipoles are separately brought to equilibrium with the states involved in the electronic transition (polSS). By comparing with reference supermolecular calculations where both solute and solvent are treated quantum mechanically, we find that the inclusion of the response of the environment to the excitation of the solute leads to superior results than the use of a frozen environment (point charges or polGS), in particular, when the solute-solvent coupling is dominated by electrostatic effects which are well recovered in the polSS condition. QMC/MMpol represents therefore a robust scheme to treat important environmental effects beyond static point charges, combining the accuracy of QMC with the simplicity of a classical approach. PMID:26959751
Vengris, Mikas; van der Horst, Michael A.; Zgrablić, Goran; van Stokkum, Ivo H. M.; Haacke, Stefan; Chergui, Majed; Hellingwerf, Klaas J.; van Grondelle, Rienk; Larsen, Delmar S.
2004-01-01
Wavelength- and time-resolved fluorescence experiments have been performed on the photoactive yellow protein, the E46Q mutant, the hybrids of these proteins containing a nonisomerizing “locked” chromophore, and the native and locked chromophores in aqueous solution. The ultrafast dynamics of these six systems is compared and spectral signatures of isomerization and solvation are discussed. We find that the ultrafast red-shifting of fluorescence is associated mostly with solvation dynamics, whereas isomerization manifests itself as quenching of fluorescence. The observed multiexponential quenching of the protein samples differs from the single-exponential lifetimes of the chromophores in solution. The locked chromophore in the protein environment decays faster than in solution. This is due to additional channels of excited-state energy dissipation via the covalent and hydrogen bonds with the protein environment. The observed large dispersion of quenching timescales observed in the protein samples that contain the native pigment favors both an inhomogeneous model and an excited-state barrier for isomerization. PMID:15345563
Luo, Jin; Hu, Jiwei; Wei, Xionghui; Li, Lingyun; Huang, Xianfei
2015-01-01
This paper presents a density functional theory (DFT)/time-dependent DFT (TD-DFT) study on the lowest lying singlet and triplet excited states of 20 selected polybrominateddiphenyl ether (PBDE) congeners, with the solvation effect included in the calculations using the polarized continuum model (PCM). The results obtained showed that for most of the brominated diphenyl ether (BDE) congeners, the lowest singlet excited state was initiated by the electron transfer from HOMO to LUMO, involving a π–σ* excitation. In triplet excited states, structure of the BDE congeners differed notably from that of the BDE ground states with one of the specific C–Br bonds bending off the aromatic plane. In addition, the partial least squares regression (PLSR), principal component analysis-multiple linear regression analysis (PCA-MLR), and back propagation artificial neural network (BP-ANN) approaches were employed for a quantitative structure-property relationship (QSPR) study. Based on the previously reported kinetic data for the debromination by ultraviolet (UV) and sunlight, obtained QSPR models exhibited a reasonable evaluation of the photodebromination reactivity even when the BDE congeners had same degree of bromination, albeit different patterns of bromination. PMID:25569092
Hu, Weifeng; Chan, Garnet Kin-Lic
2015-07-14
We describe and extend the formalism of state-specific analytic density matrix renormalization group (DMRG) energy gradients, first used by Liu et al. [J. Chem. Theor. Comput. 2013, 9, 4462]. We introduce a DMRG wave function maximum overlap following technique to facilitate state-specific DMRG excited-state optimization. Using DMRG configuration interaction (DMRG-CI) gradients, we relax the low-lying singlet states of a series of trans-polyenes up to C20H22. Using the relaxed excited-state geometries, as well as correlation functions, we elucidate the exciton, soliton, and bimagnon ("single-fission") character of the excited states, and find evidence for a planar conical intersection. PMID:26575737
Yamaki, Masahiro; Teranishi, Yoshiaki; Nakamura, Hiroki; Lin, Sheng Hsien; Fujimura, Yuichi
2016-01-21
The electron angular momentum is a fundamental quantity of high-symmetry aromatic ring molecules and finds many applications in chemistry such as molecular spectroscopy. The stationary angular momentum or unidirectional rotation of π electrons is generated by the excitation of a degenerated electronic excited state by a circularly-polarized photon. For low-symmetry aromatic ring molecules having non-degenerate states, such as chiral aromatic ring molecules, on the other hand, whether stationary angular momentum can be generated or not is uncertain and has not been clarified so far. We have found by both theoretical treatments and quantum optimal control (QOC) simulations that a stationary angular momentum can be generated even from a low-symmetry aromatic ring molecule. The generation mechanism can be explained in terms of the creation of a dressed-state, and the maximum angular momentum is generated by the dressed state with an equal contribution from the relevant two excited states in a simple three-electronic state model. The dressed state is formed by inducing selective nonresonant transitions between the ground and each excited state by two lasers with the same frequency but having different polarization directions. The selective excitation can be carried out by arranging each photon-polarization vector orthogonal to the electronic transition moment of the other transition. We have successfully analyzed the results of the QOC simulations of (P)-2,2'-biphenol of axial chirality in terms of the analytically determined optimal laser fields. The present findings may open up new types of chemical dynamics and spectroscopy by utilizing strong stationary ring currents and current-induced magnetic fields, which are created at a local site of large compounds such as biomolecules. PMID:26670839
Weakly coupled molecular photonic wires: synthesis and excited-state energy-transfer dynamics.
Ambroise, Arounaguiry; Kirmaier, Christine; Wagner, Richard W; Loewe, Robert S; Bocian, David F; Holten, Dewey; Lindsey, Jonathan S
2002-05-31
Molecular photonic wires, which absorb light and undergo excited-state energy transfer, are of interest as biomimetic models for photosynthetic light-harvesting systems and as molecular devices with potential applications in materials chemistry. We describe the stepwise synthesis of four molecular photonic wires. Each wire consists of an input unit, transmission element, and output unit. The input unit consists of a boron-dipyrrin dye or a perylene-monoimide dye (linked either at the N-imide or the C9 position); the transmission element consists of one or three zinc porphyrins affording short or long wires, respectively; and the output unit consists of a free base (Fb) porphyrin. The components in the arrays are joined in a linear architecture via diarylethyne linkers (an ethynylphenyl linker is attached to the C9-linked perylene). The wires have been examined by static absorption, static fluorescence, and time-resolved absorption spectroscopy. Each wire (with the exception of the C9-linked perylene wire) exhibits a visible absorption spectrum that is the sum of the spectra of the component parts, indicating the relatively weak electronic coupling between the components. Excitation of each wire at the wavelength where the input unit absorbs preferentially (typically 480-520 nm) results in emission almost exclusively from the Fb porphyrin. The static emission and time-resolved data indicate that the overall rate constants and quantum efficiencies for end-to-end (i.e., input to output) energy transfer are as follows: perylene-(N-imide)-linked short wire, (33 ps)(-1) and >99%; perylene-(C9)-linked short wire, (26 ps)(-1) and >99%; boron-dipyrrin-based long wire, (190 ps)(-1) and 81%; perylene-(N-imide)-linked long wire, (175 ps)(-1) and 86%. Collectively, the studies provide valuable insight into the singlet-singlet excited-state energy-transfer properties in weakly coupled molecular photonic wires. PMID:12027698
NASA Astrophysics Data System (ADS)
Glukhov, I. L.; Nekipelov, E. A.; Ovsiannikov, V. D.
2010-06-01
New features of the blackbody-induced radiation processes on Rydberg atoms were discovered on the basis of numerical data for the blackbody-induced decay Pdnl(T), excitation Penl(T) and ionization Pionnl(T) rates of nS, nP and nD Rydberg states calculated together with the spontaneous decay rates Pspnl in neutral hydrogen, and singlet and triplet helium atoms for some values of the principal quantum number n from 10 to 500 at temperatures from T = 100 K to 2000 K. The fractional rates Rd(e, ion)nl(T) = Pnld(e, ion)(T)/Pspnl equal to the ratio of the induced decay (excitation, ionization) rates to the rate of spontaneous decay were determined as functions of T and n in every series of states with a given angular momentum l = 0, 1, 2. The calculated data reveal an essential difference between the asymptotic dependence of the ionization rate Pionnl(T) and the rates of decay and excitation Pd(e)nl(T)~T/n2. The departures appear in each Rydberg series for n > 100 and introduce appreciable corrections to the formula of Cooke and Gallagher. Two different approximation formulae are proposed on the basis of the numerical data, one for Rd(e)nl(T) and another one for Rionnl(T), which reproduce the calculated values in wide ranges of principal quantum number from n = 10 to 1000 and temperatures between T = 100 K and T = 2000 K with an accuracy of 2% or better. Modified Fues' model potential approach was used for calculating matrix elements of bound-bound and bound-free radiation transitions in helium.
Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite.
Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru
2016-08-01
When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons. PMID:27439874
Control of multiple excited Rydberg states around segmented carbon nanotubes
NASA Astrophysics Data System (ADS)
Schmelcher, Peter; Sadeghpour, Hossein; Knoerzer, Johannes; Fey, Christian
2016-05-01
Electronic image Rydberg states around segmented carbon nanotubes can be confined and shaped along the nanotube axis by engineering the image potential. We show how several such image states can be prepared simultaneously along the same nanotube. The inter-electronic distance can be controlled a priori by engineering tubes of specific geometries. High sensitivity to external electric and magnetic fields can be exploited to manipulate these states and their mutual long-range interactions. These building blocks provide access to a new kind of tailored long-range interacting quantum systems.
Control of multiple excited image states around segmented carbon nanotubes.
Knörzer, J; Fey, C; Sadeghpour, H R; Schmelcher, P
2015-11-28
Electronic image states around segmented carbon nanotubes can be confined and shaped along the nanotube axis by engineering the image potential. We show how several such image states can be prepared simultaneously along the same nanotube. The inter-electronic distance can be controlled a priori by engineering tubes of specific geometries. High sensitivity to external electric and magnetic fields can be exploited to manipulate these states and their mutual long-range interactions. These building blocks provide access to a new kind of tailored interacting quantum systems. PMID:26627961
Control of multiple excited image states around segmented carbon nanotubes
Knörzer, J. Fey, C.; Sadeghpour, H. R.; Schmelcher, P.
2015-11-28
Electronic image states around segmented carbon nanotubes can be confined and shaped along the nanotube axis by engineering the image potential. We show how several such image states can be prepared simultaneously along the same nanotube. The inter-electronic distance can be controlled a priori by engineering tubes of specific geometries. High sensitivity to external electric and magnetic fields can be exploited to manipulate these states and their mutual long-range interactions. These building blocks provide access to a new kind of tailored interacting quantum systems.
Niedzwiedzki, Dariusz; Kobayashi, Masayuki; Blankenship, R. E.
2011-01-13
Light-harvesting complex 2 from the anoxygenic phototrophic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption, fluorescence and flash photolysis spectroscopy. Steady-state absorption and fluorescence measurements show that carotenoids play a negligible role as supportive energy donors and transfer excitation to bacteriochlorophyll-a with low energy transfer efficiency of ~30%. HPLC analysis determined that the dominant carotenoids in the complex are rhodopin and spirilloxanthin. Carotenoid excited triplet state formation upon direct (carotenoid) or indirect (bacteriochlorophyll-a Q{sub x} band) excitation shows that carotenoid triplets are mostly localized on spirilloxanthin. In addition, no triplet excitation transfer between carotenoids was observed. Such specific carotenoid composition and spectroscopic results strongly suggest that this organism optimized carotenoid composition in the light-harvesting complex 2 in order to maximize photoprotective capabilities of carotenoids but subsequently drastically suppressed their supporting role in light-harvesting process.
Estévez-Fregoso, Mar; Hernández-Trujillo, Jesús
2016-04-28
The four lowest singlet electronic states of benzene, the acenes from naphthalene to pentacene, phenanthrene and pyrene were studied by means of theoretical methods. Their vertical excitation energies from the ground electronic states were computed at the CASPT2 approximation. As an attempt to explain the trends observed in the excitation energies, several descriptors based on the electron density were used and the similarity of these molecules with their ground state counterparts was analyzed. It was found that the changes of the topological properties at the C-C bond critical points do not explain the decreasing trends for the excitation energies with the increase of the number of rings, in part because the small changes that take place in the electron density occur above and below the molecular plane. A similarity index based on electron delocalization between quantum topological atoms was defined to compare a molecule in two different electronic states. It was found that, mainly for the acenes, this index goes in line with the excitation energies to the first excited state. Implications of the changes in electron delocalization on the aromatic character of these molecules are also discussed. In general, local aromaticity decreases upon excitation. PMID:26795361
NASA Astrophysics Data System (ADS)
Wurstbauer, U.; Levy, A. L.; Pinczuk, A.; West, K. W.; Pfeiffer, L. N.; Manfra, M. J.; Gardner, G. C.; Watson, J. D.
2015-12-01
We report the observation of low-lying collective charge and spin excitations in the second Landau level at ν =2 +1 /3 and also for the very fragile states at ν =2 +2 /5 and 2 +3 /8 in inelastic light scattering experiments. These modes exhibit a clear dependence on filling factor and temperature substantiating the unique access to the characteristic neutral excitation spectra of the incompressible fractional quantum Hall effect (FQHE) states. A detailed mode analysis reveals low-energy modes at around 70 μ eV and a sharp mode slightly below the Zeeman energy interpreted as gap and spin-wave excitation, respectively. The lowest-energy collective charge excitation spectrum at ν =2 +1 /3 exhibits significant qualitative similarities with its cousin state in the lowest Landau level at ν =1 /3 suggesting similar magnetoroton minima in the neutral excitations. The mode energies differ by a scaling of 0.15 indicating different interaction physics in the N =0 and N =1 Landau levels. The striking polarization dependence in elastic and inelastic light scattering is discussed in the framework of anisotropic electron phases that allow for the stabilization of nematic FQHE states. The observed excitation spectra provide new insights by accessing quantum phases in the bulk of electron systems and facilitate comparison with different theoretical descriptions of those enigmatic FQHE states.
Berghout, H. Laine; Crim, F. Fleming; Zyrianov, Mikhail; Reisler, Hanna
2000-04-15
The combination of vibrationally mediated photofragment yield spectroscopy, which excites molecules prepared in single vibrational states, and multiphoton fluorescence spectroscopy, which excites molecules cooled in a supersonic expansion, provides detailed information on the energetics and vibrational structure of the first excited singlet state (S{sub 1}) of isocyanic acid (HNCO). Dissociation of molecules prepared in individual vibrational states by stimulated Raman excitation probes vibrational levels near the origin of the electronically excited state. Detection of fluorescence from dissociation products formed by multiphoton excitation through S{sub 1} of molecules cooled in a supersonic expansion reveals the vibrational structure at higher energies. Both types of spectra show long, prominent progressions in the N-C-O bending vibration built on states with different amounts of N-C stretching excitation and H-N-C bending excitation. Analyzing the spectra locates the origin of the S{sub 1} state at 32 449{+-}20 cm{sup -1} and determines the harmonic vibrational frequencies of the N-C stretch ({omega}{sub 3}=1034{+-}20 cm{sup -1}), the H-N-C bend ({omega}{sub 4}=1192{+-}19 cm{sup -1}), and the N-C-O bend ({omega}{sub 5}=599{+-}7 cm{sup -1}), values that are consistent with several ab initio calculations. The assigned spectra strongly suggest that the N-C stretching vibration is a promoting mode for internal conversion from S{sub 1} to S{sub 0}. (c) 2000 American Institute of Physics.
Permanent Magnet Synchronous Condenser with Solid State Excitation: Preprint
Hsu, P.; Muljadi, E.; Wu, Z.; Gao, W.
2015-04-07
A typical synchronous condenser (SC) consists of a free-spinning, wound-field synchronous generator and a field excitation controller. In this paper, we propose an SC that employs a permanent magnet synchronous generator (PMSG) instead of a wound-field machine. PMSGs have the advantages of higher efficiency and reliability. In the proposed configuration, the reactive power control is achieved by a voltage converter controller connected in series to the PMSG. The controller varies the phase voltage of the PMSG and creates the same effect on the reactive power flow as that of an over- or underexcited wound-field machine. The controller’s output voltage magnitude controls the amount of the reactive power produced by the SC. The phase of the controller’s output is kept within a small variation from the grid voltage phase. This small phase variation is introduced so that a small amount of power can be drawn from the grid into the controller to maintain its DC bus voltage. Because the output voltage of the controller is only a fraction of the line voltage, its VA rating is only a fraction of the rating of the PMSG. The proposed scheme is shown to be effective by computer simulations.
Model Calibration of Exciter and PSS Using Extended Kalman Filter
Kalsi, Karanjit; Du, Pengwei; Huang, Zhenyu
2012-07-26
Power system modeling and controls continue to become more complex with the advent of smart grid technologies and large-scale deployment of renewable energy resources. As demonstrated in recent studies, inaccurate system models could lead to large-scale blackouts, thereby motivating the need for model calibration. Current methods of model calibration rely on manual tuning based on engineering experience, are time consuming and could yield inaccurate parameter estimates. In this paper, the Extended Kalman Filter (EKF) is used as a tool to calibrate exciter and Power System Stabilizer (PSS) models of a particular type of machine in the Western Electricity Coordinating Council (WECC). The EKF-based parameter estimation is a recursive prediction-correction process which uses the mismatch between simulation and measurement to adjust the model parameters at every time step. Numerical simulations using actual field test data demonstrate the effectiveness of the proposed approach in calibrating the parameters.
Modelling for a spatially peaked density distribution of excited ions in an ECR plasma presheath
NASA Astrophysics Data System (ADS)
Dimoff, K.; Gulick, S. L.; Stansfield, B. L.
1996-11-01
LIF and probe measurements have been made in an ECR plasma moving along a magnetic field towards an end plate placed at normal incidence to its flow (S.L. Gulick, B.L. Stansfield et al., J. Nucl. Mater., 176&177, 1059 (1990)). A marked difference in density distribution of excited (metastable) and ground state singly-ionized argon is found if we compare LIF and probe results. This suggests the various production and loss mechanisms (e.g. ionization, excitation, charge-exchange, etc.) may play a role in determining excited ion population levels differently from ground state ions. A 1D, isothermal model footnote K.-U. Riemann, J. Phys. D, 24, 493 (1991) is extended to simulate the excited, singly ionized argon as a separate fluid. Since major change over the plasma length appears to be velocity-driven, charge-exchange has been chosen as the first loss mechanism to be tested against ionization by electron impact. Preliminary calculations suggest the position of maximum excited ion density depends mainly on these two processes.
Han, Ruixue; Wang, Jiang; Yu, Haitao; Deng, Bin; Wei, Xilei; Qin, Yingmei; Wang, Haixu
2015-04-01
Reliable signal propagation across distributed brain areas is an essential requirement for cognitive function, and it has been investigated extensively in computational studies where feed-forward network (FFN) is taken as a generic model. But it is still unclear how distinct local network states, which are intrinsically generated by synaptic interactions within each layer, would affect the ability of FFN to transmit information. Here we investigate the impact of such network states on propagating transient synchrony (synfire) and firing rate by a combination of numerical simulations and analytical approach. Specifically, local network dynamics is attributed to the competition between excitatory and inhibitory neurons within each layer. Our results show that concomitant with different local network states, the performance of signal propagation differs dramatically. For both synfire propagation and firing rate propagation, there exists an optimal local excitability state, respectively, that optimizes the performance of signal propagation. Furthermore, we find that long-range connections strongly change the dependence of spiking activity propagation on local network state and propose that these two factors work jointly to determine information transmission across distributed networks. Finally, a simple mean field approach that bridges response properties of long-range connectivity and local subnetworks is utilized to reveal the underlying mechanism. PMID:25933656
NASA Astrophysics Data System (ADS)
Han, Ruixue; Wang, Jiang; Yu, Haitao; Deng, Bin; Wei, Xilei; Qin, Yingmei; Wang, Haixu
2015-04-01
Reliable signal propagation across distributed brain areas is an essential requirement for cognitive function, and it has been investigated extensively in computational studies where feed-forward network (FFN) is taken as a generic model. But it is still unclear how distinct local network states, which are intrinsically generated by synaptic interactions within each layer, would affect the ability of FFN to transmit information. Here we investigate the impact of such network states on propagating transient synchrony (synfire) and firing rate by a combination of numerical simulations and analytical approach. Specifically, local network dynamics is attributed to the competition between excitatory and inhibitory neurons within each layer. Our results show that concomitant with different local network states, the performance of signal propagation differs dramatically. For both synfire propagation and firing rate propagation, there exists an optimal local excitability state, respectively, that optimizes the performance of signal propagation. Furthermore, we find that long-range connections strongly change the dependence of spiking activity propagation on local network state and propose that these two factors work jointly to determine information transmission across distributed networks. Finally, a simple mean field approach that bridges response properties of long-range connectivity and local subnetworks is utilized to reveal the underlying mechanism.
Dallinger, R.F.; Farquharson, S.; Woodruff, W.H.; Rodgers, M.A.J.
1981-12-16
Resonance Raman and electronic absorption spectra are reported for the S/sub 0/ and T/sub 1/ states of the carotenoids ..beta..-carotene, zeaxanthin, echinenone, canthaxanthin, dihydroxylycopene, astaxanthin, decapreno(C/sub 50/)-..beta..-carotene, ..beta..-apo-8'-carotenal, and ethyl ..beta..-apo-8'-carotenoate. The results reveal qualitatively similar ground-state spectra and similar frequency shifts in all observed resonance Raman modes between S/sub 0/ and T/sub 1/, regardless of carotenoid structure. Examinations of the relationship of the putative C--C and C==C frequencies in S/sub 0/ and T/sub 1/ reveals anomalous shifts to lower frequency in the ''single-bond'' mode upon electronic excitation. These shifts may be due to molecular distortions in the excited state which force changes in molecular motions comprising the observed modes. However, another possibility requiring no distortion is that the interaction (off-diagonal) force constants connecting the C--C and C==C modes change sign upon electronic excitation. This latter phenomenon may provide a unitary explanation for the ''anomalous'' frequency shifts in the C--C and C==C modes, both in the T/sub 1/ states of carotenoids and in the S/sub 1/ states of simpler polyenes, without postulating large, unpredicted structural changes upon excitation or general errors in existing vibrational or theoretical analyses. Resonance Raman and absorbance studies with 35-ps time resolution suggest that S/sub 1/ lifetime (of the /sup 1/B/sub u/ and/or the /sup 1/A/sub g/* states) of ..beta..-carotene in benzene is less than 1 ps.
Lockard, J. V.; Kabehie, S.; Zink, J. I.; Smolentsev, G.; Soldatov, A.; Chen, L. X.
2010-01-01
This study explores the influences of steric hindrance and excited state solvent ligation on the excited state dynamics of Cu{sup I} diimine complexes. Ultrafast excited state dynamics of Cu(I)bis(3,8-di(ethynyltrityl)-1,10-phenanthroline) [Cu{sup I}(detp){sub 2}]{sup +} are measured using femtosecond transient absorption spectroscopy. The steady state electronic absorption spectra and measured lifetimes are compared to those of Cu(I)bis(1,10-phenanthroline), [Cu{sup I}(phen){sub 2}]{sup +}, and Cu(I)bis(2-9-dimethyl-1,10-phenanthroline), [Cu{sup I}(dmp){sub 2}]{sup +}, model complexes to determine the influence of different substitution patterns of the phenanthroline ligand on the structural dynamics associated with the metal to ligand charge transfer excited states. Similarities between the [Cu{sup I}(detp){sub 2}]{sup +} and [Cu{sup I}(phen){sub 2}]{sup +} excited state lifetimes were observed in both coordinating and noncoordinating solvents and attributed to the lack of steric hindrance from substitution at the 2- and 9-positions. The solution-phase X-ray absorption spectra of [Cu{sup I}(detp){sub 2}]{sup +}, [Cu{sup I}(phen){sub 2}]{sup +}, and [Cu{sup I}(dmp){sub 2}]{sup +} are reported along with finite difference method calculations that are used to determine the degree of ground state dihedral angle distortion in solution and to account for the pre-edge features observed in the XANES region.
Excited-State Dynamics of Isolated and Microsolvated Cinnamate-Based UV-B Sunscreens.
Tan, Eric M M; Hilbers, Michiel; Buma, Wybren J
2014-07-17
Sunscreens are aimed at providing protection from solar UV radiation. However, the same mechanism that underlies this protection (absorption of UV radiation) is also responsible for their light-induced adverse effects. Here, high-resolution spectroscopic methods are applied to one of the most commonly used sunscreen chromophores to study the excited-state dynamics that determine the delicate balance between favorable and adverse effects. In contrast to common belief, we find that excitation to the "bright" ππ* state does not directly lead to repopulation of the electronic ground state. Instead, internal conversion to another electronically excited state identified as the "dark" nπ* state is a major decay pathway that impedes fast energy dissipation. Microsolvation studies of sunscreen chromophores with water demonstrate that under such conditions, this bottleneck is no longer present. These observations could be a first step toward the development of sunscreens with improved photochemical properties. PMID:26277816
NASA Astrophysics Data System (ADS)
Kaur, R.; Anastasio, C.; Valsaraj, K. T.; Vempati, H. S.; Vaitilingom, M.
2014-12-01
Reactions in fog and cloud drops are important for a number of processes, such as formation of secondary organic aerosol (SOA), cycling of organic carbon and nitrogen, and determining the lifetimes of pollutants. The rates of these processes depend upon the steady-state concentrations of the major photooxidants, namely, hydroxyl radical (.OH), singlet molecular oxygen (1O2*) and triplet excited states of organic compounds (3C*). While there are some past measurements of .OH and 1O2* concentrations in fog and cloud drops, there are no data for the concentrations of triplet excited states. However, there is increasing evidence that triplets might be important for the processing of organics in a cloudy or foggy atmosphere. To address this question, we collected fog water samples from Davis, CA and Baton Rouge, LA, illuminated them with simulated sunlight, and measured the steady-state concentrations of .OH , 1O2* and 3C* . To understand the relative importance of these photooxidants, we also measured the photochemical loss of two added model organic compounds in the illuminated fog waters - syringol (a biomass burning phenol) and methyl jasmonate (a green leaf volatile). Our results show that triplet excited states can play a major role in oxidizing the model compounds, typically accounting for 30 - 90% of the loss of both model compounds. Given that atmospheric triplets are relatively less understood, our results highlight the importance of deeper investigation into their nature.
Xie, Hongqiang; Li, Guihua; Yao, Jinping; Chu, Wei; Li, Ziting; Zeng, Bin; Wang, Zhanshan; Cheng, Ya
2015-01-01
We report on generation of third harmonic from nitrogen molecules on the excited state with a weak driver laser pulse at a mid-infrared wavelength. The excited nitrogen molecules are generated using a circularly polarized intense femtosecond pulse which produces energetic electrons by photoionization to realize collisional excitation of nitrogen molecules. Furthermore, since the third harmonic is generated using a pump-probe scheme, it enables investigation of the excited-state dynamics of nitrogen molecules produced under different conditions. We also perform a comparative investigation in excited argon atoms, revealing different decay dynamics of the molecules and atoms from the excited states in femtosecond laser induced filaments. PMID:26522886
The excited spin-triplet state of a charged exciton in quantum dots.
Molas, M R; Nicolet, A A L; Piętka, B; Babiński, A; Potemski, M
2016-09-14
We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T = 4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes + electron excitonic complex. PMID:27391126
The excited spin-triplet state of a charged exciton in quantum dots
NASA Astrophysics Data System (ADS)
Molas, M. R.; Nicolet, A. A. L.; Piętka, B.; Babiński, A.; Potemski, M.
2016-09-01
We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T = 4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes + electron excitonic complex.
Ionization potential for excited S states of the lithium atom
Puchalski, M.; KePdziera, D.; Pachucki, K.
2010-12-15
Nonrelativistic, relativistic, quantum electrodynamic, and finite nuclear mass corrections to the energy levels are obtained for the nS{sub 1/2},n=3,...,9 states of the lithium atom. Computational approach is based on the explicitly correlated Hylleraas functions with the analytic integration and recursion relations. Theoretical predictions for the ionization potential of nS{sub 1/2} states and transition energies nS{sub 1/2{yields}}2S{sub 1/2} are compared to known experimental values for {sup 6,7}Li isotopes.
Coherent Excited States in Superconductors due to a Microwave Field.
Semenov, A V; Devyatov, I A; de Visser, P J; Klapwijk, T M
2016-07-22
We describe theoretically the depairing effect of a microwave field on diffusive s-wave superconductors. The ground state of the superconductor is altered qualitatively in analogy to the depairing due to a dc current. In contrast to dc depairing, the density of states acquires, for microwaves with frequency ω_{0}, steps at multiples of the photon energy Δ±nℏω_{0} and shows an exponential-like tail in the subgap regime. We show that this ac depairing explains the measured frequency shift of a superconducting resonator with microwave power at low temperatures. PMID:27494495
Green, Ori; Simkovitch, Ron; Pinto da Silva, Luís; Esteves da Silva, Joaquim C G; Shabat, Doron; Huppert, Dan
2016-08-11
Steady-state and time-resolved fluorescence techniques and theoretical calculations were employed to study the photoprotolytic properties of a newly synthesized photoacid 3-hydroxypyridine-dipicolinium cyanine (HPPC) dye. This dye is similar to quinone cyanine 9, which we have previously studied and is the strongest photoacid currently synthesized. In this compound, we found that several proton transfer phenomena occur after excitation. We found that the excited-state proton transfer (ESPT) rate in water is ultrafast with kPT ≈ 1.5 × 10(12) s(-1). In methanol and ethanol the rate is slower by about 5 and 6 times, respectively. The fluorescence spectrum of HPPC in water consists of three bands with maxima at 520, 600, and 665 nm, whereas in monols and other protic solvents the fluorescence spectrum consists only of two emission bands at 530 and ∼700 nm. We assign the emission bands of HPPC at 520 nm to the protonated form and the 700 nm band in monols and 665 nm in water to the deprotonated form. The 600 nm band that is the most intense band in the fluorescence spectrum of HPPC in water we assign to the tautomeric form in which the proton is attached to the pyridine's nitrogen atom. On the basis of density functional calculations, we suggest that in water the proton transfer process to the pyridine's nitrogen atom occurs in a stepwise manner via a two water molecule bridge. PMID:27434051
NASA Astrophysics Data System (ADS)
Mikhailov, Ivan A.; Tafur, Sergio; Masunov, Artëm E.
2008-01-01
The effect of static and dynamic electron correlation on the nature of excited states and state-to-state transition dipole moments is studied with a multideterminant wave function approach on the example of all-trans linear polyenes ( C4H6 , C6H8 , and C8H10 ). Symmetry-forbidden singlet nAg states were found to separate into three groups: purely single, mostly single, and mostly double excitations. The excited-state absorption spectrum is dominated by two bright transitions: 1Bu-2Ag and 1Bu-mAg , where mAg is the state, corresponding to two-electron excitation from the highest occupied to lowest unoccupied molecular orbital. The richness of the excited-state absorption spectra and strong mixing of the doubly excited determinants into lower- nAg states, reported previously at the complete active space self-consistent field level of theory, were found to be an artifact of the smaller active space, limited to π orbitals. When dynamic σ-π correlation is taken into account, single- and double-excited states become relatively well separated at least at the equilibrium geometry of the ground state. This electronic structure is closely reproduced within time-dependent density-functional theory (TD DFT), where double excitations appear in a second-order coupled electronic oscillator formalism and do not mix with the single excitations obtained within the linear response. An extension of TD DFT is proposed, where the Tamm-Dancoff approximation (TDA) is invoked after the linear response equations are solved (a posteriori TDA). The numerical performance of this extension is validated against multideterminant-wave-function and quadratic-response TD DFT results. It is recommended for use with a sum-over-states approach to predict the nonlinear optical properties of conjugated molecules.
NASA Astrophysics Data System (ADS)
Guadarrama, Patricia; Terán, Gerardo; Ramos, Estrella; Gutiérrez, Jorge; Hernández, Madelyn
2015-04-01
The synthesis of novel highly delocalized push-pull dendrons is described. A modified protocol to conventional Csbnd C coupling reaction was used with moderate yields. The excited state dipole moments of synthesized dendrons were estimated by the solvatochromic model using the ETN polarity scale. In case of dendron of second generation with donor-acceptor groups, values around 23 D are obtained, denoting an efficient charge separation crucial in photovoltaic processes. From the theoretical analysis, there is a clear evidence of highly efficient electron delocalization in case of push-pull dendrons. The chosen theoretical model (M05-2X/cc-pVDZ) to describe the electronic behavior of the molecules under study was very precise in the estimation of dipole moments in excited state, with differences of 0.5-2.2 D, compared with the values obtained by the solvatochromic model.
Redox effects on the excited-state lifetime in chlorosomes and bacteriochlorophyll c oligomers.
van Noort, P I; Zhu, Y; LoBrutto, R; Blankenship, R E
1997-01-01
Oligomers of [E,E] BChl CF (8, 12-diethyl bacteriochlorophyll c esterified with farnesol (F)) and [Pr,E] BChl CF (analogously, M methyl, Pr propyl) in hexane and aqueous detergent or lipid micelles were studied by means of steady-state absorption, time-resolved fluorescence, and electron spin resonance spectroscopy. The maximum absorption wavelength, excited-state dynamics, and electron spin resonance (EPR) linewidths are similar to those of native and reconstituted chlorosomes of Chlorobium tepidum. The maximum absorption wavelength of oligomers of [E,E] BChl CF was consistently blue-shifted as compared to that of [Pr,E] BChl CF oligomers, which is ascribed to the formation of smaller oligomers with [E,E] BChl CF than [Pr,E] BChl CF. Time-resolved fluorescence measurements show an excited-state lifetime of 10 ps or less in nonreduced samples of native and reconstituted chlorosomes of Chlorobium tepidum. Under reduced conditions the excited-state lifetime increased to tens of picoseconds, and energy transfer to BChl a or long-wavelength absorbing BChl c was observed. Oligomers of [E,E] BChl CF and [Pr,E] BChl CF in aqueous detergent or lipid micelles show a similar short excited-state lifetime under nonreduced conditions and an increase up to several tens of picoseconds upon reduction. These results indicate rapid quenching of excitation energy in nonreduced samples of chlorosomes and aqueous BChl c oligomers. EPR spectroscopy shows that traces of oxidized BChl c radicals are present in nonreduced and absent in reduced samples of chlorosomes and BChl c oligomers. This suggests that the observed short excited-state lifetimes in nonreduced samples of chlorosomes and BChl c oligomers may be ascribed to excited-state quenching by BChl c radicals. The narrow EPR linewidth suggests that the BChl c are arranged in clusters of 16 and 6 molecules in chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, respectively. PMID:8994616
Halo or skin in the excited states of some light mirror nuclei
NASA Astrophysics Data System (ADS)
Chen, J. G.; Cai, X. Z.; Shen, W. Q.; Ma, Y. G.; Ren, Z. Z.; Zhang, H. Y.; Jiang, W. Z.; Zhong, C.; Wei, Y. B.; Guo, W.; Zhou, X. F.; Wang, K.; Ma, G. L.
2005-01-01
The properties of three pairs of mirror nuclei 13N- 13C, 15N- 15O and 21Na- 21Ne (these mirror nuclei are all made of a good inert core plus an unpaired valence nucleon) are investigated by using the nonlinear relativistic mean-field (RMF) theory. It is found that the calculated binding energies with two different parameter sets are very close to the experimental ones for both the ground states and the excited states except for the large deformed nuclei. The calculations show that the 2 s1/2 excited states of 15N and of 21Na are both weakly bound with a proton halo and a proton skin (or a pigmy proton skin), respectively. In addition, the 1 d5/2 excited state of 13C and the 2 s1/2 excited state of 15O are also weakly bound with a neutron skin, respectively. The ratio of the valence nucleon radius to matter radius is deduced and it can be regarded as an additional criterion for the existence of exotic structure. The unbound 2 s1/2 and 1 d5/2 excited states of 13N are also discussed.
NASA Astrophysics Data System (ADS)
Kita, Yukiumi; Tachikawa, Masanori
2014-05-01
We theoretically analyzed positron affinities (PA) of hydrogen cyanide (HCN) molecule at vibrational excited states to elucidate the effect of molecular vibrations on the binding of a positron to the molecule. Using the configuration interaction method in the multi-component molecular orbital theory and anharmonic vibrational state analysis with the variational Monte Carlo technique, we found that the vibrational excitations of the CN and CH stretching modes enhance the PA value compared to that of the vibrational ground state, whereas the excitation of bending mode deenhances it. The largest PA enhancement is found at the excited states of the CH stretching mode; the PA values are 43.02 (1) and 46.34 (2) meV for the fundamental tone and overtone states, respectively. With the linear regression analysis, we confirmed that the PA variation of HCN molecule at each vibrational state arises from the variation of permanent dipole moment and dipole-polarizability due to each vibrational excitation. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.
Skonieczny, Kamil; Yoo, Jaeduk; Larsen, Jillian M; Espinoza, Eli M; Barbasiewicz, Michał; Vullev, Valentine I; Lee, Chang-Hee; Gryko, Daniel T
2016-05-23
Photoinduced intramolecular direct arylation allows structurally unique compounds containing phenanthro[9',10':4,5]imidazo[1,2-f]phenanthridine and imidazo[1,2-f]phenanthridine skeletons, which mediate excited-state intramolecular proton transfer (ESIPT), to be efficiently synthesized. The developed polycyclic aromatics demonstrate that the combination of five-membered ring structures with a rigid arrangement between a proton donor and a proton acceptor provides a means for attaining large fluorescence quantum yields, exceeding 0.5, even in protic solvents. Steady-state and time-resolved UV/Vis spectroscopy reveals that, upon photoexcitation, the prepared protic heteroaromatics undergo ESIPT, converting them efficiently into their excited-state keto tautomers, which have lifetimes ranging from about 5 to 10 ns. The rigidity of their structures, which suppresses nonradiative decay pathways, is believed to be the underlying reason for the nanosecond lifetimes of these singlet excited states and the observed high fluorescence quantum yields. Hydrogen bonding with protic solvents does not interfere with the excited-state dynamics and, as a result, there is no difference between the occurrences of ESIPT processes in MeOH versus cyclohexane. Acidic media has a more dramatic effect on suppressing ESIPT by protonating the proton acceptor. As a result, in the presence of an acid, a larger proportion of the fluorescence of ESIPT-capable compounds originates from their enol excited states. PMID:27062363
Fast excited state dynamics in the isolated 7-azaindole-phenol H-bonded complex
NASA Astrophysics Data System (ADS)
Capello, Marcela C.; Broquier, Michel; Dedonder-Lardeux, Claude; Jouvet, Christophe; Pino, Gustavo A.
2013-02-01
The excited state dynamics of the H-bonded 7-azaindole-phenol complex (7AI-PhOH) has been studied by combination of picosecond pump and probe experiments, LIF measurements on the nanosecond time scale and ab initio calculations. A very short S1 excited state lifetime (30 ps) has been measured for the complex upon excitation of the 0_0^0 transition and the lifetime remains unchanged when the ν6 vibrational mode (0_0^0 + 127 cm-1) is excited. In addition, no UV-visible fluorescence was observed by exciting the complex with nanosecond pulses. Two possible deactivation channels have been investigated by ab initio calculations: first an excited state tautomerization assisted by a concerted double proton transfer (CDPT) and second an excited state concerted proton electron transfer (CPET) that leads to the formation of a radical pair (hydrogenated 7AIH• radical and phenoxy PhO• radical). Both channels, CDPT and CPET, seem to be opened according to the ab initio calculations. However, the analysis of the ensemble of experimental and theoretical evidence indicates that the excited state tautomerization assisted by CDPT is quite unlikely to be responsible for the fast S1 state deactivation. In contrast, the CPET mechanism is suggested to be the non-radiative process deactivating the S1 state of the complex. In this mechanism, the lengthening of the OH distance of the PhOH molecule induces an electron transfer from PhOH to 7AI that is followed by a proton transfer in the same kinetic step. This process leads to the formation of the radical pair (7AIH•ṡṡṡPhO•) in the electronically excited state through a very low barrier or to the ion pair (7AIH+ṡṡṡPhO-) in the ground state. Moreover, it should be noted that, according to the calculations the πσ* state, which is responsible for the H loss in the free PhOH molecule, does not seem to be involved at all in the quenching process of the 7AI-PhOH complex.
Excited state structural dynamics in higher lying electronic states: S2 state of malachite green
NASA Astrophysics Data System (ADS)
Laptenok, Sergey P.; Addison, Kiri; Heisler, Ismael A.; Meech, Stephen R.
2014-06-01
The S2 fluorescence of malachite green is measured with sub 100 fs time resolution. Ultrafast spectral dynamics in the S2 state preceding S2 decay are resolved. Measurements in different solvents show that these sub 100 fs dynamics are insensitive to medium polarity and viscosity. They are thus assigned to ultrafast structural evolution between the S2 Franck-Condon and equilibrium configurations.
A model of excitation and adaptation in bacterial chemotaxis.
Hauri, D C; Ross, J
1995-01-01
We present a model of the chemotactic mechanism of Escherichia coli that exhibits both initial excitation and eventual complete adaptation to any and all levels of stimulus ("exact" adaptation). In setting up the reaction network, we use only known interactions and experimentally determined cytosolic concentrations. Whenever possible, rate coefficients are first assigned experimentally measured values; second, we permit some variation in these rate coefficients by using a multiple-well optimization technique and incremental adjustment to obtain values that are sufficient to engender initial response to stimuli (excitation) and an eventual return of behavior to baseline (adaptation). The predictions of the model are similar to the observed behavior of wild-type bacteria in regard to the time scale of excitation in the presence of both attractant and repellent. The model predicts a weaker response to attractant than that observed experimentally, and the time scale of adaptation does not depend as strongly upon stimulant concentration as does that for wild-type bacteria. The mechanism responsible for long-term adaptation is local rather than global: on addition of a repellent or attractant, the receptor types not sensitive to that attractant or repellent do not change their average methylation level in the long term, although transient changes do occur. By carrying out a phenomenological simulation of bacterial chemotaxis, we find that the model is insufficiently sensitive to effect taxis in a gradient of attractant. However, by arbitrarily increasing the sensitivity of the motor to the tumble effector (phosphorylated CheY), we can obtain chemotactic behavior. Images FIGURE 6 FIGURE 7 PMID:7696522
Millimeter- and submillimeter-wave spectrum of highly excited states of water
NASA Astrophysics Data System (ADS)
Pearson, J. C.; De Lucia, Frank C.; Anderson, Todd; Herbst, Eric; Helminger, Paul
1991-09-01
To facilitate studies of water in the interstellar medium and late-type stars, the frequencies of 30 new millimeter- and submillimeter-wave transitions of H2O-16 have been measured, which lie between 100 GHz and 600 GHz. This represents almost a doubling of the number of water lines that have been observed in the laboratory in this spectral region at high resolution. All of the newly observed lines are highly excited, lying between 2400 and 4200/cm above the ground level. Some of these have large excitation energies because of their high rotational states and others because they lie in excited vibrational states. These lines are potentially of substantial astrophysical significance because they are related to the study of interstellar masers and because their high excitation eliminates the atmospheric self-absorption associated with the more well-known water lines.
Lifetime measurement of excited low-spin states via the (p, p‧ γ) reaction
NASA Astrophysics Data System (ADS)
Hennig, A.; Derya, V.; Mineva, M. N.; Petkov, P.; Pickstone, S. G.; Spieker, M.; Zilges, A.
2015-09-01
In this paper a method for lifetime measurements in the sub-picosecond regime via the Doppler-shift attenuation method (DSAM) following the inelastic proton scattering reaction is presented. In a pioneering experiment we extracted the lifetimes of 30 excited low-spin states of 96Ru, taking advantage of the coincident detection of scattered protons and de-exciting γ-rays as well as the large number of particle and γ-ray detectors provided by the SONIC@HORUS setup at the University of Cologne. The large amount of new experimental data shows that this technique is suited for the measurement of lifetimes of excited low-spin states, especially for isotopes with a low isotopic abundance, where (n ,n‧ γ) or - in case of investigating dipole excitations - (γ ,γ‧) experiments are not feasible due to the lack of sufficient isotopically enriched target material.
First-Principles Studies of the Excited States of Chromophore Monomers and Dimers
NASA Astrophysics Data System (ADS)
Hamed, Samia; Sharifzadeh, Sahar; Neaton, Jeffrey
2015-03-01
Elucidation of the energy transfer mechanism in natural photosynthetic systems remains an exciting challenge. Through the careful analysis of excited states on individual chromophores and dimers - and the predictive first-principles methods used to compute them - we are building towards an understanding of the nature of excitation transfer among arrays of chromophores embedded in protein environments. Excitation energies, transition dipoles, and natural transition orbitals for the important low-lying singlet and triplet states of experimentally-relevant chromophores are obtained from first-principles time-dependent density functional theory (TDDFT) and many body perturbation theory. The effect of the Tamm-Dancoff approximation and the performance of several exchange-correlation functionals, including an optimally-tuned range-separated hybrid, are evaluated with TDDFT, and compared to MBPT calculations and experiments. This work has been supported by the DOE; computational resources have been provided by NERSC.
Bjorgaard, J A; Velizhanin, K A; Tretiak, S
2016-04-21
The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited statemolecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited statemolecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission. PMID:27389206
Inflection, canards and excitability threshold in neuronal models.
Desroches, M; Krupa, M; Rodrigues, S
2013-10-01
A technique is presented, based on the differential geometry of planar curves, to evaluate the excitability threshold of neuronal models. The aim is to determine regions of the phase plane where solutions to the model equations have zero local curvature, thereby defining a zero-curvature (inflection) set that discerns between sub-threshold and spiking electrical activity. This transition can arise through a Hopf bifurcation, via the so-called canard explosion that happens in an exponentially small parameter variation, and this is typical for a large class of planar neuronal models (FitzHugh-Nagumo, reduced Hodgkin-Huxley), namely, type II neurons (resonators). This transition can also correspond to the crossing of the stable manifold of a saddle equilibrium, in the case of type I neurons (integrators). We compute inflection sets and study how well they approximate the excitability threshold of these neuron models, that is, both in the canard and in the non-canard regime, using tools from invariant manifold theory and singularity theory. With the latter, we investigate the topological changes that inflection sets undergo upon parameter variation. Finally, we show that the concept of inflection set gives a good approximation of the threshold in both the so-called resonator and integrator neuronal cases. PMID:22945512
Differential cross sections for electron-impact excitation of the electronic states of N sub 2
Brunger, M.J.; Teubner, P.J.O. )
1990-02-01
Differential cross sections for the electron-impact excitation of the first ten electronic states of N{sub 2} have been determined at five incident energies ranging from 15 to 50 eV. These differential cross sections were obtained for the scattering range 10{degree}--90{degree} by analyzing electron-energy-loss spectra in N{sub 2} at a number of fixed scattering angles within that range. The present study represents a comprehensive remeasurement of the earlier work of Cartwright and co-workers (Phys. Rev. A 16, 1013 (1977)) and was undertaken with a view to resolving certain anomalies which have been reported in the literature when the earlier cross-section set has been applied to model calculations of swarm parameters.
Analysis of excited-state Faraday anomalous dispersion optical filter at 1529 nm.
Xiong, Junyu; Yin, Longfei; Luo, Bin; Guo, Hong
2016-06-27
In this work, a detailed theoretical analysis of 1529 nm ES-FADOF (excited state Faraday anomalous dispersion optical filter) based on rubidium atoms pumped by 780 nm laser is introduced, where Zeeman splitting, Doppler broadening, and relaxation processes are considered. Experimental results are carefully compared with the derivation. The results prove that the optimal pumping frequency is affected by the working magnetic field. The population distribution among all hyperfine Zeeman sublevels under the optimal pumping frequency has also been obtained, which shows that ^{85}Rb atoms are the main contribution to the population. The peak transmittance above 90% is obtained, which is in accordance with the experiment. The calculation also shows that the asymmetric spectra observed in the experiment are caused by the unbalanced population distribution among Zeeman sublevels. This theoretical model can be used for all kinds of calculations for FADOF. PMID:27410643
NASA Astrophysics Data System (ADS)
Cui, Yanling; Li, Yafei; Dai, Yumei; Verpoort, Francis; Song, Peng; Xia, Lixin
2016-02-01
In the present work, TDDFT has been used to investigate the excited state intramolecular proton transfer (ESIPT) mechanism of a new chromophore II [Sensors and Actuators B: Chemical. 202 (2014) 1190]. The calculated absorption and fluorescence spectra agree well with experimental results. In addition, two types of II configurations are found in the first excited state (S1), which can be ascribed to the ESIPT reaction. Based on analysis of the calculated infrared (IR) spectra of O-H stretching vibration as well as the hydrogen bonding energies, the strengthening of the hydrogen bond in the S1 state has been confirmed. The frontier molecular orbitals (MOs), Hirshfeld charge distribution and the Natural bond orbital (NBO) have also been analyzed, which displays the tendency of the ESIPT process. Finally, potential energy curves of the S0 and S1 states were constructed, demonstrating that the ESIPT reaction can be facilitated based on the photo-excitation.
Excited state population of a 3D transmon in thermal equilibrium
NASA Astrophysics Data System (ADS)
Jin, X. Y.; Gustavsson, S.; Kamal, A.; Sears, A. P.; Gudmundsen, T.; Hover, D.; Kerman, A. J.; Yan, F.; Yoder, J.; Orlando, T. P.; Oliver, W. D.
2014-03-01
We present a systematic study of the excited state population of a 3D transmon qubit at various temperatures. We experimentally demonstrate that the population of the first excited state follows the Maxwell-Boltzmann distribution in the temperature range of 35-150 mK. For bath temperatures below 35 mK, the excited-state population saturates, with an upper-bound estimate of 0.1%. The saturation suggests a qubit effective temperature of approximately 35 mK. The Lincoln Laboratory portion of this work was sponsored by the Assistant Secretary of Defense for Research & Engineering under Air Force Contract number FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the United States Government.
Excited-state transient of vanadyl uroporphyrin I detected by resonance Raman spectroscopy
Alden, R.G.; Sparks, L.D.; Ondrias, M.R. ); Crawford, B.A.; Shelnutt, J.A. )
1990-02-22
Transient Raman spectroscopy has been used to investigate excited states of vanadyl uroporphyrin I (VOUroP) in both monomeric and dimeric forms. Uroporphyrins are water-soluble porphyrins with propionic and acetic acid groups substituted at the {beta}-pyrrole carbon positions. Monomeric VOUroP in aqueous solution is known to be six-coordinate with a ligand trans to the oxo ligand. Upon dimerization, the sixth ligand site is inaccessible, and a five-coordinate species is observed. At high laser fluence, an excited-state transient is formed in the monomeric species. Raman spectra of this species are most consistent with an {sup 2}A{sub 1u} (a{sub 1u}({pi}) {yields} d{sub xy}) charge-transfer state. In contrast, dimeric VOUroP shows little evidence of an excited state in the transient Raman spectra during a 10-ns laser pulse.
Perturbed wavefunctions of the excited states of hydrogen atom in Stark effect
Sapra, G.K.; Bhasin, V.S.; Kothari, L.S. . Dept. of Physics Astrophysics)
1994-03-15
The authors extend the procedure originally suggested by Dalgarno and Lewis in studying the second-order Stark effect for the ground-state hydrogen atom to the excited states. They solve the perturbation equations for the excited states of hydrogen atom placed in an external electric field to obtain expressions for the perturbed wavefunctions. Here the emphasis is on studying in detail the nature of the perturbed wavefunction rather than energy shifts as investigated in most of the attempts made so far. The effect of the electric field on these wavefunctions is analyzed and the values of the electric polarizability of the hydrogen atom in the excited states obtained in this way are compared with the earlier work.
Excited States In 7He From d(6He,p)7He
Wuosmaa, A.H.; Rehm, K.E.; Greene, J.P.; Henderson, D.J.; Janssens, R.V.F.; Jiang, C.L.; Moore, E.F.; Pardo, R.C.; Peterson, D.; Pieper, S.C.; Savard, G.; Schiffer, J.P.; Sinha, S.; Tang, X.; Wiringa, R.B.; Jisonna, L.; Segel, R.E.
2005-04-05
We have studied the properties of low-lying levels in 7He using the d(6He,p)7He reaction. Recent measurements of 8He breakup and the p(8He,d)7He reaction present conflicting results on 7He first excited state A broad resonance observed in the present work at E{sub X} = 2.2{sub -0.1}{sup +0.2} MeV is identified with the expected 1/2- spin-orbit partner to the 7He ground state. No evidence is seen of a lower first-excited state that was recently reported.
Obaid, Rana; Kinzel, Daniel; Oppel, Markus González, Leticia
2014-10-28
Despite the concept of nuclear spin isomers (NSIs) exists since the early days of quantum mechanics, only few approaches have been suggested to separate different NSIs. Here, a method is proposed to discriminate different NSIs of a quinodimethane derivative using its electronic excited state dynamics. After electronic excitation by a laser field with femtosecond time duration, a difference in the behavior of several quantum mechanical operators can be observed. A pump-probe experimental approach for separating these different NSIs is then proposed.
Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure
Valone, S. M.; Pilania, G.; Liu, X. Y.; Allen, J. R.; Wu, T.-C.; Atlas, S. R.; Dunlap, D. H.
2015-11-14
Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) model uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transfer hopping integrals T and on-fragment parameters U{sup (FH)}. The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. We demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U{sup (FH)}, thus providing new insight into the nature of metal-insulator transitions. This result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.
Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure
NASA Astrophysics Data System (ADS)
Valone, S. M.; Pilania, G.; Liu, X. Y.; Allen, J. R.; Wu, T.-C.; Atlas, S. R.; Dunlap, D. H.
2015-11-01
Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) model uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transfer hopping integrals T and on-fragment parameters U(FH). The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. We demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U(FH), thus providing new insight into the nature of metal-insulator transitions. This result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.
Simple models for excitable and oscillatory neural networks.
Taylor, D; Holmes, P
1998-11-01
Chains of coupled oscillators of simple "rotator" type have been used to model the central pattern generator (CPG) for locomotion in lamprey, among numerous applications in biology and elsewhere. In this paper, motivated by experiments on lamprey CPG with brainstem attached, we investigate a simple oscillator model with internal structure which captures both excitable and bursting dynamics. This model, and that for the coupling functions, is inspired by the Hodgkin-Huxley equations and two-variable simplifications thereof. We analyse pairs of coupled oscillators with both excitatory and inhibitory coupling. We also study traveling wave patterns arising from chains of oscillators, including simulations of "body shapes" generated by a double chain of oscillators providing input to a kinematic musculature model of lamprey. PMID:9836466
Excited-State Dynamics in 6-THIOGUANOSINE from Femtosecond to Microsecond Time Scale
NASA Astrophysics Data System (ADS)
Guo, Cao; Reichardt, Christian; Crespo-Hernández, Carlos E.
2011-06-01
6-thioguanine is a widely used pro-drug in which the oxygen atom in the carbonyl group of guanine is replaced by a sulfur atom. Previous studies have shown that patients treated with 6-thioguanine can metabolize and incorporate it in DNA as 6-thioguanosine (6tGuo). These patients show a high incidence of skin cancer when they are exposed to extended periods of sunlight irradiation. In this work, the photodynamics of 6tGuo is investigated by broad band time resolved transient spectroscopy. Similar to previously studied 4-thiothymidine, our results show that excitation of 6tGuo with UVA light at 340 nm results in efficient and ultrafast intersystem crossing to the triplet manifold (τ = 0.31±0.05 ps) and a high triplet quantum yield (φ = 0.8±0.2). The triplet state has a lifetime of 720±10 ns in N2-saturated vs. 460±10 ns in air-saturated aqueous solution. In addition, a minor picosecond deactivation channel (80±15 ps) is observed, which is tentatively assigned to internal conversion from the lowest-energy excited singlet state to the ground state. Quantum chemical calculations support the proposed kinetic model. Based on the high triplet quantum yield measured, it is proposed that the phototoxicity of 6tGuo is due to its ability to photosensitized singlet oxygen, which can result in oxidative damage to DNA. P. O'Donovan, C. M. Perrett, X. Zhang, B. Montaner, Y.-Z. Xu, C. A. Harwood, J. M. McGregor, S. L. Walker, F. Hanaoka, P. Karran, Science 309, 1871 (2005). C. Reichardt, C. Guo, C. E. Crespo-Hernández, J. Phys. Chem. B. in press (2011). C. Reichardt, C. E. Crespo-Hernández, J. Phys. Chem. Lett. 1, 2239 (2010) C. Reichardt, C. E. Crespo-Hernández, Chem. Comm. 46, 5963 (2010).
Dubovichenko, S. B.
2013-10-15
Radiative capture of a neutron to the ground and excited states of the 9Be nucleus is considered using the potential cluster model with forbidden states and with classification of cluster states by the Young schemes taking into account resonance at 622 keV for thermal and astrophysical energies.
Application of the Feynman-Kac Method to Find the Excited States of Quantum Systems
NASA Astrophysics Data System (ADS)
Rejcek, James Michael
1995-01-01
Exact and numerical calculations using the Feynman -Kac integral method to find the ground state of several atomic systems including hydrogen, the harmonic and infinite square wells are presented. In addition, the first few excited states are calculated applying group theory to known symmetries in order to find wave nodes of the Hamiltonian. Statistical uncertainty and the use of failure trees are also introduced.
Excitation of exciton states on a curved surface
NASA Astrophysics Data System (ADS)
Silotia, Poonam; Prasad, Vinod
2016-05-01
Excitonic transitions on the surface of a sphere have been studied in he presence of external static electric and laser fields. The spectrum and the various coupling matrix elements, <ψl,m | cosn ϑ |ψl‧,m‧ > (for n = 1 , 2 , 3), between few states of exciton have been evaluated in the absence and presence of excitonic Coulombic interaction with different values of dielectric constant. Variation of various physical quantities: energy eigenvalues, transition probability, orientational and alignment parameter, has been shown to have strong dependence on the laser field and static electric field.
Shin, Hee Won; Ocola, Esther J.; Laane, Jaan; Kim, Sunghwan
2014-01-21
The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S{sub 1}(π,π{sup *}) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S{sub 0} and S{sub 1}(π,π{sup *}) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S{sub 0} and S{sub 1}(π,π{sup *}) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S{sub 1}(π,π{sup *}) excited state.
ERIC Educational Resources Information Center
Bandyopadhyay, Subhajit; Roy, Saswata
2014-01-01
This paper describes an inexpensive experiment to determine the carbonyl stretching frequency of an organic keto compound in its ground state and first electronic excited state. The experiment is simple to execute, clarifies some of the fundamental concepts of spectroscopy, and is appropriate for a basic spectroscopy laboratory course. The…
Ultrafast Dynamics of 1,3-Cyclohexadiene in Highly Excited States
Bühler, Christine C.; Minitti, Michael P.; Deb, Sanghamitra; Bao, Jie; Weber, Peter M.
2011-01-01
The ultrafast dynamics of 1,3-cyclohexadiene has been investigated via structurally sensitive Rydberg electron binding energies and shown to differ upon excitation to the 1B state and the 3p Rydberg state. Excitation of the molecule with 4.63 eV photons into the ultrashort-lived 1B state yields the well-known ring opening to 1,3,5-hexatriene, while a 5.99 eV photon lifts the molecule directly into the 3p-Rydberg state. Excitation to 3p does not induce ring opening. In both experiments, time-dependent shifts of the Rydberg electron binding energy reflect the structural dynamics of the molecular core. Structural distortions associated with 3p-excitation cause a dynamical shift in the -more » and -binding energies by 10 and 26 meV/ps, respectively, whereas after excitation into 1B, more severe structural transformations along the ring-opening coordinate produce shifts at a rate of 40 to 60 meV/ps. The experiment validates photoionization-photoelectron spectroscopy via Rydberg states as a powerful technique to observe structural dynamics of polyatomic molecules.« less
Energy Dispersive XAFS: Characterization of Electronically Excited States of Copper(I) Complexes
2013-01-01
Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of [Cu(dmp)2]+ (dmp =2,9-dimethyl-1,10-phenanthroline) and [Cu(dbtmp)2]+ (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns. DFT calculations of the longer lived MLCT excited state of [Cu(dbp)2]+ (dbp =2,9-di-n-butyl-1,10-phenanthroline) with the bulkier diimine ligands, indicated that the excited state behaves as a Jahn–Teller distorted Cu(II) site, with the interligand dihedral angle changing from 83 to 60° as the tetrahedral coordination geometry flattens and a reduction in the Cu–N distance of 0.03 Å. PMID:23718738
Knoll, Jessica D.; Turro, Claudia
2015-01-01
The use of visible light to produce highly selective and potent drugs through photodynamic therapy (PDT) holds much potential in the treatment of cancer. PDT agents can be designed to follow an O2-dependent mechanism by producing highly reactive species such as 1O2 and/or an O2 independent mechanism through processes such as excited state electron transfer, covalent binding to DNA or photoinduced drug delivery. Ru(II)-polypyridyl and Rh2(II,II) complexes represent an important class of compounds that can be tailored to exhibit desired photophysical properties and photochemical reactivity by judicious selection of the ligand set. Complexes with relatively long-lived excited states and planar, intercalating ligands localize on the DNA strand and photocleave DNA through 1O2 production or guanine oxidation by the excited state of the chromophore. Photoinduced ligand substitution occurs through the population of triplet metal centered (3MC) excited states and facilitates covalent binding of the metal complex to DNA in a mode similar to cisplatin. Ligand photodissociation also provides a route to selective drug delivery. The ability to construct metal complexes with desired light absorbing and excited state properties by ligand variation enables the design of PDT agents that can potentially provide combination therapy from a single metal complex. PMID:25729089
Electronically Excited States of Anisotropically Extended Singly-Deprotonated PAH Anions.
Theis, Mallory L; Candian, Alessandra; Tielens, Alexander G G M; Lee, Timothy J; Fortenberry, Ryan C
2015-12-31
Polycyclic aromatic hydrocarbons (PAHs) play a significant role in the chemistry of the interstellar medium (ISM) as well as in hydrocarbon combustion. These molecules can have high levels of diversity with the inclusion of heteroatoms and the addition or removal of hydrogens to form charged or radical species. There is an abundance of data on the cationic forms of these molecules, but there have been many fewer studies on the anionic species. The present study focuses on the anionic forms of deprotonated PAHs. It has been shown in previous work that PAHs containing nitrogen heteroatoms (PANHs) have the ability to form valence excited states giving anions electronic absorption features. This work analyzes how the isoelectronic pure PAHs behave under similar structural constructions. Singly deprotonated forms of benzene, naphthalene, anthracene, and tetracene classes are examined. None of the neutral-radicals possess dipole moments large enough to support dipole-bound excited states in their corresponding closed-shell anions. Even though the PANH anion derivatives support valence excited states for three-ringed structures, it is not until four-ringed structures of the pure PAH anion derivatives that valence excited states are exhibited. However, anisotropically extended PAHs larger than tetracene will likely exhibit valence excited states. The relative energies for the anion isomers are very small for all of the systems in this study. PMID:26645382
Electromagnetic decays of excited states in {sup 261}Sg (Z=106) and {sup 257}Rf (Z=104)
Berryman, J. S.; Clark, R. M.; Gregorich, K. E.; Cromaz, M.; Dvorak, J.; Fallon, P.; Gros, S.; Lee, I. Y.; Macchiavelli, A. O.; Paschalis, S.; Petri, M.; Qian, J.; Allmond, J. M.; Bleuel, D. L.; Stoyer, M. A.; Wiedeking, M.; Dragojevic, I.; Ellison, P. A.; Garcia, M. A.
2010-06-15
An isomeric one-quasineutron state, likely based on the [725]11/2{sup -} Nilsson level, was identified in {sup 261}Sg by its decay via internal conversion electrons. The state has an excitation energy of approx =200 keV and a half-life of 9.0{sub -1.5}{sup +2.0} mus. {sup 261}Sg has the highest Z and A of any nucleus in which the electromagnetic decay of an isomeric state was observed to date. A separate experiment was performed on the alpha daughter nucleus of {sup 261}Sg, namely {sup 257}Rf. Spectroscopy of delayed gamma rays and converted electrons from {sup 257}Rf resulted in the identification of a K isomer at an excitation energy of approx =1125 keV with a half-life of 134.9 +- 7.7 mus. The spin of the isomeric state is tentatively assigned I=21/2,23/2 and the state likely decays to a rotational band built on the [725]11/2{sup -} Nilsson level via a DELTAK=5 or 6 transition. The present results provide new information on excited states in the transactinide region, which is important for testing models of the heaviest elements.
Spin-vibronic quantum dynamics for ultrafast excited-state processes.
Eng, Julien; Gourlaouen, Christophe; Gindensperger, Etienne; Daniel, Chantal
2015-03-17
. 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. PMID:25647179
User-friendly software for modeling collective spin wave excitations
NASA Astrophysics Data System (ADS)
Hahn, Steven; Peterson, Peter; Fishman, Randy; Ehlers, Georg
There exists a great need for user-friendly, integrated software that assists in the scientific analysis of collective spin wave excitations measured with inelastic neutron scattering. SpinWaveGenie is a C + + software library that simplifies the modeling of collective spin wave excitations, allowing scientists to analyze neutron scattering data with sophisticated models fast and efficiently. Furthermore, one can calculate the four-dimensional scattering function S(Q,E) to directly compare and fit calculations to experimental measurements. Its generality has been both enhanced and verified through successful modeling of a wide array of magnetic materials. Recently, we have spent considerable effort transforming SpinWaveGenie from an early prototype to a high quality free open source software package for the scientific community. S.E.H. acknowledges support by the Laboratory's Director's fund, ORNL. Work was sponsored by the Division of Scientific User Facilities, Office of Basic Energy Sciences, US Department of Energy, under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.
NASA Technical Reports Server (NTRS)
Weatherford, Charles A.; Huo, Winifred M.
1990-01-01
The Chi 1Sigma - b 3Sigma(+) transition of CO is described using the Schwinger multichannel method in the two-state approximation, in an energy range from threshold to 20 eV. The resonance structure is analyzed by performing a partial-wave decomposition and the resonance positions are established based on the typical discontinuous behavior in the K-matrix elements as well as the pi radian change in the partial-wave eigenphases. The resonance behavior is related to the concept of core-excited resonances and the 'grandparent' model of resonances. The results are related to the formation of the negative ion by carrying out bound-state calculations on the (5 sigma)(3 s sigma)-squared core-excited Rydberg state of CO(-), and the position is found to agree well with the low-energy resonance positions.
Loco, Daniele; Polack, Étienne; Caprasecca, Stefano; Lagardère, Louis; Lipparini, Filippo; Piquemal, Jean-Philip; Mennucci, Benedetta
2016-08-01
A fully polarizable implementation of the hybrid quantum mechanics/molecular mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent relaxation of both the MM induced dipoles and the QM electronic density, is used for ground state energies and extended to electronic excitations in the framework of time-dependent density functional theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET(30) scale is presented. The results show that the QM/AMOEBA model not only properly describes specific and bulk effects in the ground state but it also correctly responds to the large change in the solute electronic charge distribution upon excitation. PMID:27340904