Theoretical Studies of Kinetic Mechanisms of Negative Ion Formation in Plasmas.

DTIC Science & Technology

1987-06-01

927258 ILLUSTRATIONS Figure Title Pg e 1 Long-Range Behavior of Excited IVg States of Li2 21 . 2 Long-Range Behavior of Excited It* States of Li2 22U 2 3...34) yields a statistically better fit with X2 - 0.002 as compared to X2 - 0.01 for the Ceperley and Partridge potential (Ref. 24). A significantly...including those reported by Jordan and Amdur (Ref. 37), yield significantly poorer statistical fits. We have not analyzed the new potential of Nitz, et

Complex behavior in chains of nonlinear oscillators.

PubMed

Alonso, Leandro M

2017-06-01

This article outlines sufficient conditions under which a one-dimensional chain of identical nonlinear oscillators can display complex spatio-temporal behavior. The units are described by phase equations and consist of excitable oscillators. The interactions are local and the network is poised to a critical state by balancing excitation and inhibition locally. The results presented here suggest that in networks composed of many oscillatory units with local interactions, excitability together with balanced interactions is sufficient to give rise to complex emergent features. For values of the parameters where complex behavior occurs, the system also displays a high-dimensional bifurcation where an exponentially large number of equilibria are borne in pairs out of multiple saddle-node bifurcations.

Excited State Trends in Bidirectionally Expanded Closed-Shell PAH and PANH Anions

PubMed Central

Moore, Megan M.; Lee, Timothy J.

2018-01-01

Some anions are known to exhibit excited states independent of external forces such as dipole moments and induced polarizabilities. Such states exist simply as a result of the stabilization of valence accepting orbitals whereby the binding energy of the extra electron is greater than the valence excitation energy. Closed-shell anions are interesting candidates for such transitions since their ground-state, spin-paired nature makes the anions more stable from the beginning. Consequently, this work shows the point beyond which deprotonated, closed-shell polycyclic aromatic hydrocarbons (PAHs) and those PAHs containing nitrogen heteroatoms (PANHs) will exhibit valence excited states. This behavior has already been demonstrated in some PANHs and for anistropically-extended PAHs. This work establishes a general trend for PAHs/PANHs of arbitrary size and directional extension, whether in one dimension or two. Once seven six-membered rings make up a PAH/PANH, valence excited states are present. For most classes of PAHs/PANHs, this number is closer to four. Even though most of these excited states are weak absorbers, the sheer number of PAHs present in various astronomical environments should make them significant contributors to astronomical spectra. PMID:27585793

Excited-State Proton-Transfer-Induced Trapping Enhances the Fluorescence Emission of a Locked GFP Chromophore

PubMed Central

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

Experimental and theoretical investigation of the molecular, electronic structure and solvatochromism of phenyl salicylate: External electric field effect on the electronic structure

NASA Astrophysics Data System (ADS)

Sıdır, İsa; Sıdır, Yadigar Gülseven

2017-11-01

The UV-vis absorption and steady state fluorescence spectra of phenyl salicylate (abbreviated as PS) have been recorded in a series of non-polar, polar protic and polar aprotic solvents at room temperature and the obtained spectral data are used to determine the solvatochromic behavior and the ground and excited state dipole moments. Basis set sensitive molecular structure along with X-ray crystal data are evaluated. The ground state and excited state dipole moments are determined by using Lippert-Mataga, Bakhshiev, Bilot-Kawski and Reichardt solvatochromic shift methods as a function of dielectric constant (ε) and refractive index (n) of the solvents. The larger excited state dipole moment value indicates the more polar PS in the excited state. The rate of μe/μg is found as 2.4239. Solvatochromic behavior of PS is enlightened by using Kamlet-Taft and Catalan models. Kamlet-Taft solvatochromic model indicates that non-specific solute solvent interactions are controlled by solvent dispersion-induction forces and specific interactions are directed by hydrogen-bond donor capacity of solvent. Catalan solvatochromic model designates that solute-solvent interactions are governed by solvent polarizability. Ground and excited state dipole moments are found theoretically by using DFT/B3LYP/6-311++G(d, p) and TDDFT/B3LYP/6-31++G(d, p) methods. External electric field effect on LUMO-HOMO band gap and dipole moment have been investigated by using B3LYP/6-311++G(d, p) method.

Discrimination of nuclear spin isomers exploiting the excited state dynamics of a quinodimethane derivative

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

Obaid, Rana; Faculty of Pharmacy, Al-Quds University, Abu Dis, Palestine; Kinzel, Daniel

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.

Minimal excitation states for heat transport in driven quantum Hall systems

NASA Astrophysics Data System (ADS)

Vannucci, Luca; Ronetti, Flavio; Rech, Jérôme; Ferraro, Dario; Jonckheere, Thibaut; Martin, Thierry; Sassetti, Maura

2017-06-01

We investigate minimal excitation states for heat transport into a fractional quantum Hall system driven out of equilibrium by means of time-periodic voltage pulses. A quantum point contact allows for tunneling of fractional quasiparticles between opposite edge states, thus acting as a beam splitter in the framework of the electron quantum optics. Excitations are then studied through heat and mixed noise generated by the random partitioning at the barrier. It is shown that levitons, the single-particle excitations of a filled Fermi sea recently observed in experiments, represent the cleanest states for heat transport since excess heat and mixed shot noise both vanish only when Lorentzian voltage pulses carrying integer electric charge are applied to the conductor. This happens in the integer quantum Hall regime and for Laughlin fractional states as well, with no influence of fractional physics on the conditions for clean energy pulses. In addition, we demonstrate the robustness of such excitations to the overlap of Lorentzian wave packets. Even though mixed and heat noise have nonlinear dependence on the voltage bias, and despite the noninteger power-law behavior arising from the fractional quantum Hall physics, an arbitrary superposition of levitons always generates minimal excitation states.

Global Analysis of Perovskite Photophysics Reveals Importance of Geminate Pathways

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

Manger, Lydia H.; Rowley, Matthew B.; Fu, Yongping

Hybrid organic-inorganic perovskites demonstrate desirable photophysical behaviors and promising applications from efficient photovoltaics to lasing, but the fundamental nature of excited state species is still under debate. We also collected time-resolved photoluminescence of single-crystal nanoplates of methylammonium lead iodide perovskite (MAPbI3), with excitation over a range of fluences and repetition rates, to provide a more complete photophysical picture. A fundamentally different way of simulating the photophysics is developed that relies on unnormalized decays, global analysis over a large array of conditions, and inclusion of steady-state behavior; these details are critical to capturing observed behaviors. These additional constraints require inclusion ofmore » spatially-correlated pairs, along with free carriers and traps, demonstrating the importance of our comprehensive analysis. Modeling geminate and non-geminate pathways shows geminate processes are dominant at high carrier densities and early times. This combination of data and simulation provides a detailed picture of perovskite photophysics across multiple excitation regimes that was not previously available.« less

Global Analysis of Perovskite Photophysics Reveals Importance of Geminate Pathways

DOE PAGES

Manger, Lydia H.; Rowley, Matthew B.; Fu, Yongping; ...

2016-12-20

Hybrid organic-inorganic perovskites demonstrate desirable photophysical behaviors and promising applications from efficient photovoltaics to lasing, but the fundamental nature of excited state species is still under debate. We also collected time-resolved photoluminescence of single-crystal nanoplates of methylammonium lead iodide perovskite (MAPbI3), with excitation over a range of fluences and repetition rates, to provide a more complete photophysical picture. A fundamentally different way of simulating the photophysics is developed that relies on unnormalized decays, global analysis over a large array of conditions, and inclusion of steady-state behavior; these details are critical to capturing observed behaviors. These additional constraints require inclusion ofmore » spatially-correlated pairs, along with free carriers and traps, demonstrating the importance of our comprehensive analysis. Modeling geminate and non-geminate pathways shows geminate processes are dominant at high carrier densities and early times. This combination of data and simulation provides a detailed picture of perovskite photophysics across multiple excitation regimes that was not previously available.« less

Non-adiabatic dynamics investigation of the radiationless decay mechanism of trans-urocanic acid in the S{sub 2} state

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

Zhao, Li; University of the Chinese Academy of Sciences, Beijing 100049; Zhou, Pan-Wang, E-mail: pwzhou@dicp.ac.cn, E-mail: gjzhao@dicp.ac.cn

2016-07-28

The trans-urocanic acid, a UV chromophore in the epidermis of human skin, was found to exhibit a wavelength dependent isomerization property. The isomerization quantum yield to cis-urocanic is greatest when being excited to the S{sub 1} state, whereas exciting the molecule to the S{sub 2} state causes almost no isomerization. The comparative photochemical behavior of the trans-urocanic on the S{sub 1} and S{sub 2} states continues to be the subject of intense research effort. This study is concerned with the unique photo-behavior of this interesting molecule on the S{sub 2} state. Combining the on-the-fly surface hopping dynamics simulations and staticmore » electronic structure calculations, three decay channels were observed following excitation to the S{sub 2} state. An overwhelming majority of the molecules decay to the S{sub 1} state through a planar or pucker characterized minimum energy conical intersection (MECI), and then decay to the ground state along a relaxation coordinate driven by a pucker deformation of the ring. A very small fraction of molecules decay to the S{sub 1} state by a MECI characterized by a twisting motion around the CC double bond, which continues to drive the molecule to deactivate to the ground state. The latter channel is related with the photoisomerization process, whereas the former one will only generate the original trans-form products. The present work provides a novel S{sub 2} state decay mechanism of this molecule, which offers useful information to explain the wavelength dependent isomerization behavior.« less

XUV-induced reactions in benzene on sub-10 fs timescale: nonadiabatic relaxation and proton migration.

PubMed

Galbraith, M C E; Smeenk, C T L; Reitsma, G; Marciniak, A; Despré, V; Mikosch, J; Zhavoronkov, N; Vrakking, M J J; Kornilov, O; Lépine, F

2017-08-02

Unraveling ultrafast dynamical processes in highly excited molecular species has an impact on our understanding of chemical processes such as combustion or the chemical composition of molecular clouds in the universe. In this article we use short (<7 fs) XUV pulses to produce excited cationic states of benzene molecules and probe their dynamics using few-cycle VIS/NIR laser pulses. The excited states produced by the XUV pulses lie in an especially complex spectral region where multi-electronic effects play a dominant role. We show that very fast τ ≈ 20 fs nonadiabatic processes dominate the relaxation of these states, in agreement with the timescale expected for most excited cationic states in benzene. In the CH 3 + fragmentation channel of the doubly ionized benzene cation we identify pathways that involve structural rearrangement and proton migration to a specific carbon atom. Further, we observe non-trivial transient behavior in this fragment channel, which can be interpreted either in terms of propagation of the nuclear wavepacket in the initially excited electronic state of the cation or as a two-step electronic relaxation via an intermediate state.

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, we examine the effect of the nanoscale interfacial morphology and solvation on the electronic excited states of TFB/F8BT. Here, we employ time-dependent density functional theory (TD-DFT) to investigate the relevant excited states of two stacking configurations. We show that the calculated states agree with the excited states responsible for the experimentally observed emission peaks and that these states are blue shifted relative to those of the isolated chain. Furthermore, slight lateral shifts in the stacking orientation not only shift the excited state energies; more importantly, they alter the nature of these states altogether. Lastly, we see that solvation greatly stabilizes the charge-transfer states.

Dynamics of the bleaching of tail states in CdS1- x Se x mixed crystals

NASA Astrophysics Data System (ADS)

Breitkopf, T.; Kalt, H.; Klingshirn, C.; Reznitsky, A.

1996-06-01

The kinetics of excitons localized by statistic potential fluctuations have been studied in CdS 1-xSex ternary alloys under quasi-stationary excitation conditions and have been time resolved after picosecond-pulse excitation. In luminescence experiments we observe the filling of the band tail with rising excitation intensity. The reduction of carrier density with time by recombination leads to a red shift of the luminescence band after picosecond-pulse excitation. Bleaching of absorption of the localized states is found in pump-probe experiments. Its dynamics depend on the localization depth of the excitons and on the pump-pulse energy. Using higher excitation intensities, we observe stimulated emission in luminescence, correlated with significant changes in the behavior of the absorption bleaching. The possible origin of the stimulated emission situated in the spectral region of localized states is discussed.

Energy decomposition analysis for exciplexes using absolutely localized molecular orbitals

NASA Astrophysics Data System (ADS)

Ge, Qinghui; Mao, Yuezhi; Head-Gordon, Martin

2018-02-01

An energy decomposition analysis (EDA) scheme is developed for understanding the intermolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized molecular orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexes (e.g., formamide-water, pyridine/pyrimidine-water) and halide (F-, Cl-)-water clusters that involve charge-transfer-to-solvent excitations.

Characterizing Plasmonic Excitations of Quasi-2D Chains

NASA Astrophysics Data System (ADS)

Townsend, Emily; Bryant, Garnett

A quantum description of the optical response of nanostructures and other atomic-scale systems is desirable for modeling systems that use plasmons for quantum information transfer, or coherent transport and interference of quantum states, as well as systems small enough for electron tunneling or quantum confinement to affect the electronic states of the system. Such a quantum description is complicated by the fact that collective and single-particle excitations can have similar energies and thus will mix. We seek to better understand the excitations of nanosystems to identify which characteristics of the excitations are most relevant to modeling their behavior. In this work we use a quasi 2-dimensional linear atomic chain as a model system, and exact diagonalization of the many-body Hamiltonian to obtain its excitations. We compare this to previous work in 1-d chains which used a combination of criteria involving a many-body state's transfer dipole moment, balance, transfer charge, dynamical response, and induced-charge distribution to identify which excitations are plasmonic in character.

Numerical and analytical investigation of the chimera state excitation conditions in the Kuramoto-Sakaguchi oscillator network

NASA Astrophysics Data System (ADS)

Frolov, Nikita S.; Goremyko, Mikhail V.; Makarov, Vladimir V.; Maksimenko, Vladimir A.; Hramov, Alexander E.

2017-03-01

In this paper we study the conditions of chimera states excitation in ensemble of non-locally coupled Kuramoto-Sakaguchi (KS) oscillators. In the framework of current research we analyze the dynamics of the homogeneous network containing identical oscillators. We show the chimera state formation process is sensitive to the parameters of coupling kernel and to the KS network initial state. To perform the analysis we have used the Ott-Antonsen (OA) ansatz to consider the behavior of infinitely large KS network.

Early-Time Excited-State Relaxation Dynamics of Iridium Compounds: Distinct Roles of Electron and Hole Transfer.

PubMed

Liu, Xiang-Yang; Zhang, Ya-Hui; Fang, Wei-Hai; Cui, Ganglong

2018-06-28

Excited-state and photophysical properties of Ir-containing complexes have been extensively studied because of their potential applications as organic light-emitting diode emitting materials. However, their early time excited-state relaxation dynamics are less explored computationally. Herein we have employed our recently implemented TDDFT-based generalized surface-hopping dynamics method to simulate excited-state relaxation dynamics of three Ir(III) compounds having distinct ligands. According to our multistate dynamics simulations including five excited singlet states i.e., S n ( n = 1-5) and ten excited triplet states, i.e., T n ( n = 1-10), we have found that the intersystem crossing (ISC) processes from the S n to T n are very efficient and ultrafast in these three Ir(III) compounds. The corresponding ISC rates are estimated to be 65, 81, and 140 fs, which are reasonably close to the experimentally measured ca. 80, 80, and 110 fs. In addition, the internal conversion (IC) processes within respective singlet and triplet manifolds are also ultrafast. These ultrafast IC and ISC processes are caused by large nonadiabatic and spin-orbit couplings, respectively, as well as small energy gaps. Importantly, although these Ir(III) complexes share similar macroscopic phenomena, i.e., ultrafast IC and ISC, their microscopic excited-state relaxation mechanism and dynamics are qualitatively distinct. Specifically, the dynamical behaviors of electron and hole and their roles are variational in modulating the excited-state relaxation dynamics of these Ir(III) compounds. In other words, the electronic properties of the ligands that are coordinated with the central Ir(III) atom play important roles in regulating the microscopic excited-state relaxation dynamics. These gained insights could be useful for rationally designing Ir(III) compounds with excellent photoluminescence.

Photophysics of Zinc Porphyrin Aggregates in Dilute Water-Ethanol Solutions.

PubMed

Stevens, Amy L; Joshi, Neeraj K; Paige, Matthew F; Steer, Ronald P

2017-12-14

Dimeric and multimeric aggregates of a model metalloporphyrin, zinc tetraphenylporphyrin (ZnTPP), have been produced in a controlled manner by incrementally increasing the water content of dilute aqueous ethanol solutions. Steady state absorption, fluorescence emission, and fluorescence excitation spectra have been measured to identify the aggregates present as a function of solvent composition. The dynamics of the excited states of the aggregates produced initially by excitation in the Soret region have been measured by ultrafast fluorescence upconversion techniques. Only the monomer produces measurable emission from S 2 with a picosecond lifetime; all Soret-excited aggregates, including the dimer, decay radiationlessly on a femtosecond time scale. The S 1 state is the only significant product of the radiationless decay of the S 2 state of the excited monomer, and the aggregates also produce substantial quantum yields of S 1 fluorescence when initially excited in the Soret region. The resulting fluorescent aggregates all decay on a subnanosecond time scale, likely by a mechanism that involves dissociation of the excited monomer from the excitonic multimer. The ZnTPP dimers excited at their ground state geometries in the Soret region exhibit a dynamic behavior that is quite different from those produced following noncoherent triplet-triplet annihilation under the same conditions. The important implications of these observations in determining the aggregation conditions promoting efficient photon upconversion by excitonic annihilation in a variety of media are thoroughly discussed.

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Behavior of Excited Argon Atoms in Inductively Driven Plasmas

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

HEBNER,GREGORY A.; MILLER,PAUL A.

1999-12-07

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s{sub 5} and 1s{sub 4}, in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s{sub 5} level is metastable and the 1s{sub 4} level is radiatively coupled to the ground state but is radiation trapped. The argon data is compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the datamore » suggest that both processes play a major role in determining the excited state density. At lower rfpower and pressure, excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rfpowers and pressures investigated, the spatial distributions tended to flatten in the center of the discharge while the density at the edge of the discharge was unaffected. The spatially resolved excited state density measurements were combined with previous line integrated measurements in the same discharge geometry to derive spatially resolved, absolute densities of the 1s{sub 5} and 1s{sub 4} argon excited states and gas temperature spatial distributions. Fluorescence lifetime was a strong fi.mction of the rf power, pressure, argon fraction and spatial location. Increasing the power or pressure resulted in a factor of two decrease in the fluorescence lifetime while adding Cl{sub 2} or BCl{sub 3} increased the fluorescence lifetime. Excited state quenching rates are derived from the data. When Cl{sub 2} or BCl{sub 3} was added to the plasma, the maximum argon metastable density depended on the gas and ratio. When chlorine was added to the argon plasma, the spatial density profiles were independent of chlorine fraction. While it is energetically possible for argon excited states to dissociate some of the molecular species present in this discharge, it does not appear to be a significant source of dissociation. The major source of interaction between the argon and the molecular species BCl{sub 3} and Cl{sub 2} appears to be through modification of the electron density.« less

Effect of density of states peculiarities on Hund's metal behavior

NASA Astrophysics Data System (ADS)

Belozerov, A. S.; Katanin, A. A.; Anisimov, V. I.

2018-03-01

We investigate a possibility of Hund's metal behavior in the Hubbard model with asymmetric density of states having peak(s). Specifically, we consider the degenerate two-band model and compare its results to the five-band model with realistic density of states of iron and nickel, showing that the obtained results are more general, provided that the hybridization between states of different symmetry is sufficiently small. We find that quasiparticle damping and the formation of local magnetic moments due to Hund's exchange interaction are enhanced by both the density of states asymmetry, which yields stronger correlated electron or hole excitations, and the larger density of states at the Fermi level, increasing the number of virtual electron-hole excitations. For realistic densities of states, these two factors are often interrelated because the Fermi level is attracted towards peaks of the density of states. We discuss the implication of the obtained results to various substances and compounds, such as transition metals, iron pnictides, and cuprates.

Ultrafast excited-state deactivation of 9-methylhypoxanthine in aqueous solution: A QM/MM MD study.

PubMed

Guo, Xugeng; Yuan, Huijuan; An, Beibei; Zhu, Qiuling; Zhang, Jinglai

2016-04-21

Photoinduced ultrafast non-adiabatic decay of 9-methylhypoxanthine (9MHPX) in aqueous solution was investigated by ab initio surface-hopping dynamics calculations using a combined quantum mechanical/molecular mechanical approach. The absorption spectra of 9MHPX in aqueous solution were also explored by the hybrid cluster-continuum model at the level of time-dependent density functional theory along with the polarizable continuum model (PCM). The static electronic-structure calculations indicate that the absorption spectra of 9MHPX simulated by TD-B3LYP/PCM and TD-X3LYP/PCM can reproduce very well the experimental findings, with the accuracy of about 0.20 eV. According to dynamics simulations, irradiation of 9MHPX populates the bright excited singlet S1 state, which may undergo an ultrafast non-radiative deactivation to the S0 state. The lifetime of the S1 state of 9MHPX in aqueous solution is predicted to be 115.6 fs, slightly longer than that in the gas phase (88.8 fs), suggesting that the solventwater has no significant influence on the excited-state lifetime of 9MHPX. Such a behavior in 9MHPX is distinctly different from its parent hypoxanthine keto-N9H tautomer in which the excited-state lifetime of the latter in watersolution was remarkably enhanced as compared to the gas phase. The significant difference of the photodynamical behaviors between 9MHPX and keto-N9H can be ascribed to their different hydrogen bond environment in aqueous solution.

Magnetic Field Dependence of Excitations Near Spin-Orbital Quantum Criticality

NASA Astrophysics Data System (ADS)

Biffin, A.; Rüegg, Ch.; Embs, J.; Guidi, T.; Cheptiakov, D.; Loidl, A.; Tsurkan, V.; Coldea, R.

2017-02-01

The spinel FeSc2 S4 has been proposed to realize a near-critical spin-orbital singlet (SOS) state, where entangled spin and orbital moments fluctuate in a global singlet state on the verge of spin and orbital order. Here we report powder inelastic neutron scattering measurements that observe the full bandwidth of magnetic excitations and we find that spin-orbital triplon excitations of an SOS state can capture well key aspects of the spectrum in both zero and applied magnetic fields up to 8.5 T. The observed shift of low-energy spectral weight to higher energies upon increasing applied field is naturally explained by the entangled spin-orbital character of the magnetic states, a behavior that is in strong contrast to spin-only singlet ground state systems, where the spin gap decreases upon increasing applied field.

Constraining nuclear photon strength functions by the decay properties of photo-excited states

NASA Astrophysics Data System (ADS)

Isaak, J.; Savran, D.; Krtička, M.; Ahmed, M. W.; Beller, J.; Fiori, E.; Glorius, J.; Kelley, J. H.; Löher, B.; Pietralla, N.; Romig, C.; Rusev, G.; Scheck, M.; Schnorrenberger, L.; Silva, J.; Sonnabend, K.; Tonchev, A. P.; Tornow, W.; Weller, H. R.; Zweidinger, M.

2013-12-01

A new approach for constraining the low-energy part of the electric dipole Photon Strength Function (E1-PSF) is presented. Experiments at the Darmstadt High-Intensity Photon Setup and the High Intensity γ→-Ray Source have been performed to investigate the decay properties of 130Te between 5.50 and 8.15 MeV excitation energy. In particular, the average γ-ray branching ratio to the ground state and the population intensity of low-lying excited states have been studied. A comparison to the statistical model shows that the latter is sensitive to the low-energy behavior of the E1-PSF, while the average ground state branching ratio cannot be described by the statistical model in the energy range between 5.5 and 6.5 MeV.

Photo-assisted intersystem crossing: The predominant triplet formation mechanism in some isolated polycyclic aromatic molecules excited with pulsed lasers

DOE PAGES

Johnson, Philip M.; Sears, Trevor J.

2015-07-28

Naphthalene, anthracene, and phenanthrene are shown to have very long-lived triplet lifetimes when the isolated molecules are excited with nanosecond pulsed lasers resonant with the lowest singlet state. For naphthalene, triplet state populations are created only during the laser pulse, excluding the possibility of normal intersystem crossing at the one photon level, and all molecules have triplet lifetimes greater than hundreds of microseconds, similar to the behavior previously reported for phenylacetylene. Although containing 7–12 thousand cm⁻¹ of vibrational energy, the triplet molecules have ionization thresholds appropriate to vibrationless T₁ states. The laser power dependences (slopes of log-log power plots) ofmore » the excited singlet and triplet populations are about 0.7 for naphthalene and about 0.5 for anthracene. Kinetic modeling of the power dependences successfully reproduces the experimental results and suggests that the triplet formation mechanism involves an enhanced spin orbit coupling caused by sigma character in states at the 2-photon level. Symmetry Adapted Cluster-Configuration Interaction calculations produced excited state absorption spectra to provide guidance for estimating kinetic rates and the sigma character present in higher electronic states. It is concluded that higher excited state populations are significant when larger molecules are excited with pulsed lasers and need to be taken into account whenever discussing the molecular photodynamics.« less

Time evolution of the one-dimensional Jaynes-Cummings-Hubbard Hamiltonian

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

Makin, M. I.; Hill, Charles D.; Greentree, Andrew D.

2009-10-15

The Jaynes-Cummings-Hubbard (JCH) system describes a network of single-mode photonic cavities connected via evanescent coupling. Each cavity contains a single two-level system which can be tuned in resonance with the cavity. Here, we explore the behavior of single excitations (where an excitation can be either photonic or atomic) in the linear JCH system, which describes a coupled cavity waveguide. We use direct, analytic diagonalization of the Hamiltonian to study cases where intercavity coupling is either uniform or varies parabolically along the chain. Both excitations located in a single cavity, as well as one excitation as a Gaussian pulse spread overmore » many cavities, are investigated as initial states. We predict unusual behavior of this system in the time domain, including slower than expected propagation of the excitation and also splitting of the excitation into two distinct pulses, which travel at distinct speeds. In certain limits, we show that the JCH system mimics two Heisenberg spin chains.« less

Organization of excitable dynamics in hierarchical biological networks.

PubMed

Müller-Linow, Mark; Hilgetag, Claus C; Hütt, Marc-Thorsten

2008-09-26

This study investigates the contributions of network topology features to the dynamic behavior of hierarchically organized excitable networks. Representatives of different types of hierarchical networks as well as two biological neural networks are explored with a three-state model of node activation for systematically varying levels of random background network stimulation. The results demonstrate that two principal topological aspects of hierarchical networks, node centrality and network modularity, correlate with the network activity patterns at different levels of spontaneous network activation. The approach also shows that the dynamic behavior of the cerebral cortical systems network in the cat is dominated by the network's modular organization, while the activation behavior of the cellular neuronal network of Caenorhabditis elegans is strongly influenced by hub nodes. These findings indicate the interaction of multiple topological features and dynamic states in the function of complex biological networks.

Observation of copper atoms behavior in a vacuum arc discharge using laser spectroscopy

NASA Astrophysics Data System (ADS)

Sung, Y. M.; Hayashi, Y.; Okraku-Yirenkyi, Y.; Otsubo, M.; Honda, C.; Sakoda, T.

2003-01-01

In order to investigate the most important parameters influencing the breaking characteristic of a vacuum circuit breaker (VCB), the behavior of copper (Cu) particles emitted from electrodes designed as an imitation of a vacuum valve of the VCB was observed. The temporal-spatial intensity distributions due to Cu particles in an excited state or a neutral state were measured using the laser induced fluorescence (LIF) technique and a charge coupled device camera attached with a special filter. The diffusion velocity of a Cu atom was also investigated by evaluating a Doppler shift of the LIF signal. The results showed that most Cu particles were emitted from the anode and were in an excited state or an ionized state during an arc discharge. Also, Cu particles were distributed between electrodes even after the discharge chocked, and its diffusion velocity in the direction of the cathode from the anode was about 2.6 km/s.

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.

Thermally Driven Inhibition of Superconducting Vortex Avalanches

NASA Astrophysics Data System (ADS)

Lara, Antonio; Aliev, Farkhad G.; Moshchalkov, Victor V.; Galperin, Yuri M.

2017-09-01

Complex systems close to their critical state can exhibit abrupt transitions—avalanches—between their metastable states. It is a challenging task to understand the mechanism of the avalanches and control their behavior. Here, we investigate microwave stimulation of avalanches in the so-called vortex matter of type-II superconductors—a system of interacting Abrikosov vortices close to the critical (Bean) state. Our main finding is that the avalanche incubation strongly depends on the excitation frequency, a completely unexpected behavior observed close to the so-called depinning frequencies. Namely, the triggered vortex avalanches in Pb superconducting films become effectively inhibited approaching the critical temperature or critical magnetic field when the microwave stimulus is close to the vortex depinning frequency. We suggest a simple model explaining the observed counterintuitive behaviors as a manifestation of the strongly nonlinear dependence of the driven vortex core size on the microwave excitation intensity. This paves the way to controlling avalanches in superconductor-based devices through their nonlinear response.

Ultrafast excited-state deactivation of 9-methylhypoxanthine in aqueous solution: A QM/MM MD study

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

Guo, Xugeng, E-mail: xgguo@henu.edu.cn, E-mail: zhangjinglai@henu.edu.cn; Yuan, Huijuan; An, Beibei

Photoinduced ultrafast non-adiabatic decay of 9-methylhypoxanthine (9MHPX) in aqueous solution was investigated by ab initio surface-hopping dynamics calculations using a combined quantum mechanical/molecular mechanical approach. The absorption spectra of 9MHPX in aqueous solution were also explored by the hybrid cluster-continuum model at the level of time-dependent density functional theory along with the polarizable continuum model (PCM). The static electronic-structure calculations indicate that the absorption spectra of 9MHPX simulated by TD-B3LYP/PCM and TD-X3LYP/PCM can reproduce very well the experimental findings, with the accuracy of about 0.20 eV. According to dynamics simulations, irradiation of 9MHPX populates the bright excited singlet S{sub 1}more » state, which may undergo an ultrafast non-radiative deactivation to the S{sub 0} state. The lifetime of the S{sub 1} state of 9MHPX in aqueous solution is predicted to be 115.6 fs, slightly longer than that in the gas phase (88.8 fs), suggesting that the solvent water has no significant influence on the excited-state lifetime of 9MHPX. Such a behavior in 9MHPX is distinctly different from its parent hypoxanthine keto-N9H tautomer in which the excited-state lifetime of the latter in water solution was remarkably enhanced as compared to the gas phase. The significant difference of the photodynamical behaviors between 9MHPX and keto-N9H can be ascribed to their different hydrogen bond environment in aqueous solution.« less

Photo-physical and interactional behavior of two members of group B vitamins in different solvent media

NASA Astrophysics Data System (ADS)

Zakerhamidi, M. S.; Zare Haghighi, L.; Seyed Ahmadian, S. M.

2017-09-01

In this paper, absorption and fluorescence spectra of vitamin B12 (cyanocobalamin) and vitamin B6 (pyridoxine) were recorded in solvents with different polarity, at room temperature. These vitamins' photo-physical behavior depends strongly on the solvent's nature along with different attached groups in their structures. In order to investigate the solvent-solute interactions and environmental effect on spectral variations, linear solvation energy relationships concept, suggested by Kamlet and Taft was used. Solvatochromic method was also used for measuring the ground and excited state dipole moments of these vitamins. According to our experimental results, dipole moment of these groups of vitamins in excited state is larger than ground state. Furthermore, obtained photo-physical and interactional properties of used vitamins can give important information on how this group of vitamins behaves in biological systems.

Spectral and Photophysical Behavior of Cytisine in n-Hexane. Experimental Evidence for the S1(n,π*) → S0 Fluorescence.

PubMed

Krystkowiak, Ewa; Przybył, Anna K; Bayda, Małgorzata; Józkowiak, Julia; Maciejewski, Andrzej

2017-08-03

Spectral and photophysical properties of (-)-cytisine (the compound used as a smoking cessation aid and a potential drug in Alzheimer's and Parkinson's diseases) were investigated. The two conformers of cytisine, whose presence in the S 0 state has been earlier proved by the NMR and IR methods as well as in theoretical calculation, in nonpolar n-hexane show a rarely observed prompt fluorescence from the S 1 (n,π*) excited state. This observation is unambiguously evidenced by very small radiative rate constants of these two emitting conformers, k F = 7.4 × 10 5 and 3.0 × 10 5 s -1 . Their lifetimes in the S 1 (n,π*) state are relatively long, τ S 1 = 1.9 and 6.7 ns; therefore, their fluorescence quantum yield is relatively high ϕ F ∼ 10 -3 . The long-wavelength band in the cytisine absorption originates from the excitation to the S 2 (π,π*) state, while the S 1 (n,π*) state is not observed in this spectrum. Thus, the excited state S 2 (π,π*) is manifested only in the absorption spectrum, while the excited state S 1 (n,π*) is seen only in the fluorescence spectrum, so cytisine in n-hexane is characterized by close lying (n,π*) and (π,π*) excited singlet states.

Investigation of the Impact of Different Terms in the Second Order Hamiltonian on Excitation Energies of Valence and Rydberg States.

PubMed

Tajti, Attila; Szalay, Péter G

2016-11-08

Describing electronically excited states of molecules accurately poses a challenging problem for theoretical methods. Popular second order techniques like Linear Response CC2 (CC2-LR), Partitioned Equation-of-Motion MBPT(2) (P-EOM-MBPT(2)), or Equation-of-Motion CCSD(2) (EOM-CCSD(2)) often produce results that are controversial and are ill-balanced with their accuracy on valence and Rydberg type states. In this study, we connect the theory of these methods and, to investigate the origin of their different behavior, establish a series of intermediate variants. The accuracy of these on excitation energies of singlet valence and Rydberg electronic states is benchmarked on a large sample against high-accuracy Linear Response CC3 references. The results reveal the role of individual terms of the second order similarity transformed Hamiltonian, and the reason for the bad performance of CC2-LR in the description of Rydberg states. We also clarify the importance of the T̂ 1 transformation employed in the CC2 procedure, which is found to be very small for vertical excitation energies.

Defects formation and spiral waves in a network of neurons in presence of electromagnetic induction.

PubMed

Rostami, Zahra; Jafari, Sajad

2018-04-01

Complex anatomical and physiological structure of an excitable tissue (e.g., cardiac tissue) in the body can represent different electrical activities through normal or abnormal behavior. Abnormalities of the excitable tissue coming from different biological reasons can lead to formation of some defects. Such defects can cause some successive waves that may end up to some additional reorganizing beating behaviors like spiral waves or target waves. In this study, formation of defects and the resulting emitted waves in an excitable tissue are investigated. We have considered a square array network of neurons with nearest-neighbor connections to describe the excitable tissue. Fundamentally, electrophysiological properties of ion currents in the body are responsible for exhibition of electrical spatiotemporal patterns. More precisely, fluctuation of accumulated ions inside and outside of cell causes variable electrical and magnetic field. Considering undeniable mutual effects of electrical field and magnetic field, we have proposed the new Hindmarsh-Rose (HR) neuronal model for the local dynamics of each individual neuron in the network. In this new neuronal model, the influence of magnetic flow on membrane potential is defined. This improved model holds more bifurcation parameters. Moreover, the dynamical behavior of the tissue is investigated in different states of quiescent, spiking, bursting and even chaotic state. The resulting spatiotemporal patterns are represented and the time series of some sampled neurons are displayed, as well.

Coulomb scattering rates of excited states in monolayer electron-doped germanene

NASA Astrophysics Data System (ADS)

Shih, Po-Hsin; Chiu, Chih-Wei; Wu, Jhao-Ying; Do, Thi-Nga; Lin, Ming-Fa

2018-05-01

Excited conduction electrons, conduction holes, and valence holes in monolayer electron-doped germanene exhibit unusual Coulomb decay rates. The deexcitation processes are studied using the screened exchange energy. They might utilize the intraband single-particle excitations (SPEs), the interband SPEs, and the plasmon modes, depending on the quasiparticle states and the Fermi energies. The low-lying valence holes can decay through the undamped acoustic plasmon, so that they present very fast Coulomb deexcitations, nonmonotonous energy dependence, and anisotropic behavior. However, the low-energy conduction electrons and holes are similar to those in a two-dimensional electron gas. The higher-energy conduction states and the deeper-energy valence ones behave similarly in the available deexcitation channels and have a similar dependence of decay rate on the wave vector k .

Characterization of Different Types of Excitability in Large Somatosensory Neurons and Its Plastic Changes in Pathological Pain States

PubMed Central

Xie, Rou-Gang; Chu, Wen-Guang; Hu, San-Jue; Luo, Ceng

2018-01-01

Sensory neuron types have been distinguished by distinct morphological and transcriptional characteristics. Excitability is the most fundamental functional feature of neurons. Mathematical models described by Hodgkin have revealed three types of neuronal excitability based on the relationship between firing frequency and applied current intensity. However, whether natural sensory neurons display different functional characteristics in terms of excitability and whether this excitability type undergoes plastic changes under pathological pain states have remained elusive. Here, by utilizing whole-cell patch clamp recordings, behavioral and pharmacological assays, we demonstrated that large dorsal root ganglion (DRG) neurons can be classified into three classes and four subclasses based on their excitability patterns, which is similar to mathematical models raised by Hodgkin. Analysis of hyperpolarization-activated cation current (Ih) revealed different magnitude of Ih in different excitability types of large DRG neurons, with higher Ih in Class 2-1 than that in Class 1, 2-2 and 3. This indicates a crucial role of Ih in the determination of excitability type of large DRG neurons. More importantly, this pattern of excitability displays plastic changes and transition under pathological pain states caused by peripheral nerve injury. This study sheds new light on the functional characteristics of large DRG neurons and extends functional classification of large DRG neurons by integration of transcriptomic and morphological characteristics. PMID:29303989

Distinct Mechanisms Underlie Quiescence during Two Caenorhabditis elegans Sleep-Like States

PubMed Central

Trojanowski, Nicholas F.; Nelson, Matthew D.; Flavell, Steven W.

2015-01-01

Electrophysiological recordings have enabled identification of physiologically distinct yet behaviorally similar states of mammalian sleep. In contrast, sleep in nonmammals has generally been identified behaviorally and therefore regarded as a physiologically uniform state characterized by quiescence of feeding and locomotion, reduced responsiveness, and rapid reversibility. The nematode Caenorhabditis elegans displays sleep-like quiescent behavior under two conditions: developmentally timed quiescence (DTQ) occurs during larval transitions, and stress-induced quiescence (SIQ) occurs in response to exposure to cellular stressors. Behaviorally, DTQ and SIQ appear identical. Here, we use optogenetic manipulations of neuronal and muscular activity, pharmacology, and genetic perturbations to uncover circuit and molecular mechanisms of DTQ and SIQ. We find that locomotion quiescence induced by DTQ- and SIQ-associated neuropeptides occurs via their action on the nervous system, although their neuronal target(s) and/or molecular mechanisms likely differ. Feeding quiescence during DTQ results from a loss of pharyngeal muscle excitability, whereas feeding quiescence during SIQ results from a loss of excitability in the nervous system. Together these results indicate that, as in mammals, quiescence is subserved by different mechanisms during distinct sleep-like states in C. elegans. SIGNIFICANCE STATEMENT Sleep behavior is characterized by cessation of feeding and locomotion, reduced responsiveness, and rapid reversibility. In mammals and birds, there are sleep states that have fundamentally different electrophysiology despite outwardly similar behavior. However, it is not clear whether behavioral sleep is a uniform state in animals in which electrophysiology is not readily possible. The nematode Caenorhabditis elegans displays sleep-like behavior under two conditions: during development and after exposure to environmental stressors. Here, we show that feeding and locomotion quiescence during these two sleep-like states are produced by different mechanisms. This provides the first identification of two mechanistically distinct forms of quiescence during sleep-like states in an invertebrate. PMID:26511247

Phasic Stimulation of Midbrain Dopamine Neuron Activity Reduces Salt Consumption

PubMed Central

Sandhu, Eleanor C.; Fernando, Anushka B. P.; Tossell, Kyoko; Kokkinou, Michelle; Glegola, Justyna; Howes, Oliver D.

2018-01-01

Abstract Salt intake is an essential dietary requirement, but excessive consumption is implicated in hypertension and associated conditions. Little is known about the neural circuit mechanisms that control motivation to consume salt, although the midbrain dopamine system, which plays a key role in other reward-related behaviors, has been implicated. We, therefore, examined the effects on salt consumption of either optogenetic excitation or chemogenetic inhibition of ventral tegmental area (VTA) dopamine neurons in male mice. Strikingly, optogenetic excitation of dopamine neurons decreased salt intake in a rapid and reversible manner, despite a strong salt appetite. Importantly, optogenetic excitation was not aversive, did not induce hyperactivity, and did not alter salt concentration preferences in a need-free state. In addition, we found that chemogenetic inhibition of dopamine neurons had no effect on salt intake. Lastly, optogenetic excitation of dopamine neurons reduced consumption of sucrose following an overnight fast, suggesting a more general role of VTA dopamine neuron excitation in organizing motivated behaviors. PMID:29766048

Collisional rate coefficients of C3H2 and the determination of physical conditions in molecular clouds

NASA Technical Reports Server (NTRS)

Avery, L. W.; Green, Sheldon

1989-01-01

Collisional excitation rates for C3H2, calculated using the coupled states approximation at temperatures of 10-30 K, are presented. C3H2 produces a number of spectral line pairs whose members are close together in frequency but arise from levels with different excitation energies. The rates are used in statistical equilibrium calculations to illustrate the excitation properties and density-dependent behavior of various C3H2 line ratios.

Determination of ground and excited state dipole moments via electronic Stark spectroscopy: 5-methoxyindole

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

Wilke, Josefin; Wilke, Martin; Schmitt, Michael, E-mail: mschmitt@uni-duesseldorf.de

2016-01-28

The dipole moments of the ground and lowest electronically excited singlet state of 5-methoxyindole have been determined by means of optical Stark spectroscopy in a molecular beam. The resulting spectra arise from a superposition of different field configurations, one with the static electric field almost parallel to the polarization of the exciting laser radiation, the other nearly perpendicular. Each field configuration leads to different intensities in the rovibronic spectrum. With an automated evolutionary algorithm approach, the spectra can be fit and the ratio of both field configurations can be determined. A simultaneous fit of two spectra with both field configurationsmore » improved the precision of the dipole moment determination by a factor of two. We find a reduction of the absolute dipole moment from 1.59(3) D to 1.14(6) D upon electronic excitation to the lowest electronically excited singlet state. At the same time, the dipole moment orientation rotates by 54{sup ∘} showing the importance of the determination of the dipole moment components. The dipole moment in the electronic ground state can approximately be obtained from a vector addition of the indole and the methoxy group dipole moments. However, in the electronically excited state, vector addition completely fails to describe the observed dipole moment. Several reasons for this behavior are discussed.« less

Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.

PubMed

Santos, Fabiano da Silveira; Descalzo, Rodrigo Roceti; Gonçalves, Paulo Fernando Bruno; Benvenutti, Edilson Valmir; Rodembusch, Fabiano Severo

2012-08-21

Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.

Inhibition of Radiolytic Molecular Hydrogen Formation by Quenching of Excited State Water

DOE PAGES

Horne, Gregory P.; Pimblott, Simon M.; LaVerne, Jay A.

2017-05-11

Comparison of experimental measurements of the yield of molecular hydrogen produced in the gamma radiolysis of water and aqueous nitrate solutions with predictions of a Monte Carlo track chemistry model shows that the nitrate anion scavenging of the hydrated electron, its precursor, and hydrogen atom cannot account for the observed decrease in the yield at high nitrate anion concentrations. Inclusion of the quenching of excited states of water (formed by either direct excitation or reaction of the water radical cation with the precursor to the hydrated electron) by the nitrate anion into the reaction scheme provides excellent agreement between themore » stochastic calculations and experiment demonstrating the existence of this short-lived species and its importance in water radiolysis. Energy transfer from the excited states of water to the nitrate anion producing an excited state provides an additional pathway for the production of nitrogen containing products not accounted for in traditional radiation chemistry scenarios. Such reactions are of central importance in predicting the behavior of liquors common in the reprocessing of spent nuclear fuel and the storage of highly radioactive liquid waste prior to vitrification.« less

Sleep deprivation and the organization of the behavioral states.

NASA Technical Reports Server (NTRS)

Dement, W. C.

1972-01-01

Questions concerning the significance of sleep in the developing organism are investigated, together with the mechanisms that underlie the unique distribution of behavioral states at any particular age and during any particular experimental manipulation. It is attempted to define the states of sleep and wakefulness in terms of a temporal confluence of a number of more or less independent processes, taking also into account the functional consequences of these attributes. The results of a selective deprivation of rapid eye movement sleep are explored, giving attention to effects on sleep, behavioral changes, brain excitability, pharmacological changes, and biochemical changes.

Optical properties of an inhomogeneously broadened ΛV-system with multiple excited states

NASA Astrophysics Data System (ADS)

Kaur, Paramjit; Bharti, Vineet; Wasan, Ajay

2014-09-01

We present a theoretical model using a density matrix approach to show the influence of multiple excited states on the optical properties of an inhomogeneously broadened ?V-system of the ?Rb D2 line. These closely spaced multiple excited states cause asymmetry in absorption and dispersion profiles. We observe the reduced absorption profiles, due to dressed state interactions of the applied electromagnetic fields, which results the Mollow sideband-like transparency windows. In a room temperature vapor, we obtain a narrow enhanced absorption and steep positive dispersion at the line center when the strengths of control and pump fields are equal. Here, we show how the probe transmittance varies when it passes through the atomic medium. We also discuss the transient behavior of our system which agrees well with the corresponding absorption and dispersion profiles. This study has potential applications in controllability of group velocity, and for optical and quantum information processing.

Monte Carlo calculations of diatomic molecule gas flows including rotational mode excitation

NASA Technical Reports Server (NTRS)

Yoshikawa, K. K.; Itikawa, Y.

1976-01-01

The direct simulation Monte Carlo method was used to solve the Boltzmann equation for flows of an internally excited nonequilibrium gas, namely, of rotationally excited homonuclear diatomic nitrogen. The semi-classical transition probability model of Itikawa was investigated for its ability to simulate flow fields far from equilibrium. The behavior of diatomic nitrogen was examined for several different nonequilibrium initial states that are subjected to uniform mean flow without boundary interactions. A sample of 1000 model molecules was observed as the gas relaxed to a steady state starting from three specified initial states. The initial states considered are: (1) complete equilibrium, (2) nonequilibrium, equipartition (all rotational energy states are assigned the mean energy level obtained at equilibrium with a Boltzmann distribution at the translational temperature), and (3) nonequipartition (the mean rotational energy is different from the equilibrium mean value with respect to the translational energy states). In all cases investigated the present model satisfactorily simulated the principal features of the relaxation effects in nonequilibrium flow of diatomic molecules.

Characteristics of Excitable Dog Behavior Based on Owners’ Report from a Self-Selected Study

PubMed Central

Shabelansky, Anastasia; Dowling-Guyer, Seana

2016-01-01

Simple Summary This study provides information about owners’ experiences with their dogs’ excitable behavior. We found that certain daily scenarios tended to prompt excitable behavior. The majority of owners in this self-selected sample were very frustrated with their excitable dog. Many dogs in the sample had other behavior problems. Abstract Past research has found that excitable dog behavior is prevalent among sheltered and owned dogs and many times is a reason for canine relinquishment. In spite of its prevalence in the canine population, excitable behavior is relatively unstudied in the scientific literature. The intent of this research was to understand the experience of owners of excitable dogs through the analysis of self-administered online questionnaires completed by owners as part of another study. We found that certain daily scenarios tended to prompt excitable behavior, with excitability most common when the owner or other people came to the dog’s home. All owners experienced some level of frustration with their dog’s excitable behavior, with the majority being very frustrated. Many dogs in the sample had other behavior problems, with disobedient, destructive, chasing and barking behaviors being the most commonly reported. Other characteristics of excitable dogs also are discussed. Although the ability to generalize from these results is likely limited, due to targeted recruitment and selection of owners of more excitable dogs, this research provides valuable insights into the owner’s experience of excitable behavior. We hope this study prompts more research into canine excitable behavior which would expand our understanding of this behavior and help behaviorists, veterinarians, and shelters develop tools for managing it, as well as provide better education to owners of excitable dogs. PMID:26999222

Z-dependence of mean excitation energies for second and third row atoms and their ions

NASA Astrophysics Data System (ADS)

Sauer, Stephan P. A.; Sabin, John R.; Oddershede, Jens

2018-05-01

All mean excitation energies for second and third row atoms and their ions are calculated in the random-phase approximation using large basis sets. To a very good approximation, it turns out that mean excitation energies within an isoelectronic series are a quadratic function of the nuclear charge. It is demonstrated that this behavior is linked to the fact that the contributions from continuum electronic states give the dominate contributions to the mean excitation energies and that these contributions for atomic ions appear hydrogen-like. We argue that this finding may present a method to get a first estimate of mean excitation energies also for other non-relativistic atomic ions.

Multi-channels coupling-induced pattern transition in a tri-layer neuronal network

NASA Astrophysics Data System (ADS)

Wu, Fuqiang; Wang, Ya; Ma, Jun; Jin, Wuyin; Hobiny, Aatef

2018-03-01

Neurons in nerve system show complex electrical behaviors due to complex connection types and diversity in excitability. A tri-layer network is constructed to investigate the signal propagation and pattern formation by selecting different coupling channels between layers. Each layer is set as different states, and the local kinetics is described by Hindmarsh-Rose neuron model. By changing the number of coupling channels between layers and the state of the first layer, the collective behaviors of each layer and synchronization pattern of network are investigated. A statistical factor of synchronization on each layer is calculated. It is found that quiescent state in the second layer can be excited and disordered state in the third layer is suppressed when the first layer is controlled by a pacemaker, and the developed state is dependent on the number of coupling channels. Furthermore, the collapse in the first layer can cause breakdown of other layers in the network, and the mechanism is that disordered state in the third layer is enhanced when sampled signals from the collapsed layer can impose continuous disturbance on the next layer.

Individual Differences in Resting Corticospinal Excitability Are Correlated with Reaction Time and GABA Content in Motor Cortex

PubMed Central

Ivry, Richard B.

2017-01-01

Individuals differ in the intrinsic excitability of their corticospinal pathways and, perhaps more generally, their entire nervous system. At present, we have little understanding of the mechanisms underlying these differences and how variation in intrinsic excitability relates to behavior. Here, we examined the relationship between individual differences in intrinsic corticospinal excitability, local cortical GABA levels, and reaction time (RT) in a group of 20 healthy human adults. We measured corticospinal excitability at rest with transcranial magnetic stimulation, local concentrations of basal GABA with magnetic resonance spectroscopy, and RT with a behavioral task. All measurements were repeated in two separate sessions, and tests of reliability confirmed the presence of stable individual differences. There was a negative correlation between corticospinal excitability and RT, such that larger motor-evoked potentials (MEPs) measured at rest were associated with faster RTs. Interestingly, larger MEPs were associated with higher levels of GABA in M1, but not in three other cortical regions. Together, these results suggest that individuals with more excitable corticospinal pathways are faster to initiate planned responses and have higher levels of GABA within M1, possibly to compensate for a more excitable motor system. SIGNIFICANCE STATEMENT This study brings together physiological, behavioral, and neurochemical evidence to examine variability in the excitability of the human motor system. Previous work has focused on state-based factors (e.g., preparedness, uncertainty), with little attention given to the influence of inherent stable characteristics. Here, we examined how the excitability of the motor system relates to reaction time and the regional content of the inhibitory neurotransmitter GABA. Importantly, motor pathway excitability and GABA concentrations were measured at rest, outside a task context, providing assays of intrinsic properties of the individuals. Individuals with more excitable motor pathways had faster reaction times and, paradoxically, higher concentrations of GABA. We propose that greater GABA capacity in the motor cortex counteracts an intrinsically more excitable motor system. PMID:28179557

Excited-state proton transfer dynamics of firefly's chromophore D-luciferin in DMSO-water binary mixture.

PubMed

Kuchlyan, Jagannath; Banik, Debasis; Roy, Arpita; Kundu, Niloy; Sarkar, Nilmoni

2014-12-04

In this article we have investigated intermolecular excited-state proton transfer (ESPT) of firefly's chromophore D-luciferin in DMSO-water binary mixtures using steady-state and time-resolved fluorescence spectroscopy. The unusual behavior of DMSO-water binary mixture as reported by Bagchi et al. (J. Phys. Chem. B 2010, 114, 12875-12882) was also found using D-luciferin as intermolecular ESPT probe. The binary mixture has given evidence of its anomalous nature at low mole fractions of DMSO (below XD = 0.4) in our systematic investigation. Upon excitation of neutral D-luciferin molecule, dual fluorescence emissions (protonated and deprotonated form) are observed in DMSO-water binary mixture. A clear isoemissive point in the time-resolved area normalized emission spectra further indicates two emissive species in the excited state of D-luciferin in DMSO-water binary mixture. DMSO-water binary mixtures of different compositions are fascinating hydrogen bonding systems. Therefore, we have observed unusual changes in the fluorescence emission intensity, fluorescence quantum yield, and fluorescence lifetime of more hydrogen bonding sensitive anionic form of D-luciferin in low DMSO content of DMSO-water binary mixture.

Multiple spatially localized dynamical states in friction-excited oscillator chains

NASA Astrophysics Data System (ADS)

Papangelo, A.; Hoffmann, N.; Grolet, A.; Stender, M.; Ciavarella, M.

2018-03-01

Friction-induced vibrations are known to affect many engineering applications. Here, we study a chain of friction-excited oscillators with nearest neighbor elastic coupling. The excitation is provided by a moving belt which moves at a certain velocity vd while friction is modelled with an exponentially decaying friction law. It is shown that in a certain range of driving velocities, multiple stable spatially localized solutions exist whose dynamical behavior (i.e. regular or irregular) depends on the number of oscillators involved in the vibration. The classical non-repeatability of friction-induced vibration problems can be interpreted in light of those multiple stable dynamical states. These states are found within a "snaking-like" bifurcation pattern. Contrary to the classical Anderson localization phenomenon, here the underlying linear system is perfectly homogeneous and localization is solely triggered by the friction nonlinearity.

Transient photocurrent in molecular junctions: singlet switching on and triplet blocking.

PubMed

Petrov, E G; Leonov, V O; Snitsarev, V

2013-05-14

The kinetic approach adapted to describe charge transmission in molecular junctions, is used for the analysis of the photocurrent under conditions of moderate light intensity of the photochromic molecule. In the framework of the HOMO-LUMO model for the single electron molecular states, the analytic expressions describing the temporary behavior of the transient and steady state sequential (hopping) as well as direct (tunnel) current components have been derived. The conditions at which the current components achieve their maximal values are indicated. It is shown that if the rates of charge transmission in the unbiased molecular diode are much lower than the intramolecular singlet-singlet excitation/de-excitation rate, and the threefold degenerated triplet excited state of the molecule behaves like a trap blocking the charge transmission, a possibility of a large peak-like transient switch-on photocurrent arises.

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

Koppal, V. V., E-mail: varshakoppal@gmail.com; Muddapur, G. V., E-mail: muddapur.gangadhar@gmail.com; Patil, N. R., E-mail: patilnr23@gmail.com

In this paper we attempted to record absorption and emission spectra of 2-acetyl-3H-benzo[f]chromen-3-one [2AHBC] laser dye in different solvents of varying polarities to investigate its solvatochromic behavior. The two electronic states dipole moments of 2AHBC are calculated using solvatochromic spectral shifts which are correlated with dielectric constant (ε) refractive index (n) of various solvents. A systematic approach is made to estimate ground and excited state dipole moments on the basis of different solvent correlation methods like Bilot-Kawski equations, Lippert-Mataga, Bakhsheiv, Kawaski-Chamma-Viallet and Reichardt methods. Dipole moments in the excited state was found to be higher than the ground state bymore » confirming π→π* transition.« less

The molecular and electronic structure of s-tetrazine in the ground and first excited state: A theoretical investigation

NASA Astrophysics Data System (ADS)

Schütz, Martin; Hutter, Jürg; Lüthi, Hans Peter

1995-10-01

The ground- and first excited state of s-tetrazine arising from a π*←n excitation (1Ag,1B3u) have been studied using the complete active space (CASSCF) and the second order multiconfiguration perturbation theory (CASPT2) ab initio methods. The focus of this study is on the effect of the electronic excitation on the molecular structure and on those electronic properties which are important to model the solvatochromatic behavior of the molecule in polymer matrices as used in permanent hole burning experiments. Since the accurate computation of excited state molecular properties represents a major challenge for today's numerical quantum chemistry, some technical aspects are also considered. The present study shows that the change in geometry upon electronic excitation is small. This is in partial contradiction with the experimental studies which however disagree among themselves [see K. K. Innes, I. G. Ross, and W. R. Moomaw, J. Mol. Spectrosc. 132, 492 (1988), and R. E. Smalley, L. Wharton, and D. H. Levi, ibid. 66, 375 (1977)]. This study also confirms that the first excited state equilibrium structure is of D2h symmetry. In an earlier theoretical study it was found that the D2h symmetry structure may represent a saddle point rather than a minimum on the excited state potential surface [see A. C. Scheiner and H. F. Schaefer III, J. Chem. Phys. 87, 3539 (1987)]. In the first excited state, we observe an increase of the mean polarizability of s-tetrazine along with an enhanced anisotropy. The change in the polarizability is almost exclusively in the ``in-plane'' components of the tensor; the polarizability in the vertical direction is nearly unchanged. This observation questions recent experimental results reported for this molecule [see S. Heitz, D. Weidnauer, and A. Hese, J. Chem. Phys. 95, 7952 (1991)].

Particle-hole symmetry, many-body localization, and topological edge modes

NASA Astrophysics Data System (ADS)

Vasseur, Romain; Friedman, Aaron J.; Parameswaran, S. A.; Potter, Andrew C.

We study the excited states of interacting fermions in one dimension with particle-hole symmetric disorder (equivalently, random-bond XXZ chains) using a combination of renormalization group methods and exact diagonalization. Absent interactions, the entire many-body spectrum exhibits infinite-randomness quantum critical behavior with highly degenerate excited states. We show that though interactions are an irrelevant perturbation in the ground state, they drastically affect the structure of excited states: even arbitrarily weak interactions split the degeneracies in favor of thermalization (weak disorder) or spontaneously broken particle-hole symmetry, driving the system into a many-body localized spin glass phase (strong disorder). In both cases, the quantum critical properties of the non-interacting model are destroyed, either by thermal decoherence or spontaneous symmetry breaking. This system then has the interesting and counterintuitive property that edges of the many-body spectrum are less localized than the center of the spectrum. We argue that our results rule out the existence of certain excited state symmetry-protected topological orders. Supported by the Gordon and Betty Moore Foundation's EPiQS Initiative (Grant GBMF4307 (ACP), the Quantum Materials Program at LBNL (RV), NSF Grant DMR-1455366 and UCOP Research Catalyst Award No. CA-15-327861 (SAP).

Delocalized versus localized excitations in the photoisomerization of azobenzene-functionalized alkanethiolate SAMs

NASA Astrophysics Data System (ADS)

Bronsch, Wibke; Moldt, Thomas; Boie, Larissa; Gahl, Cornelius; Weinelt, Martin

2017-12-01

Self-assembled monolayers of azobenzene-functionalized alkanethiolates form molecular ensembles with preferential orientation and significant excitonic coupling among the azobenzene chromophores. We have studied their optical switching with differential reflectance and two-photon-photoemission spectroscopy tuning the excitation wavelength through the excitonically broadened S2 absorption band. While the effective isomerization cross-section increases towards shorter wavelengths, the fraction of cis molecules in the photostationary state decreases. We attribute this observation to the absorption of the cis isomer in the SAM. The photoisomerization in the SAM thereby follows the behavior of non-interacting chromophores in solution, despite the formation of H-aggregates. Our study thus reveals that photoswitching occurs via localized excitations while strongly excitonically coupled, delocalized states do not contribute significantly.

Discovery of Emergent Photon and Monopoles in a Quantum Spin Liquid

NASA Astrophysics Data System (ADS)

Tokiwa, Yoshifumi; Yamashita, Takuya; Terazawa, Daiki; Kimura, Kenta; Kasahara, Yuichi; Onishi, Takafumi; Kato, Yasuyuki; Halim, Mario; Gegenwart, Philipp; Shibauchi, Takasada; Nakatsuji, Satoru; Moon, Eun-Gook; Matsuda, Yuji

2018-06-01

Quantum spin liquid (QSL) is an exotic quantum phase of matter whose ground state is quantum-mechanically entangled without any magnetic ordering. A central issue concerns emergent excitations that characterize QSLs, which are hypothetically associated with quasiparticle fractionalization and topological order. Here we report highly unusual heat conduction generated by the spin degrees of freedom in a QSL state of the pyrochlore magnet Pr2Zr2O7, which hosts spin-ice correlations with strong quantum fluctuations. The thermal conductivity in high temperature regime exhibits a two-gap behavior, which is consistent with the gapped excitations of magnetic (M-) and electric monopoles (E-particles). At very low temperatures below 200 mK, the thermal conductivity unexpectedly shows a dramatic enhancement, which well exceeds purely phononic conductivity, demonstrating the presence of highly mobile spin excitations. This new type of excitations can be attributed to emergent photons (ν-particle), coherent gapless spin excitations in a spin-ice manifold.

Controlling competing orders via nonequilibrium acoustic phonons: Emergence of anisotropic effective electronic temperature

NASA Astrophysics Data System (ADS)

Schütt, Michael; Orth, Peter P.; Levchenko, Alex; Fernandes, Rafael M.

2018-01-01

Ultrafast perturbations offer a unique tool to manipulate correlated systems due to their ability to promote transient behaviors with no equilibrium counterpart. A widely employed strategy is the excitation of coherent optical phonons, as they can cause significant changes in the electronic structure and interactions on short time scales. One of the issues, however, is the inevitable heating that accompanies these resonant excitations. Here, we explore a promising alternative route: the nonequilibrium excitation of acoustic phonons, which, due to their low excitation energies, generally lead to less heating. We demonstrate that driving acoustic phonons leads to the remarkable phenomenon of a momentum-dependent effective temperature, by which electronic states at different regions of the Fermi surface are subject to distinct local temperatures. Such an anisotropic effective electronic temperature can have a profound effect on the delicate balance between competing ordered states in unconventional superconductors, opening a so far unexplored avenue to control correlated phases.

A nonlinear energy sink with an energy harvester: Harmonically forced responses

NASA Astrophysics Data System (ADS)

Kremer, Daniel; Liu, Kefu

2017-12-01

This study intends to achieve simultaneous vibration suppression and energy harvesting using a variant form of nonlinear energy sink (NES). The proposed apparatus is not a true NES as its spring is not essentially nonlinear. In a previous study [22] (Journal of Sound and Vibration, 333 (20) (2014)), it has been shown that the apparatus demonstrates the transient behaviors similar to those of the NES. As a sequel, the present paper focuses on harmonically forced responses of the system. First, the approximate solutions of steady state responses are derived. Using the approximate solutions, the steady state behaviors are investigated by using the numerical continuation method. This is followed by an experimental study. The study has shown that under harmonic excitation, the proposed apparatus functions similarly to the NES with the typical behaviors such as strongly modulated responses, amplitude jumping, excitation level dependence, etc. Overall, the apparatus meets the design objectives: the vibration suppression and energy harvesting in a broadband manner.

Generation of various radicals in nitrogen plasma and their behavior in media

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

Uhm, Han S., E-mail: hsuhm@kw.ac.kr

2015-12-15

Research on the generation of radicals in nitrogen plasma shows that the most dominant radicals are excited nitrogen molecules in the metastable state of N{sub 2}(A{sub 3}∑{sub u}{sup +}). Hydroxyl molecules are generated from the dissociation of water molecules upon contact with excited nitrogen molecules. The estimated densities of various radicals in nitrogen plasma with an electron temperature of 1 eV are presented in this study. The behavior of these radicals in media is also investigated. Excited nitrogen molecules in the N{sub 2}(A{sub 3}∑{sub u}{sup +}) state from a plasma jet are injected into water, after which the molecules disappear instantaneouslymore » within a few tens of nm, producing hydroxyl molecules. Hydrogen peroxide, hydrogen dioxide, and nitrogen monoxide molecules can diffuse much deeper into water, implying the possibility that a chemical reaction between hydrogen dioxide and nitrogen monoxide molecules produces hydroxyl molecules in deep water, even though density in this case may not be very high.« less

Multiphoton manipulations of enzymatic photoactivity in aspartate aminotransferase.

PubMed

Hill, Melissa P; Freer, Lucy H; Vang, Mai C; Carroll, Elizabeth C; Larsen, Delmar S

2011-04-21

The aspartate aminotransferase (AAT) enzyme utilizes the chromophoric pyridoxal 5'-phosphate (PLP) cofactor to facilitate the transamination of amino acids. Recently, we demonstrated that, upon exposure to blue light, PLP forms a reactive triplet state that rapidly (in microseconds) generates the high-energy quinonoid intermediate when bound to PLP-dependent enzymes [J. Am. Chem. Soc.2010, 132 (47), 16953-16961]. This increases the net catalytic activity (k(cat)) of AAT, since formation of the quinonoid is partially rate limiting via the thermally activated enzymatic pathway. The magnitude of observed photoenhancement initially scales linearly with pump fluence; however when a critical threshold is exceeded, the photoactivity saturates and is even suppressed at greater excitation fluences. The photodynamic mechanisms associated with this suppression behavior are characterized with the use of ultrafast multipulse pump-dump-probe and pump-repump-probe transient absorption techniques in combination with complementary two-color, steady-state excitation assays. Via multistate kinetic modeling of the transient ultrafast data and the steady-state assay data, the nonmonotonic incident power dependence of the photoactivty in AAT is decomposed into contributions from high-intensity dumping of the excited singlet state and repumping of the excited triplet state with induces the repopulation of the ground state via rapid intersystem crossing in the higher-lying triplet electronic manifold.

Threshold kinetics of a solar-simulator-pumped iodine laser

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Lee, Y.; Weaver, W. R.; Humes, D. H.; Lee, J. H.

1984-01-01

A model of the chemical kinetics of the n-C3F7I solar-simulator-pumped iodine laser is utilized to study the major kinetic processes associated with the threshold behavior of this experimental system. Excited-state diffusion to the cell wall is the dominant limiting factor below 5 torr. Excited-state diffusion to the cell wall is the dominant limiting factor below 5 torr. Excited-state recombination with the alkyl radical and quenching by the parent gas control threshold at higher pressures. Treatment of the hyperfine splitting and uncertainty in the pressure broadening are important factors in fixing the threshold level. In spite of scatter in the experimental data caused by instabilities in the simulator high-pressure high-pressure arc, reasonable agreement is achieved between the model and experiment. Model parameters arrived at are within the uncertainty range of values found in the literature.

Low-Spin States From Decay Studies in the Mass 80 Region

PubMed Central

Döring, J.; Aprahamian, A.; Wiescher, M.

2000-01-01

Neutron-deficient nuclei in the mass 80 region are known to exhibit strongly deformed ground states deduced mainly from yrast-state properties measured in-beam via heavy-ion fusion-evaporation reactions. Vibrational excitations and non-yrast states as well as their interplay with the observed rotational collectivity have been less studied to date within this mass region. Thus, several β-decay experiments have been performed to populate low-spin states in the neutron-deficient 80,84Y and 80,84Sr nuclei. An overview of excited 0+ states in Sr and Kr nuclei is given and conclusions about shape evolution at low-spins are presented. In general, the non-yrast states in even-even Sr nuclei show mainly vibration-like collectivity which evolves to rotational behavior with increasing spin and decreasing neutron number. PMID:27551586

Superior optical nonlinearity of an exceptional fluorescent stilbene dye

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

He, Tingchao; Division of Physics and Applied Physics, Centre for Disruptive Photonic Technologies; Sreejith, Sivaramapanicker

2015-03-16

Strong multiphoton absorption and harmonic generation in organic fluorescent chromophores are, respectively, significant in many fields of research. However, most of fluorescent chromophores fall short of the full potential due to the absence of the combination of such different nonlinear upconversion behaviors. Here, we demonstrate that an exceptional fluorescent stilbene dye could exhibit efficient two- and three-photon absorption under the excitation of femtosecond pulses in solution phase. Benefiting from its biocompatibility and strong excited state absorption behavior, in vitro two-photon bioimaging and superior optical limiting have been exploited, respectively. Simultaneously, the chromophore could generate efficient three-photon excited fluorescence and third-harmonicmore » generation (THG) when dispersed into PMMA film, circumventing the limitations of classical fluorescent chromophores. Such chromophore may find application in the production of coherent light sources of higher photon energy. Moreover, the combination of three-photon excited fluorescence and THG can be used in tandem to provide complementary information in biomedical studies.« less

Coherent excitations revealed and calculated

NASA Astrophysics Data System (ADS)

Georges, Antoine

2018-01-01

Quantum entities manifest themselves as either particles or waves. In a physical system containing a very large number of identical particles, such as electrons in a material, individualistic (particle-like) behavior prevails at high temperatures. At low temperatures, collective behavior emerges, and excitations of the system in this regime are best described as waves—long-lived phenomena that are periodic in both space and time and often dubbed “coherent excitations” by physicists. On page 186 of this issue, Goremychkin et al. (1) used experiment and theory to describe the emergence of coherent excitations in a complex quantum system with strong interactions. They studied a cerium-palladium compound, CePd3, in which the very localized electrons of 4f orbitals of Ce interact with the much more itinerant conduction electrons of the extended d orbitals of Pd at low temperatures to create a wavelike state.

The Impact of Emotional States on Cognitive Control Circuitry and Function.

PubMed

Cohen, Alexandra O; Dellarco, Danielle V; Breiner, Kaitlyn; Helion, Chelsea; Heller, Aaron S; Rahdar, Ahrareh; Pedersen, Gloria; Chein, Jason; Dyke, Jonathan P; Galvan, Adriana; Casey, B J

2016-03-01

Typically in the laboratory, cognitive and emotional processes are studied separately or as a stream of fleeting emotional stimuli embedded within a cognitive task. Yet in life, thoughts and actions often occur in more lasting emotional states of arousal. The current study examines the impact of emotions on actions using a novel behavioral paradigm and functional neuroimaging to assess cognitive control under sustained states of threat (anticipation of an aversive noise) and excitement (anticipation of winning money). Thirty-eight healthy adult participants were scanned while performing an emotional go/no-go task with positive (happy faces), negative (fearful faces), and neutral (calm faces) emotional cues, under threat or excitement. Cognitive control performance was enhanced during the excited state relative to a nonarousing control condition. This enhanced performance was paralleled by heightened activity of frontoparietal and frontostriatal circuitry. In contrast, under persistent threat, cognitive control was diminished when the valence of the emotional cue conflicted with the emotional state. Successful task performance in this conflicting emotional condition was associated with increased activity in the posterior cingulate cortex, a default mode network region implicated in complex processes such as processing emotions in the context of self and monitoring performance. This region showed positive coupling with frontoparietal circuitry implicated in cognitive control, providing support for a role of the posterior cingulate cortex in mobilizing cognitive resources to improve performance. These findings suggest that emotional states of arousal differentially modulate cognitive control and point to the potential utility of this paradigm for understanding effects of situational and pathological states of arousal on behavior.

Ultrafast dynamics of photoactive yellow protein via the photoexcitation and emission processes.

PubMed

Nakamura, Ryosuke; Hamada, Norio; Ichida, Hideki; Tokunaga, Fumio; Kanematsu, Yasuo

2007-01-01

Pump-dump fluorescence spectroscopy was performed for photoactive yellow protein (PYP) at room temperature. The effect of the dump pulse on the population of the potential energy surface of the electronic excited state was examined as depletion in the stationary fluorescence intensity. The dynamic behavior of the population in the electronic excited state was successfully probed in the various combinations of the pump-dump delay, the dump-pulse wavelength, the dump-pulse energy and the observation wavelength. The experimental results were compared with the results obtained by the femtosecond time-resolved fluorescence spectroscopy.

Highly excited bound-state resonances of short-range inverse power-law potentials

NASA Astrophysics Data System (ADS)

Hod, Shahar

2017-11-01

We study analytically the radial Schrödinger equation with long-range attractive potentials whose asymptotic behaviors are dominated by inverse power-law tails of the form V(r)=-β _n r^{-n} with n>2. In particular, assuming that the effective radial potential is characterized by a short-range infinitely repulsive core of radius R, we derive a compact analytical formula for the threshold energy E^{ {max}}_l=E^{ {max}}_l(n,β _n,R), which characterizes the most weakly bound-state resonance (the most excited energy level) of the quantum system.

Electron correlations in partially filled lowest and excited Landau levels

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

Wojs, Arkadiusz

2001-03-15

The electron correlations near the half-filling of the lowest and excited Landau levels (LL's) are studied using numerical diagonalization. It is shown that in the low-lying states electrons avoid pair states with relative angular momenta R corresponding to positive anharmonicity of the interaction pseudopotential V(R). In the lowest LL, the superharmonic behavior of V(R) causes Laughlin correlations (avoiding pairs with R=1) and the Laughlin-Jain series of incompressible ground states. In the first excited LL, V(R) is harmonic at short range and a different series of incompressible states results. Similar correlations occur in the paired Moore-Read {nu}=5/2 state and in themore » {nu}=7/3 and 8/3 states, all having small total parentage from R=1 and 3 and large parentage from R=5. The {nu}=7/3 and 8/3 states are different from Laughlin {nu}=1/3 and 2/3 states and, in finite systems, occur at a different LL degeneracy (flux). The series of Laughlin-correlated states of electron pairs at {nu}=2+2/(q{sub 2}+2)=8/3, 5/2, 12/5, and 7/3 is proposed, although only in the {nu}=5/2 state pairing has been confirmed numerically. In the second excited LL, V(R) is subharmonic at short range and (near the half-filling) the electrons group into spatially separated larger {nu}=1 droplets to minimize the number of strongly repulsive pair states at R=3 and 5.« less

Non-radiative decay paths in rhodamines: new theoretical insights.

PubMed

Savarese, Marika; Raucci, Umberto; Adamo, Carlo; Netti, Paolo A; Ciofini, Ilaria; Rega, Nadia

2014-10-14

We individuate a photoinduced electron transfer (PeT) as a quenching mechanism affecting rhodamine B photophysics in solvent. The PeT involves an electron transfer from the carboxylate group to the xanthene ring of rhodamine B. This is finely modulated by the subtle balance of coulombic and non-classical interactions between the carboxyphenyl and xanthene rings, also mediated by the solvent. We propose the use of an electronic density based index, the so called DCT index, as a new tool to assess and quantify the nature of the excited states involved in non-radiative decays near the region of their intersection. In the present case, this analysis allows us to gain insight on the interconversion process from the bright state to the dark state responsible for the quenching of rhodamine B fluorescence. Our findings encourage the use of density based indices to study the processes affecting excited state reactions that are characterized by a drastic change in the excitation nature, in order to rationalize the photophysical behavior of complex molecular systems.

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

Alcaraz, Francisco Castilho; Ibanez Berganza, Miguel; Sierra, German

In a quantum critical chain, the scaling regime of the energy and momentum of the ground state and low-lying excitations are described by conformal field theory (CFT). The same holds true for the von Neumann and Renyi entropies of the ground state, which display a universal logarithmic behavior depending on the central charge. In this Letter we generalize this result to those excited states of the chain that correspond to primary fields in CFT. It is shown that the nth Renyi entropy is related to a 2n-point correlator of primary fields. We verify this statement for the critical XX andmore » XXZ chains. This result uncovers a new link between quantum information theory and CFT.« less

Plant Cell Imaging Based on Nanodiamonds with Excitation-Dependent Fluorescence

NASA Astrophysics Data System (ADS)

Su, Li-Xia; Lou, Qing; Jiao, Zhen; Shan, Chong-Xin

2016-09-01

Despite extensive work on fluorescence behavior stemming from color centers of diamond, reports on the excitation-dependent fluorescence of nanodiamonds (NDs) with a large-scale redshift from 400 to 620 nm under different excitation wavelengths are so far much fewer, especially in biological applications. The fluorescence can be attributed to the combined effects of the fraction of sp2-hybridized carbon atoms among the surface of the fine diamond nanoparticles and the defect energy trapping states on the surface of the diamond. The excitation-dependent fluorescent NDs have been applied in plant cell imaging for the first time. The results reported in this paper may provide a promising route to multiple-color bioimaging using NDs.

Plant Cell Imaging Based on Nanodiamonds with Excitation-Dependent Fluorescence.

PubMed

Su, Li-Xia; Lou, Qing; Jiao, Zhen; Shan, Chong-Xin

2016-12-01

Despite extensive work on fluorescence behavior stemming from color centers of diamond, reports on the excitation-dependent fluorescence of nanodiamonds (NDs) with a large-scale redshift from 400 to 620 nm under different excitation wavelengths are so far much fewer, especially in biological applications. The fluorescence can be attributed to the combined effects of the fraction of sp(2)-hybridized carbon atoms among the surface of the fine diamond nanoparticles and the defect energy trapping states on the surface of the diamond. The excitation-dependent fluorescent NDs have been applied in plant cell imaging for the first time. The results reported in this paper may provide a promising route to multiple-color bioimaging using NDs.

Influence of ground-state scattering properties on photoassociation spectra near the intercombination line of bosonic ytterbium

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

Borkowski, M.; Ciurylo, R.; Julienne, P. S.

2010-10-29

We study theoretically the properties of photoassociation spectra near the {sup 1}S{sub 0}-{sup 3}P{sub 1} inter-combination line of bosonic ytterbium. We construct a mass scaled model of the excited state interaction potential that well describes bound state energies obtained in a previous photoassociation experiment. We then use it to calculate theoretical photoassociation spectra in a range of ultracold temperatures using semianalytical theory developed by Bohn and Julienne.Photoassociation spectra not only give us the energies of excited bound states, but also provide information about the behavior of the ground state wavefunction. In fact, it can be shown that within the so-calledmore » reflection approximation the line intensity is proportional to the ground state wavefunction at the transition's Condon point. We show that in the case of ytterbium, the rotational structure of the photoassociation spectra depends heavily on the behavior of the ground-state wavefunction. The change of the scattering length from one isotope to another and the resulting occurence of shape resonances in higher partial waves determines the appearance and disapperance of rotational components, especially in the deeper lying states, whose respective Condon points lie near the ground state centrifugal barrier. Thus, photoassociation spectra differ qualitatively between isotopes.« less

Prestimulus Network Integration of Auditory Cortex Predisposes Near-Threshold Perception Independently of Local Excitability

PubMed Central

Leske, Sabine; Ruhnau, Philipp; Frey, Julia; Lithari, Chrysa; Müller, Nadia; Hartmann, Thomas; Weisz, Nathan

2015-01-01

An ever-increasing number of studies are pointing to the importance of network properties of the brain for understanding behavior such as conscious perception. However, with regards to the influence of prestimulus brain states on perception, this network perspective has rarely been taken. Our recent framework predicts that brain regions crucial for a conscious percept are coupled prior to stimulus arrival, forming pre-established pathways of information flow and influencing perceptual awareness. Using magnetoencephalography (MEG) and graph theoretical measures, we investigated auditory conscious perception in a near-threshold (NT) task and found strong support for this framework. Relevant auditory regions showed an increased prestimulus interhemispheric connectivity. The left auditory cortex was characterized by a hub-like behavior and an enhanced integration into the brain functional network prior to perceptual awareness. Right auditory regions were decoupled from non-auditory regions, presumably forming an integrated information processing unit with the left auditory cortex. In addition, we show for the first time for the auditory modality that local excitability, measured by decreased alpha power in the auditory cortex, increases prior to conscious percepts. Importantly, we were able to show that connectivity states seem to be largely independent from local excitability states in the context of a NT paradigm. PMID:26408799

Photoinduced ICT vs. excited rotamer intercoversion in two quadrupolar polyaromatic N-methylpyridinium cations.

PubMed

Cesaretti, A; Carlotti, B; Elisei, F; Fortuna, C G; Spalletti, A

2018-01-24

The excited state dynamics of two quadrupolar polyaromatic N-methylpyridinium cations have been fully investigated in order to acquire detailed information on their photo-induced behavior. The two molecules are symmetric push-pull compounds having a D-π-A + -π-D motif, with the same electron-acceptor central unit (A = N-methylpyridinium) and two distinctive electron-donor polyaromatic side groups (D), namely naphthyl and pyrenyl substituents. Both molecules undergo charge transfer during the absorption, as revealed by a significant solvatochromism exhibited with solvent polarity, but the fate of their excited state was found to be markedly different. The careful analysis of the data gathered from femtosecond-resolved fluorescence up-conversion and transient absorption experiments, supported by DFT quantum mechanical calculations and temperature-dependent stationary measurements, shows the leading role of intramolecular charge transfer, assisted by symmetry breaking, in the pyrenyl derivative and that of rotamer interconversion in the naphthtyl one. Both excited state processes are controlled by the viscosity rather than polarity of the solvent, and they occur during inertial solvation in low-viscous media and lengthening up to tens of picoseconds in highly viscous solvents.

Non-adiabatic behavior in the homolytic and heterolytic bond dissociation of protonated hydrazine: A guided ion beam and theoretical investigation

NASA Astrophysics Data System (ADS)

McNary, Christopher P.; Armentrout, P. B.

2017-09-01

Threshold collision-induced dissociation using a guided ion beam tandem mass spectrometer was performed on protonated hydrazine and its perdeuterated variant. The dominant dissociation pathways observed were endothermic homolytic and heterolytic cleavages of the N-N bond. The data were analyzed using a statistical model after accounting for internal and kinetic energy distributions, multiple collisions, and kinetic shifts to obtain 0 K bond dissociation energies. Comparison with literature thermochemistry demonstrates that both channels behave non-adiabatically. Heterolytic bond cleavage yields NH2+ + NH3 products, but the NH2+ fragment is in the spin-restricted excited 1A1 state and not in the spin-forbidden ground 3B1 state, whereas homolytic bond cleavage leads to dissociation to the NH3+ + NH2 product asymptote with NH2 in its excited 2A1 state rather than the energetically favored 2B1 state. The rationale for the non-adiabatic behavior observed in the homolytic bond cleavage is revealed by detailed theoretical calculations of the relevant potential energy surfaces and the relevant occupied valence molecular orbitals. These calculations suggest that the non-adiabatic behavior results from conservation of the σ and π character of the binding and lone pair electrons on the nitrogen atoms.

Evolution of superclusters and delocalized states in GaAs1-xNx

NASA Astrophysics Data System (ADS)

Fluegel, B.; Alberi, K.; Beaton, D. A.; Crooker, S. A.; Ptak, A. J.; Mascarenhas, A.

2012-11-01

The evolution of individual nitrogen cluster bound states into an extended state infinite supercluster in dilute GaAs1-xNx was probed through temperature and intensity-dependent, time-resolved and magnetophotoluminescence (PL) measurements. Samples with compositions less than 0.23% N exhibit PL behavior that is consistent with emission from the extended states of the conduction band. Near a composition of 0.23% N, a discontinuity develops between the extended state PL peak energy and the photoluminescence excitation absorption edge. The existence of dual localized/delocalized state behavior near this composition signals the formation of an N supercluster just below the conduction band edge. The infinite supercluster is fully developed by 0.32% N.

Persistent nuclear wave packet oscillation coexistent with incoherent vibrational population at excited F centers in KI.

PubMed

Koyama, Takeshi; Takahashi, Youtarou; Nakajima, Makoto; Suemoto, Tohru

2006-06-14

We investigated nuclear wave packet dynamics in the excited state of KI F centers at 10 K using time-resolved luminescence spectroscopy. Observed transient spectrum is divided into oscillatory and non-oscillatory components. The former lasts over 11 ps without appreciable damping and is attributed to the oscillation of the wave packet consisting mainly of the A(1g) mode around the center. The non-oscillatory part rises quickly after photo-excitation exhibiting a cooling of incoherent vibrational population. This behavior suggests the fast energy dissipation due to the dephasing of the bulk phonon modes.

Statistical Thermodynamic Approach to Vibrational Solitary Waves in Acetanilide

NASA Astrophysics Data System (ADS)

Vasconcellos, Áurea R.; Mesquita, Marcus V.; Luzzi, Roberto

1998-03-01

We analyze the behavior of the macroscopic thermodynamic state of polymers, centering on acetanilide. The nonlinear equations of evolution for the populations and the statistically averaged field amplitudes of CO-stretching modes are derived. The existence of excitations of the solitary wave type is evidenced. The infrared spectrum is calculated and compared with the experimental data of Careri et al. [Phys. Rev. Lett. 51, 104 (1983)], resulting in a good agreement. We also consider the situation of a nonthermally highly excited sample, predicting the occurrence of a large increase in the lifetime of the solitary wave excitation.

Tunable emission and excited state absorption induced optical limiting in Tb2(MoO4)3: Sm3+/Eu3+ nanophosphors

NASA Astrophysics Data System (ADS)

Mani, Kamal P.; Sreekanth, Perumbilavil; Vimal, G.; Biju, P. R.; Unnikrishnan, N. V.; Ittyachen, M. A.; Philip, Reji; Joseph, Cyriac

2016-12-01

Photoluminescence properties and optical limiting behavior of pure and Sm3+/Eu3+ doped Tb2(MoO4)3 nanophosphors are investigated. The prepared nanophosphors exhibit excellent emission when excited by UV light. Color-tunable emissions in Tb2-xSmx(MoO4)3 and Tb2-xEux(MoO4)3 are realized by employing different excitation wavelengths or by controlling the doping concentration of Sm3+ and Eu3+. Luminescence quantum yield and CIE chromatic coordinates of the prepared phosphors were also presented. Optical limiting properties of the samples are investigated by open aperture Z-scan technique using 5 ns laser pulses at 532 nm. Numerical fitting of the measured Z-scan data to the relevant nonlinear transmission equations reveals that the nonlinear absorption is arising from strong excited state absorption, along with weak absorption saturation and it is found that the optical nonlinearity of Tb2(MoO4)3 increases with Sm3+/Eu3+doping. Parameters such as saturation fluence, excited state absorption cross section and ground state absorption cross section of the samples have been determined numerically, from which the figure of merit for nonlinear absorption is calculated. The excited state absorption cross-section of the samples is found to be one order of magnitude higher than that of the ground state absorption cross-section, indicating strong reverse saturable absorption. These results indicate that Sm3+/Eu3+ doped Tb2(MoO4)3 nanophosphors are efficient media for UV/n-UV pumped LEDs, and are also potential candidates for designing efficient optical limiting devices for the protection of human eyes and sensitive optical detectors from harmful laser radiation.

Light-induced flickering of DsRed provides evidence for distinct and interconvertible fluorescent states.

PubMed Central

Malvezzi-Campeggi, F; Jahnz, M; Heinze, K G; Dittrich, P; Schwille, P

2001-01-01

Green fluorescent protein (GFP) from jellyfish Aequorea victoria, the powerful genetically encoded tag presently available in a variety of mutants featuring blue to yellow emission, has found a red-emitting counterpart. The recently cloned red fluorescent protein DsRed, isolated from Discosoma corals (), with its emission maximum at 583 nm, appears to be the long awaited tool for multi-color applications in fluorescence-based biological research. Studying the emission dynamics of DsRed by fluorescence correlation spectroscopy (FCS), it can be verified that this protein exhibits strong light-dependent flickering similar to what is observed in several yellow-shifted mutants of GFP. FCS data recorded at different intensities and excitation wavelengths suggest that DsRed appears under equilibrated conditions in at minimum three interconvertible states, apparently fluorescent with different excitation and emission properties. Light absorption induces transitions and/or cycling between these states on time scales of several tens to several hundreds of microseconds, dependent on excitation intensity. With increasing intensity, the emission maximum of the static fluorescence continuously shifts to the red, implying that at least one state emitting at longer wavelength is preferably populated at higher light levels. In close resemblance to GFP, this light-induced dynamic behavior implies that the chromophore is subject to conformational rearrangements upon population of the excited state. PMID:11509387

Photochemistry of fac-[Re(CO)3(dcbH2)( trans-stpy)]+: New Insights on the Isomerization Mechanism of Coordinated Stilbene-like Ligands.

PubMed

Faustino, Leandro A; Hora Machado, Antonio Eduardo; Patrocinio, Antonio Otavio T

2018-03-05

In this work, a novel complex fac-[Re(CO) 3 (dcbH 2 )( trans-stpy)] + , (dcbH 2 = 4,4'-dicarboxylic acid-2,2'-bipyridine; trans-stpy = trans-4-styrylpyridine) was synthesized and characterized toward its spectroscopic, photochemical, and photophysical properties. The experimental data provide new insights on the mechanism of photochemical trans-to- cis isomerization of the stilbene-like ligand coordinated to Re(I) polypyridyl complexes. The new complex exhibits an unusual and strong dependence of the isomerization quantum yield (Φ t →c ) on the irradiation wavelength. Φ t →c was 0.81 ± 0.08 for irradiation at 365 nm and continuously decreased as the irradiation wavelength is shifted to the visible. At 405 nm irradiation Φ t →c is almost 2 orders of magnitude lower (0.010 ± 0.005) than that observed at 365 nm excitation. This behavior can be explained by the low-lying triplet metal-to-ligand charge-transfer excited state ( 3 MLCT) that hinders the triplet photoreaction mechanism under visible light absorption. Under UV irradiation, direct population of styrylpyridine-centered excited state ( 1 IL) leads to the occurrence of the photoisomerization via a singlet mechanism. Further experiments were performed with the complex immobilized on the surface of TiO 2 and Al 2 O 3 films. The nonoccurrence of isomerization at the oxide surfaces even under UV excitation evidences the role of energy gap between the 1 IL/ 1 MLCT states on the photochemical/photophysical processes. The results establish important relationships between the molecular structure and the photoelectrochemical behavior, which can further contribute to the development of solid-state molecular switches based on Re(I) polypyridyl complexes.

Dynamics of interacting Dicke model in a coupled-cavity array

NASA Astrophysics Data System (ADS)

Badshah, Fazal; Qamar, Shahid; Paternostro, Mauro

2014-09-01

We consider the dynamics of an array of mutually interacting cavities, each containing an ensemble of N two-level atoms. By exploring the possibilities offered by ensembles of various dimensions and a range of atom-light and photon-hopping values, we investigate the generation of multisite entanglement, as well as the performance of excitation transfer across the array, resulting from the competition between on-site nonlinearities of the matter-light interaction and intersite photon hopping. In particular, for a three-cavity interacting system it is observed that the initial excitation in the first cavity completely transfers to the ensemble in the third cavity through the hopping of photons between the adjacent cavities. Probabilities of the transfer of excitation of the cavity modes and ensembles exhibit characteristics of fast and slow oscillations governed by coupling and hopping parameters, respectively. In the large-hopping case, by seeding an initial excitation in the cavity at the center of the array, a tripartite W state, as well as a bipartite maximally entangled state, is obtained, depending on the interaction time. Population of the ensemble in a cavity has a positive impact on the rate of excitation transfer between the ensembles and their local cavity modes. In particular, for ensembles of five to seven atoms, tripartite W states can be produced even when the hopping rate is comparable to the cavity-atom coupling rate. A similar behavior of the transfer of excitation is observed for a four-coupled-cavity system with two initial excitations.

Broadband transient absorption spectroscopy with 1- and 2-photon excitations: Relaxation paths and cross sections of a triphenylamine dye in solution

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

Moreno, J.; Dobryakov, A. L.; Hecht, S., E-mail: sh@chemie.hu-berlin.de, E-mail: skovale@chemie.hu-berlin.de

2015-07-14

1-photon (382 nm) and 2-photon (752 nm) excitations to the S{sub 1} state are applied to record and compare transient absorption spectra of a push-pull triphenylamine (TrP) dye in solution. After 1-photon excitation, ultrafast vibrational and structural molecular relaxations are detected on a 0.1 ps time scale in nonpolar hexane, while in polar acetonitrile, the spectral evolution is dominated by dipolar solvation. Upon 2-photon excitation, transient spectra in hexane reveal an unexpected growth of stimulated emission (SE) and excited-state absorption (ESA) bands. The behavior is explained by strong population transfer S{sub 1} → S{sub n} due to resonant absorption ofmore » a third pump photon. Subsequent S{sub n} → S{sub 1} internal conversion (with τ{sub 1} = 1 ps) prepares a very hot S{sub 1} state which cools down with τ{sub 2} = 13 ps. The pump pulse energy dependence proves the 2-photon origin of the bleach signal. At the same time, SE and ESA are strongly affected by higher-order pump absorptions that should be taken into account in nonlinear fluorescence applications. The 2-photon excitation cross sections σ{sup (2)} = 32 ⋅ 10{sup −50} cm{sup 4} s at 752 nm are evaluated from the bleach signal.« less

Optically Guided Photoactivity: Coordinating Tautomerization, Photoisomerization, Inhomogeneity, and Reactive Intermediates within the RcaE Cyanobacteriochrome.

PubMed

Gottlieb, Sean M; Chang, Che-Wei; Martin, Shelley S; Rockwell, Nathan C; Lagarias, J Clark; Larsen, Delmar S

2014-05-01

The RcaE cyanobacteriochrome uses a linear tetrapyrrole chromophore to sense the ratio of green and red light to enable the Fremyella diplosiphon cyanobacterium to control the expression of the photosynthetic infrastructure for efficient utilization of incident light. The femtosecond photodynamics of the embedded phycocyanobilin chromophore within RcaE were characterized with dispersed femtosecond pump-dump-probe spectroscopy, which resolved a complex interplay of excited-state proton transfer, photoisomerization, multilayered inhomogeneity, and reactive intermediates. These reactions were integrated within a central model that incorporated a rapid (200 fs) excited-state Le Châtelier redistribution between parallel evolving populations ascribed to different tautomers. Three photoproducts were resolved and originates from four independent subpopulations, each with different dump-induced behavior: Lumi-Go was depleted, Lumi-Gr was unaffected, and Lumi-Gf was enhanced. This suggests that RcaE may be engineered to act either as an in vivo fluorescent probe (after single-pump excitation) or as an in vivo optogenetic sample (after pump and dump excitation).

Influence of Γ-X band mixing on the excited donor in a parabolic quantum well

NASA Astrophysics Data System (ADS)

Raghuvaran, T.; Shanthi, R. Vijaya; D'Reuben, A. Merwyn Jasper; Nithiananthi, P.

2013-06-01

Equally spaced energy levels of Parabolic Quantum Well are perturbed due to the application of hydrostatic pressure. It will modify the electronic and optical behavior of high Potential devices. The variation of excited state donor binding energy due to Γ-X band mixing at critical cross over pressures in a Parabolic GaAs/AlxGa1-x As quantum well has been investigated in the effective mass approximation using variational method.

a Computational Tddft Study on Intramolecular Charge Transfer in Di-Tert and 2,4,6-TRICYANOANILINES.

NASA Astrophysics Data System (ADS)

Fujiwara, Takashige; Zgierski, Marek Z.

2014-06-01

We have carried out TDDFT computational studies on the low-lying excited states of di-tert-butylaminobenzonitrile and 2,4,6-tricyanoaniline compounds that exhibit unusual photophysical behaviors associated with the intramolecular charge transfer (ICT). For both 3- and 4-di-tert-butylamino)benzonitriles (m-DTBABN and p-DTBABN, respectively) show the ICT formation, and p-DTBABN appears to be the only meta-substituted aminobenzonitrile that exhibits the ICT formation. The TDDFT calculations indicate evidence that the ultrafast ICT formation in p-DTBABN and m-DTBABN is due to the sequential state switches: ππ*(La)→ πσ*→ ICT in the presence of conical intersections among the three closely-lying excited-states. On the other hand, 2,4,6-tricyanoaniline does not show clear evidence for the LE (locally excited) state → ICT state formation from steady-state fluorescence studies, despite the greater electron acceptor strength of tricycanobenzene as compared to monocyanobenzene, which is part of a 4-(dimethylamino)benzonitrile (p-DMABN) compound. However, it is predicted that 2,4,6-tricyano-N,N-dimethylaniline (TCDMA), but not 2,4,6-tricyanoaniline (TCA), possesses two ICT states, which show the ICT-characterized quinoidal structures and lie below the initially photo-excited S1(ππ*) state. The CC2 calculations further predict two conformers as labeled with quinoidal (ICT--Q) and anti-quinoidal (ICT--AQ) structures are rapidly interconnecting with each other. The lower energy ICT--Q structure tends to be populated from the unstable ICT--AQ structure, which is responsible for the observed time-resolved fluorescence as well as the excited-state absorption from the mixed S1(ππ*)/ICT state of TCDMA. In both cases for TCDMA and TCA, the πσ* state locates significantly higher in energy than the S1(ππ*) state (and the ICT state for TCA), thus precluding the πσ*→ ICT formation, which is believed to occur in a p-DMABN in polar environments.

The energy structure and decay channels of the 4p6-shell excited states in Sr

NASA Astrophysics Data System (ADS)

Kupliauskienė, A.; Kerevičius, G.; Borovik, V.; Shafranyosh, I.; Borovik, A.

2017-11-01

The ejected-electron spectra arising from the decay of the 4p{}5{{nln}}{\\prime }{l}{\\prime }{n}{\\prime\\prime }{l}{\\prime\\prime } autoionizing states in Sr atoms have been studied precisely at the incident-electron energies close to excitation and ionization thresholds of the 4{{{p}}}6 subshell. The excitation behaviors for 58 lines observed between 12 and 21 eV ejected-electron kinetic energy have been investigated. Also, the ab initio calculations of excitation energies, autoionization probabilities and electron-impact excitation cross sections of the states 4p{}5{{nln}}{\\prime }{l}{\\prime }{n}{\\prime\\prime }{l}{\\prime\\prime } (nl = 4d, 5s, 5p; {n}{\\prime }{l}{\\prime } = 4d, 5s, 5p; {n}{\\prime\\prime }{l}{\\prime\\prime } = 5s, 6s, 7s, 8s, 9s, 5p, 6p, 5d, 6d, 7d, 8d, 4f, 5g) have been performed by employing the large-scale configuration-interaction method in the basis of the solutions of Dirac-Fock-Slater equations. The obtained experimental and theoretical data have been used for the accurate identification of the 60 lines in ejected-electron spectra and the 68 lines observed earlier in photoabsorption spectra. The excitation and decay processes for 105 classified states in the 4p55s{}2{nl}, 4p54d{}2{nl} and 4p55s{{nln}}{\\prime }{l}{\\prime } configurations have been considered in detail. In particular, most of the states lying below the ionization threshold of the 4p6 subshell at 26.92 eV possess up to four decay channels with formation of Sr+ in 5s{}1/2, 4d{}3/{2,5/2} and 5p{}1/{2,3/2} states. Two-step autoionization and two-electron Auger transitions with formation of Sr2+ in the 4p6 {}1{{{S}}}0 ground state are the main decay paths for high-lying autoionizing states. The excitation threshold of the 4{{{p}}}6 subshell in Sr has been established at 20.98 ± 0.05 eV.

A roaming wavepacket in the dynamics of electronically excited 2-hydroxypyridine.

PubMed

Poisson, Lionel; Nandi, Dhananjay; Soep, Benoît; Hochlaf, Majdi; Boggio-Pasqua, Martial; Mestdagh, Jean-Michel

2014-01-14

How much time does it take for a wavepacket to roam on a multidimensional potential energy surface? This combined theoretical and pump-probe femtosecond time experiment on 2-hydroxypyridine proposes an answer. Bypassing the well-established transition state and conical intersection relaxation pathways, this molecular system undergoes relaxation into the S1 excited state: the central ring is destabilized by the electronic excitation, within ~100 fs after absorption of the pump photon, then the H-atom bound to oxygen undergoes a roaming behavior when it couples to other degrees of freedom of the molecule. The timescale of the latter process is measured to be ~1.3 ps. Further evolution of the wavepacket is either an oscillation onto the S1 potential or a conversion into the triplet state for timescale larger than ~110 ps. Our work introduces a new tool for the understanding of time-resolved relaxation dynamics applied to large molecules through the roaming dynamics characterized by its strongly delocalized wavepacket on flat molecular potential energy surfaces.

Electronic properties of Al xGa 1- xAs surface passivated by ultrathin silicon interface control layer

NASA Astrophysics Data System (ADS)

Adamowicz, B.; Miczek, M.; Ikeya, K.; Mutoh, M.; Saitoh, T.; Fujikura, H.; Hasegawa, H.

1999-03-01

The photoluminescence surface state spectroscopy (PLS 3) method was applied to a study of the surface state distribution ( NSS), effective surface recombination velocity ( Seff), electron ( EFn) and hole ( EFp) quasi-Fermi levels and band bending ( VS) on the Al 0.33Ga 0.67As surface air-exposed and passivated by the Si interface control layer (ICL) technique. Using the detailed measurements of the PL quantum efficiency for different excitation intensities, combined with the rigorous computer simulations of the bulk and surface recombination processes, the behavior and correlation among the surface characteristics under photo-excitation was determined. The present analysis indicated that forming of a Si 3N 4/Si ICL double layer (with a monolayer level control) on AlGaAs surface reduces the minimum interface state density down to 10 10 cm -2 eV -1 and surface recombination velocity to the range of 10 4 cm/s under low excitations.

Theoretical Insights into the Origin of Photoluminescence of Au 25(SR) 18 – Nanoparticles

DOE PAGES

Weerawardene, K. L. Dimuthu M.; Aikens, Christine M.

2016-08-15

Understanding fundamental behavior of luminescent nanomaterials upon photoexcitation is necessary to expand photocatalytic and biological imaging applications. Despite the significant amount of experimental work into the luminescence of Au 25(SR) 18 – clusters, the origin of photoluminescence in these clusters still remains unclear. In this study, the geometric and electronic structural changes of the Au 25(SR) 18 – (R = H, CH 3, CH 2CH 3, CH 2CH 2CH 3) nanoclusters upon photoexcitation are discussed using time-dependent density functional theory (TD-DFT) methods. Geometric relaxations in the optimized excited states of up to 0.33 Å impart remarkable effects on the energymore » levels of the frontier orbitals of Au 25(SR) 18 – nanoclusters. This gives rise to a Stokes shift of 0.49 eV for Au 25(SH) 18 – in agreement with experiments. Even larger Stokes shifts are predicted for longer ligands. Vibrational frequencies in the 75–80 cm –1 range are calculated for the nuclear motion involved in the excited-state nuclear relaxation; this value is in excellent agreement with vibrational beating observed in time-resolved spectroscopy experiments. Several excited states around 0.8, 1.15, and 1.25 eV are calculated for the Au 25(SH) 18 – nanocluster. Considering the typical underestimation of DFT excitation energies, these states are likely responsible for the emission observed experimentally in the 1.15–1.55 eV range. In conclusion, all excited states arise from core-based orbitals; charge-transfer states or other “semi-ring” or ligand-based states are not implicated.« less

Theoretical Insights into the Origin of Photoluminescence of Au 25(SR) 18 – Nanoparticles

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

Weerawardene, K. L. Dimuthu M.; Aikens, Christine M.

Understanding fundamental behavior of luminescent nanomaterials upon photoexcitation is necessary to expand photocatalytic and biological imaging applications. Despite the significant amount of experimental work into the luminescence of Au 25(SR) 18 – clusters, the origin of photoluminescence in these clusters still remains unclear. In this study, the geometric and electronic structural changes of the Au 25(SR) 18 – (R = H, CH 3, CH 2CH 3, CH 2CH 2CH 3) nanoclusters upon photoexcitation are discussed using time-dependent density functional theory (TD-DFT) methods. Geometric relaxations in the optimized excited states of up to 0.33 Å impart remarkable effects on the energymore » levels of the frontier orbitals of Au 25(SR) 18 – nanoclusters. This gives rise to a Stokes shift of 0.49 eV for Au 25(SH) 18 – in agreement with experiments. Even larger Stokes shifts are predicted for longer ligands. Vibrational frequencies in the 75–80 cm –1 range are calculated for the nuclear motion involved in the excited-state nuclear relaxation; this value is in excellent agreement with vibrational beating observed in time-resolved spectroscopy experiments. Several excited states around 0.8, 1.15, and 1.25 eV are calculated for the Au 25(SH) 18 – nanocluster. Considering the typical underestimation of DFT excitation energies, these states are likely responsible for the emission observed experimentally in the 1.15–1.55 eV range. In conclusion, all excited states arise from core-based orbitals; charge-transfer states or other “semi-ring” or ligand-based states are not implicated.« less

Initial mechanisms for the unimolecular decomposition of electronically excited bisfuroxan based energetic materials.

PubMed

Yuan, Bing; Bernstein, Elliot R

2017-01-07

Unimolecular decomposition of energetic molecules, 3,3'-diamino-4,4'-bisfuroxan (labeled as A) and 4,4'-diamino-3,3'-bisfuroxan (labeled as B), has been explored via 226/236 nm single photon laser excitation/decomposition. These two energetic molecules, subsequent to UV excitation, create NO as an initial decomposition product at the nanosecond excitation energies (5.0-5.5 eV) with warm vibrational temperature (1170 ± 50 K for A, 1400 ± 50 K for B) and cold rotational temperature (<55 K). Initial decomposition mechanisms for these two electronically excited, isolated molecules are explored at the complete active space self-consistent field (CASSCF(12,12)/6-31G(d)) level with and without MP2 correction. Potential energy surface calculations illustrate that conical intersections play an essential role in the calculated decomposition mechanisms. Based on experimental observations and theoretical calculations, NO product is released through opening of the furoxan ring: ring opening can occur either on the S 1 excited or S 0 ground electronic state. The reaction path with the lowest energetic barrier is that for which the furoxan ring opens on the S 1 state via the breaking of the N1-O1 bond. Subsequently, the molecule moves to the ground S 0 state through related ring-opening conical intersections, and an NO product is formed on the ground state surface with little rotational excitation at the last NO dissociation step. For the ground state ring opening decomposition mechanism, the N-O bond and C-N bond break together in order to generate dissociated NO. With the MP2 correction for the CASSCF(12,12) surface, the potential energies of molecules with dissociated NO product are in the range from 2.04 to 3.14 eV, close to the theoretical result for the density functional theory (B3LYP) and MP2 methods. The CASMP2(12,12) corrected approach is essential in order to obtain a reasonable potential energy surface that corresponds to the observed decomposition behavior of these molecules. Apparently, highly excited states are essential for an accurate representation of the kinetics and dynamics of excited state decomposition of both of these bisfuroxan energetic molecules. The experimental vibrational temperatures of NO products of A and B are about 800-1000 K lower than previously studied energetic molecules with NO as a decomposition product.

Decay of quadrupole-octupole 1- states in 40Ca and 140Ce

NASA Astrophysics Data System (ADS)

Derya, V.; Tsoneva, N.; Aumann, T.; Bhike, M.; Endres, J.; Gooden, M.; Hennig, A.; Isaak, J.; Lenske, H.; Löher, B.; Pietralla, N.; Savran, D.; Tornow, W.; Werner, V.; Zilges, A.

2016-03-01

Background: Two-phonon excitations originating from the coupling of two collective one-phonon states are of great interest in nuclear structure physics. One possibility to generate low-lying E 1 excitations is the coupling of quadrupole and octupole phonons. Purpose: In this work, the γ -decay behavior of candidates for the (21+⊗31-)1- state in the doubly magic nucleus 40Ca and in the heavier and semimagic nucleus 140Ce is investigated. Methods: (γ ⃗,γ') experiments have been carried out at the High Intensity γ -ray Source (HI γ S ) facility in combination with the high-efficiency γ -ray spectroscopy setup γ3 consisting of HPGe and LaBr3 detectors. The setup enables the acquisition of γ -γ coincidence data and, hence, the detection of direct decay paths. Results: In addition to the known ground-state decays, for 40Ca the decay into the 31- state was observed, while for 140Ce the direct decays into the 21+ and the 02+ state were detected. The experimentally deduced transition strengths and excitation energies are compared to theoretical calculations in the framework of EDF theory plus QPM approach and systematically analyzed for N =82 isotones. In addition, negative parities for two J =1 states in 44Ca were deduced simultaneously. Conclusions: The experimental findings together with the theoretical calculations support the two-phonon character of the 11- excitation in the light-to-medium-mass nucleus 40Ca as well as in the stable even-even N =82 nuclei.

Wave-front propagation in a discrete model of excitable media

NASA Astrophysics Data System (ADS)

Feldman, A. B.; Chernyak, Y. B.; Cohen, R. J.

1998-06-01

We generalize our recent discrete cellular automata (CA) model of excitable media [Y. B. Chernyak, A. B. Feldman, and R. J. Cohen, Phys. Rev. E 55, 3215 (1997)] to incorporate the effects of inhibitory processes on the propagation of the excitation wave front. In the common two variable reaction-diffusion (RD) models of excitable media, the inhibitory process is described by the v ``controller'' variable responsible for the restoration of the equilibrium state following excitation. In myocardial tissue, the inhibitory effects are mainly due to the inactivation of the fast sodium current. We represent inhibition using a physical model in which the ``source'' contribution of excited elements to the excitation of their neighbors decreases with time as a simple function with a single adjustable parameter (a rate constant). We sought specific solutions of the CA state transition equations and obtained (both analytically and numerically) the dependence of the wave-front speed c on the four model parameters and the wave-front curvature κ. By requiring that the major characteristics of c(κ) in our CA model coincide with those obtained from solutions of a specific RD model, we find a unique set of CA parameter values for a given excitable medium. The basic structure of our CA solutions is remarkably similar to that found in typical RD systems (similar behavior is observed when the analogous model parameters are varied). Most notably, the ``turn-on'' of the inhibitory process is accompanied by the appearance of a solution branch of slow speed, unstable waves. Additionally, when κ is small, we obtain a family of ``eikonal'' relations c(κ) that are suitable for the kinematic analysis of traveling waves in the CA medium. We compared the solutions of the CA equations to CA simulations for the case of plane waves and circular (target) waves and found excellent agreement. We then studied a spiral wave using the CA model adjusted to a specific RD system and found good correspondence between the shapes of the RD and CA spiral arms in the region away from the tip where kinematic theory applies. Our analysis suggests that only four physical parameters control the behavior of wave fronts in excitable media.

Intensity and amplitude correlations in the fluorescence from atoms with interacting Rydberg states

NASA Astrophysics Data System (ADS)

Xu, Qing; Mølmer, Klaus

2015-09-01

We explore the fluorescence signals from a pair of atoms driven towards Rydberg states on a three-level ladder transition. The dipole-dipole interactions between Rydberg excited atoms significantly distort the dark state and electromagnetically induced transparency behavior observed with independent atoms and, thus, their steady-state light emission. We calculate and analyze the temporal correlations between intensities and amplitudes of the signals emitted by the atoms and explain their origin in the atomic Rydberg state interactions.

Quantum tunneling of electron snake states in an inhomogeneous magnetic field.

PubMed

Hoodbhoy, Pervez

2018-05-10

In a two dimensional free electron gas subjected to a perpendicular spatially varying magnetic field, the classical paths of electrons are snake-like trajectories that weave along the line where the field crosses zero. But quantum mechanically this system is described by a symmetric double well potential which, for low excitations, leads to very different electron behavior. We compute the spectrum, as well as the wavefunctions, for states of definite parity in the limit of nearly degenerate states, i.e. for electrons sufficiently far from the B z   =  0 line. Transitions between the states are shown to give rise to a tunneling current. If the well is made asymmetrical by a time-dependent parity breaking perturbation then Rabi-like oscillations between parity states occur. Resonances can be excited and used to stimulate the transfer of electrons from one side of the potential barrier to the other through quantum tunneling.

Binding energy and photoionization cross-section of hydrogen-like donor impurity in strongly oblate ellipsoidal quantum dot

NASA Astrophysics Data System (ADS)

Hayrapetyan, D. B.; Ohanyan, G. L.; Baghdasaryan, D. A.; Sarkisyan, H. A.; Baskoutas, S.; Kazaryan, E. M.

2018-01-01

Hydrogen-like donor impurity states in strongly oblate ellipsoidal quantum dot have been studied. The hydrogen-like donor impurity states are investigated within the framework of variational method. The trial wave function constructed on the base of wave functions of the system without impurity. The dependence of the energy and binding energy for the ground and first excited states on the geometrical parameters of the ellipsoidal quantum dot and on the impurity position have been calculated. The behavior of the oscillator strength for different angles of incident light and geometrical parameters have been revealed. Photoionization cross-section of the electron transitions from the impurity ground state to the size-quantized ground and first excited states have been studied. The effects of impurity position and the geometrical parameters of the ellipsoidal quantum dot on the photoionization cross section dependence on the photon energy have been considered.

Quantum tunneling of electron snake states in an inhomogeneous magnetic field

NASA Astrophysics Data System (ADS)

Hoodbhoy, Pervez

2018-05-01

In a two dimensional free electron gas subjected to a perpendicular spatially varying magnetic field, the classical paths of electrons are snake-like trajectories that weave along the line where the field crosses zero. But quantum mechanically this system is described by a symmetric double well potential which, for low excitations, leads to very different electron behavior. We compute the spectrum, as well as the wavefunctions, for states of definite parity in the limit of nearly degenerate states, i.e. for electrons sufficiently far from the B z   =  0 line. Transitions between the states are shown to give rise to a tunneling current. If the well is made asymmetrical by a time-dependent parity breaking perturbation then Rabi-like oscillations between parity states occur. Resonances can be excited and used to stimulate the transfer of electrons from one side of the potential barrier to the other through quantum tunneling.

Motor Behavior Activates Bergmann Glial Networks

PubMed Central

Nimmerjahn, Axel; Mukamel, Eran A.; Schnitzer, Mark J.

2010-01-01

SUMMARY Although it is firmly established neuronal activity is a prime determinant of animal behavior, relationships between astrocytic excitation and animal behavior have remained opaque. Cerebellar Bergmann glia are radial astrocytes that are implicated in motor behavior and exhibit Ca2+-excitation. However, Ca2+-excitation in these cells has not previously been studied in behaving animals. Using two-photon microscopy we found that Bergmann glia exhibit three forms of Ca2+-excitation in awake behaving mice. Two of these are ongoing within the cerebellar vermis. During locomotor performance concerted Ca2+-excitation arises in networks of at least hundreds of Bergmann glia extending across several hundred microns or more. Concerted Ca2+-excitation was abolished by anesthesia or blockade of either neural activity or glutamatergic transmission. Thus, large networks of Bergmann glia can be activated by specific animal behaviors and undergo excitation of sufficient magnitude to potentially initiate macroscopic changes in brain dynamics or blood flow. PMID:19447095

Behavioral State Modulates the Activity of Brainstem Sensorimotor Neurons

PubMed Central

McArthur, Kimberly L.

2011-01-01

Sensorimotor processing must be modulated according to the animal's behavioral state. A previous study demonstrated that motion responses were strongly state dependent in birds. Vestibular eye and head responses were significantly larger and more compensatory during simulated flight, and a flight-specific vestibular tail response was also characterized. In the current study, we investigated the neural substrates for these state-dependent vestibular behaviors by recording extracellularly from neurons in the vestibular nuclear complex and comparing their spontaneous activity and sensory responses during default and simulated flight states. We show that motion-sensitive neurons in the lateral vestibular nucleus are state dependent. Some neurons increased their spontaneous firing rates during flight, though their increased excitability was not reflected in higher sensory gains. However, other neurons exhibited state-dependent gating of sensory inputs, responding to rotational stimuli only during flight. These results demonstrate that vestibular processing in the brainstem is state dependent and lay the foundation for future studies to investigate the synaptic mechanisms responsible for these modifications. PMID:22090497

Electronic excitations in γ -Li2IrO3

NASA Astrophysics Data System (ADS)

Li, Ying; Winter, Stephen M.; Jeschke, Harald O.; Valentí, Roser

2017-01-01

We investigate the electronic properties of the three-dimensional stripyhoneycomb γ -Li2IrO3 via relativistic density functional theory calculations as well as exact diagonalization of finite clusters and explore the details of the optical conductivity. Our analysis of this quantity reveals the microscopic origin of the experimentally observed (i) optical transitions and (ii) anisotropic behavior along the various polarization directions. In particular, we find that the optical excitations are overall dominated by transitions between jeff=1 /2 and 3/2 states and the weight of transitions between jeff=1 /2 states at low frequencies can be correlated to deviations from a pure Kitaev description. We furthermore reanalyze within this approach the electronic excitations in the known two-dimensional honeycomb systems α -Li2IrO3 and Na2IrO3 and discuss the results in comparison to γ -Li2IrO3 .

Synthesis, characterization, and spectroscopic investigation of benzoxazole conjugated Schiff bases.

PubMed

Santos, Fabiano S; Costa, Tania M H; Stefani, Valter; Gonçalves, Paulo F B; Descalzo, Rodrigo R; Benvenutti, Edilson V; Rodembusch, Fabiano S

2011-11-24

Two Schiff bases were synthesized by reaction of 2-(4'-aminophenyl)benzoxazole derivatives with 4-N,N-diethylaminobenzaldehyde. UV-visible (UV-vis) and steady-state fluorescence in solution were applied in order to characterize its photophysical behavior. The Schiff bases present absorption in the UV region with fluorescence emission in the blue-green region, with a large Stokes' shift. The UV-vis data indicates that each dye behaves as two different chromophores in solution in the ground state. The fluorescence emission spectra of the dye 5a show that an intramolecular proton transfer (ESIPT) mechanism takes place in the excited state, whereas a twisted internal charge transfer (TICT) state is observed for the dye 5b. Theoretical calculations were performed in order to study the conformation and polarity of the molecules at their ground and excited electronic states. Using density functional theory (DFT) methods at theoretical levels BLYP/Aug-SV(P) for geometry optimizations and B3LYP/6-311++G(2d,p) for single-point energy evaluations, the calculations indicate that the lowest energy conformations are in all cases nonplanar and that the dipole moments of the excited state relaxed structures are much larger than those of the ground state structures, which corroborates the experimental UV-vis absorption results.

Changes in Heart Rate Variability Recorded in Natural Situation with T-Shirt Integrated Sensors and Level of Observed Behavioral Excitation: A Pilot Study of Patients with Intellectual Disabilities and Psychiatric Disorders.

PubMed

Palix, Julie; Akselrod, Michel; Cungi, Charly; Giuliani, Fabienne; Favrod, Jérôme

2017-01-01

The present study investigates the possibilities of using heart rate variability (HRV) parameters as physiological markers that precede increase in observed behavioral excitation of intellectually disabled individuals. The ability to recognize or predict such patterns, especially in patients showing unpredictable reactions and language deficiencies, might be a major step forward in clinical research. Thirteen volunteers with intellectual disabilities, who had suffered of at least one event of overt aggression in the preceding 3 months, participated to the study. The protocol consists in the acquisition of continuous electrocardiogram (ECG) throughout approximately two times of 8 h in natural situation, using a T-shirt integrated with sensors. Simultaneously, an observer evaluates the patient's level of overt excitation from calm (level 1) to extremely tense (level 5) and send online via Bluetooth these triggers into the ECG signals. The HRV indexes were then estimated offline on the basis of the inter-beat intervals recorded by the ECG, independently for the 30 min preceding each behavioral tension marking point, averaged, and compared through non-parametric Wilcoxon matched-pairs test. Of these, the RMSSD and LF/HF calculations were used to observe the fluctuations of inhibitory activity and cardiovagal balance through different tension states. Seven individuals have sufficient reliable data for analysis. They have reached at least a level 3 of behavioral excitation (moderately tense) or more (very to extremely tense, level 4 and 5) and have been retained for further analysis. In sum, a total of 197 periods of tension were kept, made up of 46 periods of slight excitation (level 2), 18 of moderate excitation (level 3), 10 of high excitation (level 4), and 5 of extreme agitation (level 5). Variations in the HRV as a function of degree of excitation are observed for RMSSD index only (inhibitory parasympathetic activity). The changes from calm to increasing levels of excitation are characterized by a significant downfall in RMSSD index when patients were evaluated to be in a very high level of tension (level 4). The presence of precursors to agitation, reflected in the falling-off of parasympathetic activity, offers potentially interesting prospects for therapeutic development.

Physiological markers of motor inhibition during human behavior

PubMed Central

Duque, Julie; Greenhouse, Ian; Labruna, Ludovica; Ivry, Richard B.

2017-01-01

Transcranial magnetic stimulation (TMS) studies in humans have shown that many behaviors engage processes that suppress excitability within the corticospinal tract. Inhibition of the motor output pathway has been extensively studied in the context of action stopping, where a planned movement needs to be abruptly aborted. Recent TMS work has also revealed markers of motor inhibition during the preparation of movement. Here, we review the evidence for motor inhibition during action stopping and action preparation, focusing on studies that have used TMS to monitor changes in the excitability of the corticospinal pathway. We discuss how these physiological results have motivated theoretical models of how the brain selects actions, regulates movement initiation and execution, and switches from one state to another. PMID:28341235

Time Crystal Behavior of Excited Eigenstates

NASA Astrophysics Data System (ADS)

Syrwid, Andrzej; Zakrzewski, Jakub; Sacha, Krzysztof

2017-12-01

In analogy to spontaneous breaking of continuous space translation symmetry in the process of space crystal formation, it was proposed that spontaneous breaking of continuous time translation symmetry could lead to time crystal formation. In other words, a time-independent system prepared in the energy ground state is expected to reveal periodic motion under infinitely weak perturbation. In the case of the system proposed originally by Wilczek, spontaneous breaking of time translation symmetry cannot be observed if one starts with the ground state. We point out that the symmetry breaking can take place if the system is prepared in an excited eigenstate. The latter can be realized experimentally in ultracold atomic gases. We simulate the process of the spontaneous symmetry breaking due to measurements of particle positions and analyze the lifetime of the resulting symmetry broken state.

Time Crystal Behavior of Excited Eigenstates.

PubMed

Syrwid, Andrzej; Zakrzewski, Jakub; Sacha, Krzysztof

2017-12-22

In analogy to spontaneous breaking of continuous space translation symmetry in the process of space crystal formation, it was proposed that spontaneous breaking of continuous time translation symmetry could lead to time crystal formation. In other words, a time-independent system prepared in the energy ground state is expected to reveal periodic motion under infinitely weak perturbation. In the case of the system proposed originally by Wilczek, spontaneous breaking of time translation symmetry cannot be observed if one starts with the ground state. We point out that the symmetry breaking can take place if the system is prepared in an excited eigenstate. The latter can be realized experimentally in ultracold atomic gases. We simulate the process of the spontaneous symmetry breaking due to measurements of particle positions and analyze the lifetime of the resulting symmetry broken state.

[Acute schizophrenia concept and definition: investigation of a French psychiatrist population].

PubMed

Baylé, F J; Misdrahi, D; Llorca, P M; Lançon, C; Olivier, V; Quintin, P; Azorin, J M

2005-01-01

For schizophrenic disorders, the clinical conception of "acute state" is widely used in clinical settings to assess the effectiveness of therapeutic programs as well as epidemiological studies. Schizophrenic-specific symptomatology modification, need for hospitalization, significant change in care, disturbances in social behavior or suicide attempts were all used to define acute schizophrenic state. The decision to hospitalize is frequently used to define acute state but refers to multiple factors such as mood disorder, suicide attempts, drug abuse or social and environmental problems. Indeed, several and distinct definitions in a criteria basis form are available but no one has reached consensus. Because recognition of acute schizophrenic state remains based on the subjective clinician's advice, epidemiological and therapeutic studies fail in validity and reliability. The aim of the study was to evaluate how a population of French psychiatrists define criteria and therapeutic targets of acute schizophrenic state in their clinical practice. Psychiatrists filled out a self administered interview. At the time the interview was given, clinicians were notified that they were participating in a clinical consensus survey about schizophrenia. Six major indicators for acute state definition based on the literature data were proposed: general schizophrenic symptomatology modification (depression, anxiety, agitation, impulsivity/aggressiveness), specific schizophrenic symptomatology modification (positive symptoms, negative symptoms, disorganization), need for hospitalization, significant change in care, disturbance in social behavior and lastly, suicidal behavior. Minimal duration (1.2 or 4 weeks) of general and specific schizophrenic symptomatology modification required to define acute state were evaluated. The booklet included the 30 PANSS symptoms listed with their definitions. Among this symptom list, clinicians were instructed to select the ten criteria which they estimated best defined the acute state, followed by the ten most important target symptoms to be treated. Out of 2,369 questionnaires, 1,584 were collected on time (66.9%). Among the six majors indicators proposed to define acute state 75% of psychiatrists considered 1 to 3 criteria. Three were more frequently rated, including core schizophrenic symptomatology disturbance (68.4%), general schizophrenic symptomatology disturbance (68.0%) and suicidal behavior (64.9%). The other criteria were rated as follows: need for hospitalization (26.8%), significant change in care (18.3%), and disturbance in social behavior (29.1%). For 53.2% of psychiatrists the definition of acute state requires the presence of specific schizophrenic symptomatology for a minimal duration of one week. Two weeks with general symptomatology was required for 45.5% of psychiatrists to define acute state. Symptoms more often rated within the four first choices for acute state definition included delusions, conceptual disorganization, hallucinatory behavior and excitement. Except for grandiosity, all the PANSS positive subscale items were chosen to be included in the definition (delusions, conceptual disorganization, hallucinatory behavior, excitement, suspiciousness/persecution and hostility). Four items, including anxiety, depression, uncontrolled hostility, inner tension from the general psychopathology subscale were chosen as part of the ten most important criteria to define acute state. On the PANSS negative subscale (blunted affect, emotional withdrawal, poor relationships, passive apathetic withdrawal, difficulty in abstract thinking, lack of spontaneity/flow of conversation and stereotyped thinking), no item was rated to be included in the acute state definition. The highest rated symptoms among the four first choices for treatment included delusions, hallucinatory behavior, excitement and anxiety. The ten most important criteria for treatment were the same as for acute state definition with differences in frequency. Excited state, depression and suspiciousness/persecution were more rated for treatment than definition whereas delusion, hostility and conceptual disorganization were less rated as treatment target than definition criteria. In clinical practice, recognition of acute schizophrenic state is underscored by the association of specific schizophrenic symptomatology (positive symptoms, negative symptoms, disorganization) and general symptomatology (impulsivity/aggressiveness, anxiety, depression, agitation) of schizophrenia. For most clinicians, acute state definition requires specific symptom for a minimum of one week and other non-specific indicators such as suicidal behaviour have to be taken into account. With regard to PANSS criteria, most positive schizophrenic symptoms and some general schizophrenic symptoms are necessary for definition and designated as treatment priorities. Negative symptoms were not taken into account. Hallucinatory behavior is the first symptom rated in definition and is considered by psychiatrists as the absolute therapeutic priority. This survey could be a first step in the construction of an operational and consensual definition. This definition is strongly needed as a valid measurement in therapeutic and epidemiological outcome studies, which remain at least partly based on clinician subjective judgment.

Dynamics of a population of oscillatory and excitable elements.

PubMed

O'Keeffe, Kevin P; Strogatz, Steven H

2016-06-01

We analyze a variant of a model proposed by Kuramoto, Shinomoto, and Sakaguchi for a large population of coupled oscillatory and excitable elements. Using the Ott-Antonsen ansatz, we reduce the behavior of the population to a two-dimensional dynamical system with three parameters. We present the stability diagram and calculate several of its bifurcation curves analytically, for both excitatory and inhibitory coupling. Our main result is that when the coupling function is broad, the system can display bistability between steady states of constant high and low activity, whereas when the coupling function is narrow and inhibitory, one of the states in the bistable regime can show persistent pulsations in activity.

Evolution of superclusters and delocalized states in GaAs 1–xN x

DOE PAGES

Fluegel, B.; Alberi, K.; Beaton, D. A.; ...

2012-11-21

The evolution of individual nitrogen cluster bound states into an extended state infinite supercluster in dilute GaAs 1–xN x was probed through temperature and intensity-dependent, time-resolved and magnetophotoluminescence (PL) measurements. Samples with compositions less than 0.23% N exhibit PL behavior that is consistent with emission from the extended states of the conduction band. Near a composition of 0.23% N, a discontinuity develops between the extended state PL peak energy and the photoluminescence excitation absorption edge. The existence of dual localized/delocalized state behavior near this composition signals the formation of an N supercluster just below the conduction band edge. The infinitemore » supercluster is fully developed by 0.32% N.« less

Near ultraviolet photodissociation spectroscopy of Mn+(H2O) and Mn+(D2O)

NASA Astrophysics Data System (ADS)

Pearson, Wright L.; Copeland, Christopher; Kocak, Abdulkadir; Sallese, Zachary; Metz, Ricardo B.

2014-11-01

The electronic spectra of Mn+(H2O) and Mn+(D2O) have been measured from 30 000 to 35 000 cm-1 using photodissociation spectroscopy. Transitions are observed from the 7A1 ground state in which the Mn+ is in a 3d54s1 electronic configuration, to the 7B2 (3d54py) and 7B1 (3d54px) excited states with T0 = 30 210 and 32 274 cm-1, respectively. Each electronic transition has partially resolved rotational and extensive vibrational structure with an extended progression in the metal-ligand stretch at a frequency of ˜450 cm-1. There are also progressions in the in-plane bend in the 7B2 state, due to vibronic coupling, and the out-of-plane bend in the 7B1 state, where the calculation illustrates that this state is slightly non-planar. Electronic structure computations at the CCSD(T)/aug-cc-pVTZ and TD-DFT B3LYP/6-311++G(3df,3pd) level are also used to characterize the ground and excited states, respectively. These calculations predict a ground state Mn-O bond length of 2.18 Å. Analysis of the experimentally observed vibrational intensities reveals that this bond length decreases by 0.15 ± 0.015 Å and 0.14 ± 0.01 Å in the excited states. The behavior is accounted for by the less repulsive px and py orbitals causing the Mn+ to interact more strongly with water in the excited states than the ground state. The result is a decrease in the Mn-O bond length, along with an increase in the H-O-H angle. The spectra have well resolved K rotational structure. Fitting this structure gives spin-rotation constants ɛaa″ = -3 ± 1 cm-1 for the ground state and ɛaa' = 0.5 ± 0.5 cm-1 and ɛaa' = -4.2 ± 0.7 cm-1 for the first and second excited states, respectively, and A' = 12.8 ± 0.7 cm-1 for the first excited state. Vibrationally mediated photodissociation studies determine the O-H antisymmetric stretching frequency in the ground electronic state to be 3658 cm-1.

Collective behavior of coupled nonuniform stochastic oscillators

NASA Astrophysics Data System (ADS)

Assis, Vladimir R. V.; Copelli, Mauro

2012-02-01

Theoretical studies of synchronization are usually based on models of coupled phase oscillators which, when isolated, have constant angular frequency. Stochastic discrete versions of these uniform oscillators have also appeared in the literature, with equal transition rates among the states. Here we start from the model recently introduced by Wood et al. [K. Wood, C. Van den Broeck, R. Kawai, K. Lindenberg, Universality of synchrony: critical behavior in a discrete model of stochastic phase-coupled oscillators, Phys. Rev. Lett. 96 (2006) 145701], which has a collectively synchronized phase, and parametrically modify the phase-coupled oscillators to render them (stochastically) nonuniform. We show that, depending on the nonuniformity parameter 0≤α≤1, a mean field analysis predicts the occurrence of several phase transitions. In particular, the phase with collective oscillations is stable for the complete graph only for α≤α‧<1. At α=1 the oscillators become excitable elements and the system has an absorbing state. In the excitable regime, no collective oscillations were found in the model.

No evidence of reduced collectivity in Coulomb-excited Sn isotopes

NASA Astrophysics Data System (ADS)

Kumar, R.; Saxena, M.; Doornenbal, P.; Jhingan, A.; Banerjee, A.; Bhowmik, R. K.; Dutt, S.; Garg, R.; Joshi, C.; Mishra, V.; Napiorkowski, P. J.; Prajapati, S.; Söderström, P.-A.; Kumar, N.; Wollersheim, H.-J.

2017-11-01

In a series of Coulomb excitation experiments the first excited 2+ states in semimagic Sn 112 ,116 ,118 ,120 ,122 ,124 isotopes were excited using a 58Ni beam at safe Coulomb energy. The B (E 2 ; 0+→2+) values were determined with high precision (˜3 %) relative to 58Ni projectile excitation. These results disagree with previously reported B (E 2 ↑) values [A. Jungclaus et al., Phys. Lett. B 695, 110 (2011)., 10.1016/j.physletb.2010.11.012] extracted from Doppler-shift attenuation lifetime measurements, whereas the reported mass dependence of B (E 2 ↑) values is very similar to a recent Coulomb excitation study [J. M. Allmond et al., Phys. Rev. C 92, 041303(R) (2015), 10.1103/PhysRevC.92.041303]. The stable Sn isotopes, key nuclei in nuclear structure, show no evidence of reduced collectivity and we, thus, reconfirm the nonsymmetric behavior of reduced transition probabilities with respect to the midshell A =116 .

N=151Pu,Cm and Cf nuclei under rotational stress: Role of higher-order deformations

DOE PAGES

Hota, S. S.; Chowdhury, P.; Khoo, T. L.; ...

2014-10-18

The fast-rotating N=151 isotones 245Pu, 247Cm and 249Cf have been studied through inelastic excitation and transfer reactions with radioactive targets. While all have a ground-state band built on a νj 15/2[734]9/2 - Nilsson configuration, new excited bands have also been observed in each isotone. These odd-N excited bands allow a comparison of the alignment behavior for two different configurations, where the νj 15/2 alignment is either blocked or allowed. The effect of higher order deformations is explored through cranking calculations, which help clarify the elusive nature of νj 15/2 alignments.

Input dependent cell assembly dynamics in a model of the striatal medium spiny neuron network.

PubMed

Ponzi, Adam; Wickens, Jeff

2012-01-01

The striatal medium spiny neuron (MSN) network is sparsely connected with fairly weak GABAergic collaterals receiving an excitatory glutamatergic cortical projection. Peri-stimulus time histograms (PSTH) of MSN population response investigated in various experimental studies display strong firing rate modulations distributed throughout behavioral task epochs. In previous work we have shown by numerical simulation that sparse random networks of inhibitory spiking neurons with characteristics appropriate for UP state MSNs form cell assemblies which fire together coherently in sequences on long behaviorally relevant timescales when the network receives a fixed pattern of constant input excitation. Here we first extend that model to the case where cortical excitation is composed of many independent noisy Poisson processes and demonstrate that cell assembly dynamics is still observed when the input is sufficiently weak. However if cortical excitation strength is increased more regularly firing and completely quiescent cells are found, which depend on the cortical stimulation. Subsequently we further extend previous work to consider what happens when the excitatory input varies as it would when the animal is engaged in behavior. We investigate how sudden switches in excitation interact with network generated patterned activity. We show that sequences of cell assembly activations can be locked to the excitatory input sequence and outline the range of parameters where this behavior is shown. Model cell population PSTH display both stimulus and temporal specificity, with large population firing rate modulations locked to elapsed time from task events. Thus the random network can generate a large diversity of temporally evolving stimulus dependent responses even though the input is fixed between switches. We suggest the MSN network is well suited to the generation of such slow coherent task dependent response which could be utilized by the animal in behavior.

Input Dependent Cell Assembly Dynamics in a Model of the Striatal Medium Spiny Neuron Network

PubMed Central

Ponzi, Adam; Wickens, Jeff

2012-01-01

The striatal medium spiny neuron (MSN) network is sparsely connected with fairly weak GABAergic collaterals receiving an excitatory glutamatergic cortical projection. Peri-stimulus time histograms (PSTH) of MSN population response investigated in various experimental studies display strong firing rate modulations distributed throughout behavioral task epochs. In previous work we have shown by numerical simulation that sparse random networks of inhibitory spiking neurons with characteristics appropriate for UP state MSNs form cell assemblies which fire together coherently in sequences on long behaviorally relevant timescales when the network receives a fixed pattern of constant input excitation. Here we first extend that model to the case where cortical excitation is composed of many independent noisy Poisson processes and demonstrate that cell assembly dynamics is still observed when the input is sufficiently weak. However if cortical excitation strength is increased more regularly firing and completely quiescent cells are found, which depend on the cortical stimulation. Subsequently we further extend previous work to consider what happens when the excitatory input varies as it would when the animal is engaged in behavior. We investigate how sudden switches in excitation interact with network generated patterned activity. We show that sequences of cell assembly activations can be locked to the excitatory input sequence and outline the range of parameters where this behavior is shown. Model cell population PSTH display both stimulus and temporal specificity, with large population firing rate modulations locked to elapsed time from task events. Thus the random network can generate a large diversity of temporally evolving stimulus dependent responses even though the input is fixed between switches. We suggest the MSN network is well suited to the generation of such slow coherent task dependent response which could be utilized by the animal in behavior. PMID:22438838

A search for two types of transverse excitations in liquid polyvalent metals at ambient pressure: An ab initio molecular dynamics study of collective excitations in liquid Al, Tl and Ni

NASA Astrophysics Data System (ADS)

Bryk, Taras; Demchuk, Taras; Jakse, Noël; Wax, Jean-François

2018-02-01

Recent findings of pressure-induced emergence of unusual high-frequency contribution to transverse current spectral functions in several simple liquid metals at high pressures raised a question whether similar features can be observed in liquid metals at ambient conditions. We report here analysis of ab initio molecular dynamics-derived longitudinal (L) and transverse (T) current spectral functions and corresponding dispersions of collective excitations in liquid polyvalent metals Al, Tl, Ni. We have not found evidences of the second branch of high-frequency transverse modes in liquid Al and Ni, while in the case of liquid Tl they were clearly present in transverse dynamics. The vibrational density of states for liquid Tl has a pronounced high-frequency shoulder, which is located right in the frequency range of the second high-frequency transverse branch, while for liquid Al and Ni the vibrational density of states has only a weak indication of possible high-frequency shoulder. The origin of specific behavior of transverse excitations in liquid Tl is discussed.

Sensitized and heavy atom induced production of acenaphthylene triplet: A laser flash photolysis study

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

Samanta, A.; Fessenden, R.W.

1989-07-27

The triplet state of acenaphthylene has been examined by nanosecond laser flash photolysis using sensitization and heavy atom perturbation techniques. Although acenaphthylene does not form any observable triplet upon direct flash excitation, a transient with microsecond lifetime ({lambda}{sub max} = 315 nm) is observable when a solution of the sample is excited by sensitizers (benzophenone, thioxanthone, benzil). This transient is ascribed to the triplet of acenaphthylene on the basis of its quenching behavior toward oxygen, ferrocene, azulene, and {beta}-carotene. Quantitative data concerning the triplet-triplet absorption and quenching constants are presented. The triplet energy is estimated to lie between 46 andmore » 47 kcal/mol. The triplet can also be produced by direct excitation in solvents containing heavy atoms (ethyl bromide, ethyl iodide). The triplet yield is found to increase with an increase of the amount of the heavy atom containing solvent. No saturation limit is obtained. These facts together with the effect of heavy atoms on the T{sub 1} {yields} S{sub 0} process allow the differing behavior of ethyl bromide and ethyl iodide on the photodimerization process of acenaphthylene to be explained. Triplet-state parameters (extinction coefficient and triplet yield) have been estimated in these solvents by the energy-transfer technique and actinometry.« less

Effect of solvent hydrogen bonding on the photophysical properties of intramolecular charge transfer probe trans-ethyl p-(dimethylamino) cinamate and its derivative

NASA Astrophysics Data System (ADS)

Singh, T. Sanjoy; Moyon, N. S.; Mitra, Sivaprasad

2009-08-01

Intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino) cinamate (EDAC) and 4-(dimethylamino) cinnamic acid (DMACA) were studied by steady state absorption and emission, picosecond time-resolved fluorescence experiments in various pure and mixed solvent systems. The large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the excited state compared to the ground state. The energy for 0,0 transition ( ν0,0) for EDAC shows very good linear correlation with static solvent dielectric property; however, fluorescence emission maximum, stokes shift and fluorescence quantum yield show significant deviation from linearity in polar protic solvents, indicating a large contribution of solvent hydrogen bonding on the excited state relaxation mechanism. A quantitative estimation of contribution from different solvatochromic parameters was made using linear free energy relationship based on Kamlet-Taft equation.

Interplay of Zero-Field Splitting and Excited State Geometry Relaxation in fac-Ir(ppy)3.

PubMed

Gonzalez-Vazquez, José P; Burn, Paul L; Powell, Benjamin J

2015-11-02

The lowest energy triplet state, T1, of organometallic complexes based on iridium(III) is of fundamental interest, as the behavior of molecules in this state determines the suitability of the complex for use in many applications, e.g., organic light-emitting diodes. Previous characterization of T1 in fac-Ir(ppy)3 suggests that the trigonal symmetry of the complex is weakly broken in the excited state. Here we report relativistic time dependent density functional calculations of the zero-field splitting (ZFS) of fac-Ir(ppy)3 in the ground state (S0) and lowest energy triplet (T1) geometries and at intermediate geometries. We show that the energy scale of the geometry relaxation in the T1 state is large compared to the ZFS. Thus, the natural analysis of the ZFS and the radiative decay rates, based on the assumption that the structural distortion is a small perturbation, fails dramatically. In contrast, our calculations of these quantities are in good agreement with experiment.

Multifaceted Quadruplet of Low-Lying Spin-Zero States in 66Ni: Emergence of Shape Isomerism in Light Nuclei

NASA Astrophysics Data System (ADS)

Leoni, S.; Fornal, B.; Mǎrginean, N.; Sferrazza, M.; Tsunoda, Y.; Otsuka, T.; Bocchi, G.; Crespi, F. C. L.; Bracco, A.; Aydin, S.; Boromiza, M.; Bucurescu, D.; Cieplicka-Oryǹczak, N.; Costache, C.; Cǎlinescu, S.; Florea, N.; GhiÅ£ǎ, D. G.; Glodariu, T.; Ionescu, A.; Iskra, Ł. W.; Krzysiek, M.; Mǎrginean, R.; Mihai, C.; Mihai, R. E.; Mitu, A.; NegreÅ£, A.; NiÅ£ǎ, C. R.; Olǎcel, A.; Oprea, A.; Pascu, S.; Petkov, P.; Petrone, C.; Porzio, G.; Şerban, A.; Sotty, C.; Stan, L.; Ştiru, I.; Stroe, L.; Şuvǎilǎ, R.; Toma, S.; Turturicǎ, A.; Ujeniuc, S.; Ur, C. A.

2017-04-01

A search for shape isomers in the 66Ni nucleus was performed, following old suggestions of various mean-field models and recent ones, based on state-of-the-art Monte Carlo shell model (MCSM), all considering 66Ni as the lightest nuclear system with shape isomerism. By employing the two-neutron transfer reaction induced by an 18O beam on a 64Ni target, at the sub-Coulomb barrier energy of 39 MeV, all three lowest-excited 0+ states in 66Ni were populated and their γ decay was observed by γ -coincidence technique. The 0+ states lifetimes were assessed with the plunger method, yielding for the 02+, 03+, and 04+ decay to the 21+ state the B (E 2 ) values of 4.3, 0.1, and 0.2 Weisskopf units (W.u.), respectively. MCSM calculations correctly predict the existence of all three excited 0+ states, pointing to the oblate, spherical, and prolate nature of the consecutive excitations. In addition, they account for the hindrance of the E 2 decay from the prolate 04+ to the spherical 21+ state, although overestimating its value. This result makes 66Ni a unique nuclear system, apart from U,238236 , in which a retarded γ transition from a 0+ deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior.

Methylation effects in state resolved quenching of highly vibrationally excited azabenzenes (Evib˜38 500 cm-1). I. Collisions with water

NASA Astrophysics Data System (ADS)

Elioff, Michael S.; Fang, Maosen; Mullin, Amy S.

2001-10-01

To investigate the role of molecular structure in collisions that quench highly vibrationally excited molecules, we have performed state resolved transient infrared absorption studies of energy gain in a number of rotational levels of H2O(000) resulting from collisions of water with vibrationally excited 2-methylpyridine (2-picoline) and 2,6-dimethylpyridine (2,6-lutidine) in a low-pressure gas-phase environment at 298 K. Vibrationally excited methylpyridines were prepared with ˜38 500 cm-1 of internal energy using 266 nm ultraviolet excitation to an S1 electronic state followed by rapid radiationless decay to the S0 electronic state. Collisions that populate rotationally excited states of H2O(000) were investigated with infrared absorption by monitoring the appearance of individual rotational states of H2O(000) with energies between 1000 and 2000 cm-1. Rotational state distributions for recoiling water molecules were characterized by Boltzmann temperatures of Trot=590±90 K for quenching of hot picoline and Trot=490±80 K for lutidine quenching. Doppler-broadened transient absorption line profiles show that the scattered H2O(000) molecules have laboratory-frame translational energy distributions corresponding to Ttrans≈600 K for deactivation of picoline and Ttrans≈590 K for lutidine. Energy transfer rate constant measurements indicate that rotational excitation of H2O(000) with Evib>1000 cm-1 occurs for one in 31 picoline/water collisions and one in 17 lutidine/water collisions. Comparison with earlier quenching studies on pyrazine [M. Fraelich, M. S. Elioff, and A. S. Mullin, J. Phys. Chem. 102, 9761 (1998)] and pyridine [M. S. Elioff, M. Fraelich, R. L. Sansom, and A. S. Mullin, J. Chem. Phys. 111, 3517 (1999)] indicate that, for the same initial internal energy in the hot donor, the extent of rotational excitation in water is diminished as the number of vibrational modes in the donor increases. The energy transfer probability for this pathway exhibits opposite behavior, with the larger donor molecules being more likely to excite the high energy rotations in water. These results are interpreted using a statistical description of the high energy donors and highlight the role of low frequency vibrational modes in the vibrationally hot donor molecules. A Fermi's golden rule approach is successful at explaining differences in the observed scattering dynamics for the various donor molecules.

Excited states with internally contracted multireference coupled-cluster linear response theory.

PubMed

Samanta, Pradipta Kumar; Mukherjee, Debashis; Hanauer, Matthias; Köhn, Andreas

2014-04-07

In this paper, the linear response (LR) theory for the variant of internally contracted multireference coupled cluster (ic-MRCC) theory described by Hanauer and Köhn [J. Chem. Phys. 134, 204211 (2011)] has been formulated and implemented for the computation of the excitation energies relative to a ground state of pronounced multireference character. We find that straightforward application of the linear-response formalism to the time-averaged ic-MRCC Lagrangian leads to unphysical second-order poles. However, the coupling matrix elements that cause this behavior are shown to be negligible whenever the internally contracted approximation as such is justified. Hence, for the numerical implementation of the method, we adopt a Tamm-Dancoff-type approximation and neglect these couplings. This approximation is also consistent with an equation-of-motion based derivation, which neglects these couplings right from the start. We have implemented the linear-response approach in the ic-MRCC singles-and-doubles framework and applied our method to calculate excitation energies for a number of molecules ranging from CH2 to p-benzyne and conjugated polyenes (up to octatetraene). The computed excitation energies are found to be very accurate, even for the notoriously difficult case of doubly excited states. The ic-MRCC-LR theory is also applicable to systems with open-shell ground-state wavefunctions and is by construction not biased towards a particular reference determinant. We have also compared the linear-response approach to the computation of energy differences by direct state-specific ic-MRCC calculations. We finally compare to Mk-MRCC-LR theory for which spurious roots have been reported [T.-C. Jagau and J. Gauss, J. Chem. Phys. 137, 044116 (2012)], being due to the use of sufficiency conditions to solve the Mk-MRCC equations. No such problem is present in ic-MRCC-LR theory.

Imaging Spatial Correlations of Rydberg Excitations in Cold Atom Clouds

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

Schwarzkopf, A.; Sapiro, R. E.; Raithel, G.

2011-09-02

We use direct spatial imaging of cold {sup 85}Rb Rydberg atom clouds to measure the Rydberg-Rydberg correlation function. The results are in qualitative agreement with theoretical predictions [F. Robicheaux and J. V. Hernandez, Phys. Rev. A 72, 063403 (2005)]. We determine the blockade radius for states 44D{sub 5/2}, 60D{sub 5/2}, and 70D{sub 5/2} and investigate the dependence of the correlation behavior on excitation conditions and detection delay. Experimental data hint at the existence of long-range order.

Electroabsorption in triphenylamine-based hole-transporting materials for organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Stampor, Waldemar; Mróz, Wojciech

2007-01-01

Electric-field modulated absorption (EA) spectra have been studied in solid films of triphenylamine (TPA)-based compounds, commonly used as hole-transporting materials in organic light-emitting diodes. The electroabsorption spectra of triphenyldiamine derivatives (TPD and TAPC) and a starburst amine dendrimer m-MTDATA are compared with those of TPA which is the building block of the molecules. The EA results indicate that properties of excited states of m-MTDATA and TAPC can be qualitatively rationalized in the terms of exciton interaction between TPA constituents. The lowest energy electronic excitations of m-MTDATA dendrimer are strongly delocalized within the area of the whole molecule. In contrast to m-MTDATA and TAPC, the TPD behavior in the electric field shows individual features that can not be derived from the optical properties of TPA monomers alone. The influence of excited state degeneracy on EA spectra is discussed. The consistent qualitative interpretation of EA spectra for compounds under investigation has been reached assuming that the second derivative lineshapes of EA signal originate from degenerate (in TPA and m-MTDATA) and possible quasi-degenerate states (in TAPC and TPD).

Observation of Vibrational Relaxation Dynamics in X(sup 3)Sigma(sup -)(sub g) Oxygen Following Stimulated Raman Excitation to the v=1 Level: Implications for the RELIEF Flow Tagging Technique

NASA Technical Reports Server (NTRS)

Diskin, Glenn S.; Lempert, Walter R.; Miles, Richard B.

1996-01-01

The vibrational relaxation of ground-state molecular oxygen (O2, X(sup 3)Sigma(sup -)(sub g)) has been observed, following stimulated Raman excitation to the first excited vibrational level (v=1). Time delayed laser-induced fluorescence probing of the ro-vibrational population distribution was used to examine the temporal relaxation behavior. In the presence of water vapor, the relaxation process is rapid, and is dominated by near-resonant vibrational energy exchange between the v=1 level of O2 and the n2 bending mode of H2O. In the absence of H2O, reequilibration proceeds via homogeneous vibrational energy transfer, in which a collision between two v=1 O2 molecules leaves one molecule in the v=2 state and the other in the v=0 state. Subsequent collisions between molecules in v=1 and v>1 result in continued transfer of population up the vibrational ladder. The implications of these results for the RELIEF flow tagging technique are discussed.

Research investigation directed toward extending the useful range of the electromagnetic spectrum

NASA Technical Reports Server (NTRS)

Hartmann, S. R.

1971-01-01

The lifetimes and fine structure of He(-) were studied using time-of-flight techniques and quenching by a static axial magnetic field. Using level-crossing spectroscopy the hyperfine constants A and B and the lifetime of the 3 2P3/2 state of Li-7 were measured. Polarization of the Ru 7S level was created as a first step in determining the hyperfine structure of the alkali excited S state. The parametric interaction between light and microwaves in optically pumped Rb-87 vapor were investigated. Measurements and analyses of transitions in formaldehyde and its isotopic species and in the lowest two excited vibrational states of H2CO were also made, as well as of transitions in furan, pyrrole, formic acid, and cyanoacetylene. The Hanle effect was studied in the NO molecule, and RF oscillators were developed with flat, wideband output to observe excited state hyperfine transitions at zero field. Data was generated on the time-dependent behavior of photon echoes in ruby. Stimulated Raman scattering was studied in atomic Tl vapor. A Q switched, temperature-tuned ruby laser was developed which operates between 6934 and 6938 A. The frequency shift due to resonant interaction between identical radiating atoms was calculated.

Removal of Default-State Associated Inhibition During Repetition Priming Improves Response Articulation

PubMed Central

Dacks, Andrew M.; Siniscalchi, Michael J.; Weiss, Klaudiusz R.

2012-01-01

Behavior is a product of both the stimuli encountered and the current internal state. At the level of the nervous system, the internal state alters the biophysical properties of, and connections between, neurons establishing a “network state”. To establish a network state, the nervous system must be altered from an initial default/resting state, but what remains unclear is the extent to which this process represents induction from a passive default state or the removal of suppression by an active default state. We use repetition priming (a history-dependent improvement of behavioral responses to repeatedly encountered stimuli) to determine the cellular mechanisms underlying the transition from the default to the primed network state. We demonstrate that both removal of active suppression and induction of neuron excitability changes each contribute separately to the production of a primed state. The feeding system of Aplysia californica displays repetition priming via an increase in the activity of the radula closure neuron B8, which results in increased bite strength with each motor program. We found that during priming, B8 received progressively less inhibitory input from the multi-functional neurons B4/5. Additionally, priming enhanced the excitability of B8, but the rate at which B8 activity increased as a result of these changes was regulated by the progressive removal of inhibitory input. Thus, the establishment of the network state involves the induction of processes from a rested state, yet the consequences of these processes are conditional upon critical gating mechanisms actively enforced by the default state. PMID:23223294

Cherenkov sound on a surface of a topological insulator

NASA Astrophysics Data System (ADS)

Smirnov, Sergey

2013-11-01

Topological insulators are currently of considerable interest due to peculiar electronic properties originating from helical states on their surfaces. Here we demonstrate that the sound excited by helical particles on surfaces of topological insulators has several exotic properties fundamentally different from sound propagating in nonhelical or even isotropic helical systems. Specifically, the sound may have strictly forward propagation absent for isotropic helical states. Its dependence on the anisotropy of the realistic surface states is of distinguished behavior which may be used as an alternative experimental tool to measure the anisotropy strength. Fascinating from the fundamental point of view backward, or anomalous, Cherenkov sound is excited above the critical angle π/2 when the anisotropy exceeds a critical value. Strikingly, at strong anisotropy the sound localizes into a few forward and backward beams propagating along specific directions.

Creation of Rydberg Polarons in a Bose Gas

NASA Astrophysics Data System (ADS)

Camargo, F.; Schmidt, R.; Whalen, J. D.; Ding, R.; Woehl, G.; Yoshida, S.; Burgdörfer, J.; Dunning, F. B.; Sadeghpour, H. R.; Demler, E.; Killian, T. C.

2018-02-01

We report spectroscopic observation of Rydberg polarons in an atomic Bose gas. Polarons are created by excitation of Rydberg atoms as impurities in a strontium Bose-Einstein condensate. They are distinguished from previously studied polarons by macroscopic occupation of bound molecular states that arise from scattering of the weakly bound Rydberg electron from ground-state atoms. The absence of a p -wave resonance in the low-energy electron-atom scattering in Sr introduces a universal behavior in the Rydberg spectral line shape and in scaling of the spectral width (narrowing) with the Rydberg principal quantum number, n . Spectral features are described with a functional determinant approach (FDA) that solves an extended Fröhlich Hamiltonian for a mobile impurity in a Bose gas. Excited states of polyatomic Rydberg molecules (trimers, tetrameters, and pentamers) are experimentally resolved and accurately reproduced with a FDA.

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

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

Egorova, Dassia

2014-01-21

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

Nonequilibrium radiation and dissociation of CO molecules in shock-heated flows

NASA Astrophysics Data System (ADS)

Macdonald, R. L.; Munafò, A.; Johnston, C. O.; Panesi, M.

2016-08-01

This work addresses the study of the behavior of the excited electronic states of CO molecules in the nonequilibrium relaxation zone behind a normal shock for a CO2-N2 mixture representative of the Mars atmosphere. The hybrid state-to-state (StS) model developed accounts for thermal nonequilibrium between the translational energy mode of the gas and the vibrational energy mode of individual molecules. The electronic states of CO molecules are treated as separate species, allowing for non-Boltzmann distributions of their populations. The StS model is coupled with a nonequilibrium radiation solver, hpc-rad, allowing for the calculation of the radiation signature from the molecular and atomic species in the gas. This study focuses on the radiation from the fourth positive system of CO, which dominates the radiation heating on the forebody for higher speed Mars entry applications. In the rapidly dissociating regime behind strong shock waves, the population of the ground electronic state of CO [ CO(X 1Σ )], departs from Maxwell-Boltzmann distributions, owing to the efficient collisional excitation to the electronically excited CO(A 1Π ) state. In general the assumption of the equilibrium between electronic and vibration fails when the excitation of electronic states is driven by heavy particles. The comparison of the radiation heating predictions obtained using the conventional quasi-steady-state (QSS) approach and the physics-based StS approach revealed differences in radiative heating predictions of up to 50%. These results demonstrate that the choice of nonequilibrium model can have a significant impact on radiative heating simulations, and more importantly, they cast serious doubts on the validity of the QSS assumption for the condition of interest to this work.

Physiological Markers of Motor Inhibition during Human Behavior.

PubMed

Duque, Julie; Greenhouse, Ian; Labruna, Ludovica; Ivry, Richard B

2017-04-01

Transcranial magnetic stimulation (TMS) studies in humans have shown that many behaviors engage processes that suppress excitability within the corticospinal tract. Inhibition of the motor output pathway has been extensively studied in the context of action stopping, where a planned movement needs to be abruptly aborted. Recent TMS work has also revealed markers of motor inhibition during the preparation of movement. Here, we review the evidence for motor inhibition during action stopping and action preparation, focusing on studies that have used TMS to monitor changes in the excitability of the corticospinal pathway. We discuss how these physiological results have motivated theoretical models of how the brain selects actions, regulates movement initiation and execution, and switches from one state to another. Copyright © 2017 Elsevier Ltd. All rights reserved.

From quantum mechanics to finance: Microfoundations for jumps, spikes and high volatility phases in diffusion price processes

NASA Astrophysics Data System (ADS)

Henkel, Christof

2017-03-01

We present an agent behavior based microscopic model that induces jumps, spikes and high volatility phases in the price process of a traded asset. We transfer dynamics of thermally activated jumps of an unexcited/excited two state system discussed in the context of quantum mechanics to agent socio-economic behavior and provide microfoundations. After we link the endogenous agent behavior to price dynamics we establish the circumstances under which the dynamics converge to an Itô-diffusion price processes in the large market limit.

Chimera states in a Hodgkin-Huxley model of thermally sensitive neurons

NASA Astrophysics Data System (ADS)

Glaze, Tera A.; Lewis, Scott; Bahar, Sonya

2016-08-01

Chimera states occur when identically coupled groups of nonlinear oscillators exhibit radically different dynamics, with one group exhibiting synchronized oscillations and the other desynchronized behavior. This dynamical phenomenon has recently been studied in computational models and demonstrated experimentally in mechanical, optical, and chemical systems. The theoretical basis of these states is currently under active investigation. Chimera behavior is of particular relevance in the context of neural synchronization, given the phenomenon of unihemispheric sleep and the recent observation of asymmetric sleep in human patients with sleep apnea. The similarity of neural chimera states to neural "bump" states, which have been suggested as a model for working memory and visual orientation tuning in the cortex, adds to their interest as objects of study. Chimera states have been demonstrated in the FitzHugh-Nagumo model of excitable cells and in the Hindmarsh-Rose neural model. Here, we demonstrate chimera states and chimera-like behaviors in a Hodgkin-Huxley-type model of thermally sensitive neurons both in a system with Abrams-Strogatz (mean field) coupling and in a system with Kuramoto (distance-dependent) coupling. We map the regions of parameter space for which chimera behavior occurs in each of the two coupling schemes.

Collective Dynamics for Heterogeneous Networks of Theta Neurons

NASA Astrophysics Data System (ADS)

Luke, Tanushree

Collective behavior in neural networks has often been used as an indicator of communication between different brain areas. These collective synchronization and desynchronization patterns are also considered an important feature in understanding normal and abnormal brain function. To understand the emergence of these collective patterns, I create an analytic model that identifies all such macroscopic steady-states attainable by a network of Type-I neurons. This network, whose basic unit is the model "theta'' neuron, contains a mixture of excitable and spiking neurons coupled via a smooth pulse-like synapse. Applying the Ott-Antonsen reduction method in the thermodynamic limit, I obtain a low-dimensional evolution equation that describes the asymptotic dynamics of the macroscopic mean field of the network. This model can be used as the basis in understanding more complicated neuronal networks when additional dynamical features are included. From this reduced dynamical equation for the mean field, I show that the network exhibits three collective attracting steady-states. The first two are equilibrium states that both reflect partial synchronization in the network, whereas the third is a limit cycle in which the degree of network synchronization oscillates in time. In addition to a comprehensive identification of all possible attracting macro-states, this analytic model permits a complete bifurcation analysis of the collective behavior of the network with respect to three key network features: the degree of excitability of the neurons, the heterogeneity of the population, and the overall coupling strength. The network typically tends towards the two macroscopic equilibrium states when the neuron's intrinsic dynamics and the network interactions reinforce each other. In contrast, the limit cycle state, bifurcations, and multistability tend to occur when there is competition between these network features. I also outline here an extension of the above model where the neurons' excitability now varies in time sinuosoidally, thus simulating a parabolic bursting network. This time-varying excitability can lead to the emergence of macroscopic chaos and multistability in the collective behavior of the network. Finally, I expand the single population model described above to examine a two-population neuronal network where each population has its own unique mixture of excitable and spiking neurons, as well as its own coupling strength (either excitatory or inhibitory in nature). Specifically, I consider the situation where the first population is only allowed to influence the second population without any feedback, thus effectively creating a feed-forward "driver-response" system. In this special arrangement, the driver's asymptotic macroscopic dynamics are fully explored in the comprehensive analysis of the single population. Then, in the presence of an influence from the driver, the modified dynamics of the second population, which now acts as a response population, can also be fully analyzed. As in the time-varying model, these modifications give rise to richer dynamics to the response population than those found from the single population formalism, including multi-periodicity and chaos.

Upconversion luminescence in Er3+ doped and Er3+/Yb3+ codoped zirconia and hafnia nanocrystals excited at 980 nm

NASA Astrophysics Data System (ADS)

Gómez, Luis A.; Menezes, Leonardo de S.; de Araújo, Cid B.; Gonçalves, Rogeria R.; Ribeiro, Sidney J. L.; Messaddeq, Younes

2010-06-01

Frequency upconversion (UC) luminescence in nanocrystalline zirconia (ZrO2) and hafnia (HfO2) doped with Er3+ and Yb3+ was studied under continuous-wave excitation at 980 nm. Samples of ZrO2:Er3+, ZrO2:Er3+/Yb3+, and HfO2:Er3+/Yb3+ were prepared by the sol-gel technique and characterized using x-ray diffraction and electron microscopy. A study of the infrared-to-green and infrared-to-red UC processes was performed including the analysis of the spectral and the temporal behavior. The mechanisms contributing to the UC luminescence were identified as excited state absorption and energy transfer among rare-earth ions.

Decay pattern of the Pygmy Dipole Resonance in 140Ce

NASA Astrophysics Data System (ADS)

Isaak, J.; Löher, B.; Savran, D.; Aumann, T.; Beller, J.; Cooper, N.; Derya, V.; Duchêne, M.; Endres, J.; Fiori, E.; Kelley, J. H.; Knörzer, M.; Pietralla, N.; Ponomarev, V. Yu.; Romig, C.; Scheck, M.; Scheit, H.; Silva, J.; Tonchev, A. P.; Tornow, W.; Weller, H. R.; Werner, V.; Zilges, A.; Zweidinger, M.

2015-05-01

The decay behavior of low-lying dipole states in 140Ce was investigated exploiting the γ3-setup at the HIγS facility using quasi-monochromatic photon beams. Branching ratios of individual excited states as well as average branching ratios to low-lying states have been extracted using γ - γ coincidence measurements. The comparison of the average branching ratios to QPM calculations shows a remarkable agreement between experiment and theory in the energy range from 5.0 to 8.5 MeV.

Targeting excited states in all-trans polyenes with electron-pair states.

PubMed

Boguslawski, Katharina

2016-12-21

Wavefunctions restricted to electron pair states are promising models for strongly correlated systems. Specifically, the pair Coupled Cluster Doubles (pCCD) ansatz allows us to accurately describe bond dissociation processes and heavy-element containing compounds with multiple quasi-degenerate single-particle states. Here, we extend the pCCD method to model excited states using the equation of motion (EOM) formalism. As the cluster operator of pCCD is restricted to electron-pair excitations, EOM-pCCD allows us to target excited electron-pair states only. To model singly excited states within EOM-pCCD, we modify the configuration interaction ansatz of EOM-pCCD to contain also single excitations. Our proposed model represents a simple and cost-effective alternative to conventional EOM-CC methods to study singly excited electronic states. The performance of the excited state models is assessed against the lowest-lying excited states of the uranyl cation and the two lowest-lying excited states of all-trans polyenes. Our numerical results suggest that EOM-pCCD including single excitations is a good starting point to target singly excited states.

Sleeping of a Complex Brain Networks with Hierarchical Organization

NASA Astrophysics Data System (ADS)

Zhang, Ying-Yue; Yang, Qiu-Ying; Chen, Tian-Lun

2009-01-01

The dynamical behavior in the cortical brain network of macaque is studied by modeling each cortical area with a subnetwork of interacting excitable neurons. We characterize the system by studying how to perform the transition, which is now topology-dependent, from the active state to that with no activity. This could be a naive model for the wakening and sleeping of a brain-like system, i.e., a multi-component system with two different dynamical behavior.

Back to Pupillometry: How Cortical Network State Fluctuations Tracked by Pupil Dynamics Could Explain Neural Signal Variability in Human Cognitive Neuroscience

PubMed Central

2017-01-01

Abstract The mammalian thalamocortical system generates intrinsic activity reflecting different states of excitability, arising from changes in the membrane potentials of underlying neuronal networks. Fluctuations between these states occur spontaneously, regularly, and frequently throughout awake periods and influence stimulus encoding, information processing, and neuronal and behavioral responses. Changes of pupil size have recently been identified as a reliable marker of underlying neuronal membrane potential and thus can encode associated network state changes in rodent cortex. This suggests that pupillometry, a ubiquitous measure of pupil dilation in cognitive neuroscience, could be used as an index for network state fluctuations also for human brain signals. Considering this variable may explain task-independent variance in neuronal and behavioral signals that were previously disregarded as noise. PMID:29379876

Delayed Triplet-State Formation through Hybrid Charge Transfer Exciton at Copper Phthalocyanine/GaAs Heterojunction.

PubMed

Lim, Heeseon; Kwon, Hyuksang; Kim, Sang Kyu; Kim, Jeong Won

2017-10-05

Light absorption in organic molecules on an inorganic substrate and subsequent electron transfer to the substrate create so-called hybrid charge transfer exciton (HCTE). The relaxation process of the HCTE states largely determines charge separation efficiency or optoelectronic device performance. Here, the study on energy and time-dispersive behavior of photoelectrons at the hybrid interface of copper phthalocyanine (CuPc)/p-GaAs(001) upon light excitation of GaAs reveals a clear pathway for HCTE relaxation and delayed triplet-state formation. According to the ground-state energy level alignment at the interface, CuPc/p-GaAs(001) shows initially fast hole injection from GaAs to CuPc. Thus, the electrons in GaAs and holes in CuPc form an unusual HCTE state manifold. Subsequent electron transfer from GaAs to CuPc generates the formation of the triplet state in CuPc with a few picoseconds delay. Such two-step charge transfer causes delayed triplet-state formation without singlet excitation and subsequent intersystem crossing within the CuPc molecules.

Electronic Interactions of Michler's Ketone with DNA Bases in Synthetic Hairpins.

PubMed

Jalilov, Almaz S; Young, Ryan M; Eaton, Samuel W; Wasielewski, Michael R; Lewis, Frederick D

2015-01-01

The mechanism and dynamics of photoinduced electron transfer in two families of DNA hairpins possessing Michler's ketone linkers have been investigated by means of steady state and time-resolved transient absorption and emission spectroscopies. The excited state behavior of the diol linker employed in hairpin synthesis is similar to that of Michler's ketone in methanol solution. Hairpins possessing only a Michler's ketone linker undergo fast singlet state charge separation and charge recombination with an adjacent purine base, attributed to well-stacked ground state conformations, and intersystem crossing to the triplet state, attributed to poorly stacked ground state conformations. The failure of the triplet to undergo electron transfer reactions on the 7 ns time scale of our measurements is attributed to the low triplet energy and reduction potential of the twisted triplet state. Hairpins possessing both a Michler's ketone linker and a perylenediimide base surrogate separated by four base pairs undergo photoinduced hole transport from the diimide to Michler's ketone upon excitation of the diimide. The efficiency of hole transport is dependent upon the sequence of the intervening purine bases. © 2014 The American Society of Photobiology.

Laser-induced fluorescence fiber optic probe measurement of oil dilution by fuel

DOEpatents

Parks, II, James E [Knoxville, TN; Partridge, Jr., William P [Oak Ridge, TN

2010-11-23

Apparatus for detecting fuel in oil includes an excitation light source in optical communication with an oil sample for exposing the oil sample to excitation light in order to excite the oil sample from a non-excited state to an excited state and a spectrally selective device in optical communication with the oil sample for detecting light emitted from the oil sample as the oil sample returns from the excited state to a non-excited state to produce spectral indicia that can be analyzed to determine the presence of fuel in the oil sample. A method of detecting fuel in oil includes the steps of exposing a oil sample to excitation light in order to excite the oil sample from a non-excited state to an excited state, as the oil sample returns from the excited state to a non-excited state, detecting light emitted from the oil sample to produce spectral indicia; and analyzing the spectral indicia to determine the presence of fuel in the oil sample.

Ab initio study of the Jπ=0± continuum structures in 4He

NASA Astrophysics Data System (ADS)

Aoyama, S.; Baye, D.

2018-05-01

The Jπ=0± continuum structures in 4He are investigated by using an ab initio reaction theory with the microscopic R -matrix method. In the Ex≥˜20 MeV excitation energy region of 4He, the continuum states are mainly described by the t +p , h +n , and d +d channels. The Jπ=0± elastic phase shifts of the t +p and h +n channels show an apparently resonant behavior which might indicate the existence of excited 03+ and 02- resonance states of 4He above the known 02+ and 01- ones. However, the corresponding 03+ and 02- resonances have not been observed yet, although an experimental candidate with a large decay width is reported for 02-. In this paper, by analyzing the Jπ=0± S matrices, we discuss why the observation of these states is unlikely.

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

Chu, S.; Wang, K.; Layton, E.

In this paper we accomplish three goals. First, we present new nonperturbative results of complex quasi-energies (shifts and widths) for several low-lying excited states of atomic H in strong fields, using the {ital L}{sup 2} non-Hermitian Floquet matrix technique. Second, we present a new nonperturbative {ital L}{sup 2} technique for the treatment of ac Stark shifts of arbitrary excited states. We found that all the Rydberg states in weak fields are upshifted and closely follow the quadratic field dependence described by the ponderomotive potential {ital e}{sup 2}{ital F}{sup 2}/4{ital mgw}{sup 2}. Large deviation from the ponderomotive shift and intricate level-shiftmore » behaviors, however, occur in strong fields. Finally, we present a classical nonperturbative treatment of the electronic motion in intense laser fields. We show that the spectral analysis of classical trajectories can provide detailed insights regarding the mechanisms responsible for the multiple-harmonic generation recently observed in high-intensity experiments.« less

Transcranial direct current stimulation of the medial prefrontal cortex modulates the propensity to help in costly helping behavior.

PubMed

Liao, Chong; Wu, Song; Luo, Yue-Jia; Guan, Qing; Cui, Fang

2018-05-01

Social decision-making engages traditional decision-making processes (e.g. valuation), as well as social cognition processes (e.g. inferring the affective and mental states of another person). Neuroimaging and neuro-stimulation studies have suggested the involvement of the medial prefrontal cortex (mPFC) in a variety of social decision-making tasks. Yet no study has investigated the effect of the cortical excitability of mPFC in the decision-making of costly helping behavior. Here, we used tDCS to demonstrate the causal relationship between the cortical excitability of mPFC and costly helping decision-making. Subjects assigned to the anodal, cathodal and sham groups were required to decide whether they would like to cost their own money to relieve another subject (a confederate actually) from painful electrical shocks with a certain probability of success. Results showed that the subjects receiving anodal stimulation acted more prosaically than the subjects receiving cathodal stimulation. And this effect was only significant when the probability of success was high. We proposed that tDCS induced modulation of the cortical excitability, targeting the mPFC, can affect the prosocial propensity in costly helping behavior, and the possible underlying mechanisms were discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

Sum rules and the role of pressure on the excitation spectrum of a confined hydrogen atom by a spherical cavity

NASA Astrophysics Data System (ADS)

Cabrera-Trujillo, R.

2017-08-01

Sum rule relations over the excitation spectrum of a quantum system contain information about both the energy spectrum and eigenfunctions of the system in a compact form, particularly regarding closure relations. In this work, the effects of pressure induced by a spherical cavity on an atomic hydrogen impurity on the dipole oscillator strength (DOS) sum rule, S k , and its logarithmic version, L k , are studied by means of a numerical approach based on a finite-difference solution to the Schrödinger equation. Pressure effects are accounted for by means of a spherical cavity of radius R 0 immersed in a medium characterized by a penetrable potential height V 0. The DOS sum rules S k and L k are investigated as a function of these cavity parameters and thus directly related to the impurity static pressure and surrounding material. One finds that the sum rules are fulfilled within the numerical precision for low pressure conditions. However, when the barrier height is large or infinite (a non-penetrable cavity), the sum rule, for positive k, differs from its closure relation. One finds that this occurs for a cavity radius {R}0< 6 au, corresponding to a pressure such that the first p-state that contributes to the sum rule has positive energy and it is due to the fact that the spherical confinement cavity potential dominates over the Coulombic interaction for the hydrogenic impurity. Thus, as pressure increases, the excitation spectrum approaches that of a particle confined by a spherical cavity while the ground state is slightly affected by the cavity and more closely resembles a hydrogenic atom. Therefore, the sum rule over the excitation spectrum tends to a particle confined by a spherical cavity, while the closure relation gives that of a confined hydrogen atom in the ground state. For negative k, low excitations are the most important and this behavior is not presented. As the {S}-2 sum rule is the static dipole polarizability, the results are compared to available data in the literature, showing excellent agreement. This behavior in the sum rule and oscillator strength in electron-impurity excitations affects optical transitions of importance in semiconductor nanostructures.

Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

NASA Astrophysics Data System (ADS)

Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

2016-03-01

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications. Electronic supplementary information (ESI) available: The pump dependent transient absorption spectra and the corresponding global analysis results. See DOI: 10.1039/c6nr01008c

Dynamic conductivity from audio to optical frequencies of semiconducting manganites approaching the metal-insulator transition

NASA Astrophysics Data System (ADS)

Lunkenheimer, P.; Mayr, F.; Loidl, A.

2006-07-01

We report the frequency-dependent conductivity of the manganite system La1-xSrxMnO3 (x0.2) when approaching the metal-insulator transition from the insulating side. Results from low-frequency dielectric measurements are combined with spectra in the infrared region. For low doping levels the behavior is dominated by hopping transport of localized charge carriers at low frequencies and by phononic and electronic excitations in the infrared region. For the higher Sr contents the approach of the metallic state is accompanied by the successive suppression of the hopping contribution at low frequencies and by the development of polaronic excitations in the infrared region, which finally become superimposed by a strong Drude contribution in the fully metallic state.

Polar and low polar solvents media effect on dipole moments of some diazo Sudan dyes

NASA Astrophysics Data System (ADS)

Zakerhamidi, M. S.; Golghasemi Sorkhabi, Sh.; Shamkhali, A. N.

2014-06-01

Absorption and fluorescence spectra of three Sudan dyes (SudanIII, SudanIV and Sudan black B) were recorded in various solvents with different polarity in the range of 300-800 nm, at room temperature. The solvatochromic method was used to investigate dipole moments of these dyes in ground and excited states, in different media. The solvatochromic behavior of these substances and their solvent-solute interactions were analyzed via solvent polarity parameters. Obtained results express the effects of solvation on tautomerism and molecular configuration (geometry) of Sudan dyes in solvent media with different polarity. Furthermore, analyze of solvent-solute interactions and value of ground and excited states dipole moments suggests different forms of resonance structures for Sudan dyes in polar and low-polar solvents.

Sexual Excitability and Dysfunctional Coping Determine Cybersex Addiction in Homosexual Males.

PubMed

Laier, Christian; Pekal, Jaro; Brand, Matthias

2015-10-01

Cybersex addiction (CA) has been mostly investigated in heterosexual males. Recent findings have demonstrated an association between CA severity and indicators of sexual excitability, and that coping by sexual behaviors mediated the relationship between sexual excitability and CA symptoms. The aim of this study was to test this mediation in a sample of homosexual males. Seventy-one homosexual males were surveyed online. Questionnaires assessed symptoms of CA, sensitivity to sexual excitation, pornography use motivation, problematic sexual behavior, psychological symptoms, and sexual behaviors in real life and online. Moreover, participants viewed pornographic videos and indicated their sexual arousal before and after the video presentation. Results showed strong correlations between CA symptoms and indicators of sexual arousal and sexual excitability, coping by sexual behaviors, and psychological symptoms. CA was not associated with offline sexual behaviors and weekly cybersex use time. Coping by sexual behaviors partially mediated the relationship between sexual excitability and CA. The results are comparable with those reported for heterosexual males and females in previous studies and are discussed against the background of theoretical assumptions of CA, which highlight the role of positive and negative reinforcement due to cybersex use.

The behavior of exciplex decay processes and interplay of radiationless transition and preliminary reorganization mechanisms of electron transfer in loose and tight pairs of reactants.

PubMed

Kuzmin, Michael G; Soboleva, Irina V; Dolotova, Elena V

2007-01-18

Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

Subcycle dynamics of high-order-harmonic generation of He atoms excited by attosecond pulses and driven by near-infrared laser fields: A self-interaction-free time-dependent density-functional-theory approach

NASA Astrophysics Data System (ADS)

Heslar, John; Telnov, Dmitry A.; Chu, Shih-I.

2014-05-01

In the framework of the self-interaction-free time-dependent density-functional theory, we have performed three-dimensional (3D) ab initio calculations of He atoms in near-infrared (NIR) laser fields subject to excitation by a single extreme ultraviolet (XUV) attosecond pulse (SAP). We have explored the dynamical behavior of the subcycle high harmonic generation (HHG) for transitions from the excited states to the ground state and found oscillation structures with respect to the time delay between the SAP and NIR fields. The oscillatory pattern in the photon emission spectra has a period of ˜1.3 fs which is half of the NIR laser optical cycle, similar to that recently measured in the experiments on transient absorption of He [M. Chini et al., Sci. Rep. 3, 1105 (2013), 10.1038/srep01105]. We present the photon emission spectra from 1s2p, 1s3p, 1s4p, 1s5p, and 1s6p excited states as functions of the time delay. We explore the subcycle Stark shift phenomenon in NIR fields and its influence on the photon emission process. Our analysis reveals several interesting features of the subcycle HHG dynamics and we identify the mechanisms responsible for the observed peak splitting in the photon emission spectra.

Experiment and Theory for Nuclear Reactions in Nano-Materials Show e14 - e16 Solid-State Fusion Reactions

NASA Astrophysics Data System (ADS)

George, Russ

2005-03-01

Nano-lattices of deuterium loving metals exhibit coherent behavior by populations of deuterons (d's) occupying a Bloch state. Therein, coherent d-overlap occurs wherein the Bloch condition reduces the Coulomb barrier.Overlap of dd pairs provides a high probability fusion will/must occur. SEM photo evidence showing fusion events is now revealed by laboratories that load or flux d into metal nano-domains. Solid-state dd fusion creates an excited ^4He nucleus entangled in the large coherent population of d's.This contrasts with plasma dd fusion in collision space where an isolated excited ^4He nucleus seeks the ground state via fast particle emission. In momentum limited solid state fusion,fast particle emission is effectively forbidden.Photographed nano-explosive events are beyond the scope of chemistry. Corroboration of the nuclear nature derives from photographic observation of similar events on spontaneous fission, e.g. Cf. We present predictive theory, heat production, and helium isotope data showing reproducible e14 to e16 solid-state fusion reactions.

Collective and non-collective structures in nuclei of mass region A ≈ 125

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

Singh, A. K.; Collaboration: INGA Collaboration; Gammasphere Collaboration

Generation of angular momentum in nuclei is a key question in nuclear structure studies. In single particle model, it is due to alignment of spin of individual nucleon available in the valence space, whereas coherent motion of nucleons are assumed in the collective model. The nuclei near the closed shell at Z = 50 with mass number A ≈ 120-125 represent ideal cases to explore the interplay between these competing mechanisms and the transition from non-collective to collective behavior or vice versa. Recent spectroscopic studies of nuclei in this region reveal several non-collective maximally aligned states representing the first kindmore » of excitation mechanism, where 8-12 particles above the {sup 114}Sn align their spins to generate these states. Deformed rotational bands feeding the non-collective states in the spin range I=20-25 and excitation energies around 10 MeV have also been observed. Structure of the collective and non-collective states are discussed in the framework of Cranked-Nilsson-Strutinsky model.« less

Detection and characterization of the tin dihydride (SnH2 and SnD2) molecule in the gas phase

NASA Astrophysics Data System (ADS)

Smith, Tony C.; Clouthier, Dennis J.

2018-01-01

The SnH2 and SnD2 molecules have been detected for the first time in the gas phase by laser-induced fluorescence (LIF) and emission spectroscopic techniques through the à 1B1-X ˜ 1A1 electronic transition. These reactive species were prepared in a pulsed electric discharge jet using (CH3)4Sn or SnH4/SnD4 precursors diluted in high pressure argon. Transitions to the electronic excited state of the jet-cooled molecules were probed with LIF, and the ground state energy levels were measured from single rovibronic level emission spectra. The LIF spectrum of SnD2 afforded sufficient rotational structure to determine the ground and excited state geometries: r0″ = 1.768 Å, θ0″ = 91.0°, r0' = 1.729 Å, θ0' = 122.9°. All of the observed LIF bands show evidence of a rotational-level-dependent predissociation process which rapidly decreases the fluorescence yield and lifetime with increasing rotational angular momentum in each excited vibronic level. This behavior is analogous to that observed in SiH2 and GeH2 and is suggested to lead to the formation of ground state tin atoms and hydrogen molecules.

Emergent thermal kinetic behavior of artificial spin ice

NASA Astrophysics Data System (ADS)

Lao, Yuyang; Sheikh, Mohammed; Sklenar, Joseph; Gardeazabal, Daniel; Watts, Justin; Albrecht, Alan; Leighton, Chris; Scholl, Andreas; Chern, Gia-Wei; Dahmen, Karin; Nisoli, Cristiano; Schiffer, Peter

Artificial spin ice systems are two dimensional arrays of single-domain nanomagnets designed to study frustration phenomena. By careful choice of the geometry of the system, the lattices can have ground states with non-trivial degeneracy. We study the kinetics of such systems through photoemission electron microscopy (PEEM) measurements of the fluctuations of the individual nanomagnet moments, looking at excitations above the magnetic ground states of the systems and how those excitations are impacted by lattice geometry. Detailed analysis of different systems shows non-trivial kinetics that originate from different interaction patterns. The study indicates the important role of effective excitation in the near-ground-state kinetics of these frustrated systems. This work was funded by the US Department of Energy under Grant Number DE-SC0010778. The work of M.S. and K.D. was supported by DOE DE-FE0011194. Work at UMN was supported by the NSF MRSEC under DMR-1420013, and DMR-1507048. The work of C.N. was carried out under the auspices of the US Department of Energy at LANL under Contract Number DE-AC52-06NA253962. The ALS was supported by the US Department of Energy under Contract Number DE-AC02-05CH11231.

Dynamics of hot random quantum spin chains: from anyons to Heisenberg spins

NASA Astrophysics Data System (ADS)

Parameswaran, Siddharth; Potter, Andrew; Vasseur, Romain

2015-03-01

We argue that the dynamics of the random-bond Heisenberg spin chain are ergodic at infinite temperature, in contrast to the many-body localized behavior seen in its random-field counterpart. First, we show that excited-state real-space renormalization group (RSRG-X) techniques suffer from a fatal breakdown of perturbation theory due to the proliferation of large effective spins that grow without bound. We repair this problem by deforming the SU (2) symmetry of the Heisenberg chain to its `anyonic' version, SU(2)k , where the growth of effective spins is truncated at spin S = k / 2 . This enables us to construct a self-consistent RSRG-X scheme that is particularly simple at infinite temperature. Solving the flow equations, we compute the excited-state entanglement and show that it crosses over from volume-law to logarithmic scaling at a length scale ξk ~eαk3 . This reveals that (a) anyon chains have random-singlet-like excited states for any finite k; and (b) ergodicity is restored in the Heisenberg limit k --> ∞ . We acknowledge support from the Quantum Materials program of LBNL (RV), the Gordon and Betty Moore Foundation (ACP), and UC Irvine startup funds (SAP).

Flight and analytical investigations of a structural mode excitation system on the YF-12A airplane

NASA Technical Reports Server (NTRS)

Goforth, E. A.; Murphy, R. C.; Beranek, J. A.; Davis, R. A.

1987-01-01

A structural excitation system, using an oscillating canard vane to generate force, was mounted on the forebody of the YF-12A airplane. The canard vane was used to excite the airframe structural modes during flight in the subsonic, transonic, and supersonic regimes. Structural modal responses generated by the canard vane forces were measured at the flight test conditions by airframe-mounted accelerometers. Correlations of analytical and experimental aeroelastic results were made. Doublet lattice, steady state double lattice with uniform lag, Mach box, and piston theory all produced acceptable analytical aerodynamic results within the restrictions that apply to each. In general, the aerodynamic theory methods, carefully applied, were found to predict the dynamic behavior of the YF-12A aircraft adequately.

Dissociative chemisorption of methane on metal surfaces: Tests of dynamical assumptions using quantum models and ab initio molecular dynamics

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

Jackson, Bret, E-mail: jackson@chem.umass.edu; Nattino, Francesco; Kroes, Geert-Jan

The dissociative chemisorption of methane on metal surfaces is of great practical and fundamental importance. Not only is it the rate-limiting step in the steam reforming of natural gas, the reaction exhibits interesting mode-selective behavior and a strong dependence on the temperature of the metal. We present a quantum model for this reaction on Ni(100) and Ni(111) surfaces based on the reaction path Hamiltonian. The dissociative sticking probabilities computed using this model agree well with available experimental data with regard to variation with incident energy, substrate temperature, and the vibrational state of the incident molecule. We significantly expand the vibrationalmore » basis set relative to earlier studies, which allows reaction probabilities to be calculated for doubly excited initial vibrational states, though it does not lead to appreciable changes in the reaction probabilities for singly excited initial states. Sudden models used to treat the center of mass motion parallel to the surface are compared with results from ab initio molecular dynamics and found to be reasonable. Similar comparisons for molecular rotation suggest that our rotationally adiabatic model is incorrect, and that sudden behavior is closer to reality. Such a model is proposed and tested. A model for predicting mode-selective behavior is tested, with mixed results, though we find it is consistent with experimental studies of normal vs. total (kinetic) energy scaling. Models for energy transfer into lattice vibrations are also examined.« less

THE ASTEROID BELT AS A RELIC FROM A CHAOTIC EARLY SOLAR SYSTEM

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

Izidoro, André; Raymond, Sean N.; Pierens, Arnaud

The orbital structure of the asteroid belt holds a record of the solar system’s dynamical history. The current belt only contains ∼10{sup −3} Earth masses yet the asteroids’ orbits are dynamically excited, with a large spread in eccentricity and inclination. In the context of models of terrestrial planet formation, the belt may have been excited by Jupiter’s orbital migration. The terrestrial planets can also be reproduced without invoking a migrating Jupiter; however, as it requires a severe mass deficit beyond Earth’s orbit, this model systematically under-excites the asteroid belt. Here we show that the orbits of the asteroids may havemore » been excited to their current state if Jupiter’s and Saturn’s early orbits were chaotic. Stochastic variations in the gas giants’ orbits cause resonances to continually jump across the main belt and excite the asteroids’ orbits on a timescale of tens of millions of years. While hydrodynamical simulations show that the gas giants were likely in mean motion resonance at the end of the gaseous disk phase, small perturbations could have driven them into a chaotic but stable state. The gas giants’ current orbits were achieved later, during an instability in the outer solar system. Although it is well known that the present-day solar system exhibits chaotic behavior, our results suggest that the early solar system may also have been chaotic.« less

Universal properties of materials with the Dirac dispersion relation of low-energy excitations

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

Protogenov, A. P., E-mail: alprot@appl.sci-nnov.ru; Chulkov, E. V.

2015-12-15

The N-terminal scheme is considered for studying the contribution of edge states to the response of a two-dimensional topological insulator. A universal distribution of the nonlocal resistance between terminals is determined in the ballistic transport approach. The calculated responses are identical to experimentally observed values. The spectral properties of surface electronic states in Weyl semimetals are also studied. The density of surface states is accurately determined. The universal behavior of these characteristics is a distinctive feature of the considered Dirac materials which can be used in practical applications.

Anesthetic state modulates excitability but not spectral tuning or neural discrimination in single auditory midbrain neurons

PubMed Central

Schumacher, Joseph W.; Schneider, David M.

2011-01-01

The majority of sensory physiology experiments have used anesthesia to facilitate the recording of neural activity. Current techniques allow researchers to study sensory function in the context of varying behavioral states. To reconcile results across multiple behavioral and anesthetic states, it is important to consider how and to what extent anesthesia plays a role in shaping neural response properties. The role of anesthesia has been the subject of much debate, but the extent to which sensory coding properties are altered by anesthesia has yet to be fully defined. In this study we asked how urethane, an anesthetic commonly used for avian and mammalian sensory physiology, affects the coding of complex communication vocalizations (songs) and simple artificial stimuli in the songbird auditory midbrain. We measured spontaneous and song-driven spike rates, spectrotemporal receptive fields, and neural discriminability from responses to songs in single auditory midbrain neurons. In the same neurons, we recorded responses to pure tone stimuli ranging in frequency and intensity. Finally, we assessed the effect of urethane on population-level representations of birdsong. Results showed that intrinsic neural excitability is significantly depressed by urethane but that spectral tuning, single neuron discriminability, and population representations of song do not differ significantly between unanesthetized and anesthetized animals. PMID:21543752

Evidence for Cation-Controlled Excited-State Localization in a Ruthenium Polypyridyl Compound.

PubMed

Beauvilliers, Evan E; Meyer, Gerald J

2016-08-01

The visible absorption and photoluminescence (PL) properties of the four neutral ruthenium diimine compounds [Ru(bpy)2(dcb)] (B2B), [Ru(dtb)2(dcb)] (D2B), [Ru(bpy)2(dcbq)] (B2Q), and [Ru(dtb)2(dcbq)] (D2Q), where bpy is 2,2'-bipyridine, dcb is 4,4'-(CO2(-))2-bpy, dtb is 4,4'-(tert-butyl)2-bpy, and dcbq is 4,4'-(CO2(-))2-2,2'-biquinoline, are reported in the presence of Lewis acidic cations present in fluid solutions at room temperature. In methanol solutions, the measured spectra were insensitive to the presence of these cations, while in acetonitrile a significant red shift in the PL spectra (≤1400 cm(-1)) was observed consistent with stabilization of the metal-to-ligand charge transfer (MLCT) excited state through Lewis acid-base adduct formation. No significant spectral changes were observed in control experiments with the tetrabutylammonium cation. Titration data with Li(+), Na(+), Mg(2+), Ca(2+), Zn(2+), Al(3+), Y(3+), and La(3+) showed that the extent of stabilization saturated at high cation concentration with magnitudes that scaled roughly with the cation charge-to-size ratio. The visible absorption spectra of D2Q was particularly informative due to the presence of two well-resolved MLCT absorption bands: (1) Ru → bpy, λmax ≈ 450 nm; and (2) Ru → dcbq, λmax ≈ 540 nm. The higher-energy band blue-shifted and the lower-energy band red-shifted upon cation addition. The PL intensity and lifetime of the excited state of B2B first increased with cation addition without significant shifts in the measured spectra, behavior attributed to a cation-induced change in the localization of the emissive excited state from bpy to dcb. The importance of excited-state localization and stabilization for solar energy conversion is discussed.

Multiple normalized solutions for a planar gauged nonlinear Schrödinger equation

NASA Astrophysics Data System (ADS)

Luo, Xiao

2018-06-01

We study the existence, multiplicity, quantitative property and asymptotic behavior of normalized solutions for a gauged nonlinear Schrödinger equation arising from the Chern-Simons theory Δ u + ω u +|x|^2u+ λ ( {{h^2}(| x | )}/{{{| x | ^2}}} + \\int \\limits _{| x | }^{ + ∞} {{h(s)}/s} {u^2}(s)ds) u = {| u | ^{p - 2}}u,\\quad x\\in R^2, where ω \\in R, λ >0, p>4 and h(s) = 1/2\\int \\limits _0^s {r{u^2}(r)dr} . Combining constraint minimization method and minimax principle, we prove that the problem possesses at least two normalized solutions: One is a ground state and the other is an excited state. Furthermore, the asymptotic behavior and quantitative property of the ground state are analyzed.

Tuning the Photophysical Properties of Ru(II) Monometallic and Ru(II),Rh(III) Bimetallic Supramolecular Complexes by Selective Ligand Deuteration.

PubMed

Wagner, Alec T; Zhou, Rongwei; Quinn, Kevan S; White, Travis A; Wang, Jing; Brewer, Karen J

2015-07-02

A series of three new complexes of the design [(TL)2Ru(BL)](2+), two new complexes of the design [(TL)2Ru(BL)Ru(TL)2](4+), and three new complexes of the design [(TL)2Ru(BL)RhCl2(TL)](3+) (TL = bpy or d8-bpy; BL = dpp or d10-dpp; TL = terminal ligand; BL = bridging ligand; bpy = 2,2'-bipyridine; dpp = 2,3-bis(2-pyridyl)pyrazine) were synthesized and the (1)H NMR spectroscopy, electrochemistry, electronic absorbance spectroscopy, and photophysical properties studied. Incorporation of deuterated ligands into the molecular architecture simplifies the (1)H NMR spectra, allowing for complete (1)H assignment of [(d8-bpy)2Ru(dpp)](PF6)2 and partial assignment of [(bpy)2Ru(d10-dpp)](PF6)2. The electrochemistry for the deuterated and nondeuterated species showed nearly identical redox properties. Electronic absorption spectroscopy of the deuterated and nondeuterated complexes are superimposable with the lowest energy transition being Ru(dπ) → BL(π*) charge transfer in nature (BL = dpp or d10-dpp). Ligand deuteration impacts the excited-state properties with an observed increase in the quantum yield of emission (Φ(em)) and excited-state lifetime (τ) of the Ru(dπ) → d10-dpp(π*) triplet metal-to-ligand charge transfer ((3)MLCT) excited state when dpp is deuterated, and a decrease in the rate constant for nonradiative decay (knr). Choice of ligand deuteration between bpy and dpp strongly impacts the observed photophysical properties with BL = d10-dpp complexes showing an enhanced Φ(em) and τ, providing further support that the lowest electronic excited state populated via UV or visible excitation is the photoactive Ru(dπ) → dpp(π*) CT excited state. The Ru(II),Rh(III) complex incorporating the deuterated BL shows increased hydrogen production compared to the variants incorporating the protiated BL, while demonstrating identical dynamic quenching behaviors in the presence of sacrificial electron donor.

Competing 1πσ* mediated dynamics in mequinol: O-H versus O-CH3 photodissociation pathways.

PubMed

Hadden, David J; Roberts, Gareth M; Karsili, Tolga N V; Ashfold, Michael N R; Stavros, Vasilios G

2012-10-14

Deactivation of excited electronic states through coupling to dissociative (1)πσ* states in heteroaromatic systems has received considerable attention in recent years, particularly as a mechanism that contributes to the ultraviolet (UV) photostability of numerous aromatic biomolecules and their chromophores. Recent studies have expanded upon this work to look at more complex species, which involves understanding competing dynamics on two different (1)πσ* potential energy surfaces (PESs) localized on different heteroatom hydride coordinates (O-H and N-H bonds) within the same molecule. In a similar spirit, the work presented here utilizes ultrafast time-resolved velocity map ion imaging to study competing dissociation pathways along (1)πσ* PESs in mequinol (p-methoxyphenol), localized at O-H and O-CH(3) bonds yielding H atoms or CH(3) radicals, respectively, over an excitation wavelength range of 298-238 nm and at 200 nm. H atom elimination is found to be operative via either tunneling under a conical intersection (CI) (298 ≥ λ ≥ 280 nm) or ultrafast internal conversion through appropriate CIs (λ ≤ 245 nm), both of which provide mechanisms for coupling onto the dissociative state associated with the O-H bond. In the intermediate wavelength range of 280 ≥ λ ≥ 245 nm, mediated H atom elimination is not observed. In contrast, we find that state driven CH(3) radical elimination is only observed in the excitation range 264 ≥ λ ≥ 238 nm. Interpretation of these experimental results is guided by: (i) high level complete active space with second order perturbation theory (CASPT2) calculations, which provide 1-D potential energy cuts of the ground and low lying singlet excited electronic states along the O-H and O-CH(3) bond coordinates; and (ii) calculated excitation energies using CASPT2 and the equation-of-motion coupled cluster with singles and doubles excitations (EOM-CCSD) formalism. From these comprehensive studies, we find that the dynamics along the O-H coordinate generally mimic H atom elimination previously observed in phenol, whereas O-CH(3) bond fission in mequinol appears to present notably different behavior to the CH(3) elimination dynamics previously observed in anisole (methoxybenzene).

Spin liquid state in the disordered triangular lattice Sc 2Ga 2CuO 7 revealed by NMR

DOE PAGES

Khuntia, P.; Kumar, R.; Mahajan, A. V.; ...

2016-04-18

We present microscopic magnetic properties of a two-dimensional triangular lattice Sc 2Ga 2CuO 7, consisting of single and double triangular Cu planes. An antiferromagnetic (AFM) exchange interaction J/k B ≈ 35 K between Cu 2+ (S = 1/2) spins in the triangular biplane is obtained from the analysis of intrinsic magnetic susceptibility data. The intrinsic magnetic susceptibility, extracted from 71Ga NMR shift data, displays the presence of AFM short range spin correlations and remains finite down to 50 mK, suggesting a nonsinglet ground state. The nuclear spin-lattice relaxation rate (1/T 1) reveals a slowing down of Cu 2+ spin fluctuationsmore » with decreasing T down to 100 mK. Magnetic specific heat (C m) and 1/T 1 exhibit power law behavior at low temperatures, implying the gapless nature of the spin excitation spectrum. The absence of long range magnetic ordering down to ~J/700, nonzero spin susceptibility at low T, and the power law behavior of C m and 1/T 1 suggest a gapless quantum spin liquid (QSL) state. Our results demonstrate that persistent spin dynamics induced by frustration maintain a quantum-disordered state at T → 0 in this triangular lattice antiferromagnet. Furthermore, this suggests that the low energy modes are dominated by spinon excitations in the QSL state due to randomness engendered by disorder and frustration.« less

Organic Micro/Nanoscale Lasers.

PubMed

Zhang, Wei; Yao, Jiannian; Zhao, Yong Sheng

2016-09-20

Micro/nanoscale lasers that can deliver intense coherent light signals at (sub)wavelength scale have recently captured broad research interest because of their potential applications ranging from on-chip information processing to high-throughput sensing. Organic molecular materials are a promising kind of ideal platform to construct high-performance microlasers, mainly because of their superiority in abundant excited-state processes with large active cross sections for high gain emissions and flexibly assembled structures for high-quality microcavities. In recent years, ever-increasing efforts have been dedicated to developing such organic microlasers toward low threshold, multicolor output, broadband tunability, and easy integration. Therefore, it is increasingly important to summarize this research field and give deep insight into the structure-property relationships of organic microlasers to accelerate the future development. In this Account, we will review the recent advances in organic miniaturized lasers, with an emphasis on tunable laser performances based on the tailorable microcavity structures and controlled excited-state gain processes of organic materials toward integrated photonic applications. Organic π-conjugated molecules with weak intermolecular interactions readily assemble into regular nanostructures that can serve as high-quality optical microcavities for the strong confinement of photons. On the basis of rational material design, a series of optical microcavities with different structures have been controllably synthesized. These microcavity nanostructures can be endowed with effective four-level dynamic gain processes, such as excited-state intramolecular charge transfer, excited-state intramolecular proton transfer, and excimer processes, that exhibit large dipole optical transitions for strongly active gain behaviors. By tailoring these excited-state processes with molecular/crystal engineering and external stimuli, people have effectively modulated the performances of organic micro/nanolasers. Furthermore, by means of controlled assembly and tunable laser performances, efficient outcoupling of microlasers has been successfully achieved in various organic hybrid microstructures, showing considerable potential for the integrated photonic applications. This Account starts by presenting an overview of the research evolution of organic microlasers in terms of microcavity resonators and energy-level gain. Then a series of strategies to tailor the microcavity structures and excited-state dynamics of organic nanomaterials for the modulation of lasing performances are highlighted. In the following part, we introduce the construction and advanced photonic functionalities of organic-microlaser-based hybrid structures and their applications in integrated nanophotonics. Finally, we provide our outlook on the current challenges as well as the future development of organic microlasers. It is anticipated that this Account will provide inspiration for the development of miniaturized lasers with desired performances by tailoring of excited-state processes and microcavity structures toward integrated photonic applications.

New Theoretical Developments in Exploring Electronically Excited States: Including Localized Configuration Interaction Singles and Application to Large Helium Clusters

NASA Astrophysics Data System (ADS)

Closser, Kristina Danielle

This thesis presents new developments in excited state electronic structure theory. Contrasted with the ground state, the electronically excited states of atoms and molecules often are unstable and have short lifetimes, exhibit a greater diversity of character and are generally less well understood. The very unusual excited states of helium clusters motivated much of this work. These clusters consist of large numbers of atoms (experimentally 103--109 atoms) and bands of nearly degenerate excited states. For an isolated atom the lowest energy excitation energies are from 1s → 2s and 1s → 2 p transitions, and in clusters describing the lowest energy band minimally requires four states per atom. In the ground state the clusters are weakly bound by van der Waals interactions, however in the excited state they can form well-defined covalent bonds. The computational cost of quantum chemical calculations rapidly becomes prohibitive as the size of the systems increase. Standard excited-state methods such as configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) can be used with ≈100 atoms, and are optimized to treat only a few states. Thus, one of our primary aims is to develop a method which can treat these large systems with large numbers of nearly degenerate excited states. Additionally, excited states are generally formed far from their equilibrium structures. Vertical excitations from the ground state induce dynamics in the excited states. Thus, another focus of this work is to explore the results of these forces and the fate of the excited states. Very little was known about helium cluster excited states when this work began, thus we first investigated the excitations in small helium clusters consisting of 7 or 25 atoms using CIS. The character of these excited states was determined using attachment/detachment density analysis and we found that in the n = 2 manifold the excitations could generally be interpreted as superpositions of atomic states with surface states appearing close to the atomic excitation energies and interior states being blue shifted by up to ≈2 eV. The dynamics resulting from excitation of He_7 were subsequently explored using ab initio molecular dynamics (AIMD). These simulations were performed with classical adiabatic dynamics coupled to a new state-following algorithm on CIS potential energy surfaces. Most clusters were found to completely dissociate and resulted in a single excited atomic state (90%), however, some trajectories formed bound, He*2 (3%), and a few yielded excited trimers (<0.5%). Comparisons were made with available experimental information on much larger clusters. Various applications of this state following algorithm are also presented. In addition to AIMD, these include excited-state geometry optimization and minimal energy path finding via the growing string method. When using state following we demonstrate that more physical results can be obtained with AIMD calculations. Also, the optimized geometries of three excited states of cytosine, two of which were not found without state following, and the minimal energy path between the lowest two singlet excited states of protonated formaldimine are offered as example applications. Finally, to address large clusters, a local variation of CIS was developed. This method exploits the properties of absolutely localized molecular orbitals (ALMOs) to limit the total number of excitations to scaling only linearly with cluster size, which results in formal scaling with the third power of the system size. The derivation of the equations and design of the algorithm are discussed in detail, and computational timings as well as a pilot application to the size dependence of the helium cluster spectrum are presented.

Effects of alcohol on the membrane excitability and synaptic transmission of medium spiny neurons in the nucleus accumbens

PubMed Central

Marty, Vincent N.; Spigelman, Igor

2013-01-01

Chronic and excessive alcohol drinking lead to alcohol dependence and loss of control over alcohol consumption, with serious detrimental health consequences. Chronic alcohol exposure followed by protracted withdrawal causes profound alterations in the brain reward system that leads to marked changes in reinforcement mechanisms and motivational state. These long-lasting neuroadaptations are thought to contribute to the development of cravings and relapse. The nucleus accumbens (NAcc), a central component of the brain reward system, plays a critical role in alcohol-induced neuroadaptive changes underlying alcohol-seeking behaviors. Here we review the findings that chronic alcohol exposure produces long-lasting neuroadaptive changes in various ion channels that govern intrinsic membrane properties and neuronal excitability, as well as excitatory and inhibitory synaptic transmission in the NAcc that underlie alcohol-seeking behavior during protracted withdrawal. PMID:22445807

Channel branching ratios in CH2CN- photodetachment: Rotational structure and vibrational energy redistribution in autodetachment

NASA Astrophysics Data System (ADS)

Lyle, Justin; Wedig, Olivia; Gulania, Sahil; Krylov, Anna I.; Mabbs, Richard

2017-12-01

We report photoelectron spectra of CH2CN-, recorded at photon energies between 13 460 and 15 384 cm-1, which show rapid intensity variations in particular detachment channels. The branching ratios for various spectral features reveal rotational structure associated with autodetachment from an intermediate anion state. Calculations using equation-of-motion coupled-cluster method with single and double excitations reveal the presence of two dipole-bound excited anion states (a singlet and a triplet). The computed oscillator strength for the transition to the singlet dipole-bound state provides an estimate of the autodetachment channel contribution to the total photoelectron yield. Analysis of the different spectral features allows identification of the dipole-bound and neutral vibrational levels involved in the autodetachment processes. For the most part, the autodetachment channels are consistent with the vibrational propensity rule and normal mode expectation. However, examination of the rotational structure shows that autodetachment from the ν3 (v = 1 and v = 2) levels of the dipole-bound state displays behavior counter to the normal mode expectation with the final state vibrational level belonging to a different mode.

Doping evolution of spin and charge excitations in the Hubbard model

DOE PAGES

Kung, Y. F.; Nowadnick, E. A.; Jia, C. J.; ...

2015-11-05

We shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, examining the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achievedmore » in the cuprates). Ultimately, these fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.« less

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.

MiR-980 is a memory suppressor microRNA that regulates the autism-susceptibility gene, A2bp1

PubMed Central

Guven-Ozkan, Tugba; Busto, Germain U.; Schutte, Soleil S.; Cervantes-Sandoval, Isaac; O’Dowd, Diane K.; Davis, Ronald L.

2016-01-01

SUMMARY MicroRNAs have been associated with many different biological functions but little is known about their roles in conditioned behavior. We demonstrate that Drosophila miR-980 is a memory suppressor gene functioning in multiple regions of the adult brain. Memory acquisition and stability were both increased by miR-980 inhibition. Whole cell recordings and functional imaging experiments indicated that miR-980 regulates neuronal excitability. We identified the autism susceptibility gene, A2bp1, as an mRNA target for miR-980. A2bp1 levels varied inversely with miR-980 expression; memory performance was directly related to A2bp1 levels. In addition, A2bp1 knockdown reversed the memory gains produced by miR-980 inhibition, consistent with A2bp1 being a downstream target of miR-980 responsible for the memory phenotypes. Our results indicate that miR-980 represses A2bp1 expression to tune the excitable state of neurons, and the overall state of excitability translates to memory impairment or improvement. PMID:26876166

Picosecond absorption anisotropy of polymethine and squarylium dyes in liquid and polymeric media

NASA Astrophysics Data System (ADS)

Przhonska, Olga V.; Hagan, David J.; Novikov, Evgueni; Lepkowicz, Richard; Van Stryland, Eric W.; Bondar, Mikhail V.; Slominsky, Yuriy L.; Kachkovski, Alexei D.

2001-11-01

Time-resolved excitation-probe polarization measurements are performed for polymethine and squarylium dyes in ethanol and an elastopolymer of polyurethane acrylate (PUA). These molecules exhibit strong excited-state absorption in the visible, which results in reverse saturable absorption (RSA). In pump-probe experiments, we observe a strong angular dependence of the RSA decay kinetics upon variation of the angle between pump and probe polarizations. The difference in absorption anisotropy kinetics in ethanol and PUA is detected and analyzed. Anisotropy decay curves in ethanol follow a single exponential decay leading to complete depolarization of the excited state. We also observe complete depolarization in PUA, in which case the anisotropy decay follows a double exponential behavior. Possible rotations in the PUA polymeric matrix are connected with the existence of local microcavities of free volume. We believe that the fast decay component is connected with the rotation of molecular fragments and the slower decay component is connected with the rotation of entire molecules in local microcavities, which is possible because of the elasticity of the polymeric material.

Ionization studies in laser-excited alkaline-earth vapors.

PubMed

Hermann, J P; Wynne, J J

1980-06-01

We report on the time behavior of ionization signals produced by laser excitation of Ca and Ba atomic vapor to high-Rydberg states. A space-charge-limited thermionic diode detector shows a long-lived (>I-msec) ionization signal. However, optical detection of atomic ions (Ca+, Ba+) shows that these species live for much shorter times (<100 microsec). These results, in conjunction with published results on mass-spectrometric studies of high-density atomic beams, suggest that our ionization signal is primarily due to molecular species (Ca2+, Ba2+). We also observed optically pumped amplified spontaneous emission and stimulated electronic Raman scattering in Ca+ and Ba+.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Comparison of behavioral characteristics of dogs in the United States and Japan.

PubMed

Nagasawa, Miho; Kanbayashi, Shunichi; Mogi, Kazutaka; Serpell, James A; Kikusui, Takefumi

2016-02-01

This study examined the difference in dog owning between Japan and the United States, and the effect of these differences on dogs' behavioral characteristics. Behavioral evaluations of privately-owned dogs were obtained by using online questionnaire. We compared background and demographic information from the two countries and analyzed the effects of these differences on behavioral characteristics in dogs. The results indicated that there was a bias in the dog breeds kept in Japan compared to the United States and that Japanese dogs' body weight was lower than the US dogs. The main source of dog acquisition was pet stores in Japan and breeders and/or shelters in the United States. Multiple linear regression analysis found that Japanese dogs showed more aggression to household members and higher energy, restlessness and fear of non-social stimuli than US dogs, while US dogs showed more fear of unfamiliar persons, separation-related behavior and excitability. US dogs also showed higher levels of trainability and attachment to owners. The lower dog's body weight was, the higher the behavioral scores except for trainability were. When dogs that were obtained under 3 months of age were analyzed, the younger the dogs were when their owners obtained them, the higher the scores on some behavioral problem factors were. The higher rates of problem behaviors among Japanese dogs compared with US dogs suggest that the preference for small breed dogs and poor early development environment influenced the behavioral characteristics of dogs.

l- and n-changing collisions during interaction of a pulsed beam of Li Rydberg atoms with CO2

NASA Astrophysics Data System (ADS)

Dubreuil, B.; Harnafi, M.

1989-07-01

The pulsed Li atomic beam produced in our experiment is based on controlled transversely-excited-atmospheric CO2 laser-induced ablation of a Li metal target. The atomic beam is propagated in vacuum or in CO2 gas at low pressure. Atoms in the beam are probed by laser-induced fluorescence spectroscopy. This allows the determination of time-of-flight and velocity distributions. Li Rydberg states (n=5-13) are populated in the beam by two-step pulsed-laser excitation. The excited atoms interact with CO2 molecules. l- and n-changing cross sections are deduced from the time evolution of the resonant or collision-induced fluorescence following this selective excitation. l-changing cross sections of the order of 104 AṦ are measured; they increase with n as opposed to the plateau observed for Li* colliding with a diatomic molecule. This behavior is qualitatively well explained in the framework of the free-electron model. n-->n' changing processes with large cross sections (10-100 AṦ) are also observed even in the case of large electronic energy change (ΔEnn'>103 cm-1). These results can be interpreted in terms of resonant-electronic to vibrational energy transfers between Li Rydberg states and CO2 vibrational modes.

Growth mechanism and magnon excitation in NiO nanowalls

PubMed Central

2011-01-01

The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature. PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di PMID:21824408

Multiple hydrogen bonding in excited states of aminopyrazine in methanol solution: time-dependent density functional theory study.

PubMed

Chai, Shuo; Yu, Jie; Han, Yong-Chang; Cong, Shu-Lin

2013-11-01

Aminopyrazine (AP) and AP-methanol complexes have been theoretically studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The excited-state hydrogen bonds are discussed in detail. In the ground state the intermolecular multiple hydrogen bonds can be formed between AP molecule and protic solvents. The AP monomer and hydrogen-bonded complex of AP with one methanol are photoexcited initially to the S2 state, and then transferred to the S1 state via internal conversion. However the complex of AP with two methanol molecules is directly excited to the S1 state. From the calculated electronic excited energies and simulated absorption spectra, we find that the intermolecular hydrogen bonds are strengthened in the electronic excited states. The strengthening is confirmed by the optimized excited-state geometries. The photochemical processes in the electronic excited states are significantly influenced by the excited-state hydrogen bond strengthening. Copyright © 2013 Elsevier B.V. All rights reserved.

Micromanipulation and physiological monitoring of cells using two-photon excited fluorescence in cw laser tweezers

NASA Astrophysics Data System (ADS)

Sonek, Gregory J.; Liu, Yagang; Berns, Michael W.; Tromberg, Bruce J.

1996-05-01

We report the observation of two-photon fluorescence excitation and cell confinement, simultaneously, in a continuous-wave (cw) single-beam gradient force optical trap, and demonstrate its use as an in-situ probe to study the physiological state of an optically confined cell sample. At the wavelength of 1064 nm, a single focused gaussian laser beam is used to simultaneously confine, and excite visible fluorescence from, a human sperm cell that has been tagged with propidium iodide, a exogenous fluorescent dye that functions as a viability assay of cellular physiological state. The intensity at the dye peak emission wavelength of 620 nm exhibits a near-square-law dependence on incident trapping beam photon laser power, a behavior consistent with a two-photon absorption process. In addition, for a sperm cell held stationary in the optical tweezers for a period of several minutes at a constant trapping power, red fluorescence emission was observed to increase the time, indicating that the cell has gradually transitioned between a live and dead state. Two-photon excited fluorescence was also observed in chinese hamster ovary cells that were confined by cw laser tweezers and stained with either propidium iodide or Snarf, a pH-sensitive dye probe. These results suggest that, for samples suitably tagged with fluorescent probes and vital stains, optical tweezers can be used to generate their own in-situ diagnostic optical probes of cellular viability or induced photodamage, via two-photon processes.

Oxidation of atomic gold ions: thermochemistry for the activation of O(2) and N(2)O BY Au(+) ((1)S(0) and (3)D).

PubMed

Li, Feng-Xia; Gorham, Katrine; Armentrout, P B

2010-10-28

Reaction of Au(+) ((1)S(0) and (3)D) with O(2) and N(2)O is studied as a function of kinetic energy using guided ion beam tandem mass spectrometry. A flow tube ion source produces Au(+) primarily in its (1)S(0) (5d(10)) electronic ground state level but with some (3)D and perhaps higher lying excited states. The distribution of states can be altered by adding N(2)O, which completely quenches the excited states, or CH(4) to the flow gases. Cross sections as a function of kinetic energy are measured for both neutral reagents and both ground and excited states of Au(+). Formation of AuO(+) is common to both systems with the N(2)O system also exhibiting AuN(2)(+) and AuNO(+) formation. All reactions of Au(+) ((1)S(0)) are observed to be endothermic, whereas the excitation energy available to the (3)D state allows some reactions to be exothermic. Because of the closed shell character of ground state Au(+) ((1)S(0), 5d(10)), the reactivity of these systems is low and has cross sections with onsets and peaks at higher energies than expected from the known thermochemistry but lower than energies expected from impulsive processes. Analyses of the endothermic reaction cross sections yield the 0 K bond dissociation energy (BDE) in eV of D(0)(Au(+)-O) = 1.12 ± 0.08, D(0)(Au(+)-N(2)) ≥ 0.30 ± 0.04, and D(0)(Au(+)-NO) = 0.89 ± 0.17, values that are all speculative because of the unusual experimental behavior. Combining the AuO(+) BDE measured here with literature data also yields the ionization energy of AuO as 10.38 ± 0.23 eV. Quantum chemical calculations show reasonable agreement with the experimental bond energies and provide the electronic structures of these species.

Switching Dynamics Between Two Movement Patterns Varies According to Time Interval

NASA Astrophysics Data System (ADS)

Hirakawa, Takehito; Suzuki, Hiroo; Okumura, Motoki; Gohara, Kazutoshi; Yamamoto, Yuji

This study investigated the regularity that characterizes the behavior of dissipative dynamical systems excited by external temporal inputs for pointing movements. Right-handed healthy male participants were asked to continuously point their right index finger at two light-emitting diodes (LEDs) located in the oblique left and right directions in front of them. These movements were performed under two conditions: one in which the direction was repeated and one in which the directions were switched on a stochastic basis. These conditions consisted of 12 tempos (30, 36, 42, 48, 51, 54, 57, 60, 63, 66, 69, and 72 beats per minute). Data from the conditions under which the input pattern was repeated revealed two different trajectories in hyper-cylindrical state space ℳ, whereas the conditions under which the inputs were switched induced transitions between the two trajectories, which were considered to be excited attractors. The transitions between the two excited attractors were characterized by a self-similar structure. Moreover, the correlation dimensions increased as the tempos increased. These results suggest a relationship of D ∝ 1/T (T is the switching-time length; i.e. the condition) between temporal input and pointing behavior and that continuous pointing movements are regular rather than random noise.

Communication: Direct comparison between theory and experiment for correlated angular and product-state distributions of the ground-state and stretching-excited O(3P) + CH4 reactions

NASA Astrophysics Data System (ADS)

Czakó, Gábor

2014-06-01

Motivated by a recent experiment [H. Pan and K. Liu, J. Chem. Phys. 140, 191101 (2014)], we report a quasiclassical trajectory study of the O(3P) + CH4(vk = 0, 1) → OH + CH3 [k = 1 and 3] reactions on an ab initio potential energy surface. The computed angular distributions and cross sections correlated to the OH(v = 0, 1) + CH3(v = 0) coincident product states can be directly compared to experiment for O + CH4(v3 = 0, 1). Both theory and experiment show that the ground-state reaction is backward scattered, whereas the angular distributions shift toward sideways and forward directions upon antisymmetric stretching (v3) excitation of the reactant. Theory predicts similar behavior for the O + CH4(v1 = 1) reaction. The simulations show that stretching excitation enhances the reaction up to about 15 kcal/mol collision energy, whereas the O + CH4(vk = 1) reactions produce smaller cross sections for OH(v = 1) + CH3(v = 0) than those of O + CH4(v = 0) → OH(v = 0) + CH3(v = 0). The former finding agrees with experiment and the latter awaits for confirmation. The computed cold OH rotational distributions of O + CH4(v = 0) are in good agreement with experiment.

Communication: direct comparison between theory and experiment for correlated angular and product-state distributions of the ground-state and stretching-excited O((3)P) + CH4 reactions.

PubMed

Czakó, Gábor

2014-06-21

Motivated by a recent experiment [H. Pan and K. Liu, J. Chem. Phys. 140, 191101 (2014)], we report a quasiclassical trajectory study of the O((3)P) + CH4(vk = 0, 1) → OH + CH3 [k = 1 and 3] reactions on an ab initio potential energy surface. The computed angular distributions and cross sections correlated to the OH(v = 0, 1) + CH3(v = 0) coincident product states can be directly compared to experiment for O + CH4(v3 = 0, 1). Both theory and experiment show that the ground-state reaction is backward scattered, whereas the angular distributions shift toward sideways and forward directions upon antisymmetric stretching (v3) excitation of the reactant. Theory predicts similar behavior for the O + CH4(v1 = 1) reaction. The simulations show that stretching excitation enhances the reaction up to about 15 kcal/mol collision energy, whereas the O + CH4(vk = 1) reactions produce smaller cross sections for OH(v = 1) + CH3(v = 0) than those of O + CH4(v = 0) → OH(v = 0) + CH3(v = 0). The former finding agrees with experiment and the latter awaits for confirmation. The computed cold OH rotational distributions of O + CH4(v = 0) are in good agreement with experiment.

Activated recombinative desorption: A potential component in mechanisms of spacecraft glow

NASA Technical Reports Server (NTRS)

Cross, J. B.

1985-01-01

The concept of activated recombination of atomic species on surfaces can explain the production of vibrationally and translationally excited desorbed molecular species. Equilibrium statistical mechanics predicts that the molecular quantum state distributions of desorbing molecules is a function of surface temperature only when the adsorption probability is unity and independent of initial collision conditions. In most cases, the adsorption probability is dependent upon initial conditions such as collision energy or internal quantum state distribution of impinging molecules. From detailed balance, such dynamical behavior is reflected in the internal quantum state distribution of the desorbing molecule. This concept, activated recombinative desorption, may offer a common thread in proposed mechanisms of spacecraft glow. Using molecular beam techniques and equipment available at Los Alamos, which includes a high translational energy 0-atom beam source, mass spectrometric detection of desorbed species, chemiluminescence/laser induced fluorescence detection of electronic and vibrationally excited reaction products, and Auger detection of surface adsorbed reaction products, a fundamental study of the gas surface chemistry underlying the glow process is proposed.

Thermal Hall conductivity in the spin-triplet superconductor with broken time-reversal symmetry

NASA Astrophysics Data System (ADS)

Imai, Yoshiki; Wakabayashi, Katsunori; Sigrist, Manfred

2017-01-01

Motivated by the spin-triplet superconductor Sr2RuO4 , the thermal Hall conductivity is investigated for several pairing symmetries with broken time-reversal symmetry. In the chiral p -wave phase with a fully opened quasiparticle excitation gap, the temperature dependence of the thermal Hall conductivity has a temperature linear term associated with the topological property directly and an exponential term, which shows a drastic change around the Lifshitz transition. Examining f -wave states as alternative candidates with d =Δ0z ̂(kx2-ky2) (kx±i ky) and Δ0z ̂kxky(kx±i ky) with gapless quasiparticle excitations, we study the temperature dependence of the thermal Hall conductivity, where for the former state the thermal Hall conductivity has a quadratic dependence on temperature, originating from the linear dispersions, in addition to linear and exponential behavior. The obtained result may enable us to distinguish between the chiral p -wave and f -wave states in Sr2RuO4 .

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

Time-resolved analysis of the white photoluminescence from chemically synthesized SiC{sub x}O{sub y} thin films and nanowires

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

Tabassum, Natasha; Nikas, Vasileios; Ford, Brian

2016-07-25

The study reported herein presents results on the room-temperature photoluminescence (PL) dynamics of chemically synthesized SiC{sub x}O{sub y≤1.6} (0.19 < x < 0.6) thin films and corresponding nanowire (NW) arrays. The PL decay transients of the SiC{sub x}O{sub y} films/NWs are characterized by fast luminescence decay lifetimes that span in the range of 350–950 ps, as determined from their deconvoluted PL decay spectra and their stretched-exponential recombination behavior. Complementary steady-state PL emission peak position studies for SiC{sub x}O{sub y} thin films with varying C content showed similar characteristics pertaining to the variation of their emission peak position with respect to the excitation photon energy.more » A nearly monotonic increase in the PL energy emission peak, before reaching an energy plateau, was observed with increasing excitation energy. This behavior suggests that band-tail states, related to C-Si/Si-O-C bonding, play a prominent role in the recombination of photo-generated carriers in SiC{sub x}O{sub y}. Furthermore, the PL lifetime behavior of the SiC{sub x}O{sub y} thin films and their NWs was analyzed with respect to their luminescence emission energy. An emission-energy-dependent lifetime was observed, as a result of the modulation of their band-tail states statistics with varying C content and with the reduced dimensionality of the NWs.« less

Theoretical studies of electronically excited states

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

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.

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

Yang, Jiayue; Zhang, Dong; Chen, Zhen

The vibrationally excited reaction of F + CHD{sub 3}(ν{sub 1} = 1) → DF + CHD{sub 2} at a collision energy of 9.0 kcal/mol is investigated using the crossed-beams and time-sliced velocity map imaging techniques. Detailed and quantitative information of the CH stretching excitation effects on the reactivity and dynamics of the title reaction is extracted with the help of an accurate determination of the fraction of the excited CHD{sub 3} reagent in the crossed-beam region. It is found that all vibrational states of the CHD{sub 2} products observed in the ground-state reaction, which mainly involve the excitation of themore » umbrella mode of the CHD{sub 2} products, are severely suppressed by the CH stretching excitation. However, there are four additional vibrational states of the CHD{sub 2} products appearing in the excited-state reaction which are not presented in the ground-state reaction. These vibrational states either have the CH stretching excitation retained or involve one quantum excitation in the CH stretching and the excitation of the umbrella mode. Including all observed vibrational states, the overall cross section of the excited-state reaction is estimated to be 66.6% of that of the ground-state one. Experimental results also show that when the energy of CH stretching excitation is released during the reaction, it is deposited almost exclusively as the rovibrational energy of the DF products, with little portion in the translational degree of freedom. For vibrational states of the CHD{sub 2} products observed in both ground- and excited-state reactions, the CH stretching excitation greatly suppresses the forward scattered products, causing a noticeable change in the product angular distributions.« less

Thermal bleaching in single fluorescent molecules under two-photon excitation regime

NASA Astrophysics Data System (ADS)

Chirico, Giuseppe; Cannone, Fabio; Baldini, Giancarlo; Diaspro, Alberto

2003-07-01

Single molecule spectroscopy often requires the immobilization of the molecules onto solid or quasi-solid substrates and the use of relatively high excitation intensity We have studied the fluorescence emission of four common dyes used for bio-imaging studies, rhodamine 6G, fluorescein, pyrene and indo-1 at the single molecule level under two-photon excitation regime. We focus on two-photon excitation thermal effects on the stability of the single molecules, influencing the internal photo-dynamics and the total duration of the fluorescent emission. Single dye molecules, spread on a glass substrate by spin coating, show a constant fluorescence output till a sudden transition to a dark state very close to the background. The bleaching time that is found to vary in the series pyrene, Indo-1, fluorescein and rhodamine 6G from the fastest to the slowest one respectively, has a Gaussian distribution suggesting that bleaching is not due to photo-bleaching. Moreover it shows a correlation to the amount of absorbed power not re-irradiated as fluorescence and to the complexity of the molecule. These observations are interpreted as thermal bleaching where the temperature increase is induced by the two-photon excitation process. This study should be extended to different trapping media of interest in single molecule basic research and applications, such as silica and polyacrylamide gels or nanosctructured polyelectrolyte matrices. We think that the observed behavior and the correlations found to the molecular chemical and physical parameters, may be of some help for the design of molecules with switching on-off behavior of longer duration.

Persistence of collective behavior at high spin in the N = 88 nucleus Tb 153

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

Hartley, D. J.; Riley, M. A.; Wang, X.

Excited states in the N = 88 nucleus Tb-153 were observed up to spin similar to 40 in an experiment utilizing the Gammasphere array. The Tb-153 states were populated in a weak alpha 4n evaporation channel of the Cl-37 + Sn-124 reaction. Two previously known sequences were extended to higher spins, and a new decoupled structure was identified. The pi h(11/2) band was observed in the spin region where other N = 88 isotopes exhibit effects of prolate to oblate shape changes leading to band termination along the yrast line, whereas Tb-153 displays a persistent collective behavior. However, minor perturbationsmore » of the very highest state in both signatures of this h(11/2) band are observed, which perhaps signal the start of the transition towards band termination.« less

Coherent control of alkali cluster fragmentation dynamics

NASA Astrophysics Data System (ADS)

Lindinger, Albrecht; Lupulescu, Cosmin; Bartelt, Andreas; Vajda, Štefan; Wöste, Ludger

2003-06-01

Metal clusters exhibit extraordinary chemical and catalytic properties, which sensitively depend upon their size. This behavior makes them interesting candidates for the real-time analysis of ultrafast photo-induced processes—ultimately leading to coherent control scenarii. We have performed transient multi-photon ionization experiments on small alkali clusters of different size in order to probe their wave packet dynamics, structural reorientations, charge transfers and dissociative events in different vibrationally excited electronic states including their ground state. The observed processes were highly dependent on the irradiated pulse parameters, like its phase, amplitude and duration; an emphasis to employ a feedback control system for generating the optimum pulse shapes. Their spectral and temporal behavior reflects interesting properties about the investigated system and the irradiated photochemical process. We present first the vibrational dynamics of bound, dissociated, and pre-dissociated electronically excited states of alkali dimers and trimers. The scheme for observing the wave packet dynamics in the electronic ground state using stimulated Raman-pumping is shown. Since the employed pulse parameters significantly influence the efficiency of the irradiated dynamic pathways photo-induced fragmentation experiments on bifurcating reaction channels were carried out. In these experiments different branching ionization and fragmentation pathways of electronically excited Na 2K were investigated. By employing an evolutionary algorithm for optimizing the phase and amplitude of the applied laser field, the yield of the resulting parent or fragment ions could significantly be influenced and interesting features could be concluded from the obtained optimum pulse shapes revealing the characteristic molecular oscillation period. Moreover, the influence on the optimal pulse shape due to fragmentation from larger clusters into NaK is obtained. The substructure of the optimal pulse shape thereby offers new insight into the fragmentation channel during the control process. Characteristic motions of the involved wave packets are proposed, in order to explain the optimized dynamic dissociation pathways.

Interference effects on vibration-mediated tunneling through interacting degenerate molecular states.

PubMed

Zhong, X; Cao, J C

2009-07-22

We study the combined effects of quantum electronic interference and Coulomb interaction on electron transport through near-degenerate molecular states with strong electron-vibration interaction. It is found that quantum electronic interference strongly affects the current and its noise properties. In particular, destructive interference induces pronounced negative differential conductances (NDCs) accompanying the vibrational excited states, and such NDC characters are not related to asymmetric tunnel coupling and are robust to the damping of a thermal bath. In a certain transport regime, the non-equilibrium vibration distribution even shows a peculiar sub-Poissonian behavior, which is enhanced by quantum electronic interference.

Photoisomerization of Stilbene: The Detailed XMCQDPT2 Treatment.

PubMed

Ioffe, I N; Granovsky, A A

2013-11-12

We report the detailed XMCQDPT2/cc-pVTZ study of trans-cis photoisomerization in one of the core systems of both experimental and computational photochemistry-the stilbene molecule. For the first time, the potential energy surface (PES) of the S1 state has been directly optimized and scanned using a multistate multiconfiguration second-order perturbation theory. We characterize the trans-stilbene, pyramidalized (phantom), and DHP-cis-stilbene geometric domains of the S1 state and describe their stationary points including the transition states between them, as well as S1/S0 intersections. Also reported are the minima and the activation barriers in the ground state. Our calculations correctly predict the kinetic isotope effect due to H/D exchange at ethylenic hydrogens, the dynamic behavior of excited cis-stilbene, and trans-cis branching ratio after relaxation to S0 through a rather unsymmetric conical intersection. In general, the XMCQDPT2 results confirm the qualitative adequacy of the TDDFT (especially SF-TDDFT) picture of the excited stilbene but also reveal quantitative discrepancies that deserve further exploration.

Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

DOE PAGES

Zhang, Wenkai; Kjaer, Kasper S.; Alonso-Mori, Roberto; ...

2016-08-25

Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover – the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand iron complexes with four cyanide (CN –) ligands and one 2,2'-bipyridine (bpy) ligand. This enablesmore » MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN) 4(bpy)] 2–. The two experimental techniques are highly complementary; the time-resolved UV-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. Here, we conclude that the MLCT excited state of [Fe(CN) 4(bpy)] 2– decays with roughly a 20 ps lifetime without undergoing spin crossover, exceeding the MLCT excited state lifetime of [Fe(2,2'-bipyridine) 3] 2+ by more than two orders of magnitude.« less

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

Zhai, Liangjun; Zheng, Yujun, E-mail: yzheng@sdu.edu.cn

In the present study, the dynamical behaviors of tripartite entanglement of vibrations in triatomic molecules are studied based on the Lie algebraic models of molecules. The dynamical behaviors of tripartite entanglement of the local mode molecule H{sub 2}O and normal mode molecule NO{sub 2} are comparatively studied for different initial states by employing the general concurrence. Our results show that the dynamics of tripartite entanglement are relied on the dynamics of intramolecular energy distribution. The local mode molecule is more suitable to construct the tripartite entangled states. Also, the greater degree of tripartite entanglement can be obtained if the stretchingmore » vibration is first excited. These results shed new light on the understanding of quantum multipartite entanglement of vibrations in the polyatomic molecules.« less

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

Yuan, Bing; Bernstein, Elliot R., E-mail: erb@lamar.colostate.edu

Unimolecular decomposition of nitrogen-rich energetic molecules 1,2-bis(1H-tetrazol-1-yl)ethane (1-DTE), 1,2-bis(1H-tetrazol-5-yl)ethane (5-DET), N,N-bis(1H-tetrazol-5-yl)amine (BTA), and 5,5’-bis(tetrazolyl)hydrazine (BTH) has been explored via 283 nm two photon laser excitation. The maximum absorption wavelength in the UV-vis spectra of all four materials is around 186–222 nm. The N{sub 2} molecule, with a cold rotational temperature (<30 K), is observed as an initial decomposition product from the four molecules, subsequent to UV excitation. Initial decomposition mechanisms for these four electronically excited isolated molecules are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersectionsmore » play an essential role in the decomposition mechanism. The tetrazole ring opens on the S{sub 1} excited state and through conical intersections (S{sub 1}/S{sub 0}){sub CI}, N{sub 2} product is formed on the ground state potential energy surface without rotational excitation. The tetrazole rings of all four energetic molecules open at the N1—N2 ring bond with the lowest energy barrier: the C—N bond opening has higher energy barrier than that for any of the N—N ring bonds. Therefore, the tetrazole rings open at their N—N bonds to release N{sub 2}. The vibrational temperatures of N{sub 2} product from all four energetic materials are hot based on theoretical calculations. The different groups (CH{sub 2}—CH{sub 2}, NH—NH, and NH) joining the tetrazole rings can cause apparent differences in explosive behavior of 1-DTE, 5-DTE, BTA, and BTH. Conical intersections, non-Born-Oppenheimer interactions, and dynamics are the key features for excited electronic state chemistry of organic molecules, in general, and energetic molecules, in particular.« less

Electronic Relaxation Processes of Transition Metal Atoms in Helium Nanodroplets

NASA Astrophysics Data System (ADS)

Kautsch, Andreas; Lindebner, Friedrich; Koch, Markus; Ernst, Wolfgang E.

2014-06-01

Spectroscopy of doped superfluid helium nanodroplets (He_N) gives information about the influence of this cold, chemically inert, and least interacting matrix environment on the excitation and relaxation dynamics of dopant atoms and molecules. We present the results from laser induced fluorescence (LIF), photoionization (PI), and mass spectroscopy of Cr and Cu doped He_N. From these results, we can draw a comprehensive picture of the complex behavior of such transition metal atoms in He_N upon photo-excitation. The strong Cr and Cu ground state transitions show an excitation blueshift and broadening with respect to the bare atom transitions which can be taken as indication for the solvation inside the droplet. From the originally excited states the atoms relax to energetically lower states and are ejected from the He_N. The relaxation processes include bare atom spin-forbidden transitions, which clearly bears the signature of the He_N influence. Two-color resonant two-photon ionization (2CR2PI) also shows the formation of bare atoms and small Cr-He_n and Cu-He_n clusters in their ground and metastable states ^c. Currently, Cr dimer excitation studies are in progress and a brief outlook on the available results will be given. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, 2011. A. Kautsch, M. Koch, and W. E. Ernst, J. Phys. Chem. A, 117 (2013) 9621-9625, DOI: 10.1021/jp312336m F. Lindebner, A. Kautsch, M. Koch, and W. E. Ernst, Int. J. Mass Spectrom. (2014) in press, DOI: 10.1016/j.ijms.2013.12.022 M. Koch, A. Kautsch, F. Lackner, and W. E. Ernst, submitted to J. Phys. Chem. A

Excited-State Dynamics of Biological Molecules in Solution: Photoinduced Charge Transfer in Oxidatively Damaged DNA and Deactivation of Violacein in Viscous Solvents

NASA Astrophysics Data System (ADS)

Beckstead, Ashley Ann

UV radiation from the sun is strongly absorbed by DNA, and the resulting electronic excited states can lead to the formation of mutagenic photoproducts. Decades of research have brought to light the excited-state dynamics of single RNA and DNA nucleobases, but questions remain about the nature of excited states accessed in DNA strands. In this thesis, I present ultrafast spectroscopic observations of photoinduced electron transfer from the oxidatively damaged bases, 8-oxo-7,8-dihydro-2'-deoxyguanosine, 5-hydroxy-2'-deoxycytidine and 5-hydroxy-2'-deoxyuridine, to adenine in three dinucleotides. The results reveal that charge transfer states are formed on a timescale faster than our instrumental resolution (<0.5 ps), and back electron transfer efficiently returns the excited-state population to the ground state on timescales from tens to hundreds of ps. In addition to recent spectroscopic observations of charge transfer state species in DNA by other groups, our results have augmented understanding of the long-lived transient signals observed in DNA strands. The observation of photoinduced electron transfer in these oxidatively damaged nucleobases also supports a recent proposal regarding the role of oxidative products in pre-RNA catalysis. I discuss these observations in the contexts of fundamental DNA excited-state dynamics and prebiotic chemical evolution. In this thesis, I also present the first ultrafast spectroscopic investigation of violacein, a pigment isolated from Antarctic bacteria. Despite claims for the photoprotective role of this pigment, there has never been a spectroscopic analysis of excited-state deactivation in violacein. Emission spectra, fluorescence quantum yields and excited-state lifetimes of violacein in various solvents were measured for the first time. Both the fluorescence quantum yield and excited-state lifetime of violacein increase in increasingly viscous solvents, suggesting a large-scale motion mediates excited-state deactivation. I compare these results to similar observations of viscosity-dependent excited-state decay rates in other molecules. I also consider the relevance of violacein's excited-state properties to the hypothesized sunscreening role of violacein. Overall, the studies presented in this dissertation illustrate how ultrafast spectroscopic techniques can be used to unravel complex biomolecular excited-state dynamics in solution.

σ-SCF: A direct energy-targeting method to mean-field excited states.

PubMed

Ye, Hong-Zhou; Welborn, Matthew; Ricke, Nathan D; Van Voorhis, Troy

2017-12-07

The mean-field solutions of electronic excited states are much less accessible than ground state (e.g., Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF (self-consistent field), tend to fall into the lowest solution consistent with a given symmetry-a problem known as "variational collapse." In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states-ground or excited-are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H 2 , HF). We find that σ-SCF is very effective at locating excited states, including individual, high energy excitations within a dense manifold of excited states. Like all single determinant methods, σ-SCF shows prominent spin-symmetry breaking for open shell states and our results suggest that this method could be further improved with spin projection.

Renyi entropy for local quenches in 2D CFT from numerical conformal blocks

NASA Astrophysics Data System (ADS)

Kusuki, Yuya; Takayanagi, Tadashi

2018-01-01

We study the time evolution of Renyi entanglement entropy for locally excited states in two dimensional large central charge CFTs. It generically shows a logarithmical growth and we compute the coefficient of log t term. Our analysis covers the entire parameter regions with respect to the replica number n and the conformal dimension h O of the primary operator which creates the excitation. We numerically analyse relevant vacuum conformal blocks by using Zamolodchikov's recursion relation. We find that the behavior of the conformal blocks in two dimensional CFTs with a central charge c, drastically changes when the dimensions of external primary states reach the value c/32. In particular, when h O ≥ c/32 and n ≥ 2, we find a new universal formula Δ {S}_A^{(n)}˜eq nc/24(n-1) log t. Our numerical results also confirm existing analytical results using the HHLL approximation.

Low-energy measurements of electron-photon angular correlation in electron-impact excitation of the 2/sup 1/P state of helium

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

Steph, N.C.; Golden, D.E.

1983-03-01

Electron-photon angular correlations between electrons which have excited the 2/sup 1/P state of He and photons from the 2/sup 1/P..-->..1/sup 1/S transition have been studied for 27-, 30-, 35-, and 40-eV incident electrons. Values of lambda and Vertical BarchiVertical Bar obtained from these measurements are compared to values obtained in distorted-wave and R-matrix calculations. The values of lambda and Vertical BarchiVertical Bar have been combined to examine the behavior of Vertical BarO/sub 1//sub -//sup colvertical-bar/ (lambda(1-lambda)sinVertical BarchiVertical Bar), the nonvanishing component of orientation. At 27 eV, a substantial decrease was observed in the values of lambda and Vertical BarO/sub 1//submore » -//sup colvertical-bar/, compared with their values for E> or =30 eV.« less

Memory replay in balanced recurrent networks

PubMed Central

Chenkov, Nikolay; Sprekeler, Henning; Kempter, Richard

2017-01-01

Complex patterns of neural activity appear during up-states in the neocortex and sharp waves in the hippocampus, including sequences that resemble those during prior behavioral experience. The mechanisms underlying this replay are not well understood. How can small synaptic footprints engraved by experience control large-scale network activity during memory retrieval and consolidation? We hypothesize that sparse and weak synaptic connectivity between Hebbian assemblies are boosted by pre-existing recurrent connectivity within them. To investigate this idea, we connect sequences of assemblies in randomly connected spiking neuronal networks with a balance of excitation and inhibition. Simulations and analytical calculations show that recurrent connections within assemblies allow for a fast amplification of signals that indeed reduces the required number of inter-assembly connections. Replay can be evoked by small sensory-like cues or emerge spontaneously by activity fluctuations. Global—potentially neuromodulatory—alterations of neuronal excitability can switch between network states that favor retrieval and consolidation. PMID:28135266

Bidirectional Modulation of Intrinsic Excitability in Rat Prelimbic Cortex Neuronal Ensembles and Non-Ensembles after Operant Learning.

PubMed

Whitaker, Leslie R; Warren, Brandon L; Venniro, Marco; Harte, Tyler C; McPherson, Kylie B; Beidel, Jennifer; Bossert, Jennifer M; Shaham, Yavin; Bonci, Antonello; Hope, Bruce T

2017-09-06

Learned associations between environmental stimuli and rewards drive goal-directed learning and motivated behavior. These memories are thought to be encoded by alterations within specific patterns of sparsely distributed neurons called neuronal ensembles that are activated selectively by reward-predictive stimuli. Here, we use the Fos promoter to identify strongly activated neuronal ensembles in rat prelimbic cortex (PLC) and assess altered intrinsic excitability after 10 d of operant food self-administration training (1 h/d). First, we used the Daun02 inactivation procedure in male FosLacZ-transgenic rats to ablate selectively Fos-expressing PLC neurons that were active during operant food self-administration. Selective ablation of these neurons decreased food seeking. We then used male FosGFP-transgenic rats to assess selective alterations of intrinsic excitability in Fos-expressing neuronal ensembles (FosGFP + ) that were activated during food self-administration and compared these with alterations in less activated non-ensemble neurons (FosGFP - ). Using whole-cell recordings of layer V pyramidal neurons in an ex vivo brain slice preparation, we found that operant self-administration increased excitability of FosGFP + neurons and decreased excitability of FosGFP - neurons. Increased excitability of FosGFP + neurons was driven by increased steady-state input resistance. Decreased excitability of FosGFP - neurons was driven by increased contribution of small-conductance calcium-activated potassium (SK) channels. Injections of the specific SK channel antagonist apamin into PLC increased Fos expression but had no effect on food seeking. Overall, operant learning increased intrinsic excitability of PLC Fos-expressing neuronal ensembles that play a role in food seeking but decreased intrinsic excitability of Fos - non-ensembles. SIGNIFICANCE STATEMENT Prefrontal cortex activity plays a critical role in operant learning, but the underlying cellular mechanisms are unknown. Using the chemogenetic Daun02 inactivation procedure, we found that a small number of strongly activated Fos-expressing neuronal ensembles in rat PLC play an important role in learned operant food seeking. Using GFP expression to identify Fos-expressing layer V pyramidal neurons in prelimbic cortex (PLC) of FosGFP-transgenic rats, we found that operant food self-administration led to increased intrinsic excitability in the behaviorally relevant Fos-expressing neuronal ensembles, but decreased intrinsic excitability in Fos - neurons using distinct cellular mechanisms. Copyright © 2017 the authors 0270-6474/17/378845-12$15.00/0.

Collisional Processes Probed by using Resonant Four-Wave Mixing Spectroscopy

NASA Astrophysics Data System (ADS)

McCormack, E. F.; Stampanoni, A.; Hemmerling, B.

2000-06-01

Collisionally-induced decay processes in excited-state nitric oxide (NO) have been measured by using time-resolved two-color, resonant four-wave mixing (TC-RFWM) spectroscopy and polarization spectroscopy (PS). Markedly different time dependencies were observed in the data obtained by using TC-RFWM when compared to PS. Oscillations in the PS signal as a function of delay between the pump and probe laser pulses were observed and it was determined that their characteristics depend very sensitively on laser polarization. Analysis reveals that the oscillations in the decay curves are due to coherent excitation of unresolved hyperfine structure in the A state of NO. A comparison of beat frequencies obtained by taking Fourier transforms of the time data to the predicted hyperfine structure of the A state support this explanation. Further, based on a time-dependent model of PS as a FWM process, the signal’s dependence as a function of time on polarization configuration and excitation scheme can be predicted. By using the beat frequency values, fits of the model results to experimental decay curves for different pressures allows a study of the quenching rate in the A state due to collisional processes. A comparison of the PS data to laser-induced fluorescence decay measurements reveals different decay rates which suggests that the PS signal decay depends on the orientation and alignment of the excited molecules. The different behavior of the decay curves obtained by using TC-RFWM and PS can be understood in terms of the various contributions to the decay as described by the model and this has a direct bearing on which technique is preferable for a given set of experimental parameters.

Energy shift and Casimir-Polder force for an atom out of thermal equilibrium near a dielectric substrate

NASA Astrophysics Data System (ADS)

Zhou, Wenting; Yu, Hongwei

2014-09-01

We study the energy shift and the Casimir-Polder force of an atom out of thermal equilibrium near the surface of a dielectric substrate. We first generalize, adopting the local source hypothesis, the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji [J. Phys. (Paris) 43, 1617 (1982), 10.1051/jphys:0198200430110161700; J. Phys. (Paris) 45, 637 (1984), 10.1051/jphys:01984004504063700], which separates the contributions of thermal fluctuations and radiation reaction to the energy shift and allows a distinct treatment of atoms in the ground and excited states, to the case out of thermal equilibrium, and then we use the generalized formalism to calculate the energy shift and the Casimir-Polder force of an isotropically polarizable neutral atom. We identify the effects of the thermal fluctuations that originate from the substrate and the environment and discuss in detail how the Casimir-Polder force out of thermal equilibrium behaves in three different distance regions in both the low-temperature limit and the high-temperature limit for both the ground-state and excited-state atoms, with special attention devoted to the distinctive features as opposed to thermal equilibrium. In particular, we recover the distinctive behavior of the atom-wall force out of thermal equilibrium at large distances in the low-temperature limit recently found in a different theoretical framework, and furthermore we give a concrete region where this behavior holds.

Universality of nonthermal behavior in spinor Bose condensates

NASA Astrophysics Data System (ADS)

Patil, Yogesh Sharad; Cheung, Hil F. H.; Shaffer, Airlia; Chen, Huiyao Y.; Vengalattore, Mukund

2016-05-01

Spinor Bose condensates exhibit a rich phase diagram with varied magnetic ordering and topological defects because of the close competition between their spin and charge dependent interactions. Quenching such a spinor condensate into a ferromagnetic state realizes robust non-equilibrium and prethermalized states whose macroscopic behavior differs from thermodynamic predictions. In previous work, we have identified the microscopic origin of prethermalization in Rubidium spinor gases as being the disparate energy scales of the phonon and magnon excitations in this gas. This identification of the microscopic origin enables us to broaden the scope of our studies to address fundamental questions regarding the equilibration of isolated quantum systems. We will discuss our recent results that suggest the universality of this coarsening behavior and evidence that this system can be mapped on to a non-thermal fixed point studied in high energy field theories. This work is supported by the ARO MURI on non-equilibrium dynamics.

Distinguishing Majorana bound states and Andreev bound states with microwave spectra

NASA Astrophysics Data System (ADS)

Zhang, Zhen-Tao

2018-04-01

Majorana fermions are a fascinating and not yet confirmed quasiparticles in condensed matter physics. Here we propose using microwave spectra to distinguish Majorana bound states (MBSs) from topological trivial Andreev bound states. By numerically calculating the transmission and Zeeman field dependence of the many-body excitation spectrum of a 1D Josephson junction, we find that the two kinds of bound states have distinct responses to variations in the related parameters. Furthermore, the singular behaviors of the MBSs spectrum could be attributed to the robust fractional Josephson coupling and nonlocality of MBSs. Our results provide a feasible method to verify the existence of MBSs and could accelerate its application to topological quantum computation.

Nested variant of the method of moments of coupled cluster equations for vertical excitation energies and excited-state potential energy surfaces.

PubMed

Kowalski, Karol

2009-05-21

In this article we discuss the problem of proper balancing of the noniterative 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 nested variant of the method of moments of CC equations provides mathematically rigorous way of balancing the ground- and excited-state correlation effects. The resulting noniterative methodology accounting for the effect of triples 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 are numerically feasible.

Experimental evidence of exciton-plasmon coupling in densely packed dye doped core-shell nanoparticles obtained via microfluidic technique

NASA Astrophysics Data System (ADS)

De Luca, A.; Iazzolino, A.; Salmon, J.-B.; Leng, J.; Ravaine, S.; Grigorenko, A. N.; Strangi, G.

2014-09-01

The interplay between plasmons and excitons in bulk metamaterials are investigated by performing spectroscopic studies, including variable angle pump-probe ellipsometry. Gain functionalized gold nanoparticles have been densely packed through a microfluidic chip, representing a scalable process towards bulk metamaterials based on self-assembly approach. Chromophores placed at the hearth of plasmonic subunits ensure exciton-plasmon coupling to convey excitation energy to the quasi-static electric field of the plasmon states. The overall complex polarizability of the system, probed by variable angle spectroscopic ellipsometry, shows a significant modification under optical excitation, as demonstrated by the behavior of the ellipsometric angles Ψ and Δ as a function of suitable excitation fields. The plasmon resonances observed in densely packed gain functionalized core-shell gold nanoparticles represent a promising step to enable a wide range of electromagnetic properties and fascinating applications of plasmonic bulk systems for advanced optical materials.

A direct evidence of allocating yellow luminescence band in undoped GaN by two-wavelength excited photoluminescence

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

Julkarnain, M., E-mail: s13ds053@mail.saitama-u.ac.jp, E-mail: jnain.apee@ru.ac.bd; Department of Applied Physics and Electronic Engineering, University of Rajshahi, Rajshahi 6205; Fukuda, T.

2015-11-23

The behavior of below-gap luminescence of undoped GaN grown by MOCVD has been studied by the scheme of two-wavelength-excited photoluminescence. The emission intensity of shallow donor to valence band transition (I{sub OX}) increased while intensities of donor-acceptor pair transition and the Yellow Luminescence band (YLB) decreased after the irradiation of a below-gap excitation source of 1.17 eV. The conventional energy schemes and recombination models have been considered to explain our experimental result but only one model in which YLB is the transition of a shallow donor to a deep state placed at ∼1 eV above the valence band maximum satisfies our result.more » The defect related parameters that give a qualitative insight in the samples have been evaluated by systematically solving the rate equations and fitting the result with the experiment.« less

Synthesis, characterization and properties of Dy3+-activated single host borosilicate phosphors

NASA Astrophysics Data System (ADS)

Yu, Hong; Chen, Shanyong; Chen, Jinlei

2017-12-01

New phosphors Sr3B2SiO8: Dy3+ have been successfully synthesized via solid-state reaction process. Emission/excitation spectra, photoluminescence decay behaviors were investigated in detail. Under the excitation of 351 nm, the emission spectrum consisting of the characteristic transitions of Dy3+ which mainly peaking at 480, 487 nm and 574 nm corresponding to the4F9/2→6H15/2 and4F9/2→6H13/2, respectively, the intensity of the blue emission stronger than the yellow one which indicated that Dy3+ ions take the site without inversion symmetry. The chromaticity coordinates of Sr3-xB2SiO8: x Dy3+ fixed in the white region. The results showed the kind of phosphor may be act potential applications in the fields of UV-excited white LEDs.

["Animal hypnosis" and defensive dominant, behavioral aspect].

PubMed

Pavlygina, R A; Galashina, A G; Bogdanov, A V

2002-01-01

A stationary excitation focus produced in the sensorimotor cortex of a rabbit by rhythmic electrodermal paw stimulation was manifested in the reaction to a testing sound stimulus earlier indifferent for the animal. Regardless of the stimulated paw (left or right), reactions to the testing stimuli appeared approximately in the equal percent of cases (70.7% and 71.5%, respectively). After a single-trial induction of the "animal hypnosis" state, it was difficult to produce the dominant focus by simulation of the left paw, whereas the results of the right-paw stimulation did not differ from those obtained during control stimulation. Consequently, the influence of hypnosis on defensive stationary excitation foci in different hemispheres was not the same.

Dynamic analysis of a fibre-optic ring resonator excited by a sinewave-modulated laser diode

NASA Astrophysics Data System (ADS)

Pandian, G. Soundra; Seraji, Faramarz

1990-10-01

The present theoretical dynamic analysis of a fiber-optic ring resonator upon excitation by a sinusoidally-modulated laser diode (LD) yields results for such resonator conditions as modulating frequency, amplitude-modulation index, coupler power-coupling coefficient, loop-delay time (tau), and the phase angle between the LD's AM and FM responses. It is found that when the modulation frequency f(m) exceeds a threshold value such that f(m)tau exceeds 0.0002, the output response diverges from steady state and engages in an oscillatory behavior characterized by overshoots. When f(m)tau exceeds 1.0, the output approximates the intensity modulation of the LD.

Total photoionization cross-sections of excited electronic states by the algebraic diagrammatic construction-Stieltjes-Lanczos method.

PubMed

Ruberti, M; Yun, R; Gokhberg, K; Kopelke, S; Cederbaum, L S; Tarantelli, F; Averbukh, V

2014-05-14

Here, we extend the L2 ab initio method for molecular photoionization cross-sections introduced in Gokhberg et al. [J. Chem. Phys. 130, 064104 (2009)] and benchmarked in Ruberti et al. [J. Chem. Phys. 139, 144107 (2013)] to the calculation of total photoionization cross-sections of molecules in electronically excited states. The method is based on the ab initio description of molecular electronic states within the many-electron Green's function approach, known as algebraic diagrammatic construction (ADC), and on the application of Stieltjes-Chebyshev moment theory to Lanczos pseudospectra of the ADC electronic Hamiltonian. The intermediate state representation of the dipole operator in the ADC basis is used to compute the transition moments between the excited states of the molecule. We compare the results obtained using different levels of the many-body theory, i.e., ADC(1), ADC(2), and ADC(2)x for the first two excited states of CO, N2, and H2O both at the ground state and the excited state equilibrium or saddle point geometries. We find that the single excitation ADC(1) method is not adequate even at the qualitative level and that the inclusion of double electronic excitations for description of excited state photoionization is essential. Moreover, we show that the use of the extended ADC(2)x method leads to a substantial systematic difference from the strictly second-order ADC(2). Our calculations demonstrate that a theoretical modelling of photoionization of excited states requires an intrinsically double excitation theory with respect to the ground state and cannot be achieved by the standard single excitation methods with the ground state as a reference.

Total photoionization cross-sections of excited electronic states by the algebraic diagrammatic construction-Stieltjes-Lanczos method

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

Ruberti, M.; Yun, R.; Averbukh, V.

2014-05-14

Here, we extend the L{sup 2} ab initio method for molecular photoionization cross-sections introduced in Gokhberg et al. [J. Chem. Phys. 130, 064104 (2009)] and benchmarked in Ruberti et al. [J. Chem. Phys. 139, 144107 (2013)] to the calculation of total photoionization cross-sections of molecules in electronically excited states. The method is based on the ab initio description of molecular electronic states within the many-electron Green's function approach, known as algebraic diagrammatic construction (ADC), and on the application of Stieltjes-Chebyshev moment theory to Lanczos pseudospectra of the ADC electronic Hamiltonian. The intermediate state representation of the dipole operator in themore » ADC basis is used to compute the transition moments between the excited states of the molecule. We compare the results obtained using different levels of the many-body theory, i.e., ADC(1), ADC(2), and ADC(2)x for the first two excited states of CO, N{sub 2}, and H{sub 2}O both at the ground state and the excited state equilibrium or saddle point geometries. We find that the single excitation ADC(1) method is not adequate even at the qualitative level and that the inclusion of double electronic excitations for description of excited state photoionization is essential. Moreover, we show that the use of the extended ADC(2)x method leads to a substantial systematic difference from the strictly second-order ADC(2). Our calculations demonstrate that a theoretical modelling of photoionization of excited states requires an intrinsically double excitation theory with respect to the ground state and cannot be achieved by the standard single excitation methods with the ground state as a reference.« less

Scattering of 42 MeV alpha particles from copper-65

NASA Technical Reports Server (NTRS)

Stewart, W. M.; Seth, K. K.

1973-01-01

Beams of 42-MeV alpha particles were elastically and inelastically scattered from Cu-65 in an attempt to excite states which may be described in terms of an excited core model. Angular distributions were measured for 17 excited states. Seven of the excited states had angular distributions similar to a core quadrupole excitation and eight of the excited states had angular distributions similar to a core octupole excitation. The excited state at 2.858 MeV had an angular distribution which suggests that it may have results from the particle coupling to a two-phonon core state. An extended particle-core coupling calculation was performed and the predicted energy levels and reduced transition probabilities compared to the experimental data. The low lying levels are described quite well and the wavefunctions of these states explain the large spectroscopic factors measured in stripping reactions. For Cu-65 the coupling of the particle to the core is no larger weak as in the simpler model, and configuration mixing results.

Excitation of lowest electronic states of thymine by slow electrons

NASA Astrophysics Data System (ADS)

Chernyshova, I. V.; Kontros, E. J.; Markush, P. P.; Shpenik, O. B.

2013-11-01

Excitation of lowest electronic states of the thymine molecules in the gas phase is studied by elec- tron energy loss spectroscopy. In addition to dipole-allowed transitions to singlet states, transitions to the lowest triplet states were observed. The low-energy features of the spectrum at 3.66 and 4.61 eV are identified with the excitation of the first triplet states 13 A' (π → π*) and 13 A″ ( n → π*). The higher-lying features at 4.96, 5.75, 6.17, and 7.35 eV are assigned mainly to the excitation of the π → π* transitions to the singlet states of the molecule. The excitation dynamics of the lowest states is studied. It is found that the first triplet state 13 A'(π → π*) is most efficiently excited at a residual energy close to zero, while the singlet 21 A'(π → π*) state is excited with almost identical efficiency at different residual energies.

A novel energy transfer inducing strong enhancement of electric dipole transition in Na3Mo12PO40:xEu3+ phosphors

NASA Astrophysics Data System (ADS)

Long, Jinqiao; Wang, Tianman; Luo, Zhirong; Gao, Yong; Song, Baoling; Liang, Jing; Liao, Sen; Huang, Yingheng; Zhang, Huaxin

2017-08-01

A series of Na3Mo12PO40:xEu3+ phosphors have been successfully synthesized by a solid-state method, and characterized by powder x-ray diffraction (PXRD). The PXRD results confirm that the samples have crystal phases of Na3Mo12PO40. For PL spectra of Na3Mo12PO40:2.0Eu3+ excited by 394 and 465 nm, R (R is the peak area ratio of 5D0  →  7F2 to 5D0  →  7F1) is only 1.46 with an excitation of 394 nm, but increases to 3.03 with an excitation of 465 nm. Furthermore, a new enhancement of electric dipole transition is observed. Emission spectrum (PL) intensity at 617 nm excited by 465 nm is 1.95 times as high as the excitation spectrum (PLE) intensity at 465 nm. Thus, cooperative energy transfers from the magnetic dipole (MD) Eu3+ center to the electric dipole (ED) Eu3+ center when excited by 465 nm is demonstrated for the new fluorescent behavior.

Multipoint entanglement in disordered systems

NASA Astrophysics Data System (ADS)

Magán, Javier M.; Paganelli, Simone; Oganesyan, Vadim

2017-02-01

We develop an approach to characterize excited states of disordered many-body systems using spatially resolved structures of entanglement. We show that the behavior of the mutual information (MI) between two parties of a many-body system can signal a qualitative difference between thermal and localized phases - MI is finite in insulators while it approaches zero in the thermodynamic limit in the ergodic phase. Related quantities, such as the recently introduced Codification Volume (CV), are shown to be suitable to quantify the correlation length of the system. These ideas are illustrated using prototypical non-interacting wavefunctions of localized and extended particles and then applied to characterize states of strongly excited interacting spin chains. We especially focus on evolution of spatial structure of quantum information between high temperature diffusive and many-body localized (MBL) phases believed to exist in these models. We study MI as a function of disorder strength both averaged over the eigenstates and in time-evolved product states drawn from continuously deformed family of initial states realizable experimentally. As expected, spectral and time-evolved averages coincide inside the ergodic phase and differ significantly outside. We also highlight dispersion among the initial states within the localized phase - some of these show considerable generation and delocalization of quantum information.

Nitric oxide excited under auroral conditions: Excited state densities and band emissions

NASA Astrophysics Data System (ADS)

Cartwright, D. C.; Brunger, M. J.; Campbell, L.; Mojarrabi, B.; Teubner, P. J. O.

2000-09-01

Electron impact excitation of vibrational levels in the ground electronic state and nine excited electronic states in NO has been simulated for an IBC II aurora (i.e., ˜10 kR in 3914 Å radiation) in order to predict NO excited state number densities and band emission intensities. New integral electron impact excitation cross sections for NO were combined with a measured IBC II auroral secondary electron distribution, and the vibrational populations of 10 NO electronic states were determined under conditions of statistical equilibrium. This model predicts an extended vibrational distribution in the NO ground electronic state produced by radiative cascade from the seven higher-lying doublet excited electronic states populated by electron impact. In addition to significant energy storage in vibrational excitation of the ground electronic state, both the a 4Π and L2 Φ excited electronic states are predicted to have relatively high number densities because they are only weakly connected to lower electronic states by radiative decay. Fundamental mode radiative transitions involving the lowest nine excited vibrational levels in the ground electronic state are predicted to produce infrared (IR) radiation from 5.33 to 6.05 μm with greater intensity than any single NO electronic emission band. Fundamental mode radiative transitions within the a 4Π electronic state, in the 10.08-11.37 μm region, are predicted to have IR intensities comparable to individual electronic emission bands in the Heath and ɛ band systems. Results from this model quantitatively predict the vibrational quantum number dependence of the NO IR measurements of Espy et al. [1988].

Physical modeling of Tibetan bowls

NASA Astrophysics Data System (ADS)

Antunes, Jose; Inacio, Octavio

2004-05-01

Tibetan bowls produce rich penetrating sounds, used in musical contexts and to induce a state of relaxation for meditation or therapy purposes. To understand the dynamics of these instruments under impact and rubbing excitation, we developed a simulation method based on the modal approach, following our previous papers on physical modeling of plucked/bowed strings and impacted/bowed bars. This technique is based on a compact representation of the system dynamics, in terms of the unconstrained bowl modes. Nonlinear contact/friction interaction forces, between the exciter (puja) and the bowl, are computed at each time step and projected on the bowl modal basis, followed by step integration of the modal equations. We explore the behavior of two different-sized bowls, for extensive ranges of excitation conditions (contact/friction parameters, normal force, and tangential puja velocity). Numerical results and experiments show that various self-excited motions may arise depending on the playing conditions and, mainly, on the contact/friction interaction parameters. Indeed, triggering of a given bowl modal frequency mainly depends on the puja material. Computed animations and experiments demonstrate that self-excited modes spin, following the puja motion. Accordingly, the sensed pressure field pulsates, with frequency controlled by the puja spinning velocity and the spatial pattern of the singing mode.

A simplified Tamm-Dancoff density functional approach for the electronic excitation spectra of very large molecules

NASA Astrophysics Data System (ADS)

Grimme, Stefan

2013-06-01

Two approximations in the Tamm-Dancoff density functional theory approach (TDA-DFT) to electronically excited states are proposed which allow routine computations for electronic ultraviolet (UV)- or circular dichroism (CD) spectra of molecules with 500-1000 atoms. Speed-ups compared to conventional time-dependent DFT (TD-DFT) treatments of about two to three orders of magnitude in the excited state part at only minor loss of accuracy are obtained. The method termed sTDA ("s" for simplified) employs atom-centered Löwdin-monopole based two-electron repulsion integrals with the asymptotically correct 1/R behavior and perturbative single excitation configuration selection. It is formulated generally for any standard global hybrid density functional with given Fock-exchange mixing parameter ax. The method performs well for two standard benchmark sets of vertical singlet-singlet excitations for values of ax in the range 0.2-0.6. The mean absolute deviations from reference data are only 0.2-0.3 eV and similar to those from standard TD-DFT. In three cases (two dyes and one polypeptide), good mutual agreement between the electronic spectra (up to 10-11 eV excitation energy) from the sTDA method and those from TD(A)-DFT is obtained. The computed UV- and CD-spectra of a few typical systems (e.g., C60, two transition metal complexes, [7]helicene, polyalanine, a supramolecular aggregate with 483 atoms and about 7000 basis functions) compare well with corresponding experimental data. The method is proposed together with medium-sized double- or triple-zeta type atomic-orbital basis sets as a quantum chemical tool to investigate the spectra of huge molecular systems at a reliable DFT level.

Quasimodo mediates daily and acute light effects on Drosophila clock neuron excitability.

PubMed

Buhl, Edgar; Bradlaugh, Adam; Ogueta, Maite; Chen, Ko-Fan; Stanewsky, Ralf; Hodge, James J L

2016-11-22

We have characterized a light-input pathway regulating Drosophila clock neuron excitability. The molecular clock drives rhythmic electrical excitability of clock neurons, and we show that the recently discovered light-input factor Quasimodo (Qsm) regulates this variation, presumably via an Na + , K + , Cl - cotransporter (NKCC) and the Shaw K + channel (dK V 3.1). Because of light-dependent degradation of the clock protein Timeless (Tim), constant illumination (LL) leads to a breakdown of molecular and behavioral rhythms. Both overexpression ( OX ) and knockdown ( RNAi ) of qsm, NKCC, or Shaw led to robust LL rhythmicity. Whole-cell recordings of the large ventral lateral neurons (l-LNv) showed that altering Qsm levels reduced the daily variation in neuronal activity: qsm OX led to a constitutive less active, night-like state, and qsm RNAi led to a more active, day-like state. Qsm also affected daily changes in K + currents and the GABA reversal potential, suggesting a role in modifying membrane currents and GABA responses in a daily fashion, potentially modulating light arousal and input to the clock. When directly challenged with blue light, wild-type l-LNvs responded with increased firing at night and no net response during the day, whereas altering Qsm, NKKC, or Shaw levels abolished these day/night differences. Finally, coexpression of Shaw OX and NKCC RNAi in a qsm mutant background restored LL-induced behavioral arrhythmicity and wild-type neuronal activity patterns, suggesting that the three genes operate in the same pathway. We propose that Qsm affects both daily and acute light effects in l-LNvs probably acting on Shaw and NKCC.

Quasimodo mediates daily and acute light effects on Drosophila clock neuron excitability

PubMed Central

Bradlaugh, Adam; Ogueta, Maite; Chen, Ko-Fan; Stanewsky, Ralf; Hodge, James J. L.

2016-01-01

We have characterized a light-input pathway regulating Drosophila clock neuron excitability. The molecular clock drives rhythmic electrical excitability of clock neurons, and we show that the recently discovered light-input factor Quasimodo (Qsm) regulates this variation, presumably via an Na+, K+, Cl− cotransporter (NKCC) and the Shaw K+ channel (dKV3.1). Because of light-dependent degradation of the clock protein Timeless (Tim), constant illumination (LL) leads to a breakdown of molecular and behavioral rhythms. Both overexpression (OX) and knockdown (RNAi) of qsm, NKCC, or Shaw led to robust LL rhythmicity. Whole-cell recordings of the large ventral lateral neurons (l-LNv) showed that altering Qsm levels reduced the daily variation in neuronal activity: qsmOX led to a constitutive less active, night-like state, and qsmRNAi led to a more active, day-like state. Qsm also affected daily changes in K+ currents and the GABA reversal potential, suggesting a role in modifying membrane currents and GABA responses in a daily fashion, potentially modulating light arousal and input to the clock. When directly challenged with blue light, wild-type l-LNvs responded with increased firing at night and no net response during the day, whereas altering Qsm, NKKC, or Shaw levels abolished these day/night differences. Finally, coexpression of ShawOX and NKCCRNAi in a qsm mutant background restored LL-induced behavioral arrhythmicity and wild-type neuronal activity patterns, suggesting that the three genes operate in the same pathway. We propose that Qsm affects both daily and acute light effects in l-LNvs probably acting on Shaw and NKCC. PMID:27821737

Effect of sexual excitation on testosterone and nitric oxide levels of water buffalo bulls (Bubalus bubalis) with different categories of sexual behavior and their correlation with each other.

PubMed

Swelum, Ayman Abdel-Aziz; Saadeldin, Islam M; Zaher, Hany A; Alsharifi, Sawsan A M; Alowaimer, Abdullah N

2017-06-01

We studied the effect of sexual excitation on serum testosterone and nitric oxide (NO) levels in water buffalo bulls with different categories of sexual behavior and their correlation with each other. Buffalo bulls were classified according to their sexual behavior (including reaction time, sexual aggressiveness and mating ability): acceptable (good to excellent) (n=5), fair (n=5), and unacceptable (poor) (n=5) sexual behavior. Blood samples were collected from all animals immediately before and after sexual teasing and/or mounting to estimate the testosterone and NO levels using a commercial radioimmunoassay kit and Griess reaction test, respectively. Comparisons among groups were evaluated using a mixed-design analysis of variance. Pearson's correlation coefficients were calculated to determine the relationship between testosterone and NO levels before and after sexual excitation besides sexual behavior. The level of testosterone before sexual excitation was higher (p≤0.05) in bulls with acceptable and fair sexual behavior than in bulls with unacceptable sexual behavior (0.86±0.01, 0.69±0.02, and 0.29±0.02ng/mL, respectively). The level of NO was higher (p≤0.05) in bulls with acceptable and fair sexual behavior than in bulls with unacceptable sexual behavior (8.00±0.03, 7.66±0.19, and 6.29±0.33μM, respectively). Sexual excitation significantly (p<0.05) increase testosterone and NO levels in bulls with acceptable (1.45±0.01ng/mL and 19.04±0.32μM, respectively) or fair (0.92±0.02ng/mL and 14.95±0.34μM, respectively) sexual behavior, but not in bulls with unacceptable sexual behavior. The unacceptable sexual behavior bulls had significantly lower testosterone and NO levels than the other bulls. There was a strong correlation and association between serum testosterone and NO levels besides sexual behavior of buffalo bulls. In conclusion, the alteration in the testosterone and NO levels after sexual excitation depends on the sexual behavior category of buffalo-bull. Testosterone and NO can be used to create a sexual behavior score. The testosterone and NO levels of can be predicted via evaluation of sexual behavior of buffalo bull. Copyright © 2017 Elsevier B.V. All rights reserved.

Three-photon Gaussian-Gaussian-Laguerre-Gaussian excitation of a localized atom to a highly excited Rydberg state

NASA Astrophysics Data System (ADS)

Mashhadi, L.

2017-12-01

Optical vortices are currently one of the most intensively studied topics in light-matter interaction. In this work, a three-step axial Doppler- and recoil-free Gaussian-Gaussian-Laguerre-Gaussian (GGLG) excitation of a localized atom to the highly excited Rydberg state is presented. By assuming a large detuning for intermediate states, an effective quadrupole excitation related to the Laguerre-Gaussian (LG) excitation to the highly excited Rydberg state is obtained. This special excitation system radially confines the single highly excited Rydberg atom independently of the trapping system into a sharp potential landscape into the so-called ‘far-off-resonance optical dipole-quadrupole trap’ (FORDQT). The key parameters of the Rydberg excitation to the highly excited state, namely the effective Rabi frequency and the effective detuning including a position-dependent AC Stark shift, are calculated in terms of the basic parameters of the LG beam and of the polarization of the excitation lasers. It is shown that the obtained parameters can be tuned to have a precise excitation of a single atom to the desired Rydberg state as well. The features of transferring the optical orbital and spin angular momentum of the polarized LG beam to the atom via quadrupole Rydberg excitation offer a long-lived and controllable qudit quantum memory. In addition, in contrast to the Gaussian laser beam, the doughnut-shaped LG beam makes it possible to use a high intensity laser beam to increase the signal-to-noise ratio in quadrupole excitation with minimized perturbations coming from stray light broadening in the last Rydberg excitation process.

Stark effect and dipole moments of the ammonia dimer in different vibration-rotation-tunneling states

NASA Astrophysics Data System (ADS)

Cotti, Gina; Linnartz, Harold; Meerts, W. Leo; van der Avoird, Ad; Olthof, Edgar H. T.

1996-03-01

In this paper we present Stark measurements on the G:K=-1 vibration-rotation-tunneling (VRT) transition, band origin 747.2 GHz, of the ammonia dimer. The observed splitting pattern and selection rules can be explained by considering the G36 and G144 symmetries of the inversion states involved, and almost complete mixing of these states by the applied electric field. The absolute values of the electric dipole moments of the ground and excited state are determined to be 0.763(15) and 0.365(10) D, respectively. From the theoretical analysis and the observed selection rules it is possible to establish that the dipole moments of the two interchange states must have opposite sign. The theoretical calculations are in good agreement with the experimental results: The calculated dipole moments are -0.74 D for the lower and +0.35 D for the higher state. Our results, in combination with the earlier dipole measurements on the G:K=0 ground state and the G:K=1 transition with band origin 486.8 GHz, confirm that the ammonia dimer is highly nonrigid. Its relatively small and strongly K-dependent dipole moment, which changes sign upon far-infrared excitation, originates from the difference in dynamical behavior of ortho and para NH3.

Coherent stimulated light emission (lasing) in covalently linked chlorophyll dimers

PubMed Central

Hindman, James C.; Kugel, Roger; Wasielewski, Michael R.; Katz, Joseph J.

1978-01-01

The covalently linked chlorophyll a dimer exhibits remarkably different properties in the folded and open configurations. In the folded configuration the absorption maximum is at 695 nm and the fluorescence maximum is at 730 nm. Laser output at 733 and 735 nm is obtained for solutions in wet benzene and 0.1 M ethanol/toluene, respectively. Measurements of fluorescence lineshapes, made with a transverse excited atmospheric (TEA) nitrogen laser for excitation, show the lifetime shortening associated with stimulated emission resulting from appreciable concentrations of molecules in S1 excited states. In contrast, the open dimer has absorption and fluorescence spectra essentially the same as those of chlorophyll a monomer. Unlike either the folded dimer or chlorophyll a monomer, the open dimer shows no laser emission or fluorescene lifetime shortening. It does not appear that the behavior of the open dimer can be explained in terms of excimer or triplet formation or by nonradiative decay processes. It is suggested that absorption of the exciting radiation by S1, leading to the formation of an exciplex or charge transfer state, may be involved. Significantly, no large changes in fluorescence quantum yield or fluorescence lifetime are observed for these dimers as compared to monomer chlorophyll. This suggests that concentration quenching and lifetime shortening in condensed chlorophyll systems involve more than the simple proximity of two chlorophyll molecules. Images PMID:16592524

Dirac materials

NASA Astrophysics Data System (ADS)

Wehling, T. O.; Black-Schaffer, A. M.; Balatsky, A. V.

2014-01-01

A wide range of materials, like d-wave superconductors, graphene, and topological insulators, share a fundamental similarity: their low-energy fermionic excitations behave as massless Dirac particles rather than fermions obeying the usual Schrodinger Hamiltonian. This emergent behavior of Dirac fermions in condensed matter systems defines the unifying framework for a class of materials we call "Dirac materials''. In order to establish this class of materials, we illustrate how Dirac fermions emerge in multiple entirely different condensed matter systems and we discuss how Dirac fermions have been identified experimentally using electron spectroscopy techniques (angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy). As a consequence of their common low-energy excitations, this diverse set of materials shares a significant number of universal properties in the low-energy (infrared) limit. We review these common properties including nodal points in the excitation spectrum, density of states, specific heat, transport, thermodynamic properties, impurity resonances, and magnetic field responses, as well as discuss many-body interaction effects. We further review how the emergence of Dirac excitations is controlled by specific symmetries of the material, such as time-reversal, gauge, and spin-orbit symmetries, and how by breaking these symmetries a finite Dirac mass is generated. We give examples of how the interaction of Dirac fermions with their distinct real material background leads to rich novel physics with common fingerprints such as the suppression of back scattering and impurity-induced resonant states.

Population trapping in the excited states using vacuum-induced coherence and adiabatic process

NASA Astrophysics Data System (ADS)

Lal Kumawat, Babu; Kumar, Pardeep; Dasgupta, Shubhrangshu

2018-02-01

We theoretically investigate how population can be trapped in the closely spaced excited levels in presence of vacuum-induced coherence (VIC). We employ delayed pulses to transfer population from a meta-stable state to the excited states. Subsequently, spontaneous emission from these excited states builds coherence between them. This coherence can be probed by using chirping, which leads to the decoupling of the excited states from the ground state thereby ensuring population transfer via delayed pulses. Our results indicate that the existence of VIC leads to the generation of a mixed state in the excited state manifold, where trapping of the population occurs even in the presence of large decay. This trapping may be realized in molecular systems and can be interpreted as a sensitive probe of VIC. We present suitable numerical analysis to support our results.

The triplet excited state of Bodipy: formation, modulation and application.

PubMed

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 briefly discussed.

The laser versus the lamp: Reactivity of the diphenyl ketyl radical in the ground and excited states

NASA Astrophysics Data System (ADS)

Baumann, H.; Merckel, C.; Timpe, H.-J.; Graness, A.; Kleinschmidt, J.; Gould, I. R.; Turro, N. J.

1984-01-01

The diphenyl ketyl radical which is formed upon photolysis of α-phenyl benzoin is produced in its excited state upon intense pulsed laser irradiation. Using the techniques of time-resolved absorption and emission spectroscopy, reaction rate constants for the ground and excited states of this radical were obtained. For the radical quenchers employed, the excited state reactivity is found to be typically several orders of magnitude greater than that of the ground state. It is concluded that the excited state of diphenyl ketyl radical reacts predominantly by electron transfer processes.

Bound state and localization of excitation in many-body open systems

NASA Astrophysics Data System (ADS)

Cui, H. T.; Shen, H. Z.; Hou, S. C.; Yi, X. X.

2018-04-01

We study the exact bound state and time evolution for single excitations in one-dimensional X X Z spin chains within a non-Markovian reservoir. For the bound state, a common feature is the localization of single excitations, which means the spontaneous emission of excitations into the reservoir is prohibited. Exceptionally, the pseudo-bound state can be found, for which the single excitation has a finite probability of emission into the reservoir. In addition, a critical energy scale for bound states is also identified, below which only one bound state exists, and it is also the pseudo-bound state. The effect of quasirandom disorder in the spin chain is also discussed; such disorder induces the single excitation to locate at some spin sites. Furthermore, to display the effect of bound state and disorder on the preservation of quantum information, the time evolution of single excitations in spin chains is studied exactly. An interesting observation is that the excitation can stay at its initial location with high probability only when the bound state and disorder coexist. In contrast, when either one of them is absent, the information of the initial state can be erased completely or becomes mixed. This finding shows that the combination of bound state and disorder can provide an ideal mechanism for quantum memory.

Shining light on the antenna chromophore in lanthanide based dyes.

PubMed

Junker, Anne Kathrine R; Hill, Leila R; Thompson, Amber L; Faulkner, Stephen; Sørensen, Thomas Just

2018-04-03

Lanthanide based dyes and assays exploit the antenna effect, where a sensitiser-chromophore is used as a light harvesting antenna and subsequent excited state energy transfer populates the emitting lanthanide centred excited state. A rudimentary understanding of the design criteria for designing efficient dyes and assays based on the antenna effect is in place. By preparing kinetically inert lanthanide complexes based on the DO3A scaffold, we are able to study the excited state energy transfer from a 7-methoxy-coumarin antenna chromophore to europium(iii) and terbium(iii) centred excited states. By contrasting the photophysical properties of complexes of metal centres with and without accessible excited states, we are able to separate the contributions from the heavy atom effect, photoinduced electron transfer quenching, excited state energy transfer and molecular conformations. Furthermore, by studying the photophysical properties of the antenna chromophore, we can directly monitor the solution structure and are able to conclude that excited state energy transfer from the chromophore singlet state to the lanthanide centre does occur.

Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

NASA Astrophysics Data System (ADS)

Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

2016-10-01

We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

Spectrum and Structure of Excited Baryons with CLAS

NASA Astrophysics Data System (ADS)

Burkert, Volker D.

2017-01-01

In this contribution I discuss recent results in light quark baryon spectroscopy involving CLAS data and higher level analysis results from the partial wave analysis by the Bonn-Gatchina group. New baryon states were discovered largely based on the open strangeness production channels γp → K+Λ and γp → K+Σ0. The data illustrate the great potential of the kaon-hyperon channel in the discovery of higher mass baryon resonances in s-channel production. Other channels with discovery potential, such as γp → pω and γp → ϕp are also discussed. In the second part I will demonstrate on data the sensitivity of meson electroproduction to expose the active degrees of freedom underlying resonance transitions as a function of the probed distance scale. For several of the prominent excited states in the lower mass range the short distance behavior is described by a core of three dressed-quarks with running quark mass, and meson-baryon contributions make up significant parts of the excitation strength at large distances. Finally, I give an outlook of baryon resonance physics at the 12 GeV CEBAF electron accelerator. Talk presented at the CRC-16 Symposium, Bonn University, June 6-9, 2016.

Dynamics of ionization of H2 by Ne*(3P) investigated by electron spectroscopy

NASA Astrophysics Data System (ADS)

Noroski, Joseph H.; Siska, P. E.

2006-10-01

The Penning ionization reaction Ne*(2p53sP3)+H2→[NeH2]++e- has been studied in crossed supersonic molecular beams with electron-energy analysis at four collision energies E =1.83, 2.50, 3.16, and 3.89kcal/mol. The electron kinetic-energy spectra, which directly reflect the ionizing transition region, show resolved peaks assignable to v'=0-4 of H2+. The vibrational populations deviate systematically from Franck-Condon behavior, suggesting that the discrete-continuum coupling increases with H2 bond stretching. Each peak displays both increasing breadth and increasing blueshift with increasing E, and the blueshift also increases with increasing v'. The first two properties are consistent with a predominantly repulsive excited-state potential-energy surface, while the last is speculated to be a reflection of the rHH dependence of the ionic surface. Quantum scattering calculations based on ab initio potential surfaces for the excited and ionic states in spherical and infinite-order-sudden rigid rotor approximations are in semiquantitative agreement with the measurements. Discrepancies suggest changes in the imaginary, absorptive part of the excited surface, which probably can be best effected by multiproperty fitting calculations.

MiR-980 Is a Memory Suppressor MicroRNA that Regulates the Autism-Susceptibility Gene A2bp1.

PubMed

Guven-Ozkan, Tugba; Busto, Germain U; Schutte, Soleil S; Cervantes-Sandoval, Isaac; O'Dowd, Diane K; Davis, Ronald L

2016-02-23

MicroRNAs have been associated with many different biological functions, but little is known about their roles in conditioned behavior. We demonstrate that Drosophila miR-980 is a memory suppressor gene functioning in multiple regions of the adult brain. Memory acquisition and stability were both increased by miR-980 inhibition. Whole cell recordings and functional imaging experiments indicated that miR-980 regulates neuronal excitability. We identified the autism susceptibility gene, A2bp1, as an mRNA target for miR-980. A2bp1 levels varied inversely with miR-980 expression; memory performance was directly related to A2bp1 levels. In addition, A2bp1 knockdown reversed the memory gains produced by miR-980 inhibition, consistent with A2bp1 being a downstream target of miR-980 responsible for the memory phenotypes. Our results indicate that miR-980 represses A2bp1 expression to tune the excitable state of neurons, and the overall state of excitability translates to memory impairment or improvement. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Coherence parameter measurements for neon and hydrogen

NASA Astrophysics Data System (ADS)

Wright, Robert; Hargreaves, Leigh; Khakoo, Murtadha; Zatsarinny, Oleg; Bartschat, Klaus; Stauffer, Al

2015-09-01

We present recent coherence parameter measurements for excitation of neon and hydrogen by 50 eV electrons. The measurements were made using a crossed electron/gas beam spectrometer, featuring a hemispherically selected electron energy analyzer for detecting scattered electrons and double-reflection VUV polarization analyzer to register fluorescence photons. Time-coincidence counting methods on the electron and photon signals were employed to determine Stokes Parameters at each scattering angle, with data measured at angles between 20 - 115 degrees. The data are compared with calculated results using the B-Spline R-Matrix (BSR) and Relativistic Distorted Wave (RDW) approaches. Measurements were made of both the linear (Plin and γ) and circular (Lperp) parameters for the lowest lying excited states in these two targets. We particularly focus on results in the Lperp parameter, which shows unusual behavior in these particular targets, including strong sign changes implying reversal of the angular momentum transfer. In the case of neon, the unusual behavior is well captured by the BSR, but not by other models.

Strong coupling effects in hybrid plexitonic systems

NASA Astrophysics Data System (ADS)

Melnikau, Dzmitry; Esteban, Ruben; Govyadinov, Alexander A.; Savateeva, Diana; Simon, Thomas; Sánchez-Iglesias, Ana; Grzelczak, Marek; Schmidt, Mikolaj K.; Urban, Alexander S.; Liz-Marzán, Luis M.; Feldmann, Jochen; Aizpurua, Javier; Rakovich, Yury P.

2017-08-01

We investigated the interactions between localized plasmons in gold nanorods and excitons in J-aggregates and were able to track an anticrossing behavior of the hybridized modes both in the extinction and in the photoluminescence spectra of this hybrid system. We identified the nonlinear optical behavior of this system by transient absorption spectroscopy. Finally using magnetic circular dichroism spectroscopy we showed that nonmagnetic organic molecules exhibit magnetooptical response due to binding to a plasmonic nanoparticles. In our experiments we also studied the effect of detuning as well as the effect of off- and on resonance excitation on the hybrid states

Fusion energy science: Clean, safe, and abundant energy through innovative science and technology

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

None

Fusion energy science combines the study of the behavior of plasmas--the state of matter that forms 99% of the visible universe--with a vision of using fusion--the energy source of the stars--to create an affordable, plentiful, and environmentally benign energy source for humankind. The dual nature of fusion energy science provides an unfolding panorama of exciting intellectual challenge and a promise of an attractive energy source for generations to come. The goal of this report is a comprehensive understanding of plasma behavior leading to an affordable and attractive fusion energy source.

Self-Consistent Optimization of Excited States within Density-Functional Tight-Binding.

PubMed

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.

Excitation of lowest electronic states of the uracil molecule by slow electrons

NASA Astrophysics Data System (ADS)

Chernyshova, I. V.; Kontros, J. E.; Markush, P. P.; Shpenik, O. B.

2012-07-01

The excitation of lowest electronic states of the uracil molecule in the gas phase has been studied by electron energy loss spectroscopy. Along with excitation of lowest singlet states, excitation of two lowest triplet states at 3.75 and 4.76 eV (±0.05 eV) and vibrational excitation of the molecule in two resonant ranges (1-2 and 3-4 eV) have been observed for the first time. The peak of the excitation band related to the lowest singlet state (5.50 eV) is found to be blueshifted by 0.4 eV in comparison with the optical absorption spectroscopy data. The threshold excitation spectra have been measured for the first time, with detection of electrons inelastically scattered by an angle of 180°. These spectra exhibit clear separation of the 5.50-eV-wide band into two bands, which are due to the excitation of the triplet 13 A″ and singlet 11 A' states.

Role of electronic excited N2 in vibrational excitation of the N2 ground state at high latitudes

NASA Astrophysics Data System (ADS)

Campbell, L.; Cartwright, D. C.; Brunger, M. J.; Teubner, P. J. O.

2006-09-01

Vibrationally excited N2 is important in determining the ionospheric electron density and has also been proposed to play a role in the production of NO in disturbed atmospheres. We report here predictions of the absolute vibrational distributions in the ground electronic state of N2 produced by electron impact excitation, at noon and midnight under quiet geomagnetic conditions and disturbed conditions corresponding to the aurora IBCII+ and IBCIII+ at 60°N latitude and 0° longitude, at altitudes between 130 and 350 km. These predictions were obtained from a model which includes thermal excitation and direct electron impact excitation of the vibrational levels of the N2 ground state and its excited electronic states; radiative cascade from all excited electronic states to all vibrational levels of the ground electronic state; quenching by O, O2, and N2; molecular and ambipolar diffusion; and the dominant chemical reactions. Results from this study show that for both aurora and daytime electron environments: (1) cascade from the higher electronic states of N2 determines the population of the higher vibrational levels in the N2 ground state and (2) the effective ground state vibrational temperature for levels greater than 4 in N2 is predicted to be in the range 4000-13000 K for altitudes greater than 200 km. Correspondingly, the associated enhancement factor for the O+ reaction with vibrationally excited N2 to produce NO+ is predicted to increase with increasing altitude (up to a maximum at a height which increases with auroral strength) for both aurora and daytime environments and to increase with increasing auroral strength. The contribution of the cascade from the excited electronic states was evaluated and found to be relatively minor compared to the direct excitation process.

Perspectives for laboratory implementation of the Duan-Lukin-Cirac-Zoller protocol for quantum repeaters

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

Mendes, Milrian S.; Felinto, Daniel

2011-12-15

We analyze the efficiency and scalability of the Duan-Lukin-Cirac-Zoller (DLCZ) protocol for quantum repeaters focusing on the behavior of the experimentally accessible measures of entanglement for the system, taking into account crucial imperfections of the stored entangled states. We calculate then the degradation of the final state of the quantum-repeater linear chain for increasing sizes of the chain, and characterize it by a lower bound on its concurrence and the ability to violate the Clausner-Horne-Shimony-Holt inequality. The states are calculated up to an arbitrary number of stored excitations, as this number is not fundamentally bound for experiments involving large atomicmore » ensembles. The measurement by avalanche photodetectors is modeled by ''ON/OFF'' positive operator-valued measure operators. As a result, we are able to consistently test the approximation of the real fields by fields with a finite number of excitations, determining the minimum number of excitations required to achieve a desired precision in the prediction of the various measured quantities. This analysis finally determines the minimum purity of the initial state that is required to succeed in the protocol as the size of the chain increases. We also provide a more accurate estimate for the average time required to succeed in each step of the protocol. The minimum purity analysis and the new time estimates are then combined to trace the perspectives for implementation of the DLCZ protocol in present-day laboratory setups.« less

Perspectives for laboratory implementation of the Duan-Lukin-Cirac-Zoller protocol for quantum repeaters

NASA Astrophysics Data System (ADS)

Mendes, Milrian S.; Felinto, Daniel

2011-12-01

We analyze the efficiency and scalability of the Duan-Lukin-Cirac-Zoller (DLCZ) protocol for quantum repeaters focusing on the behavior of the experimentally accessible measures of entanglement for the system, taking into account crucial imperfections of the stored entangled states. We calculate then the degradation of the final state of the quantum-repeater linear chain for increasing sizes of the chain, and characterize it by a lower bound on its concurrence and the ability to violate the Clausner-Horne-Shimony-Holt inequality. The states are calculated up to an arbitrary number of stored excitations, as this number is not fundamentally bound for experiments involving large atomic ensembles. The measurement by avalanche photodetectors is modeled by “ON/OFF” positive operator-valued measure operators. As a result, we are able to consistently test the approximation of the real fields by fields with a finite number of excitations, determining the minimum number of excitations required to achieve a desired precision in the prediction of the various measured quantities. This analysis finally determines the minimum purity of the initial state that is required to succeed in the protocol as the size of the chain increases. We also provide a more accurate estimate for the average time required to succeed in each step of the protocol. The minimum purity analysis and the new time estimates are then combined to trace the perspectives for implementation of the DLCZ protocol in present-day laboratory setups.

σ-SCF: A direct energy-targeting method to mean-field excited states

NASA Astrophysics Data System (ADS)

Ye, Hong-Zhou; Welborn, Matthew; Ricke, Nathan D.; Van Voorhis, Troy

2017-12-01

The mean-field solutions of electronic excited states are much less accessible than ground state (e.g., Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF (self-consistent field), tend to fall into the lowest solution consistent with a given symmetry—a problem known as "variational collapse." In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states—ground or excited—are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H2, HF). We find that σ-SCF is very effective at locating excited states, including individual, high energy excitations within a dense manifold of excited states. Like all single determinant methods, σ-SCF shows prominent spin-symmetry breaking for open shell states and our results suggest that this method could be further improved with spin projection.

Structure of Low-Lying Excited States of Guanine in DNA and Solution: Combined Molecular Mechanics and High-Level Coupled Cluster Studies

DOE PAGES

Kowalski, Karol; Valiev, Marat

2007-01-01

High-level ab-initio equation-of-motion coupled-cluster methods with singles, doubles, and noniterative triples are used, in conjunction with the combined quantum mechanical molecular mechanics approach, to investigate the structure of low-lying excited states of the guanine base in DNA and solvated environments. Our results indicate that while the excitation energy of the first excited state is barely changed compared to its gas-phase counterpart, the excitation energy of the second excited state is blue-shifted by 0.24 eV.

Microwave-optical two-photon excitation of Rydberg states

NASA Astrophysics Data System (ADS)

Tate, D. A.; Gallagher, T. F.

2018-03-01

We report efficient microwave-optical two photon excitation of Rb Rydberg atoms in a magneto-optical trap. This approach allows the excitation of normally inaccessible states and provides a path toward excitation of high-angular-momentum states. The efficiency stems from the elimination of the Doppler width, the use of a narrow-band pulsed laser, and the enormous electric-dipole matrix element connecting the intermediate and final states of the transition. The excitation is efficient in spite of the low optical and microwave powers, of order 1 kW and 1 mW, respectively. This is an application of the large dipole coupling strengths between Rydberg states to achieve two-photon excitation of Rydberg atoms.

Laser-induced transitions between triply excited hollow states

NASA Astrophysics Data System (ADS)

Madsen, L. B.; Schlagheck, P.; Lambropoulos, P.

2000-12-01

Using complex scaling and a correlated basis constructed in terms of B splines, we calculate the Li+ photoion yield in the presence of a laser-induced coupling between the triply excited 2s22p(2Po) and 2s2p2(2De) resonances in lithium, the first of which is assumed to be excited by synchrotron radiation from the ground state. The laser coupling between the triply excited states is shown to lead to a significant and readily measurable modification of the line profile which provides a unique probe of the dipole strength between highly correlated triply excited states. We also present results for some higher-lying triply excited states of 2Po symmetry.

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)

Investigation of the coupling of the momentum distribution of a BEC with its collective of modes

NASA Astrophysics Data System (ADS)

Henn, Emanuel; Tavares, Pedro; Fritsch, Amilson; Vivanco, Franklin; Telles, Gustavo; Bagnato, Vanderlei

In our group we have a strong research line on quantum turbulence and the general investigation of Bose-Einstein condensates (BEC) subjected to oscillatory excitations. Inside this research line we investigate first the behavior of the normal modes of the BEC under this excitation and observe a non-linear behavior in the amplitude of the quadrupolar mode. Also, inside this same procedure of investigation we study the momentum distribution of a BEC to understand if it is possible to extract Kolmogorov like excitation spectra which would point to a turbulent state of matter. The condensate is perturbed, and we let it evolve in-trap after which we perform standard time-of- flight absorption imaging. The momentum distribution is extracted and analyzed as a function of the in-trap free evolution time for a 2D projected cloud. We show that the momentum distribution has its features varying periodically with the same frequency as the quadrupolar mode displayed by the atomic gas hinting at a strong coupling of both. The main consequence of that one cannot be assertive about the quantitative features of the extract spectrum of momentum and we can only rely on its qualitative features. Financial Support: FAPESP, CNPq.

Scattering of lattice solitons and decay of heat-current correlation in the Fermi-Pasta-Ulam-α -β model

NASA Astrophysics Data System (ADS)

Jin, Tao; Yu, Jian; Zhang, Nan; Zhao, Hong

2017-08-01

As is well known, solitons can be excited in nonlinear lattice systems; however, whether, and if so, how, this kind of nonlinear excitation can affect the energy transport behavior is not yet fully understood. Here we study both the scattering dynamics of solitons and heat transport properties in the Fermi-Pasta-Ulam-α -β model with an asymmetric interparticle interaction. By varying the asymmetry degree of the interaction (characterized by α ), we find that (i) for each α there exists a momentum threshold for exciting solitons from which one may infer an α -dependent feature of probability of presentation of solitons at a finite-temperature equilibrium state and (ii) the scattering rate of solitons is sensitively dependent on α . Based on these findings, we conjecture that the scattering between solitons will cause the nonmonotonic α -dependent feature of heat conduction. Fortunately, such a conjecture is indeed verified by our detailed examination of the time decay behavior of the heat current correlation function, but it is only valid for an early time stage. Thus, this result may suggest that solitons can have only a relatively short survival time when exposed in a thermal environment, eventually affecting the heat transport in a short time.

Development and Applications of Orthogonality Constrained Density Functional Theory for the Accurate Simulation of X-Ray Absorption Spectroscopy

NASA Astrophysics Data System (ADS)

Derricotte, Wallace D.

The aim of this dissertation is to address the theoretical challenges of calculating core-excited states within the framework of orthogonality constrained density functional theory (OCDFT). OCDFT is a well-established variational, time independent formulation of DFT for the computation of electronic excited states. In this work, the theory is first extended to compute core-excited states and generalized to calculate multiple excited state solutions. An initial benchmark is performed on a set of 40 unique core-excitations, highlighting that OCDFT excitation energies have a mean absolute error of 1.0 eV. Next, a novel implementation of the spin-free exact-two-component (X2C) one-electron treatment of scalar relativistic effects is presented and combined with OCDFT in an effort to calculate core excited states of transition metal complexes. The X2C-OCDFT spectra of three organotitanium complexes (TiCl4, TiCpCl3, and TiCp2Cl2) are shown to be in good agreement with experimental results and show a maximum absolute error of 5-6 eV. Next the issue of assigning core excited states is addressed by introducing an automated approach to analyzing the excited state MO by quantifying its local contributions using a unique orbital basis known as localized intrinsic valence virtual orbitals (LIVVOs). The utility of this approach is highlighted by studying sulfur core-excitations in ethanethiol and benzenethiol, as well as the hydrogen bonding in the water dimer. Finally, an approach to selectively target specic core-excited states in OCDFT based on atomic orbital subspace projection is presented in an effort to target core excited states of chemisorbed organic molecules. The core excitation spectrum of pyrazine chemisorbed on Si(100) is calculated using OCDFT and further characterized using the LIVVO approach.

Influence of Spin-Orbit Quenching on the Solvation of Indium in Helium Droplets

NASA Astrophysics Data System (ADS)

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

2017-06-01

Recent experimental interest of the collaborating group of M. Koch on the dynamics of electronic excitations of indium in helium droplets triggered a series of computational studies on the group 13 elements Al, Ga and In and their indecisive behavior between wetting and non wetting when placed onto superfluid helium droplets. We employ a combination of multiconfigurational self consistent field calculations (MCSCF) and multireference configuration interaction (MRCI) to calculate the diatomic potentials. Particularly interesting is the case of indium with an Ancilotto parameter λ close to the threshold value of 1.9. As shown by Reho et al. the spin-orbit splitting of metal atoms solvated in helium droplets is subject to a quenching effect. This can drastically change the solvation behavior. In this work we extend the approach presented by Reho et al. to include distance dependent spin-orbit coupling. The resulting potential surfaces are used to calculate the solvation energy of the ground state and the first excited state with orbital-free helium density functional theory. F. Ancilotto, P. B. Lerner and M. W. Cole, Journal of Low Temperature Physics, 1995, 101, 1123-1146 J. H. Reho, U. Merker, M. R. Radcliff, K. K. Lehmann and G. Scoles, The Journal of Physical Chemistry A, 2000, 104, 3620-3626

Observation of microscopic dynamics of phase transition in ferroelectric crystals using fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Sedarous, Salah S.

1996-03-01

Despite the large quantity of data on the macroscopic changes in the physical properties of ferroelectric crystals during phase transition, there is a continued need for understanding their microscopic origin. Here we describe a novel method for examining the microscopic dynamics of the ferroelectric phase transition using time-resolved fluorescence spectroscopy. The fluorescence properties of organic chromophores embedded in the ferroelectric crystals triglycine sulfate and potassium dihydrogen phosphate are altered in response to the structural phase transitions. The lifetime and the fractional intensity decay show large changes around Tc and the order of the phase transition is readily recovered (first or second order). To explain the fluorescence lifetime data we present a novel theoretical model based on the concept of polaritons in these crystals. Deactivation of the excited state chromophore involves the participation of the vibrational modes of the chromophore. These modes are coupled to the polarization dispersion of the matrix and facilitate the coupling of the excited state to the collective modes in the crystal. The net result is the flow of energy from the excited state chromophore to the lattice phonon. The data indicate that changes in fluorescence lifetime can be used to examine directly the collective modes in these crystals. Our work provides important insight into the emergence of macroscopic phase transition behavior out of microscopic fluctuations.

Pump-probe photoelectron velocity-map imaging of autoionizing singly excited 4s{sup 1}4p{sup 6}np{sup 1}(n=7,8) and doubly excited 4s{sup 2}4p{sup 4}5s{sup 1}6p{sup 1} resonances in atomic krypton

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

Doughty, Benjamin; Haber, Louis H.; Leone, Stephen R.

2011-10-15

Pump-probe photoelectron velocity-map imaging, using 27-eV high-harmonic excitation and 786-nm ionization, is used to resolve overlapping autoionizing resonances in atomic krypton, obtaining two-photon photoelectron angular distributions (PADs) for singly and doubly excited states. Two features in the photoelectron spectrum are assigned to singly excited 4s{sup 1}4p{sup 6}np{sup 1} (n = 7,8) configurations and four features provide information about double excitation configurations. The anisotropy parameters for the singly excited 7p configuration are measured to be {beta}{sub 2} = 1.61 {+-} 0.06 and {beta}{sub 4} = 1.54 {+-} 0.16 while the 8p configuration gives {beta}{sub 2} = 1.23 {+-} 0.19 and {beta}{submore » 4} = 0.60 {+-} 0.15. These anisotropies most likely represent the sum of overlapping PADs from states of singlet and triplet spin multiplicities. Of the four bands corresponding to ionization of doubly excited states, two are assigned to 4s{sup 2}4p{sup 4}5s{sup 1}6p{sup 1} configurations that are probed to different J-split ion states. The two remaining doubly excited states are attributed to a previously observed, but unassigned, resonance in the vacuum-ultraviolet photoabsorption spectrum. The PADs from each of the double excitation states are also influenced by overlap from neighboring states that are not completely spectrally resolved. The anisotropies of the observed double excitation states are reported, anticipating future theoretical and experimental work to separate the overlapping PADs into the state resolved PADs. The results can be used to test theories of excited state ionization.« less

Excited-state dynamics of pentacene derivatives with stable radical substituents.

PubMed

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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Observation and control of coherent torsional dynamics in a quinquethiophene molecule.

PubMed

Cirmi, Giovanni; Brida, Daniele; Gambetta, Alessio; Piacenza, Manuel; Della Sala, Fabio; Favaretto, Laura; Cerullo, Giulio; Lanzani, Guglielmo

2010-07-28

By applying femtosecond pump-probe spectroscopy to a substituted quinquethiophene molecule in solution, we observe in the time domain the coherent torsional dynamics that drives planarization of the excited state. Our interpretation is based on numerical modeling of the ground and excited state potential energy surfaces and simulation of wavepacket dynamics, which reveals two symmetric excited state deactivation pathways per oscillation period. We use the acquired knowledge on torsional dynamics to coherently control the excited state population with a pump-dump scheme, exploiting the non-stationary Franck-Condon overlap between ground and excited states.

Excited-State Effective Masses in Lattice QCD

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

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.

Protolytic dissociation of cyano derivatives of naphthol, biphenyl and phenol in the excited state: A review

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.

Electron-Driven Processes: From Single Collision Experiments to High-Pressure Discharge Plasmas

NASA Astrophysics Data System (ADS)

Becker, Kurt

2001-10-01

Plasmas are complex systems which consist of various groups of interacting particles (neutral atoms and molecules in their ground states and in excite states, electrons, and positive and negative ions). In principle, one needs to understand and describe all interactions between these particles in order to model the properties of the plasma and to predict its behavior. However, two-body interactions are often the only processes of relevance and only a subset of all possible collisional interactions are important. The focus of this talk is on collisional and radiative processes in low-temperature plasmas, both at low and high pressures. We will limit the discussion (i) to ionization and dissociation processes in molecular low-pressure plasmas and (ii) to collisional and radiative processes in high-pressure plasmas in rare gases and mixtures of rare gases and N2, O2, and H2. Electron-impact dissociation processes can be divided into dissociative excitation and dissociation into neutral ground-state fragments. Neutral molecular dissociation has only recently received attention from experimentalists and theorists because of the serious difficulties associated with the investigation of these processes. Collisional and radiative processes in high-pressure plasmas provide a fertile environment to the study of interactions that go beyond binary collisions involving ground-state species. Step-wise processes and three-body collisions begin to dominate the behavior of such plasmas. We will discuss examples of such processes as they relate to high-pressure rare gas discharge plasmas. Work supported by NSF, DOE, DARPA, NASA, and ABA Inc.

The Relationship Between Hypersexual Behavior, Sexual Excitation, Sexual Inhibition, and Personality Traits.

PubMed

Rettenberger, Martin; Klein, Verena; Briken, Peer

2016-01-01

The term hypersexuality was introduced to describe excessive sexual behavior associated with a person's inability to control his or her sexual behavior. The main aim of the present study was to investigate the impact of different personality traits on the degree of hypersexual behavior as measured by the Hypersexual Behavior Inventory (HBI). A further aim was to evaluate the association between sexual inhibition and excitation [as described in the Dual Control Model (DCM)] and hypersexual behavior. A sample of 1,749 participants completed an internet-based survey comprised the HBI, the short form of the Sexual Inhibition/Sexual Excitation Scales (SIS/SES-SF) as well as more general personality measures: the Behavioral Inhibition System/Behavioral Activation System-scales (BIS/BAS-scales) and a short version of the Big Five Inventory (BFI-10). Using the recommended HBI cut-off, 6.0 % (n = 105) of the present sample could be categorized as hypersexual, which is comparable to the results of previous studies about the prevalence of hypersexual behavior in the general population. The results provided strong support for the components of the DCM-sexual excitation and inhibition-to explain hypersexual behavior, irrespective of gender and sexual orientation. Some of the general personality traits also showed significant relationships with hypersexual behavior. Taken together, the results of the present study provide further support for the relevance of research about the relationships between sexual problems and disorders, the DCM, and personality variables.

Vibrational wave packets in the B 1Πu and D 1Σu+ states of Cs2: Determination of improved Cs2+(X) and Cs2(B) spectroscopic constants

NASA Astrophysics Data System (ADS)

Oldenburg, A. L.; John, P. C.; Eden, J. G.

2000-12-01

Vibrational wave packets in the B 1Πu and D 1Σu+ excited states of Cs2 have been studied on the ˜100 fs time scale by pump-probe laser spectroscopy. The temporal behavior of the wave packets was monitored by photoionizing the electronically excited molecule with a time-delayed probe pulse and recording the time and energy-integrated photoelectron signal as a function of time delay between the pump and probe pulses. For the B 1Σu+ experiments, wave packets were produced by exciting the B 1Σu+←X 1Σg+ transition in the ˜740-790 nm region and subsequently detected by photoionizing the molecule at wavelengths between 565 nm and 600 nm. By simulating the experimentally observed transients with the density matrix formalism (and explicitly accounting for laser chirp and |Δv|>1 coherences), improved values for the equilibrium internuclear separation for the Cs2(B1Πu) state and Te for the Cs2+(X) state were determined to be Re(B 1Πu)=4.93±0.03 Å and Te[Cs2+(X)]=29 930±100 cm-1, respectively. Similar experiments were conducted for the D 1Σu+ state. Wave packets composed of vibrational levels (v'≈40-50) perturbed by the bound 2 3Πou state were produced on the D 1Σu+ potential surface by driving the D 1Σu+←X 1Σg+ transition in the 575-610 nm spectral interval.

Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters.

PubMed

Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y; Nobusada, Katsuyuki; Jin, Rongchao

2016-04-07

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.

Ultrafast photoinduced dynamics of the 3,6-diaminoacridinium derivative ATTO 465 in solution.

PubMed

Arden-Jacob, Jutta; Drexhage, Karl-Heinz; Druzhinin, Sergey I; Ekimova, Maria; Flender, Oliver; Lenzer, Thomas; Oum, Kawon; Scholz, Mirko

2013-02-14

The excited state dynamics of the dye ATTO 465, a well-known fluorescence marker for biological applications, have been characterized in various solvents including THF, ethanol, methanol, water and the highly polar protic ionic liquid 2-hydroxyethylammonium formate (2-OH-EAF) by combining results from time-correlated single-photon counting (TCSPC) and ultrafast pump-supercontinuum probe (PSCP) spectroscopy as well as steady-state absorption and fluorescence. In water, 2-OH-EAF and two fluorinated alcohols, there is a pronounced blue-shift and broadening of the S(0) → S(1) absorption band and also a larger Stokes shift than in the other solvents, indicating a particular influence of hydrogen-bonding interactions. S(1) lifetimes from TCSPC at 25 °C range from 3.3 ns to 5.6 ns. An unusual increase in the S(1) lifetime with temperature is observed for ethanol and methanol, however water behaves in the opposite way. The behavior can be tentatively explained by a solvent- and temperature-dependent "proximity effect", where coupling of the close-lying S(1) and S(2) states influences the intramolecular relaxation rate of the dye. In addition, temperature-dependent complex equilibria of ATTO 465 with solvent molecules may influence the measured lifetimes. Several excited-state absorption (ESA) transitions are identified in the PSCP spectra, which are in good agreement with the position of the UV bands in the steady-state absorption spectra. Small shifts of the stimulated emission and ESA bands are consistent with solvation dynamics in the excited electronic state. An additional ~16 ps component in water, visible over the entire spectral range, is tentatively ascribed to a fast IC channel which is accessed by a fraction of ATTO 465 molecules.

Effects of single atom doping on the ultrafast electron dynamics of M 1Au 24(SR) 18 (M = Pd, Pt) nanoclusters

DOE PAGES

Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; ...

2016-02-29

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M 1@Au 24(SR) 18 (M = Pd, Pt; R = CH 2CH 2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M 1Au 12 core states; (2) core to shell relaxation in a few picoseconds; and (3)more » relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au 25(SR) 18 cluster. As a result, the detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.« less

Double-pulse dichromatic photolysis of fac-CIRe(CO){sub 3}L{sub 2} (L=4-phenylpyridine or 4-cyanopyridine): Photohomolysis of Re-L bonds insuced by irradiation of photochemically unreactive charge transfer states

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

Feliz, M.; Ferraudi, G.

1992-04-02

Photochemical reactions of fac-ClRe(CO){sub 3}L{sub 2} (L=4-phenylpyridine or 4-cyanopyridine), were investigated by sequential biphotonic excitations: one laser flash was used for the preparation of the compounds in the lowest lying MLCT (Re{r_arrow}) state and another flash for the irradiation of the compounds in such excited states. These photolyses led to photodecompostions into CIRe(CO){sub 3}L{sup +} and L{sup .} in a charge transfer state placed 40 Kk above ground state. Quantum yields determined or various excitation energies show that not all the excited state populated in monophotonic excitations can be reached under the sequential biphotonic regime. Therefore, photogeneration of the biradicalmore » intermediate, ClRe(CO){sub 3}L{sup +} and L{sup .}, from ligand-centered states has not been detected in these experiments. Results from monophotonic and biphotonic excitations have been used for a semiquantitative mapping of the excited-state potential surfaces. 41 refs., 6 figs.« less

Fast intramolecular electron transfer and dual fluorescence. Configurational change of the amino nitrogen (pyramidal{yields}planar)

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

Haar, Th. von der; Hebecker, A.; Il'Ichev, Yu.

1996-04-01

The fast excited state intramolecular charge transfer (ICT) and dual fluorescence observed with several 4-aminobenzonitriles is discussed. It is shown that the magnitude of the energy gap between the two lowest excited states determines the occurrence or absence of ICT. The photophysical behavior of a series of four 4-aminobenzonitriles in which the amino nitrogen atom is part of a four- to seven-membered heterocyclic ring, P4C to P7C, is studied by using time-resolved fluorescence measurements. The ICT rate constant strongly decreases with decreasing ring size. With P4C in diethyl ether ICT does not occur. This is attributed to the increase ofmore » the amino nitrogen inversion barrier with decreasing ring size. The change of the amino nitrogen from pyramidal to planar is considered to be an important reaction coordinate. The photophysics of the 4-aminobenzonitriles is different from that of other ICT systems such as donor/acceptor-substituted stilbenes and 9,9'-bianthryl, which are governed by the charge distribution and macroscopic Coulombic interaction in their CT states.« less

Fast intramolecular electron transfer and dual fluorescence. Configurational change of the amino nitrogen (pyramidal-->planar)

NASA Astrophysics Data System (ADS)

von der Haar, Th.; Hebecker, A.; Il'Ichev, Yu.; Kühnle, W.; Zachariasse, K. A.

1996-04-01

The fast excited state intramolecular charge transfer (ICT) and dual fluorescence observed with several 4-aminobenzonitriles is discussed. It is shown that the magnitude of the energy gap between the two lowest excited states determines the occurrence or absence of ICT. The photophysical behavior of a series of four 4-aminobenzonitriles in which the amino nitrogen atom is part of a four- to seven-membered heterocyclic ring, P4C to P7C, is studied by using time-resolved fluorescence measurements. The ICT rate constant strongly decreases with decreasing ring size. With P4C in diethyl ether ICT does not occur. This is attributed to the increase of the amino nitrogen inversion barrier with decreasing ring size. The change of the amino nitrogen from pyramidal to planar is considered to be an important reaction coordinate. The photophysics of the 4-aminobenzonitriles is different from that of other ICT systems such as donor/acceptor-substituted stilbenes and 9,9'-bianthryl, which are governed by the charge distribution and macroscopic Coulombic interaction in their CT states.

Neutron-19C scattering: Emergence of universal properties in a finite range potential

NASA Astrophysics Data System (ADS)

Shalchi, M. A.; Yamashita, M. T.; Hadizadeh, M. R.; Frederico, T.; Tomio, Lauro

2017-01-01

The low-energy properties of the elastic s-wave scattering for the n-19C are studied near the critical condition for the occurrence of an excited Efimov state in n-n-18C. It is established to which extent the universal scaling laws, strictly valid in the zero-range limit, survive when finite range potentials are considered. By fixing the two-neutrons separation energy in 20C with available experimental data, it is studied the scaling of the real (δ0R) and imaginary parts of the s-wave phase-shift with the variation of the n-18C binding energy. We obtain some universal characteristics given by the pole-position of kcot ⁡ (δ0R) and effective-range parameters. By increasing the n-18C binding energy, it was verified that the excited state of 20C goes to a virtual state, resembling the neutron-deuteron behavior in the triton. It is confirmed that the analytical structure of the unitary cut is not affected by the range of the potential or mass asymmetry of the three-body system.

Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2'-bipyridine)(CN) 4] 2-

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

Kjær, Kasper S.; Kunnus, Kristjan; Harlang, Tobias C. B.

The excited state dynamics of solvated [Fe(bpy)(CN) 4] 2-, where bpy = 2,2'-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN) 4] 2- has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile. Here, in the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN) 4] 2-more » in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet ( 3MC) character, unlike other reported six-coordinate Fe(II)-centered coordination compounds, which form MC quintet ( 5MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN) 4] 2- allows us to infer the influence of the solvent on the electronic structure of the complex. Lastly, the robust characterization of the dynamics and optical spectral signatures of the isolated 3MC intermediate provides a strong foundation for identifying 3MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.« less

Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2'-bipyridine)(CN) 4] 2-

DOE PAGES

Kjær, Kasper S.; Kunnus, Kristjan; Harlang, Tobias C. B.; ...

2018-01-19

The excited state dynamics of solvated [Fe(bpy)(CN) 4] 2-, where bpy = 2,2'-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN) 4] 2- has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile. Here, in the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN) 4] 2-more » in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet ( 3MC) character, unlike other reported six-coordinate Fe(II)-centered coordination compounds, which form MC quintet ( 5MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN) 4] 2- allows us to infer the influence of the solvent on the electronic structure of the complex. Lastly, the robust characterization of the dynamics and optical spectral signatures of the isolated 3MC intermediate provides a strong foundation for identifying 3MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.« less

Solvent effects in time-dependent self-consistent field methods. II. Variational formulations and analytical gradients

DOE PAGES

Bjorgaard, J. A.; Velizhanin, K. A.; Tretiak, S.

2015-08-06

This study describes variational energy expressions and analytical excited state energy gradients for time-dependent self-consistent field methods with polarizable solvent effects. Linear response, vertical excitation, and state-specific solventmodels are examined. Enforcing a variational ground stateenergy expression in the state-specific model is found to reduce it to the vertical excitation model. Variational excited state energy expressions are then provided for the linear response and vertical excitation models and analytical gradients are formulated. Using semiempiricalmodel chemistry, the variational expressions are verified by numerical and analytical differentiation with respect to a static external electric field. Lastly, analytical gradients are further tested by performingmore » microcanonical excited state molecular dynamics with p-nitroaniline.« less

Histaminergic responses by hypothalamic neurons that regulate lordosis and their modulation by estradiol.

PubMed

Dupré, Christophe; Lovett-Barron, Matthew; Pfaff, Donald W; Kow, Lee-Ming

2010-07-06

How do fluctuations in the level of generalized arousal of the brain affect the performance of specific motivated behaviors, such as sexual behaviors that depend on sexual arousal? A great deal of previous work has provided us with two important starting points in answering this question: (i) that histamine (HA) serves generalized CNS arousal and (ii) that heightened electrical activity of neurons in the ventromedial nucleus of the hypothalamus (VMN) is necessary and sufficient for facilitating the primary female sex behavior in laboratory animals, lordosis behavior. Here we used patch clamp recording technology to analyze HA effects on VMN neuronal activity. The results show that HA acting through H1 receptors (H1R) depolarizes these neurons. Further, acute administration of estradiol, an estrogen necessary for lordosis behavior to occur, heightens this effect. Hyperpolarization, which tends to decrease excitability and enhance inhibition, was not affected by acute estradiol or mediated by H1R but was mediated by other HA receptor subtypes, H2 and H3. Sampling of mRNA from individual VMN neurons showed colocalization of expression of H1 receptor mRNA with estrogen receptor (ER)-alpha mRNA but also revealed ER colocalization with the other HA receptor subtypes and colocalization of different subtypes with each other. The latter finding provides the molecular basis for complex "push-pull" regulation of VMN neuronal excitability by HA. Thus, in the simplest causal route, HA, acting on VMN neurons through H1R provides a mechanism by which elevated states of generalized CNS arousal can foster a specific estrogen-dependent, aroused behavior, sexual behavior.

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

Chow, Colin M.; Yu, Hongyi; Jones, Aaron M.

In monolayer semiconductor transition metal dichalcogenides, the exciton–phonon interaction strongly affects the photocarrier dynamics. Here, we report on an unusual oscillatory enhancement of the neutral exciton photoluminescence with the excitation laser frequency in monolayer MoSe 2. The frequency of oscillation matches that of the M-point longitudinal acoustic phonon, LA(M), suggesting the significance of zone-edge acoustic phonons and hence the deformation potential in exciton-phonon coupling in MoSe 2. Moreover, oscillatory behavior is observed in the steady-state emission linewidth and in time-resolved PLE data, which reveals variation with excitation energy in the exciton lifetime. These results clearly expose the key role playedmore » by phonons in the exciton formation and relaxation dynamics of two-dimensional van der Waals semiconductors.« less

Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

DOE PAGES

Brajuskovic, V.; Barrows, F.; Phatak, C.; ...

2016-10-03

Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. In addition, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1Dmore » avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism.« less

Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating BaFeO_{3} Thin Films.

PubMed

Tsuyama, T; Chakraverty, S; Macke, S; Pontius, N; Schüßler-Langeheine, C; Hwang, H Y; Tokura, Y; Wadati, H

2016-06-24

We studied the electronic and magnetic dynamics of ferromagnetic insulating BaFeO_{3} thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe 2p edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow (∼150  ps) to fast (<70  ps) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information.

Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

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

Brajuskovic, V.; Barrows, F.; Phatak, C.

Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. In addition, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1Dmore » avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism.« less

Detailed spectroscopy of 110Cd: Evidence for weak mixing and the emergence of γ-soft behavior

NASA Astrophysics Data System (ADS)

Garrett, P. E.; Bangay, J.; Diaz Varela, A.; Ball, G. C.; Cross, D. S.; Demand, G. A.; Finlay, P.; Garnsworthy, A. B.; Green, K. L.; Hackman, G.; Hannant, C. D.; Jigmeddorj, B.; Jolie, J.; Kulp, W. D.; Leach, K. G.; Orce, J. N.; Phillips, A. A.; Radich, A. J.; Rand, E. T.; Schumaker, M. A.; Svensson, C. E.; Sumithrarachchi, C.; Triambak, S.; Warr, N.; Wong, J.; Wood, J. L.; Yates, S. W.

2012-10-01

A study of the β+-electron capture decay of 110In into levels of 110Cd is combined with a reanalysis of data from a previous study of 110Cd with the (n,n'γ) reaction with monoenergetic neutrons. The γγ coincidences from the 110In decay leads to many new assignments of γ rays observed in the (n,n'γ) reaction, permitting the observation of weak low-energy transitions, and setting stringent upper limits on unobserved decay branches. The uncertainties on many of the lifetimes from the (n,n'γ) reaction are significantly reduced, and limits are established for the lifetimes of levels too long for a direct measurement. The absence of enhanced transitions between the previously assigned phonon states and the deformed intruder states strongly suggests that mixing between the configurations is generally weak, refuting the strong-mixing scenario as an explanation of the decay pattern of the excited 0+ states in 110Cd. The decay pattern of the nonintruder states is suggestive of a γ-soft rotor, or O(6) nucleus, rather than a vibrational, or U(5), pattern. The existence of a four-particle-six-hole proton excitation in 110Cd is also suggested.

Mode-selective chemistry on metal surfaces: The dissociative chemisorption of CH 4 on Pt(111)

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

Guo, Han; Jackson, Bret

A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH 4 dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v 3 and 2v 3, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v 1 symmetric stretch of CH 4 is more effective at promoting the dissociative chemisorption of CH 4 than exciting the 1v 3 antisymmetric stretch. This behavior is explained in terms of symmetry,more » mode-softening, and nonadiabatic transitions between vibrationally adiabatic states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v 3 state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. As a result, our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies.« less

Mode-selective chemistry on metal surfaces: The dissociative chemisorption of CH{sub 4} on Pt(111)

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

Guo, Han; Jackson, Bret, E-mail: jackson@chem.umass.edu

A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH{sub 4} dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v{sub 3} and 2v{sub 3}, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v{sub 1} symmetric stretch of CH{sub 4} is more effective at promoting the dissociative chemisorption of CH{sub 4} than exciting the 1v{sub 3} antisymmetric stretch. This behavior is explained in terms of symmetry,more » mode-softening, and nonadiabatic transitions between vibrationally adiabatic states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v{sub 3} state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. Our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies.« less

Mode-selective chemistry on metal surfaces: The dissociative chemisorption of CH 4 on Pt(111)

DOE PAGES

Guo, Han; Jackson, Bret

2016-05-13

A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH 4 dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v 3 and 2v 3, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v 1 symmetric stretch of CH 4 is more effective at promoting the dissociative chemisorption of CH 4 than exciting the 1v 3 antisymmetric stretch. This behavior is explained in terms of symmetry,more » mode-softening, and nonadiabatic transitions between vibrationally adiabatic states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v 3 state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. As a result, our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies.« less

Vibronic coupling in the excited-states of carotenoids

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

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

2016-01-01

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

Vibronic coupling in the excited-states of carotenoids

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

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

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

σ -SCF: A Direct Energy-targeting Method To Mean-field Excited States

NASA Astrophysics Data System (ADS)

Ye, Hongzhou; Welborn, Matthew; Ricke, Nathan; van Voorhis, Troy

The mean-field solutions of electronic excited states are much less accessible than ground state (e.g. Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF, tend to fall into the lowest solution consistent with a given symmetry - a problem known as ``variational collapse''. In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states - ground or excited - are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H2, HF). This work was funded by a Grant from NSF (CHE-1464804).

Calculation of Vibrational and Electronic Excited-State Absorption Spectra of Arsenic-Water Complexes Using Density Functional Theory

DTIC Science & Technology

2016-06-03

Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6390--16-9681 Calculation of Vibrational and Electronic Excited-State Absorption Spectra...NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Calculation of Vibrational and Electronic Excited-State Absorption Spectra of Arsenic-Water Complexes Using...Unclassified Unlimited Unclassified Unlimited 59 Samuel G. Lambrakos (202) 767-2601 Calculations are presented of vibrational and electronic excited-state

Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2'-bipyridine) 2(CN) 2

DOE PAGES

Kjaer, Kasper S.; Zhang, Wenkai; Alonso-Mori, Roberto; ...

2017-07-06

Here, we have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy) 2(CN) 2], where bpy=2,2'-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2'-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy) 2(CN) 2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a shortmore » lived metal-centered triplet transient species. These measurements of [Fe(bpy) 2(CN) 2] complement prior measurement performed on [Fe(bpy) 3] 2+ and [Fe(bpy)(CN) 4] 2– in dimethylsulfoxide solution and help complete the chemical series [Fe(bpy) N(CN) 6–2N] 2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3 d transition metal complexes.« less

Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2'-bipyridine) 2(CN) 2

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

Kjaer, Kasper S.; Zhang, Wenkai; Alonso-Mori, Roberto

Here, we have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy) 2(CN) 2], where bpy=2,2'-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2'-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy) 2(CN) 2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a shortmore » lived metal-centered triplet transient species. These measurements of [Fe(bpy) 2(CN) 2] complement prior measurement performed on [Fe(bpy) 3] 2+ and [Fe(bpy)(CN) 4] 2– in dimethylsulfoxide solution and help complete the chemical series [Fe(bpy) N(CN) 6–2N] 2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3 d transition metal complexes.« less

Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine)2(CN)2

PubMed Central

Kjær, Kasper S.; Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe; Chollet, Matthieu; Hadt, Ryan G.; Hartsock, Robert W.; Harlang, Tobias; Kroll, Thomas; Kubiček, Katharina; Lemke, Henrik T.; Liang, Huiyang W.; Liu, Yizhu; Nielsen, Martin M.; Robinson, Joseph S.; Solomon, Edward I.; Sokaras, Dimosthenis; van Driel, Tim B.; Weng, Tsu-Chien; Zhu, Diling; Persson, Petter; Wärnmark, Kenneth; Sundström, Villy; Gaffney, Kelly J.

2017-01-01

We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy)2(CN)2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy)2(CN)2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy)2(CN)2] complement prior measurement performed on [Fe(bpy)3]2+ and [Fe(bpy)(CN)4]2− in dimethylsulfoxide solution and help complete the chemical series [Fe(bpy)N(CN)6–2N]2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes. PMID:28653021

Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

NASA Astrophysics Data System (ADS)

Hsiao, F.-M.; Schnedler, M.; Portz, V.; Huang, Y.-C.; Huang, B.-C.; Shih, M.-C.; Chang, C.-W.; Tu, L.-W.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.; Chiu, Y.-P.

2017-01-01

We demonstrate the potential of sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy to investigate the presence of defect states in semiconductors. The characterization method is illustrated on GaN layers grown on Si(111) substrates without intentional buffer layers. According to high-resolution transmission electron microscopy and cathodoluminescence spectroscopy, the GaN layers consist of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. In order to discriminate between band-to-band excitation and defect state excitations, we use sub-bandgap laser excitation. We probe a clear increase in the tunnel current at positive sample voltages during sub-bandgap laser illumination for the GaN layer with high defect density, but no effect is found for high quality GaN epitaxial layers. This demonstrates the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy is a powerful complimentary characterization tool for defect states.

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

Pan, Huilin; Yang, Jiayue; Zhang, Dong

The effect of antisymmetric C–H stretching excitation of CH{sub 4} on the dynamics and reactivity of the O({sup 1}D) + CH{sub 4} → OH + CD{sub 3} reaction at the collision energy of 6.10 kcal/mol has been investigated using the crossed-beam and time-sliced velocity map imaging techniques. The antisymmetric C–H stretching mode excited CH{sub 4} molecule was prepared by direct infrared excitation. From the measured images of the CH{sub 3} products with the infrared laser on and off, the product translational energy and angular distributions were derived for both the ground and vibrationally excited reactions. Experimental results show that themore » vibrational energy of the antisymmetric stretching excited CH{sub 4} reagent is channeled exclusively into the vibrational energy of the OH co-products and, hence, the OH products from the excited-state reaction are about one vibrational quantum hotter than those from the ground-state reaction, and the product angular distributions are barely affected by the vibrational excitation of the CH{sub 4} reagent. The reactivity was found to be suppressed by the antisymmetric stretching excitation of CH{sub 4} for all observed CH{sub 3} vibrational states. The degree of suppression is different for different CH{sub 3} vibrational states: the suppression is about 40%–60% for the ground state and the umbrella mode excited CH{sub 3} products, while for the CH{sub 3} products with one quantum symmetric stretching mode excitation, the suppression is much less pronounced. In consequence, the vibrational state distribution of the CH{sub 3} product from the excited-state reaction is considerably different from that of the ground-state reaction.« less

Spectroscopic Diagnosis of Excited-State Aromaticity: Capturing Electronic Structures and Conformations upon Aromaticity Reversal.

PubMed

Oh, Juwon; Sung, Young Mo; Hong, Yongseok; Kim, Dongho

2018-03-06

Aromaticity, the special energetic stability derived from cyclic [4 n + 2]π-conjugated electronic structures, has been the topic of intense interest in chemistry because it plays a critical role in rationalizing molecular stability, reactivity, and physical/chemical properties. Recently, the pioneering work by Colin Baird on aromaticity reversal, postulating that aromatic (antiaromatic) character in the ground state reverses to antiaromatic (aromatic) character in the lowest excited triplet state, has attracted much scientific attention. The completely reversed aromaticity in the excited state provides direct insight into understanding the photophysical/chemical properties of photoactive materials. In turn, the application of aromatic molecules to photoactive materials has led to numerous studies revealing this aromaticity reversal. However, most studies of excited-state aromaticity have been based on the theoretical point of view. The experimental evaluation of aromaticity in the excited state is still challenging and strenuous because the assessment of (anti)aromaticity with conventional magnetic, energetic, and geometric indices is difficult in the excited state, which practically restricts the extension and application of the concept of excited-state aromaticity. Time-resolved optical spectroscopies can provide a new and alternative avenue to evaluate excited-state aromaticity experimentally while observing changes in the molecular features in the excited states. Time-resolved optical spectroscopies take advantage of ultrafast laser pulses to achieve high time resolution, making them suitable for monitoring ultrafast changes in the excited states of molecular systems. This can provide valuable information for understanding the aromaticity reversal. This Account presents recent breakthroughs in the experimental assessment of excited-state aromaticity and the verification of aromaticity reversal with time-resolved optical spectroscopic measurements. To scrutinize this intriguing and challenging scientific issue, expanded porphyrins have been utilized as the ideal testing platform for investigating aromaticity because they show distinct aromatic and antiaromatic characters with aromaticity-specific spectroscopic features. Expanded porphyrins exhibit perfect aromatic and antiaromatic congener pairs having the same molecular framework but different numbers of π electrons, which facilitates the study of the pure effect of aromaticity by comparative analyses. On the basis of the characteristics of expanded porphyrins, time-resolved electronic and vibrational absorption spectroscopies capture the changes in electronic structure and molecular conformations driven by the change in aromaticity and provide clear evidence for aromaticity reversal in the excited states. The approaches described in this Account pave the way for the development of new and alternative experimental indices for the evaluation of excited-state aromaticity, which will enable overarching and fundamental comprehension of the role of (anti)aromaticity in the stability, dynamics, and reactivity in the excited states with possible implications for practical applications.

Excited-State Deactivation of Branched Phthalocyanine Compounds.

PubMed

Zhu, Huaning; Li, Yang; Chen, Jun; Zhou, Meng; Niu, Yingli; Zhang, Xinxing; Guo, Qianjin; Wang, Shuangqing; Yang, Guoqiang; Xia, Andong

2015-12-21

The excited-state relaxation dynamics and chromophore interactions in two phthalocyanine compounds (bis- and trisphthalocyanines) are studied by using steady-state and femtosecond transient absorption spectral measurements, where the excited-state energy-transfer mechanism is explored. By exciting phthalocyanine compounds to their second electronically excited states and probing the subsequent relaxation dynamics, a multitude of deactivation pathways are identified. The transient absorption spectra show the relaxation pathway from the exciton state to excimer state and then back to the ground state in bisphthalocyanine (bis-Pc). In trisphthalocyanine (tris-Pc), the monomeric and dimeric subunits are excited and the excitation energy transfers from the monomeric vibrationally hot S1 state to the exciton state of a pre-associated dimer, with subsequent relaxation to the ground state through the excimer state. The theoretical calculations and steady-state spectra also show a face-to-face conformation in bis-Pc, whereas in tris-Pc, two of the three phthalocyanine branches form a pre-associated face-to-face dimeric conformation with the third one acting as a monomeric unit; this is consistent with the results of the transient absorption experiments from the perspective of molecular structure. The detailed structure-property relationships in phthalocyanine compounds is useful for exploring the function of molecular aggregates in energy migration of natural photosynthesis systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Probing the Quantum States of a Single Atom Transistor at Microwave Frequencies.

PubMed

Tettamanzi, Giuseppe Carlo; Hile, Samuel James; House, Matthew Gregory; Fuechsle, Martin; Rogge, Sven; Simmons, Michelle Y

2017-03-28

The ability to apply gigahertz frequencies to control the quantum state of a single P atom is an essential requirement for the fast gate pulsing needed for qubit control in donor-based silicon quantum computation. Here, we demonstrate this with nanosecond accuracy in an all epitaxial single atom transistor by applying excitation signals at frequencies up to ≈13 GHz to heavily phosphorus-doped silicon leads. These measurements allow the differentiation between the excited states of the single atom and the density of states in the one-dimensional leads. Our pulse spectroscopy experiments confirm the presence of an excited state at an energy ≈9 meV, consistent with the first excited state of a single P donor in silicon. The relaxation rate of this first excited state to the ground state is estimated to be larger than 2.5 GHz, consistent with theoretical predictions. These results represent a systematic investigation of how an atomically precise single atom transistor device behaves under radio frequency excitations.

Two-photon absorption by spectrally shaped entangled photons

NASA Astrophysics Data System (ADS)

Oka, Hisaki

2018-03-01

We theoretically investigate two-photon excitation by spectrally shaped entangled photons with energy anticorrelation in terms of how the real excitation of an intermediate state affects two-photon absorption by entangled photons. Spectral holes are introduced in the entangled photons around the energy levels of an intermediate state so that two-step excitation via the real excitation of the intermediated state can be suppressed. Using a three-level atomic system as an example, we show that the spectral holes well suppress the real excitation of the intermediate state and recover two-photon absorption via a virtual state. Furthermore, for a short pulse close to a monocycle, we show that the excitation efficiency by the spectrally shaped entangled photons can be enhanced a thousand times as large as that by uncorrelated photons.

Photoinduced relaxation dynamics of nitrogen-capped silicon nanoclusters: a TD-DFT study

NASA Astrophysics Data System (ADS)

Liu, Xiang-Yang; Xie, Xiao-Ying; Fang, Wei-Hai; Cui, Ganglong

2018-04-01

Herein we have developed and implemented a TD-DFT-based surface-hopping dynamics simulation method with a recently proposed numerical algorithm capable of efficiently computing nonadiabatic couplings, a semiclassical spectrum simulation method, and an excited-state character analysis method based on one-electron transition density matrix. With the use of these developed methods, we have studied the spectroscopic properties, excited-state characters, and photoinduced relaxation dynamics of three silicon nanoclusters capped with different chromophores (Cl@SiQD, Car@SiQD, Azo@SiQD). Spectroscopically, the main absorption peak is visibly red-shifted from Cl@SiQD via Car@SiQD to Azo@SiQD. In contrast to Cl@SiQD and Car@SiQD, there are two peaks observed in Azo@SiQD. Mechanistically, the excited-state relaxation to the lowest S1 excited singlet state is ultrafast in Cl@SiQD, which is less than 190 fs and without involving excited-state trapping. In comparison, there are clear excited-state trappings in Car@SiQD and Azo@SiQD. In the former, the S2 state is trapped more than 300 fs; in the latter, the S3 excited-state trapping is more than 615 fs. These results demonstrate that the interfacial interaction has significant influences on the spectroscopic properties and excited-state relaxation dynamics. The knowledge gained in this work could be helpful for the design of silicon nanoclusters with better photoluminescence performance.

Excitation of photosystem I by 760 nm femtosecond laser pulses: transient absorption spectra and intermediates

NASA Astrophysics Data System (ADS)

Cherepanov, Dmitry A.; Shelaev, Ivan V.; Gostev, Fedor E.; Mamedov, Mahir D.; Petrova, Anastasia A.; Aybush, Arseniy V.; Shuvalov, Vladimir A.; Semenov, Alexey Yu; Nadtochenko, Victor A.

2017-09-01

Excitation of photosystem I (PS I) by a femtosecond 760 nm pump leads to one- and two-photon absorption. The one-photon excitation produces intermediates with transient absorption spectra similar to the spectra of the primary [{{{P}}700}+{{{A}}0}-{{A}}1] and secondary [{{{P}}700}+{{A}}0{{{A}}1}-] ion-radical pairs in the PS I reaction center. The two-photon absorption generates the upper level excited states of chlorophyll (Chl) and carotenoid molecules in the antenna. These excited states are converted into the long-lived intermediates and can be tentatively attributed to the excited and charge-transfer ion-radical states of Chl molecules and to the excited states of carotenoids in the antenna. The transient spectra of intermediates generated by two-photon excitation differ from the transient one-photon spectra of the primary and secondary ion-radical pairs.

Excitation wavelength dependence of excited state intramolecular proton transfer reaction of 4'-N,N-diethylamino-3-hydroxyflavone in room temperature ionic liquids studied by optical Kerr gate fluorescence measurement.

PubMed

Suda, Kayo; Terazima, Masahide; Sato, Hirofumi; Kimura, Yoshifumi

2013-10-17

Excited state intramolecular proton transfer reactions (ESIPT) of 4'-N,N-diethylamino-3-hydroxyflavone (DEAHF) in ionic liquids have been studied by steady-state and time-resolved fluorescence measurements at different excitation wavelengths. Steady-state measurements show the relative yield of the tautomeric form to the normal form of DEAHF decreases as excitation wavelength is increased from 380 to 450 nm. The decrease in yield is significant in ionic liquids that have cations with long alkyl chains. The extent of the decrease is correlated with the number of carbon atoms in the alkyl chains. Time-resolved fluorescence measurements using optical Kerr gate spectroscopy show that ESIPT rate has a strong excitation wavelength dependence. There is a large difference between the spectra at a 200 ps delay from different excitation wavelengths in each ionic liquid. The difference is pronounced in ionic liquids having a long alkyl chain. The equilibrium constant in the electronic excited state obtained at a 200 ps delay and the average reaction rate are also correlated with the alkyl chain length. Considering the results of the steady-state fluorescence and time-resolved measurements, the excitation wavelength dependence of ESIPT is explained by state selective excitation due to the difference of the solvation, and the number of alkyl chain carbon atoms is found to be a good indicator of the effect of inhomogeneity for this reaction.

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-). Theoretical evidence for a competitive charge transfer mechanism.

PubMed

Hu, Zhenming; Boyd, Russell J; Nakatsuji, Hiroshi

2002-03-20

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-) complexes have been investigated using the B3LYP and the symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theoretical methods. All the dicarbonyl complexes have singlet ground electronic states with large singlet-triplet separations. Thermal dissociations of CO from the parent dicarbonyls are energetically unfavorable. CO thermal dissociation is an activation process for [Cl(2)Rh(CO)(2)](-) while it is a repulsive potential for CpM(CO)(2). The natures of the main excited states of CpM(CO)(2) and [Cl(2)Rh(CO)(2)](-) are found to be quite different. For [Cl(2)Rh(CO)(2)](-), all the strong transitions are identified to be metal to ligand CO charge transfer (MLCT) excitations. A significant feature of the excited states of CpM(CO)(2) is that both MLCT excitation and a ligand Cp to metal and CO charge transfer excitation are strongly mixed in the higher energy states with the latter having the largest oscillator strength. A competitive charge transfer excited state has therefore been identified theoretically for CpRh(CO)(2) and CpIr(CO)(2). The wavelength dependence of the quantum efficiencies for the photoreactions of CpM(CO)(2) reported by Lees et al. can be explained by the existence of two different types of excited states. The origin of the low quantum efficiencies for the C-H/S-H bond activations of CpM(CO)(2) can be attributed to the smaller proportion of the MLCT excitation in the higher energy states.

Time-dependent density functional theory study of the luminescence properties of gold phosphine thiolate complexes.

PubMed

Guidez, Emilie B; Aikens, Christine M

2015-04-09

The origin of the emission of the gold phosphine thiolate complex (TPA)AuSCH(CH3)2 (TPA = 1,3,5-triaza-7-phosphaadamantanetriylphosphine) is investigated using time-dependent density functional theory (TDDFT). This system absorbs light at 3.6 eV, which corresponds mostly to a ligand-to-metal transition with some interligand character. The P-Au-S angle decreases upon relaxation in the S1 and T1 states. Our calculations show that these two states are strongly spin-orbit coupled at the ground state geometry. Ligand effects on the optical properties of this complex are also discussed by looking at the simple AuP(CH3)3SCH3 complex. The excitation energies differ by several tenths of an electronvolt. Excited state optimizations show that the excited singlet and triplet of the (TPA)AuSCH(CH3)2 complex are bent. On the other hand, the Au-S bond breaks in the excited state for the simple complex, and TDDFT is no longer an adequate method. The excited state energy landscape of gold phosphine thiolate systems is very complex, with several state crossings. This study also shows that the formation of the [(TPA)AuSCH(CH3)2]2 dimer is favorable in the ground state. The inclusion of dispersion interactions in the calculations affects the optimized geometries of both ground and excited states. Upon excitation, the formation of a Au-Au bond occurs, which results in an increase in energy of the low energy excited states in comparison to the monomer. The experimentally observed emission of the (TPA)AuSCH(CH3)2 complex at 1.86 eV cannot be unambiguously assigned and may originate from several excited states.

Damping of spin-dipole mode and generation of quadrupole mode excitations in a spin-orbit coupled Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Li, Chuan-Hsun; Blasing, David; Chen, Yong

2017-04-01

In cold atom systems, spin excitations have been shown to be a sensitive probe of interactions and quantum statistical effects, and can be used to study spin transport in both Fermi and Bose gases. In particular, spin-dipole mode (SDM) is a type of excitation that can generate a spin current without a net mass current. We present recent measurements and analysis of SDM in a disorder-free, interacting three-dimensional (3D) 87Rb Bose-Einstein condensate (BEC) by applying spin-dependent synthetic electric fields to actuate head-on collisions between two BECs of different spin states. We experimentally study and compare the behaviors of the system following SDM excitations in the presence as well as absence of synthetic 1D spin-orbit coupling (SOC). We find that in the absence of SOC, SDM is relatively weakly damped, accompanied with collision-induced thermalization which heats up the atomic cloud. However, in the presence of SOC, we find that SDM is more strongly damped with reduced thermalization, and observe excitation of a quadrupole mode that exhibits BEC shape oscillation even after SDM is damped out. Such a mode conversion bears analogies with the Beliaev coupling process or the parametric frequency down conversion of light in nonlinear optics.

Ionic wave propagation and collision in an excitable circuit model of microtubules

NASA Astrophysics Data System (ADS)

Guemkam Ghomsi, P.; Tameh Berinyoh, J. T.; Moukam Kakmeni, F. M.

2018-02-01

In this paper, we report the propensity to excitability of the internal structure of cellular microtubules, modelled as a relatively large one-dimensional spatial array of electrical units with nonlinear resistive features. We propose a model mimicking the dynamics of a large set of such intracellular dynamical entities as an excitable medium. We show that the behavior of such lattices can be described by a complex Ginzburg-Landau equation, which admits several wave solutions, including the plane waves paradigm. A stability analysis of the plane waves solutions of our dynamical system is conducted both analytically and numerically. It is observed that perturbed plane waves will always evolve toward promoting the generation of localized periodic waves trains. These modes include both stationary and travelling spatial excitations. They encompass, on one hand, localized structures such as solitary waves embracing bright solitons, dark solitons, and bisolitonic impulses with head-on collisions phenomena, and on the other hand, the appearance of both spatially homogeneous and spatially inhomogeneous stationary patterns. This ability exhibited by our array of proteinic elements to display several states of excitability exposes their stunning biological and physical complexity and is of high relevance in the description of the developmental and informative processes occurring on the subcellular scale.

Ionic wave propagation and collision in an excitable circuit model of microtubules.

PubMed

Guemkam Ghomsi, P; Tameh Berinyoh, J T; Moukam Kakmeni, F M

2018-02-01

In this paper, we report the propensity to excitability of the internal structure of cellular microtubules, modelled as a relatively large one-dimensional spatial array of electrical units with nonlinear resistive features. We propose a model mimicking the dynamics of a large set of such intracellular dynamical entities as an excitable medium. We show that the behavior of such lattices can be described by a complex Ginzburg-Landau equation, which admits several wave solutions, including the plane waves paradigm. A stability analysis of the plane waves solutions of our dynamical system is conducted both analytically and numerically. It is observed that perturbed plane waves will always evolve toward promoting the generation of localized periodic waves trains. These modes include both stationary and travelling spatial excitations. They encompass, on one hand, localized structures such as solitary waves embracing bright solitons, dark solitons, and bisolitonic impulses with head-on collisions phenomena, and on the other hand, the appearance of both spatially homogeneous and spatially inhomogeneous stationary patterns. This ability exhibited by our array of proteinic elements to display several states of excitability exposes their stunning biological and physical complexity and is of high relevance in the description of the developmental and informative processes occurring on the subcellular scale.

Optical evidence of quantum rotor orbital excitations in orthorhombic manganites

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

Kovaleva, N. N., E-mail: nkovaleva@sci.lebedev.ru; Kugel, K. I.; Potůček, Z.

2016-05-15

In magnetic compounds with Jahn–Teller (JT) ions (such as Mn{sup 3+} or Cu{sup 2+}), the ordering of the electron or hole orbitals is associated with cooperative lattice distortions. There the role of JT effect, although widely recognized, is still elusive in the ground state properties. Here we discovered that, in these materials, there exist excitations whose energy spectrum is described in terms of the total angular momentum eigenstates and is quantized as in quantum rotors found in JT centers. We observed features originating from these excitations in the optical spectra of a model compound LaMnO{sub 3} using ellipsometry technique. Theymore » appear clearly as narrow sidebands accompanying the electron transition between the JT split orbitals at neighboring Mn{sup 3+} ions, displaying anomalous temperature behavior around the Néel temperature T{sub N} ≈ 140 K. We present these results together with new experimental data on photoluminescence found in LaMnO{sub 3}, which lend additional support to the ellipsometry implying the electronic-vibrational origin of the quantum rotor orbital excitations. We note that the discovered orbital excitations of quantum rotors may play an important role in many unusual properties observed in these materials upon doping, such as high-temperature superconductivity and colossal magnetoresistance.« less

State-selective optimization of local excited electronic states in extended systems

NASA Astrophysics Data System (ADS)

Kovyrshin, Arseny; Neugebauer, Johannes

2010-11-01

Standard implementations of time-dependent density-functional theory (TDDFT) for the calculation of excitation energies give access to a number of the lowest-lying electronic excitations of a molecule under study. For extended systems, this can become cumbersome if a particular excited state is sought-after because many electronic transitions may be present. This often means that even for systems of moderate size, a multitude of excited states needs to be calculated to cover a certain energy range. Here, we present an algorithm for the selective determination of predefined excited electronic states in an extended system. A guess transition density in terms of orbital transitions has to be provided for the excitation that shall be optimized. The approach employs root-homing techniques together with iterative subspace diagonalization methods to optimize the electronic transition. We illustrate the advantages of this method for solvated molecules, core-excitations of metal complexes, and adsorbates at cluster surfaces. In particular, we study the local π →π∗ excitation of a pyridine molecule adsorbed at a silver cluster. It is shown that the method works very efficiently even for high-lying excited states. We demonstrate that the assumption of a single, well-defined local excitation is, in general, not justified for extended systems, which can lead to root-switching during optimization. In those cases, the method can give important information about the spectral distribution of the orbital transition employed as a guess.

Parametric excitation and squeezing in a many-body spinor condensate

PubMed Central

Hoang, T. M.; Anquez, M.; Robbins, B. A.; Yang, X. Y.; Land, B. J.; Hamley, C. D.; Chapman, M. S.

2016-01-01

Atomic spins are usually manipulated using radio frequency or microwave fields to excite Rabi oscillations between different spin states. These are single-particle quantum control techniques that perform ideally with individual particles or non-interacting ensembles. In many-body systems, inter-particle interactions are unavoidable; however, interactions can be used to realize new control schemes unique to interacting systems. Here we demonstrate a many-body control scheme to coherently excite and control the quantum spin states of an atomic Bose gas that realizes parametric excitation of many-body collective spin states by time varying the relative strength of the Zeeman and spin-dependent collisional interaction energies at multiples of the natural frequency of the system. Although parametric excitation of a classical system is ineffective from the ground state, we show that in our experiment, parametric excitation from the quantum ground state leads to the generation of quantum squeezed states. PMID:27044675

Theoretical Study of Tautomerization Reactions for the Ground and First Excited Electronic States of Adenine

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.

Parametric excitation and squeezing in a many-body spinor condensate

NASA Astrophysics Data System (ADS)

Hoang, T. M.; Anquez, M.; Robbins, B. A.; Yang, X. Y.; Land, B. J.; Hamley, C. D.; Chapman, M. S.

2016-04-01

Atomic spins are usually manipulated using radio frequency or microwave fields to excite Rabi oscillations between different spin states. These are single-particle quantum control techniques that perform ideally with individual particles or non-interacting ensembles. In many-body systems, inter-particle interactions are unavoidable; however, interactions can be used to realize new control schemes unique to interacting systems. Here we demonstrate a many-body control scheme to coherently excite and control the quantum spin states of an atomic Bose gas that realizes parametric excitation of many-body collective spin states by time varying the relative strength of the Zeeman and spin-dependent collisional interaction energies at multiples of the natural frequency of the system. Although parametric excitation of a classical system is ineffective from the ground state, we show that in our experiment, parametric excitation from the quantum ground state leads to the generation of quantum squeezed states.

Multiconfiguration pair-density functional theory for doublet excitation energies and excited state geometries: the excited states of CN.

PubMed

Bao, Jie J; Gagliardi, Laura; Truhlar, Donald G

2017-11-15

Multiconfiguration pair-density functional theory (MC-PDFT) is a post multiconfiguration self-consistent field (MCSCF) method with similar performance to complete active space second-order perturbation theory (CASPT2) but with greater computational efficiency. Cyano radical (CN) is a molecule whose spectrum is well established from experiments and whose excitation energies have been used as a testing ground for theoretical methods to treat excited states of open-shell systems, which are harder and much less studied than excitation energies of closed-shell singlets. In the present work, we studied the adiabatic excitation energies of CN with MC-PDFT. Then we compared this multireference (MR) method to some single-reference (SR) methods, including time-dependent density functional theory (TDDFT) and completely renormalized equation-of-motion coupled-cluster theory with singles, doubles and noniterative triples [CR-EOM-CCSD(T)]; we also compared to some other MR methods, including configuration interaction singles and doubles (MR-CISD) and multistate CASPT2 (MS-CASPT2). Through a comparison between SR and MR methods, we achieved a better appreciation of the need to use MR methods to accurately describe higher excited states, and we found that among the MR methods, MC-PDFT stands out for its accuracy for the first four states out of the five doublet states studied this paper; this shows its efficiency for calculating doublet excited states.

Optical studies of dynamical processes in disordered materials

NASA Astrophysics Data System (ADS)

Yen, William M.

1990-12-01

The research continues to focus on the study of the structure and the dynamic behavior of insulating solids which can be activated optically. The physical processes which produce relaxation and energy transfer in the optical excited states were of particular interest. The studies were based principally on optical laser spectroscopic techniques which reveal a more detailed view of the materials of interest and which will ultimately lead to the development of more efficient optoelectronic materials.

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases

PubMed Central

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

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases.

PubMed

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.

Enhanced pre-synaptic glutamate release in deep-dorsal horn contributes to calcium channel alpha-2-delta-1 protein-mediated spinal sensitization and behavioral hypersensitivity

PubMed Central

Nguyen, David; Deng, Ping; Matthews, Elizabeth A; Kim, Doo-Sik; Feng, Guoping; Dickenson, Anthony H; Xu, Zao C; Luo, Z David

2009-01-01

Nerve injury-induced expression of the spinal calcium channel alpha-2-delta-1 subunit (Cavα2δ1) has been shown to mediate behavioral hypersensitivity through a yet identified mechanism. We examined if this neuroplasticity modulates behavioral hypersensitivity by regulating spinal glutamatergic neurotransmission in injury-free transgenic mice overexpressing the Cavα2δ1 proteins in neuronal tissues. The transgenic mice exhibited hypersensitivity to mechanical stimulation (allodynia) similar to the spinal nerve ligation injury model. Intrathecally delivered antagonists for N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxyl-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors, but not for the metabotropic glutamate receptors, caused a dose-dependent allodynia reversal in the transgenic mice without changing the behavioral sensitivity in wild-type mice. This suggests that elevated spinal Cavα2δ1 mediates allodynia through a pathway involving activation of selective glutamate receptors. To determine if this is mediated by enhanced spinal neuronal excitability or pre-synaptic glutamate release in deep-dorsal horn, we examined wide-dynamic-range (WDR) neuron excitability with extracellular recording and glutamate-mediated excitatory postsynaptic currents with whole-cell patch recording in deep-dorsal horn of the Cavα2δ1 transgenic mice. Our data indicated that overexpression of Cavα2δ1 in neuronal tissues led to increased frequency, but not amplitude, of miniature excitatory post synaptic currents mediated mainly by AMPA/kainate receptors at physiological membrane potentials, and also by NMDA receptors upon depolarization, without changing the excitability of WDR neurons to high intensity stimulation. Together, these findings support a mechanism of Cavα2δ1-mediated spinal sensitization in which elevated Cavα2δ1 causes increased pre-synaptic glutamate release that leads to reduced excitation thresholds of post-synaptic dorsal horn neurons to innocuous stimuli. This spinal sensitization mechanism may mediate at least partially the neuropathic pain states derived from increased pre-synaptic Cavα2δ1 expression. PMID:19216737

Synthesis, Characterization, Tautomeric Structure and Solvatochromic Behavior of Novel 4-(5-Arylazo-2-Hydroxystyryl)-1-Methylpyridinium Iodide as Potential Molecular Photoprobe

PubMed Central

Altalbawy, Farag; Darwish, Elham; Medhat, Mohamed; El-Zaiat, Sayed; Saleh, Hagar

2016-01-01

A novel series of the title compound 4-(5-arylazo-2-hydroxystyryl)-1-methylpyridinium iodide 6 has been synthesized via condensation reactions of the arylazosalicylaldehyde derivatives 4a–i with 1-methyl-picolinium iodide 5. The structures of the new arylazo compounds were characterized by 1H NMR, IR, mass spectroscopy, as well as spectral and elemental analyses. The electronic absorption spectra of arylazomerocyanine compounds 6 were measured in different buffer solutions and solvents. The pK′s and pK*′s in both the ground and excited states, respectively, were determined for the series and their correlations with the Hammett equation were examined. The results indicated that the title arylazomerocyanine dyes 6 exist in the azo form 6A in both ground and excited states. The substituent and solvent effects (solvatochromism) of the title compound arylazomerocyanine dyes were determined using the Kamlet-Taft equation and subsequently discussed. PMID:28774142

Synthesis, Characterization, Tautomeric Structure and Solvatochromic Behavior of Novel 4-(5-Arylazo-2-Hydroxystyryl)-1-Methylpyridinium Iodide as Potential Molecular Photoprobe.

PubMed

Altalbawy, Farag; Darwish, Elham; Medhat, Mohamed; El-Zaiat, Sayed; Saleh, Hagar

2016-12-19

A novel series of the title compound 4-(5-arylazo-2-hydroxystyryl)-1-methylpyridinium iodide 6 has been synthesized via condensation reactions of the arylazosalicylaldehyde derivatives 4a - i with 1-methyl-picolinium iodide 5 . The structures of the new arylazo compounds were characterized by ¹H NMR, IR, mass spectroscopy, as well as spectral and elemental analyses. The electronic absorption spectra of arylazomerocyanine compounds 6 were measured in different buffer solutions and solvents. The pK's and pK*'s in both the ground and excited states, respectively, were determined for the series and their correlations with the Hammett equation were examined. The results indicated that the title arylazomerocyanine dyes 6 exist in the azo form 6A in both ground and excited states. The substituent and solvent effects (solvatochromism) of the title compound arylazomerocyanine dyes were determined using the Kamlet-Taft equation and subsequently discussed.

Fingerprints of quantum spin ice in Raman scattering

NASA Astrophysics Data System (ADS)

Perkins, Natalia

Quantum spin liquids (QSLs) emerging in frustrated magnetic systems have been a fascinating and challenging subject in modern condensed matter physics for over four decades. In these systems the conventional ordering is suppressed and, instead, unusual behaviors strongly dependent on the topology of the system are observed. The difficulty in the experimental observation of QSLs comes from the fact that unlike the states with broken symmetry, the topological order characteristic of cannot be captured by a local order parameter and thus cannot be detected by local measurements. Identifying QSLs therefore requires reconsideration of experimental probes to find ones sensitive to features characteristic of topological order. The fractionalization of excitations associated with this order can offer signatures that can be probed by conventional methods such as inelastic neutron scattering, Raman or Resonant X-ray scattering experiments. In my talk I will discuss the possibility to use Raman scattering to probe the excitations of Quantum Spin Ice, a model which has long been believed to host a U(1) spin liquid ground state. NSF DMR-1511768.

Hydrogen bond strengthening between o-nitroaniline and formaldehyde in electronic excited states: A theoretical study

NASA Astrophysics Data System (ADS)

Yang, Juan; Li, An Yong

2018-06-01

To study the hydrogen bonds upon photoexcited, the time dependent density function method (TD DFT) was performed to investigate the excited state hydrogen bond properties of between o-nitroaniline (ONA) and formaldehyde (CH2O). The optimized structures of the complex and the monomers both in the ground state and the electronically excited states are calculated using DFT and TD DFT method respectively. Quantum chemical calculations of the electronic and vibrational absorption spectra are also carried out by TD DFT method at the different level. The complex ONA⋯CH2O forms the intramolecular hydrogen bond and intermolecular hydrogen bonds. Since the strength of hydrogen bonds can be measured by studying the vibrational absorption spectra of the characteristic groups on the hydrogen bonding acceptor and donor, it evidently confirms that the hydrogen bonds is strengthened in the S1/S2/T1 excited states upon photoexcitation. As a result, the hydrogen bonds cause that the CH stretch frequency of the proton donor CH2O has a blue shift, and the electron excitations leads to a frequency red shift of Ndbnd O and Nsbnd H stretch modes in the o-nitroaniline(ONA) and a small frequency blue shift of CH stretch mode in the formaldehyde(CH2O) in the S1 and S2 excited states. The excited states S1, S2 and T1 are locally excited states where only the ONA moiety is excited, but the CH2O moiety remains in its ground state.

Influence and adjustment goals: sources of cultural differences in ideal affect.

PubMed

Tsai, Jeanne L; Miao, Felicity F; Seppala, Emma; Fung, Helene H; Yeung, Dannii Y

2007-06-01

Previous studies have found that in American culture high-arousal positive states (HAP) such as excitement are valued more and low-arousal positive states (LAP) such as calm are valued less than they are in Chinese culture. What specific factors account for these differences? The authors predicted that when people and cultures aimed to influence others (i.e., assert personal needs and change others' behaviors to meet those needs), they would value HAP more and LAP less than when they aimed to adjust to others (i.e., suppress personal needs and change their own behaviors to meet others' needs). They test these predictions in 1 survey and 3 experimental studies. The findings suggest that within and across American and Chinese contexts, differences in ideal affect are due to specific interpersonal goals. (c) 2007 APA, all rights reserved.

Turbine blade-tip clearance excitation forces

NASA Technical Reports Server (NTRS)

Martinez-Sanchez, M.; Greitzer, E. M.

1985-01-01

The results of an effort to assess the existing knowledge and plan the required experimentation in the area of turbine blade tip excitation forces is summarized. The work was carried out in three phases. The first was a literature search and evaluation, which served to highlight the state of the art and to expose the need for an articulated theoretical experimental effort to provide not only design data, but also a rational framework for their extrapolation to new configurations and regimes. The second phase was a start in this direction, in which several of the explicit or implicit assumptions contained in the usual formulations of the Alford force effect were removed and a rigorous linearized flow analysis of the behavior of a nonsymmetric actuator disc was carried out. In the third phase a preliminary design of a turbine test facility that would be used to measure both the excitation forces themselves and the flow patterns responsible for them were conducted and do so over a realistic range of dimensionless parameters.

The properties of 4'-N,N-dimethylaminoflavonol in the ground and excited states

NASA Astrophysics Data System (ADS)

Moroz, V. V.; Chalyi, A. G.; Roshal, A. D.

2008-09-01

The mechanism of protonation of 4-N,N-dimethylaminoflavonol and the structure of its protolytic forms in the ground and excited states were studied by electron absorption and fluorescence (steady-state and time-resolved) spectroscopy and with the use of the RM1 quantum-chemical method. A comparison of equilibrium constants and the theoretical enthalpies of formation showed that excitation should be accompanied by the inversion of the basicity of the electron acceptor groups of this compound and, as a consequence, changes in the structure of its monocationic form. An analysis of the spectral parameters of the protolytic 4-N,N-dimethylaminoflavonol forms, however, showed that their structure and the sequence of protonation in the excited state were the same as in the ground state. Changes in the structure of the monocation in the excited state were not observed because of the fast radiationless deactivation of this form and the occurrence of excited state intramolecular proton transfer in aprotic solvents.

Heat of formation determination of the ground and excited state of cyanomethylene (HCCN) radical

NASA Technical Reports Server (NTRS)

Francisco, Joseph S.

1994-01-01

Ab initio electronic structure theory has been used to characterize the structure of the ground triplet and lowest singlet excited states of cyanomethylene. The geometries, vibrational frequencies, and heats of formation have been determined using second-order Moller-Plesset perturbation, single and double excitation configuration interaction, and quadratic configuration interaction theory. The heat of formation is predicted with isodesmic reaction and Gaussian-2 theory (G2) for the ground triplet and first excited singlet states of cyanomethylene. For the ground state Delta-H(sub 0)(sup f,0) is 114.8+/-2 kcal/mol while for the excited single state it is 126.5+/-2 kcal/mol.

Exploring Photoinduced Excited State Evolution in Heterobimetallic Ru(II)-Co(III) Complexes.

PubMed

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.

Laser pulse induced multi-exciton dynamics in molecular systems

NASA Astrophysics Data System (ADS)

Wang, Luxia; May, Volkhard

2018-03-01

Ultrafast optical excitation of an arrangement of identical molecules is analyzed theoretically. The computations are particularly dedicated to molecules where the excitation energy into the second excited singlet state E(S 2) - E(S 0) is larger than twice the excitation energy into the first excited singlet state E(S 1) - E(S 0). Then, exciton-exciton annihilation is diminished and resonant and intensive excitation may simultaneously move different molecules into their first excited singlet state | {S}1> . To describe the temporal evolution of the thus created multi-exciton state a direct computation of the related wave function is circumvented. Instead, we derive equations of motion for expectation values formed by different arrangements of single-molecule transition operators | {S}1> < {S}0| . First simulation results are presented and the approximate treatment suggested recently in 2016 Phys. Rev. B 94 195413 is evaluated.

Stark-assisted population control of coherent CS(2) 4f and 5p Rydberg wave packets studied by femtosecond time-resolved photoelectron spectroscopy.

PubMed

Knappenberger, Kenneth L; Lerch, Eliza-Beth W; Wen, Patrick; Leone, Stephen R

2007-09-28

A two-color (3+1(')) pump-probe scheme is employed to investigate Rydberg wave packet dynamics in carbon disulfide (CS(2) (*)). The state superpositions are created within the 4f and 5p Rydberg manifolds by three photons of the 400 nm pump pulse, and their temporal evolution is monitored with femtosecond time-resolved photoelectron spectroscopy using an 800 nm ionizing probe pulse. The coherent behavior of the non-stationary superpositions are observed through wavepacket revivals upon ionization to either the upper (12) or lower (32) spin-orbit components of CS(2) (+). The results show clearly that the composition of the wavepacket can be efficiently controlled by the power density of the excitation pulse over a range from 500 GWcm(2) to 10 TWcm(2). The results are consistent with the anticipated ac-Stark shift for 400 nm light and demonstrate an effective method for population control in molecular systems. Moreover, it is shown that Rydberg wavepackets can be formed in CS(2) with excitation power densities up to 10 TWcm(2) without significant fragmentation. The exponential 1e population decay (T(1)) of specific excited Rydberg states are recovered by analysis of the coherent part of the signal. The dissociation lifetimes of these states are typically 1.5 ps. However, a region exhibiting a more rapid decay ( approximately 800 fs) is observed for states residing in the energy range of 74 450-74 550 cm(-1), suggestive of an enhanced surface crossing in this region.

Energy and rotation-dependent stereodynamics of reaction

NASA Astrophysics Data System (ADS)

Yong-Qing, Li; Yun-Fan, Yang; Yang, Yu; Yong-Jia, Zhang; Feng-Cai, Ma

2016-02-01

Quasi-classical trajectory calculations are performed to study the stereodynamics of the reaction based on the first excited state NH2(12A‧) potential energy surface reported by Li et al. [Li Y Q and Varandas A J C 2010 J. Phys. Chem. A 114 9644] for the first time. We observe the changes of differential cross-sections at different collision energies and different initial reagent rotational excitations. The influence of collision energy on the k-k‧ distribution can be attributed to a purely impulsive effect. Initial reagent rotational excitation transforms the reaction mechanism from insertion to abstraction. The effect of initial reagent rotational excitations on k-k‧ distribution can be explained by the rotational excitation enlarging the rotational rate of reagent NH in the entrance channel to reduce the probability of collision between incidence H atom and H atom of target molecular. We also investigate the changes of vector correlations and find that the rotational angular momentum vector j‧ of the product H2 is not only aligned, but also oriented along the y axis. The alignment parameter, the disposal of total angular momentum and the reaction mechanism are all analyzed carefully to explain the polarization behavior of the product rotational angular moment. Project supported by the National Natural Science Foundation of China (Grant Nos. 11474141and 11274149), the Program for Liaoning Excellent Talents in University, China (Grant No. LJQ2015040), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, China (Grant No. 2014-1685), and the Special Fund Based Research New Technology of Methanol Conversion and Coal Instead of Oil and the China Postdoctoral Science Foundation (Grant No. 2014M550158).

Direct observation of a photochemical activation energy: a case study of acetone photodissociation

NASA Astrophysics Data System (ADS)

Koch, Markus; Heim, Pascal; Thaler, Bernhard; Kitzler, Markus; Ernst, Wolfgang E.

2017-06-01

The ability to observe and quantify the conversion of electronic potential energy to vibrational kinetic energy in a molecule after photoexcitation is essential to understand and control the outcome of photoinduced molecular fragmentation. We exploit the high selectivity of photoelectron-photoion coincidence detection to distinguish different relaxation channels and observe the fragmentation behavior of each channel. We demonstrate the concept by investigating the fragmentation of gas-phase acetone molecules initiated by three-photon excitation to high lying Rydberg states between 9.0 and 9.5 eV above the ground state. By applying variations of the photon energy, pulse duration (100-200 fs) and pulse energy, we are able to fully characterize the fragmentation process. Rydberg states between 5s and 8s are populated, which undergo ultrafast internal conversion to lower states. The corresponding non-adiabatic dynamics in the neutral molecule cause the conversion of electronic to vibrational energy, leading to fragmentation. Our scheme allows us to directly measure the activation energy for fragmentation of acetone to an acetyl ion and a methyl radical, which we determine to be (0.79 ± 0.04) eV. Longer laser pulses result in an increased fragment-to-parent ratio, representing a higher probability for relaxation because the relaxation time constants are comparable to the pulse duration. Upon excitation to Rydberg states at 9.5 eV we surprisingly observe reduced fragmentation, although ˜2 eV are coupled into vibrational energy, indicating that different relaxation pathways become active, which results in a change of the redistribution of vibrational energy within the molecule. Fragmentation due to subsequent excitation of the cation is found to play a minor role.

Ultrafast Intramolecular Electron and Proton Transfer in Bis(imino)isoindole Derivatives.

PubMed

Driscoll, Eric; Sorenson, Shayne; Dawlaty, Jahan M

2015-06-04

Concerted motion of electrons and protons in the excited state is pertinent to a wide range of chemical phenomena, including those relevant for solar-to-fuel light harvesting. The excited state dynamics of small proton-bearing molecules are expected to serve as models for better understanding such phenomena. In particular, for designing the next generation of multielectron and multiproton redox catalysts, understanding the dynamics of more than one proton in the excited state is important. Toward this goal, we have measured the ultrafast dynamics of intramolecular excited state proton transfer in a recently synthesized dye with two equivalent transferable protons. We have used a visible ultrafast pump to initiate the proton transfer in the excited state, and have probed the transient absorption of the molecule over a wide bandwidth in the visible range. The measurement shows that the signal which is characteristic of proton transfer emerges within ∼710 fs. To identify whether both protons were transferred in the excited state, we have measured the ultrafast dynamics of a related derivative, where only a single proton was available for transfer. The measured proton transfer time in that molecule was ∼427 fs. The observed dynamics in both cases were reasonably fit with single exponentials. Supported by the ultrafast observations, steady-state fluorescence, and preliminary computations of the relaxed excited states, we argue that the doubly protonated derivative most likely transfers only one of its two protons in the excited state. We have performed calculations of the frontier molecular orbitals in the Franck-Condon region. The calculations show that in both derivatives, the excitation is primarily from the HOMO to LUMO causing a large rearrangement of the electronic charge density immediately after photoexcitation. In particular, charge density is shifted away from the phenolic protons and toward the proton acceptor nitrogens. The proton transfer is hypothesized to occur both due to enhanced acidity of the phenolic proton and enhanced basicity of the nitrogen in the excited state. We hope this study can provide insight for better understanding of the general class of excited state concerted electron-proton dynamics.

Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite

PubMed Central

Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

2016-01-01

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 κxy which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2⋅2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that κxy 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 κxy 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

Dynamics of harpooning studied by transition state spectroscopy. II. LiṡṡFH

NASA Astrophysics Data System (ADS)

Hudson, A. J.; Oh, H. B.; Polanyi, J. C.; Piecuch, P.

2000-12-01

The van der Waals complex LiṡṡFH was formed in crossed beams and the transition state of the excited-state reaction, Li*(2p 2P)+HF→LiF+H, was accessed by photoexcitation of this complex. The dynamics of the excited-state reaction were probed by varying the excitation wavelength over the range 570-970 nm while recording the photodepletion of the complex. The findings were interpreted using high-level ab initio calculations of the ground and lowest excited-state potential-energy surfaces.

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

Liu Kun; Zhao Hongmei; Wang Caixia

Bromoiodomethane photodissociation in the low-lying excited states has been characterized using unrestricted Hartree-Fock, configuration-interaction-singles, and complete active space self-consistent field calculations with the SDB-aug-cc-pVTZ, aug-cc-pVTZ, and 3-21g** basis sets. According to the results of the vertical excited energies and oscillator strengths of these low-lying excited states, bond selectivity is predicted. Subsequently, the minimum energy paths of the first excited singlet state and the third excited state for the dissociation reactions were calculated using the complete active space self-consistent field method with 3-21g** basis set. Good agreement is found between the calculations and experimental data. The relationships of excitations, the electronicmore » structures at Franck-Condon points, and bond selectivity are discussed.« less

Two-photon excitation of 2,5-diphenyloxazole using a low power green solid state laser

NASA Astrophysics Data System (ADS)

Luchowski, Rafal

2011-01-01

This Letter concerns two-photon excitation of 2,5-diphenyloxazole (PPO) upon illumination from a pulsed 532 nm solid state laser, with an average power of 30 mW, and a repetition rate of 20 MHz. A very agreeable emission spectrum position and shape has been achieved for PPO receiving one- and two-photon excitation, which suggests that the same excited state is involved for both excitation modes. Also, a perfect quadratic dependence of laser power in the emission intensity function has been recorded. We tested the application of a small solid state green laser to two-photon induced time-resolved fluorescence, revealing the emission anisotropy of PPO to be considerably higher for two-photon than for one-photon excitation.

Nucleon Axial and Electromagnetic Form Factors

NASA Astrophysics Data System (ADS)

Jang, Yong-Chull; Bhattacharya, Tanmoy; Gupta, Rajan; Lin, Huey-Wen; Yoon, Boram

2018-03-01

We present results for the isovector axial, induced pseudoscalar, electric, and magnetic form factors of the nucleon. The calculations were done using 2 + 1 + 1-flavor HISQ ensembles generated by the MILC collaboration with lattice spacings a ≈ 0.12, 0.09, 0.06 fm and pion masses Mπ ≈ 310, 220, 130 MeV. Excited-states contamination is controlled by using four-state fits to two-point correlators and by comparing two-versus three-states in three-point correlators. The Q2 behavior is analyzed using the model independent z-expansion and the dipole ansatz. Final results for the charge radii and magnetic moment are obtained using a simultaneous fit in Mπ, lattice spacing a and finite volume.

The small impact of various partial charge distributions in ground and excited state on the computational Stokes shift of 1-methyl-6-oxyquinolinium betaine in diverse water models

NASA Astrophysics Data System (ADS)

Heid, Esther; Harringer, Sophia; Schröder, Christian

2016-10-01

The influence of the partial charge distribution obtained from quantum mechanics of the solute 1-methyl-6-oxyquinolinium betaine in the ground- and first excited state on the time-dependent Stokes shift is studied via molecular dynamics computer simulation. Furthermore, the effect of the employed solvent model — here the non-polarizable SPC, TIP4P and TIP4P/2005 and the polarizable SWM4 water model — on the solvation dynamics of the system is investigated. The use of different functionals and calculation methods influences the partial charge distribution and the magnitude of the dipole moment of the solute, but not the orientation of the dipole moment. Simulations based on the calculated charge distributions show nearly the same relaxation behavior. Approximating the whole solute molecule by a dipole results in the same relaxation behavior, but lower solvation energies, indicating that the time scale of the Stokes shift does not depend on peculiarities of the solute. However, the SPC and TIP4P water models show too fast dynamics which can be ascribed to a too large diffusion coefficient and too low viscosity. The calculated diffusion coefficient and viscosity for the SWM4 and TIP4P/2005 models coincide well with experimental values and the corresponding relaxation behavior is comparable to experimental values. Furthermore we found that for a quantitative description of the Stokes shift of the applied system at least two solvation shells around the solute have to be taken into account.

Excited states of neutral donor bound excitons in GaN

NASA Astrophysics Data System (ADS)

Callsen, G.; Kure, T.; Wagner, M. R.; Butté, R.; Grandjean, N.

2018-06-01

We investigate the excited states of a neutral donor bound exciton (D0X) in bulk GaN by means of high-resolution, polychromatic photoluminescence excitation (PLE) spectroscopy. The optically most prominent donor in our sample is silicon accompanied by only a minor contribution of oxygen—the key for an unambiguous assignment of excited states. Consequently, we can observe a multitude of Si0X-related excitation channels with linewidths down to 200 μeV. Two groups of excitation channels are identified, belonging either to rotational-vibrational or electronic excited states of the hole in the Si0X complex. Such identification is achieved by modeling the excited states based on the equations of motion for a Kratzer potential, taking into account the particularly large anisotropy of effective hole masses in GaN. Furthermore, several ground- and excited states of the exciton-polaritons and the dominant bound exciton are observed in the photoluminescence (PL) and PLE spectra, facilitating an estimate of the associated complex binding energies. Our data clearly show that great care must be taken if only PL spectra of D0X centers in GaN are analyzed. Every PL feature we observe at higher emission energies with regard to the Si0X ground state corresponds to an excited state. Hence, any unambiguous peak identification renders PLE spectra highly valuable, as important spectral features are obscured in common PL spectra. Here, GaN represents a particular case among the wide-bandgap, wurtzite semiconductors, as comparably low localization energies for common D0X centers are usually paired with large emission linewidths and the prominent optical signature of exciton-polaritons, making the sole analysis of PL spectra a challenging task.

Derivation of the RPA (Random Phase Approximation) Equation of ATDDFT (Adiabatic Time Dependent Density Functional Ground State Response Theory) from an Excited State Variational Approach Based on the Ground State Functional.

PubMed

Ziegler, Tom; Krykunov, Mykhaylo; Autschbach, Jochen

2014-09-09

The random phase approximation (RPA) equation of adiabatic time dependent density functional ground state response theory (ATDDFT) has been used extensively in studies of excited states. It extracts information about excited states from frequency dependent ground state response properties and avoids, thus, in an elegant way, direct Kohn-Sham calculations on excited states in accordance with the status of DFT as a ground state theory. Thus, excitation energies can be found as resonance poles of frequency dependent ground state polarizability from the eigenvalues of the RPA equation. ATDDFT is approximate in that it makes use of a frequency independent energy kernel derived from the ground state functional. It is shown in this study that one can derive the RPA equation of ATDDFT from a purely variational approach in which stationary states above the ground state are located using our constricted variational DFT (CV-DFT) method and the ground state functional. Thus, locating stationary states above the ground state due to one-electron excitations with a ground state functional is completely equivalent to solving the RPA equation of TDDFT employing the same functional. The present study is an extension of a previous work in which we demonstrated the equivalence between ATDDFT and CV-DFT within the Tamm-Dancoff approximation.

Properties of excited states in organic light emitting diodes and lasers

NASA Astrophysics Data System (ADS)

Giebink, Noel C.

The field of organic semiconductors has grown rapidly over the past decade with the development of light emitting diodes, solar cells, and lasers that promise a new generation of low-cost, flexible optoelectronic devices. In each case, the behavior of molecular excited states, or excitons, is of fundamental importance. The present study explores the nature and interactions of such excited states in the attempt to develop an electrically pumped organic semiconductor laser, and to improve the performance and operational stability of organic light emitting diodes. We begin by investigating intrinsic loss processes in optically pumped organic semiconductor lasers and demonstrate that exciton annihilation implies a fundamental limit that will prevent lasing by electrical injection in currently known materials. Searching for an alternative approach to reach threshold leads us to study metastable geminate charge pairs, where we find that optically generated excitons can be accumulated over time in an external electric field via these intermediate states. Upon field turn-off, the excitons are immediately restored, leading to a sudden burst of excitation density over 30 times higher than that generated by the pump alone. Unfortunately, we identify limitations that have thus far prevented reaching laser threshold with this technique. In a parallel push toward high power density, we investigate the origins of quantum efficiency roll-off in organic light emitting diodes (OLEDs) and find that it is dominated by loss of charge balance in the majority of fluorescent and phosphorescent devices. The second major theme of this work involves understanding the intrinsic modes of OLED operational degradation. Based on extensive modeling and supported directly by experimental evidence, we identify exciton-charge carrier annihilation reactions as a principle degradation pathway. Exploiting the diffusion of triplet excitons, we show that fluorescence and phosphorescence can be combined to increase the operational lifetime of white OLEDs and still retain the potential for unity internal quantum efficiency.

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures.

PubMed

Niedzwiedzki, Dariusz; Koscielecki, Jeremy F; Cong, Hong; Sullivan, James O; Gibson, George N; Birge, Robert R; Frank, Harry A

2007-05-31

Many of the spectroscopic features and photophysical properties of carotenoids are explained using a three-state model in which the strong visible absorption of the molecules is associated with an S0 (1(1)Ag-) --> S2 (1(1)Bu+) transition, and the lowest lying singlet state, S1 (2(1)Ag-), is a state into which absorption from the ground state is forbidden by symmetry. However, semiempirical and ab initio quantum calculations have suggested additional excited singlet states may lie either between or in the vicinity of S1 (2(1)Ag-) and S2 (1(1)Bu+), and some ultrafast spectroscopic studies have reported evidence for these states. One such state, denoted S*, has been implicated as an intermediate in the depopulation of S2 (1(1)Bu+) and as a pathway for the formation of carotenoid triplet states in light-harvesting complexes. In this work, we present the results of an ultrafast, time-resolved spectroscopic investigation of a series of open-chain carotenoids derived from photosynthetic bacteria and systematically increasing in their number of pi-electron carbon-carbon double bonds (n). The molecules are neurosporene (n = 9), spheroidene (n = 10), rhodopin glucoside (n = 11), rhodovibrin (n = 12), and spirilloxanthin (n = 13). The molecules were studied in acetone and CS2 solvents at room temperature. These experiments explore the effect of solvent polarity and polarizability on the spectroscopic and kinetic behavior of the molecules. The molecules were also studied in ether/isopentane/ethanol (EPA) glasses at 77 K, in which the spectral resolution is greatly enhanced. Analysis of the data using global fitting techniques has revealed the ultrafast dynamics of the excited states and spectral changes associated with their decay, including spectroscopic features not previously reported. The data are consistent with S* being identified with a twisted conformational structure, the yield of which is increased in molecules having longer pi-electron conjugations. In particular, for the longest molecule in the series, spirilloxanthin, the experiments and a detailed quantum computational analysis reveal the presence of two S* states associated with relaxed S1 (2(1)Ag-) conformations involving nearly planar 6-s-cis and 6-s-trans geometries. We propose that in polar solvents, the ground state of spirilloxanthin takes on a corkscrew conformation that generates a net solute dipole moment while decreasing the cavity formation energy. Upon excitation and relaxation into the S1 (2(1)Ag-) state, the polyene unravels and flattens into a more planar geometry with comparable populations of 6-s-trans and 6-s-cis conformations.

Persistent order due to transiently enhanced nesting in an electronically excited charge density wave

DOE PAGES

Rettig, L.; Cortés, R.; Chu, J. -H.; ...

2016-01-25

Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time-and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of themore » dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. In conclusion, our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order.« less

Time-resolved two-photon spectroscopy of photosystem I determines hidden carotenoid dark-state dynamics.

PubMed

Wehling, Axel; Walla, Peter J

2005-12-29

We present time-resolved fs two-photon pump-probe data measured with photosystem I (PS I) of Thermosynechococcus elongatus. Two-photon excitation (lambda(exc)/2 = 575 nm) in the spectral region of the optically forbidden first excited singlet state of the carotenoids, Car S1, gives rise to a 800 fs and a 9 ps decay component of the Car S1 --> S(n) excited-state absorption with an amplitude of about 47 +/- 16% and 53 +/- 10%, respectively. By measuring a solution of pure beta-carotene under exactly the same conditions, only a 9 ps decay component can be observed. Exciting PS I at exactly the same spectral region via one-photon excitation (lambda(exc) = 575 nm) also does not show any sub-ps component. We ascribe the observed constant of 800 fs to a portion of about 47 +/- 16% beta-carotene states that can potentially transfer their energy efficiently to chlorophyll pigments via the optically dark Car S1 state. We compared these data with conventional one-photon pump-probe data, exciting the optically allowed second excited state, Car S2. This comparison demonstrates that the fast dynamics of the optically forbidden state can hardly be unravelled via conventional one-photon excitation only because the corresponding Car S1 populations are too small after Car S2 --> Car S1 internal conversion. A direct comparison of the amplitudes of the Car S1 --> S(n) excited-state absorption of PS I and beta-carotene observed after Car S2 excitation allows determination of a quantum yield for the Car S1 formation in PS I of 44 +/- 5%. In conclusion, an overall Car S2 --> Chl energy-transfer efficiency of approximately 69 +/- 5% is observed at room temperature with 56 +/- 5% being transferred via Car S2 and probably very hot Car S1 states and 13 +/- 5% being transferred via hot and "cold" Car S1 states.

Timescales of Coherent Dynamics in the Light Harvesting Complex 2 (LH2) of Rhodobacter sphaeroides.

PubMed

Fidler, Andrew F; Singh, Ved P; Long, Phillip D; Dahlberg, Peter D; Engel, Gregory S

2013-05-02

The initial dynamics of energy transfer in the light harvesting complex 2 from Rhodobacter sphaeroides were investigated with polarization controlled two-dimensional spectroscopy. This method allows only the coherent electronic motions to be observed revealing the timescale of dephasing among the excited states. We observe persistent coherence among all states and assign ensemble dephasing rates for the various coherences. A simple model is utilized to connect the spectroscopic transitions to the molecular structure, allowing us to distinguish coherences between the two rings of chromophores and coherences within the rings. We also compare dephasing rates between excited states to dephasing rates between the ground and excited states, revealing that the coherences between excited states dephase on a slower timescale than coherences between the ground and excited states.

Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

NASA Technical Reports Server (NTRS)

Chaban, Galina M.; Salter, Latasha M.; Kwak, Dochan (Technical Monitor)

2002-01-01

Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

The nature of the lower excited state of the special pair of bacterial photosynthetic reaction center of Rhodobacter Sphaeroides and the dynamics of primary charge separation

NASA Astrophysics Data System (ADS)

Ivashin, N. V.; Shchupak, E. E.

2016-08-01

Quantum-chemical calculations of the structure in the ground and lower singlet excited states and the vibrations (in the ground state) of special pair P of photosynthetic reaction center of purple bacteria (RCPb) Rhodobacter Sphaeroides, consisting of two bacteriochlorophyll molecules PA and PB, have been carried out. It is shown that excitation of the special pair is followed by fast relaxation dynamics, accompanied by the transformation of the initial P* state into the P A δ+ P B δ- state (δ ~ 0.5) with charge separation. This behavior is due to the presence of several nonplanar vibrations with participation of the acetyl group of macrocycle PB in the nuclear wave packet on the potential surface of the P* state; these vibrations facilitate destabilization of the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of the macrocycle PA and formation of the P A δ+ P B δ- state. The structural transformations in the P* state are due to its linking character in the contact region of the acetyl group-containing pyrrole rings of PA and PB. The transition from the P* state to specifically the P A δ+ P B δ- state is related to the fact that the acetyl group PA is involved in the intermolecular hydrogen bond with amino acid residue HisL168; for this reason, this group and the pyrrole ring linked with it can hardly participate in structural transformations. The electronic matrix element H12 of the electron transfer from the special pair in the P A δ+ P B δ- state to a molecule of accessory bacteriochlorophyll BA greatly exceeds that for the transfer to BB. This circumstance and the fact that the P A δ+ P B δ- state is energetically more favorable than the P* state facilitate the preferred directionality of the electron transfer in RCPb Rhodobacter Sphaeroides with participation of the cofactors located in its subunit L.

Alignment, vibronic level splitting, and coherent coupling effects on the pump-probe polarization anisotropy.

PubMed

Smith, Eric R; Jonas, David M

2011-04-28

The pump-probe polarization anisotropy is computed for molecules with a nondegenerate ground state, two degenerate or nearly degenerate excited states with perpendicular transition dipoles, and no resonant excited-state absorption. Including finite pulse effects, the initial polarization anisotropy at zero pump-probe delay is predicted to be r(0) = 3/10 with coherent excitation. During pulse overlap, it is shown that the four-wave mixing classification of signal pathways as ground or excited state is not useful for pump-probe signals. Therefore, a reclassification useful for pump-probe experiments is proposed, and the coherent anisotropy is discussed in terms of a more general transition dipole and molecular axis alignment instead of experiment-dependent ground- versus excited-state pathways. Although coherent excitation enhances alignment of the transition dipole, the molecular axes are less aligned than for a single dipole transition, lowering the initial anisotropy. As the splitting between excited states increases beyond the laser bandwidth and absorption line width, the initial anisotropy increases from 3/10 to 4/10. Asymmetric vibrational coordinates that lift the degeneracy control the electronic energy gap and off-diagonal coupling between electronic states. These vibrations dephase coherence and equilibrate the populations of the (nearly) degenerate states, causing the anisotropy to decay (possibly with oscillations) to 1/10. Small amounts of asymmetric inhomogeneity (2 cm(-1)) cause rapid (130 fs) suppression of both vibrational and electronic anisotropy beats on the excited state, but not vibrational beats on the ground electronic state. Recent measurements of conical intersection dynamics in a silicon napthalocyanine revealed anisotropic quantum beats that had to be assigned to asymmetric vibrations on the ground electronic state only [Farrow, D. A.; J. Chem. Phys. 2008, 128, 144510]. Small environmental asymmetries likely explain the observed absence of excited-state asymmetric vibrations in those experiments.

Dispersive charge density wave excitations in Bi2Sr2CaCu2O8+δ

DOE PAGES

Chaix, L.; Ghiringhelli, G.; Peng, Y. Y.; ...

2017-06-12

Experimental evidence on high-Tc cuprates reveals ubiquitous charge density wave (CDW) modulations, which coexist with superconductivity. Although the CDW had been predicted by theory, important questions remain about the extent to which the CDW influences lattice and charge degrees of freedom and its characteristics as functions of doping and temperature. These questions are intimately connected to the origin of the CDW and its relation to the mysterious cuprate pseudogap. Here, we use ultrahigh resolution resonant inelastic x-ray scattering (RIXS) to reveal new CDW character in underdoped Bi2Sr2CaCu2O8+{\\delta} (Bi2212). At low temperature, we observe dispersive excitations from an incommensurate CDW thatmore » induces anomalously enhanced phonon intensity, unseen using other techniques. Near the pseudogap temperature T*, the CDW persists, but the associated excitations significantly weaken and the CDW wavevector shifts, becoming nearly commensurate with a periodicity of four lattice constants. The dispersive CDW excitations, phonon anomaly, and temperature dependent commensuration provide a comprehensive momentum space picture of complex CDW behavior and point to a closer relationship with the pseudogap state.« less

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

Lin, C.T.

Linear and nonlinear photochemistries of 1,4-diazabicyclo(2.2.2)octane (DABCO) are investigated at room temperature by using ArF (193 nm) and KrF (248 nm) lasers. With an unfocused beam geometry, DABCO vapor displays a strong fluorescence when excited at 248 nm, but it shows no detectable emission with 193-nm excitation. The linear photochemistry quantum yield for DABCO is determined as phi/sub p/(248nm) approx. 0.1 and phi/sub p/(193 nm) approx. 0.3. The main stable photochemical products are analyzed as C/sub 2/H/sub 4/ and C/sub 2/H/sub 2/ for 248- and 193-nm excitation, respectively. When focused beam excitation is used, both ArF and KrF lasers dissociatemore » DABCO molecules and give three strong radical emissions of CN*(B vector /sup 2/..sigma.. ..-->.. X vector /sup 2/ ..sigma../sup +/), CH*(A vector /sup 2/..delta.. ..-->.. X vector /sup 2/II), and C/sub 2/*(D vector /sup 3/II/sub g/ ..-->.. a vector /sup 3/II/sub u/). The time behavior, the laser power dependence, and the sample pressure dependence of these emissive radicals are examined. The possible mechanisms for the Rydberg state photochemistry of DABCO are discussed.« less

[Influence of electrical stimulation of "hunger center" of the lateral hypothalamus and food reinforcements on myoelectrical activity of the gastro-esophageal sphincter and stomach in rabbits under the conditions of hunger and satiation].

PubMed

Kromin, A A; Zenina, O Iu

2013-01-01

To study the combined effect of electrostimulation of "hunger center" of the lateral hypothalamus (LH) and food-obtaining behavior arising from it on myoelectrical activity of gastro-esophageal sphincter (GES) and the stomach in pre-fed and subjected to food deprivation animals . MATERIAL AND METHODS. Registration of myoelectrical GES and the stomach activity was carried out under free-behavior conditions in rabbits subjected to food deprivation or pre-fed before the experiment. It was done by means of chronically implanted electrodes during LH electrostimulation in the presence of food. Simultaneously using the web-camera the animals behavior was recorded. LH stimulation was produced by STM-100C stimulator (USA) with implanted bipolar nichrome electrodes. Analysis of temporal parameters of myoelectrical activity of GES and the stomach were carried out by the program AcqKnowledge (USA), and statistical analysis of the data by the program Statistica 6. Significanse of differences between the samples was assessed by the U-Mann-Whitney test (p < 0.05). Electrostimulation of "hunger center" of the lateral hypothalamus in pre-fed rabbits and the rabbits subjected to daily food deprivation, in the presence of food causes resultant food behavior which is accompanied by regular generations of bursts of peak potentials, frequency of which is essentially different in hungry and satiated animals and depends on intensity of artificially induced and artificially reinforced food motivation. In the process of LH stimulation arising resultant food behavior in satiated animals is accompanied by regular generation of high-amplitude slow electrical waves (SEW) by the muscles of lesser curvature (LC), the body and antrum of the stomach (AS) and this is reflected in the structure of temporal organization of slow electrical activity (SEA) in the form of monomodal distributions of SEW periods, typical of satiation state. Despite the increase in food motivation level, due to LH stimulation, additional entry of food into the stomach of satiated rabbits completely eliminates inhibitory effect of starvational motivational excitation on SEA of the muscles of LC, the body and AS. SEA alterations of the stomach muscles in hungry rabbits in the presence of food and thus arising of food-obtaining behavior during LH stimulation have two-phase character. At the initial stage of food behavior in hungry animals during LH stimulation high extent of scaterring of the values of SEW periods generated by the body and AS muscles is preserved, as evidenced by the bimodal distribution of SEW periods characteristic of the state of hunger. In spite of food entry into the stomach at the 1-st phase of LH stimulation, inhibitory effect of artificially reinforced starvational motivational excitation on pacemaker activity of the stomach is retained. At the 2-nd phase of LH electrostimulation food reinforcement eliminates inhibitory effect of food motivational excitation on myoelectrical activity of pacemaker of the stomach that gives maximal rhythm of SEW generation to the body and AS, monomodal distributions of SEW periods indicate to it. lnteraction of artificially induced and artificially reinforced food motivational excitation with afferentation from food reinforcement on neurons of the central generator of deglutition pattern and dorsal vagal complex due to LH electrostimulation and thereby arising resultant food obtaining behavior is specifically reflected in patterns of myoelectrical activity of GES, LC, the body and AS.

Chronic stress induces a selective decrease in AMPA receptor-mediated synaptic excitation at hippocampal temporoammonic-CA1 synapses.

PubMed

Kallarackal, Angy J; Kvarta, Mark D; Cammarata, Erin; Jaberi, Leelah; Cai, Xiang; Bailey, Aileen M; Thompson, Scott M

2013-10-02

Chronic stress promotes depression, but how it disrupts cognition and mood remains unknown. Chronic stress causes atrophy of pyramidal cell dendrites in the hippocampus and cortex in human and animal models, and a depressive-like behavioral state. We now test the hypothesis that excitatory temporoammonic (TA) synapses in the distal dendrites of CA1 pyramidal cells in rats are altered by chronic unpredictable stress (CUS) and restored by chronic antidepressant treatment, in conjunction with the behavioral consequences of CUS. We observed a decrease in AMPAR-mediated excitation at TA-CA1 synapses, but not Schaffer collateral-CA1 synapses, after CUS, with a corresponding layer-specific decrease in GluA1 expression. Both changes were reversed by chronic fluoxetine. CUS also disrupted long-term memory consolidation in the Morris water maze, a function of TA-CA1 synapses. The decreases in TA-CA1 AMPAR-mediated excitation and performance in the consolidation test were correlated positively with decreases in sucrose preference, a measure of anhedonia. We conclude that chronic stress selectively decreases AMPAR number and function at specific synapses and suggest that this underlies various depressive endophenotypes. Our findings provide evidence that glutamatergic dysfunction is an underlying cause of depression and that current first-line antidepressant drugs act by restoring excitatory synaptic strength. Our findings suggest novel therapeutic targets for this debilitating disease.

Sexual motivation is reflected by stimulus-dependent motor cortex excitability.

PubMed

Schecklmann, Martin; Engelhardt, Kristina; Konzok, Julian; Rupprecht, Rainer; Greenlee, Mark W; Mokros, Andreas; Langguth, Berthold; Poeppl, Timm B

2015-08-01

Sexual behavior involves motivational processes. Findings from both animal models and neuroimaging in humans suggest that the recruitment of neural motor networks is an integral part of the sexual response. However, no study so far has directly linked sexual motivation to physiologically measurable changes in cerebral motor systems in humans. Using transcranial magnetic stimulation in hetero- and homosexual men, we here show that sexual motivation modulates cortical excitability. More specifically, our results demonstrate that visual sexual stimuli corresponding with one's sexual orientation, compared with non-corresponding visual sexual stimuli, increase the excitability of the motor cortex. The reflection of sexual motivation in motor cortex excitability provides evidence for motor preparation processes in sexual behavior in humans. Moreover, such interrelationship links theoretical models and previous neuroimaging findings of sexual behavior. © The Author (2015). Published by Oxford University Press. For Permissions, please email: journals.permissions@oup.com.

Population Dynamics of Excited Atoms in Dissipative Cavities

NASA Astrophysics Data System (ADS)

Zou, Hong-Mei; Liu, Yu; Fang, Mao-Fa

2016-10-01

Population dynamics of excited atoms in dissipative cavities is investigated in this work. We present a method of controlling populations of excited atoms in dissipative cavities. For the initial state | e e> A B |00> a b , the repopulation of excited atoms can be obtained by using atom-cavity couplings and non-Markovian effects after the atomic excited energy decays to zero. For the initial state | g g> A B |11> a b , the two atoms can also be populated to the excited states from the initial ground states by using atom-cavity couplings and non-Markovian effects. And the stronger the atom-cavity coupling or the non-Markovian effect is, the larger the number of repopulation of excited atoms is. Particularly, when the atom-cavity coupling or the non-Markovian effect is very strong, the number of repopulation of excited atoms can be close to one in a short time and will tend to a steady value in a long time.

Biexponential photon antibunching: recombination kinetics within the Förster-cycle in DMSO.

PubMed

Vester, Michael; Grueter, Andreas; Finkler, Björn; Becker, Robert; Jung, Gregor

2016-04-21

Time-resolved experiments with pulsed-laser excitation are the standard approach to map the dynamic evolution of excited states, but ground-state kinetics remain hidden or require pump-dump-probe schemes. Here, we exploit the so-called photon antibunching, a purely quantum-optical effect related to single molecule detection to assess the rate constants for a chemical reaction in the electronic ground state. The measurement of the second-order correlation function g((2)), i.e. the evaluation of inter-photon arrival times, is applied to the reprotonation in a Förster-cycle. We find that the antibunching of three different photoacids in the aprotic solvent DMSO significantly differs from the behavior in water. The longer decay constant of the biexponential antibunching tl is linked to the bimolecular reprotonation kinetics of the fully separated ion-pair, independent of the acidic additives. The value of the corresponding bimolecular rate constant, kp = 4 × 10(9) M(-1) s(-1), indicates diffusion-controlled reprotonation. The analysis of tl also allows for the extraction of the separation yield of proton and the conjugated base after excitation and amounts to approximately 15%. The shorter time component ts is connected to the decay of the solvent-separated ion pair. The associated time constant for geminate reprotonation is approximately 3 ± 1 ns in agreement with independent tcspc experiments. These experiments verify that the transfer of quantum-optical experiments to problems in chemistry enables mechanistic conclusions which are hardly accessible by other methods.

Non-equilibrium plasma kinetics of reacting CO: an improved state to state approach

NASA Astrophysics Data System (ADS)

Pietanza, L. D.; Colonna, G.; Capitelli, M.

2017-12-01

Non-equilibrium plasma kinetics of reacting CO for conditions typically met in microwave discharges have been developed based on the coupling of excited state kinetics and the Boltzmann equation for the electron energy distribution function (EEDF). Particular attention is given to the insertion in the vibrational kinetics of a complete set of electron molecule resonant processes linking the whole vibrational ladder of the CO molecule, as well as to the role of Boudouard reaction, i.e. the process of forming CO2 by two vibrationally excited CO molecules, in shaping the vibrational distribution of CO and promoting reaction channels assisted by vibrational excitation (pure vibrational mechanisms, PVM). PVM mechanisms can become competitive with electron impact dissociation processes (DEM) in the activation of CO. A case study reproducing the conditions of a microwave discharge has been considered following the coupled kinetics also in the post discharge conditions. Results include the evolution of EEDF in discharge and post discharge conditions highlighting the role of superelastic vibrational and electronic collisions in shaping the EEDF. Moreover, PVM rate coefficients and DEM ones are studied as a function of gas temperature, showing a non-Arrhenius behavior, i.e. the rate coefficients increase with decreasing gas temperature as a result of a vibrational-vibrational (V-V) pumping up mechanism able to form plateaux in the vibrational distribution function. The accuracy of the results is discussed in particular in connection to the present knowledge of the activation energy of the Boudouard process.

Temperature dependence of resonant secondary emission in NaNO 2: Spectral behavior

NASA Astrophysics Data System (ADS)

Kato, Riso; Kawaguchi, Yoshizo; Ashida, Masaaki

1990-05-01

Spectral behavior of resonant secondary emission in NaNO 2 has been investigated in the temperature range from 2 to 30 K under the excitation near the v00 line of the lowest singlet absorption. With increasing temperature, luminescence lines separated from multiple-order Raman lines become detectable even under the excitation with the off-resonance energy Δ c ≳ 13 cm -1. The intensity of the luminescence line IL( T) increases with temperature in proportion to the phonon number n( hvp, T) in the temperature range T ≲ Δ c/ k, while it increases more steeply in the range T ≳ Δ c/ k. The temperature dependence of IL( T) is ascribed to the increase in the luminescence from the v00 level after the one-phonon assisted transition to the level induced by the off-resonant incident light. The intensity of the Raman line IR( T) decreases gradually in 2-12 K range and shows rapid drop above 12 K. The temperature dependence of IR( T) is ascribed to the dephasing of the intermediate state due to the two-phonon interaction with the reservoir.

Phonon-assisted oscillatory exciton dynamics in monolayer MoSe 2

DOE PAGES

Chow, Colin M.; Yu, Hongyi; Jones, Aaron M.; ...

2017-10-13

In monolayer semiconductor transition metal dichalcogenides, the exciton–phonon interaction strongly affects the photocarrier dynamics. Here, we report on an unusual oscillatory enhancement of the neutral exciton photoluminescence with the excitation laser frequency in monolayer MoSe 2. The frequency of oscillation matches that of the M-point longitudinal acoustic phonon, LA(M), suggesting the significance of zone-edge acoustic phonons and hence the deformation potential in exciton-phonon coupling in MoSe 2. Moreover, oscillatory behavior is observed in the steady-state emission linewidth and in time-resolved PLE data, which reveals variation with excitation energy in the exciton lifetime. These results clearly expose the key role playedmore » by phonons in the exciton formation and relaxation dynamics of two-dimensional van der Waals semiconductors.« less

Quantum Scattering Study of Ro-Vibrational Excitations in N+N(sub 2) Collisions under Re-entry Conditions

NASA Technical Reports Server (NTRS)

Wang, Dunyou; Stallcop, James R.; Dateo, Christopher E.; Schwenke, David W.; Huo, Winifred M.

2004-01-01

A three-dimensional time-dependent quantum dynamics approach using a recently developed ab initio potential energy surface is applied to study ro-vibrational excitation in N+N2 exchange scattering for collision energies in the range 2.1- 3.2 eV. State-to-state integral exchange cross sections are examined to determine the distribution of excited rotational states of N(sub 2). The results demonstrate that highly-excited rotational states are produced by exchange scattering and furthermore, that the maximum value of (Delta)j increases rapidly with increasing collision energies. Integral exchange cross sections and exchange rate constants for excitation to the lower (upsilon = 0-3) vibrational energy levels are presented as a function of the collision energy. Excited-vibrational-state distributions for temperatures at 2,000 K and 10,000 K are included.

Multiple-photon excitation of nitrogen vacancy centers in diamond

NASA Astrophysics Data System (ADS)

Ji, Peng; Balili, R.; Beaumariage, J.; Mukherjee, S.; Snoke, D.; Dutt, M. V. Gurudev

2018-04-01

We report the observation of multiphoton photoluminescence excitation (PLE) below the resonant energies of nitrogen vacancy (NV) centers in diamond. The quadratic and cubic dependence of the integrated fluorescence intensity as a function of excitation power indicates a two-photon excitation pathway for the NV- charge state and a three-photon process involved for the neutral NV0 charge state, respectively. Comparing the total multiphoton energy with its single-photon equivalent, the PLE spectra follows the absorption spectrum of single photon excitation. We also observed that the efficiency of photoluminescence for different charge states, as well as the decay time constant, was dependent on the excitation wavelength and power.

Ultrafast studies of the excited-state dynamics of copper and nickel phthalocyanine tetrasulfonates: potential sensitizers for the two-photon photodynamic therapy of tumors.

PubMed

Fournier, Michel; Pépin, Claude; Houde, Daniel; Ouellet, René; van Lier, Johan E

2004-01-01

In order to evaluate the potential of copper and nickel phthalocyanine tetrasulfonates as sensitizers for two-photon photodynamic therapy, we conducted kinetic femtosecond measurements of transient absorption and bleaching of their excited state dynamics in aqueous solution. Samples were pumped with 620 nm and 310 nm laser light, which allowed us to study relaxation processes from both the first and second singlet (or doublet for the copper phthalocyanine) excited states. A second excitation from the first excited triplet state, approximately 685 and 105 ps after the first excitation for copper and nickel phthalocyanine tetrasulfonate respectively, was the most efficient way to bring the molecules to an upper triplet state. Presumably this highest triplet state can inflict molecular damage on adjacent biomolecules int eh absence of oxygen, resulting in the desired cytotoxic cellular response. Transient absorption spectra at different fixed delays indicate that optimum efficiency would require that the second photon has a wavelength of approximately 750 nm.

Search for isobar-analog states of superheavy hydrogen isotopes5-7He

NASA Astrophysics Data System (ADS)

Chernyshev, B. A.; Gurov, Yu B.; Korotkova, L. Yu; Kuznetsov, D. S.; Lapushkin, S. V.; Tel'kushev, M. V.; Schurenkova, T. D.

2016-02-01

Search for isobar-analog states (IAS) of superheavy hydrogen isotopes 5-7H was performed among the high-excited states of helium isotopes 5-7He. The excited spectra were measured in stopped pion absorption by light nuclei. The experiment was performed at low energy pion channel of LANL with two-arm multilayer semiconductor spectrometer. Excited states of 5-7He were observed in three-body reaction channels on 10,11B nuclei. Several excited levels were observed for the first time. 6He excited state with Ex = 27.0(8) MeV observed in 10B(π-,pt)X channel is an IAS candidate for 6H with Er ∼ 5.5 MeV. 7He excited state with Ex = 24.8(4) MeV observed in 10B(π-,pd)X, nB(π-,pt)X and nB(π-,dd)X channels is an IAS candidate for 7H with Er ∼ 3 MeV.

Study of dynamics of glucose-glucose oxidase-ferricyanide reaction

NASA Astrophysics Data System (ADS)

Nováková, A.; Schreiberová, L.; Schreiber, I.

2011-12-01

This work is focused on dynamics of the glucose-glucose oxidase-ferricyanide enzymatic reaction with or without sodium hydroxide in a continuous-flow stirred tank reactor (CSTR) and in a batch reactor. This reaction exhibits pH-variations having autocatalytic character and is reported to provide nonlinear dynamic behavior (bistability, excitability). The dynamical behavior of the reaction was examined within a wide range of inlet parameters. The main inlet parameters were the ratio of concentrations of sodium hydroxide and ferricyanide and the flow rate. In a batch reactor we observed an autocatalytic drop of pH from slightly basic to medium acidic values. In a CSTR our aim was to find bistability in the presence of sodium hydroxide. However, only a basic steady state was found. In order to reach an acidic steady state, we investigated the system in the absence of sodium hydroxide. Under these conditions the transition from the basic to the acidic steady state was observed when inlet glucose concentration was increased.

Experimental and theoretical studies of the npσ1Σu+ and npπ1 Πu+ (n ⩾ 4,N‧ = 1 -6) states of D2: Energies, natural widths, absorption line intensities, and dynamics

NASA Astrophysics Data System (ADS)

Glass-Maujean, M.; Jungen, Ch.; Vasserot, A. M.; Schmoranzer, H.; Knie, A.; Kübler, S.; Ehresmann, A.; Ubachs, W.

2017-08-01

Over a thousand spectral lines in the photoexcitation spectrum of molecular deuterium (D2) to np1 Σu+ and 1Πu+ Rydberg levels (n ⩾ 4) were measured for rotational levels N‧ = 1 -6 in the 117 000-137 000 cm-1 spectral range by two different types of experiments at two synchrotron radiation sources: a vacuum ultraviolet (VUV) Fourier-transform (FT) spectrometer at SOLEIL, Paris and a 10 m-normal-incidence monochromator (NIM) at BESSY II, Berlin. The experimental energies, the absorption cross sections, Einstein A-coefficients, and line widths are compared with ab initio multi-channel quantum defect (MQDT) calculations for these levels. More than 350 R(0) or P(2) lines were assigned, some 280 R(1) or P(3) lines, some 270 R(2) or P(4) lines, over 100 R(3) or P(5) lines, over 90 R(4) lines, and 24 R(5) lines to extract information on the N‧ = 1 -6 excited levels. Transition energies were determined up to excitation energies of 137 000 cm-1 above the ground state, thereby extending earlier work by various authors and considerably improving the spectral accuracy (< 0.1 cm-1), leading to several reassignments. The absorption and the dissociation, ionization and fluorescence excitation cross sections from the NIM experiment are measured on absolute scale and are used to calibrate intensities in the VUV-FT spectra. The overall agreement between experiment and first principles calculations, without adjustable parameters, is excellent in view of the multi-state interferences treated within the MQDT-framework: For the low N‧ values the averaged deviations between those observed in the FT-SOLEIL spectra and those calculated with MQDT are ∼ 0.1 cm-1 with a spread of ∼ 0.5 cm-1. The line intensities in terms of Einstein coefficients are well represented in the MQDT-framework, as are the level widths representing the lifetimes associated with the sum of the three decay channels. These line intensities follow, in general, the 1 /n3 scaling behavior as characteristic in Rydberg series, but deviations occur and those are explained by MQDT. The decay dynamics of the excited N Rydberg levels is analyzed on the basis of the measured quantum yields for ionization, dissociation and fluorescence observed in the NIM experiment in terms of absolute cross sections for the distinctive channels. In particular in the n = 4 manifolds dissociation is found to play a major role, where in the n = 5 manifolds the behavior is most erratic due to strong competition between decay channels. At n = 6 , ionization takes over as the dominant channel. Despite the excellent agreement between observations and the outcome of the MQDT calculations for both level energies and dynamics, some pronounced deviations are found as in the splitting of the 5 pπ, v = 4 -6, N‧ = 1 levels. The shortcomings of the MQDT calculations are ascribed to the treatment of the excited states in terms of a 1 snp single electron configuration, therewith neglecting possible interferences with 1 snf or 2 s core excited states. Some 27 lines remained unassigned; in view of their observation in fluorescence it is stipulated that these lines probe levels in the nf manifold.

Excited state characteristics of acridine dyes: acriflavine and acridine orange.

PubMed

Sharma, Vijay K; Sahare, P D; Rastogi, Ramesh C; Ghoshal, S K; Mohan, D

2003-06-01

The magnitude of the Stokes shift (frequency shifts in absorption and fluorescence spectra) is observed on changing the solvents and further has been used to calculate experimentally the dipole moments (ground state and excited state) of acriflavine and acridine orange dye molecules. Theoretically, dipole moments are calculated using PM 3 Model. The dipole moments of excited states, for both molecules investigated here, are higher than the corresponding values in the ground states. The increase in the dipole moment has been explained in terms of the nature of the excited state. Acriflavine dye overcomes the non-lasing behaviour of acridine orange due to quaternization of the central nitrogen atom.

Structure Effect of Squarylium Cyanine Dyes on Third-Order Optical Nonlinearities in Ground and Excited States

NASA Astrophysics Data System (ADS)

Liu, Xu-chun; Xu, Gang; Si, Jin-hai; Ye, Pei-xian; Lin, Tong; Peng, Bi-xian

1999-08-01

A series of squarylium cyanine dyes with different substituents were synthesized and the third-order optical nonlinearities of their ground and excited states were investigated by backward degenerate four-wave-mixing. For the ground state, the molecular hyperpolarizability γg increases with the red-shift of the absorption peak λmaxab of the squaraine with different substituents, whereas for the excited-state molecular hyperpolarizability γe, the nonlinear enhancement γe/γg decreases, which may indicate that in the excited state the electron accepting-donating ability of different substituents changes in the reverse order compared with the order in the ground state.

Monte Carlo wave-packet approach to trace nuclear dynamics in molecular excited states by XUV-pump-IR-probe spectroscopy

NASA Astrophysics Data System (ADS)

Jing, Qingli; Bello, Roger Y.; Martín, Fernando; Palacios, Alicia; Madsen, Lars Bojer

2018-04-01

Recent research interests have been raised in uncovering and controlling ultrafast dynamics in excited neutral molecules. In this work we generalize the Monte Carlo wave packet (MCWP) approach to XUV-pump-IR-probe schemes to simulate the process of dissociative double ionization of H2 where singly excited states in H2 are involved. The XUV pulse is chosen to resonantly excite the initial ground state of H2 to the lowest excited electronic state of 1Σu + symmetry in H2 within the Franck-Condon region. The delayed intense IR pulse couples the excited states of 1Σu + symmetry with the nearby excited states of 1Σg + symmetry. It also induces the first ionization from H2 to H2 + and the second ionization from H2 + to H++H+. To reduce the computational costs in the MCWP approach, a sampling method is proposed to determine in time the dominant ionization events from H2 to H2+. By conducting a trajectory analysis, which is a unique possibility within the MCWP approach, the origins of the characteristic features in the nuclear kinetic energy release spectra are identified for delays ranging from 0 to 140 fs and the nuclear dynamics in the singly excited states in H2 is mapped out.

A theoretical study of bond selective photochemistry in CH2BrI

NASA Astrophysics Data System (ADS)

Liu, Kun; Zhao, Hongmei; Wang, Caixia; Zhang, Aihua; Ma, Siyu; Li, Zonghe

2005-01-01

Bromoiodomethane photodissociation in the low-lying excited states has been characterized using unrestricted Hartree-Fock, configuration-interaction-singles, and complete active space self-consistent field calculations with the SDB-aug-cc-pVTZ, aug-cc-pVTZ, and 3-21g** basis sets. According to the results of the vertical excited energies and oscillator strengths of these low-lying excited states, bond selectivity is predicted. Subsequently, the minimum energy paths of the first excited singlet state and the third excited state for the dissociation reactions were calculated using the complete active space self-consistent field method with 3-21g** basis set. Good agreement is found between the calculations and experimental data. The relationships of excitations, the electronic structures at Franck-Condon points, and bond selectivity are discussed.

Spin-isospin excitations from the ground-state of 64Ni

NASA Astrophysics Data System (ADS)

Popescu, L.; Adachi, T.; Bäumer, C.; Berg, G. P. A.; van den Berg, A. M.; von Brentano, P.; Frekers, D.; de Frenne, D.; Fujita, K.; Fujita, Y.; Grewe, E. W.; Haefner, P.; Hatanaka, K.; Hunyadi, M.; de Huu, M.; Jacobs, E.; Johansson, H.; Korff, A.; Negret, A.; Nakanishi, K.; von Neumann-Cosel, P.; Rakers, S.; Ryezayeva, N.; Sakemi, Y.; Shevchenko, A.; Shimbara, Y.; Shimizu, Y.; Simon, H.; Tameshige, Y.; Tamii, A.; Uchida, M.; Wörtche, H. J.; Yosoi, M.

2006-03-01

Spin-isospin (Gamow-Teller) excitations in 64Cu and 64Co have been studied using (3He,t) and (d,2He) charge-exchange reactions on 64Ni. As the isospin of the 64Ni ground-state is T0=4, states with T=3, 4 and 5 in 64Cu are excited via the (3He,t) reaction and states with T=5 in 64Co via (d,2He). If we assume that the nuclear interaction is charge symmetric, the T=5 states in 64Cu should appear at corresponding excitation energies (if corrected for the Coulomb displacement) and with similar strengths as the T=5 states in 64Co. As in the 64Cu spectrum the T=5 states are very weakly excited, only by combining the results of the two complementary experiments one can estimate the Gamow-Teller strength starting from 64Ni in a consistent way.

Spin-isospin excitations from the ground-state of 64Ni

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

Popescu, L.; Frenne, D. de; Jacobs, E.

2006-03-13

Spin-isospin (Gamow-Teller) excitations in 64Cu and 64Co have been studied using (3He,t) and (d,2He) charge-exchange reactions on 64Ni. As the isospin of the 64Ni ground-state is T0=4, states with T=3, 4 and 5 in 64Cu are excited via the (3He,t) reaction and states with T=5 in 64Co via (d,2He). If we assume that the nuclear interaction is charge symmetric, the T=5 states in 64Cu should appear at corresponding excitation energies (if corrected for the Coulomb displacement) and with similar strengths as the T=5 states in 64Co. As in the 64Cu spectrum the T=5 states are very weakly excited, only bymore » combining the results of the two complementary experiments one can estimate the Gamow-Teller strength starting from 64Ni in a consistent way.« less

Influence of solvent and substituent on excited state characteristics of laser grade coumarin dyes.

PubMed

Sharma, Vijay K; Saharo, P D; Sharma, Neera; Rastogi, Ramesh C; Ghoshal, S K; Mohan, D

2003-04-01

Absorption and fluorescence emission of 4 and 7 substituted coumarins viz. C 440, C 490, C 485 and C 311 have been studied in various polar and non-polar organic solvents. These coumarin dyes are substituted with alkyl, amine and fluorine groups at 4- and 7-positions. They give different absorption and emission spectra in different solvents. The study leads to a possible assignment of energy level scheme for such coumarins including the effect on ground state and excited state dipole moments due to substitutions. Excited state dipole moments of these dyes are calculated by solvetochromic data experimentally and theoretically these are calculated by PM 3 method. The dipole moments in excited state, for all molecules investigated here, are higher than the corresponding values in the ground state. The increase in dipole moment has been explained in terms of the nature of excited state and resonance structure.

Slippery Wave Functions

NASA Astrophysics Data System (ADS)

Kadanoff, Leo P.

2013-09-01

Superfluids and superconductors show a very surprising behavior at low temperatures. As their temperature is reduced, materials of both kinds can abruptly fall into a state in which they will support a persistent, essentially immortal, flow of particles. Unlike anything in classical physics, these flows produce neither friction nor resistance. A major accomplishment of Twentieth Century physics was the development of an understanding of this very surprising behavior via the construction of partially microscopic and partially macroscopic quantum theories of superfluid helium and superconducting metals. Such theories come in two parts: a theory of the motion of particle-like excitations, called quasiparticles, and of the persistent flows itself via a huge coherent excitation, called a condensate. Two people, above all others, were responsible for the construction of the quasiparticle side of the theories of these very special low-temperature behaviors: Lev Landau and John Bardeen. Curiously enough they both partially ignored and partially downplayed the importance of the condensate. In both cases, this neglect of the actual superfluid or superconducting flow interfered with their ability to understand the implications of the theory they had created. They then had difficulty assessing the important advances that occurred immediately after their own great work. Some speculations are offered about the source of this unevenness in the judgments of these two leading scientists.

Multimode optical fibers: steady state mode exciter.

PubMed

Ikeda, M; Sugimura, A; Ikegami, T

1976-09-01

The steady state mode power distribution of the multimode graded index fiber was measured. A simple and effective steady state mode exciter was fabricated by an etching technique. Its insertion loss was 0.5 dB for an injection laser. Deviation in transmission characteristics of multimode graded index fibers can be avoided by using the steady state mode exciter.

Controlling the charge transfer in phenylene-bridged borylene-amine pi-conjugated systems.

PubMed

Proń, Agnieszka; Zhou, Gang; Norouzi-Arasi, Hassan; Baumgarten, Martin; Müllen, Klaus

2009-08-20

Novel boron-nitrogen-containing pi-conjugated compounds 3,3'- and 4,4'-((2,4,6-triisopropylphenyl)borylene)bis(N,N-diarylbenzenamine) (1-2), m- and p-phenylene bridged to the boron center, respectively, have been synthesized and characterized. Optical studies by means of UV-vis absorption and emission measurements as well as DFT calculations reveal a different charge transfer behavior between the para series and the meta series at ground and excited states.

Experimental studies of tuned particle damper: Design and characterization

NASA Astrophysics Data System (ADS)

Zhang, Kai; Xi, Yanhui; Chen, Tianning; Ma, Zhihao

2018-01-01

To better suppress the structural vibration in the micro vibration and harsh environment, a new type of damper, tuned particle damper (TPD), was designed by combining the advantage of classical dynamic vibration absorber (DVA) and particle damper (PD). An equivalent theoretical model was established to describe the dynamic behavior of a cantilever system treated with TPD. By means of a series of sine sweep tests, the dynamic characteristic of TPD under different excitation intensity was explored and the damping performance of TPD was investigated by comparing with classical DVA and PD with the same mass ratio. Experimental results show that with the increasing of excitation intensity TPD shows two different dynamic characteristics successively, i.e., PD-like and DVA-like. TPD shows a wider suppression frequency band than classical DVA and better practicability than PD in the micro vibration environment. Moreover, to characterize the dynamic characteristic of TPD, a simple evaluation of the equivalent dynamic mass and equivalent dynamic damping of the cantilever system treated with TPD was performed by fitting the experimental data to the presented theoretical model. Finally, based on the rheology behaviors of damping particles reported by the previous research results, an approximate phase diagram which shows the motion states of damping particles in TPD was employed to analyze the dynamic characteristic of TPD and several motion states of damping particles in TPD were presented via a high-speed camera.

Deformed photon-added entangled squeezed vacuum and one-photon states: Entanglement, polarization, and nonclassical properties

NASA Astrophysics Data System (ADS)

A, Karimi; M, K. Tavassoly

2016-04-01

In this paper, after a brief review on the entangled squeezed states, we produce a new class of the continuous-variable-type entangled states, namely, deformed photon-added entangled squeezed states. These states are obtained via the iterated action of the f-deformed creation operator A = f (n)a † on the entangled squeezed states. In the continuation, by studying the criteria such as the degree of entanglement, quantum polarization as well as sub-Poissonian photon statistics, the two-mode correlation function, one-mode and two-mode squeezing, we investigate the nonclassical behaviors of the introduced states in detail by choosing a particular f-deformation function. It is revealed that the above-mentioned physical properties can be affected and so may be tuned by justifying the excitation number, after choosing a nonlinearity function. Finally, to generate the introduced states, we propose a theoretical scheme using the nonlinear Jaynes-Cummings model.

Nonadiabatic nuclear dynamics of the ammonia cation studied by surface hopping classical trajectory calculations

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

Belyaev, Andrey K., E-mail: belyaev@herzen.spb.ru; Domcke, Wolfgang, E-mail: wolfgang.domcke@ch.tum.de; Lasser, Caroline, E-mail: classer@ma.tum.de

The Landau–Zener (LZ) type classical-trajectory surface-hopping algorithm is applied to the nonadiabatic nuclear dynamics of the ammonia cation after photoionization of the ground-state neutral molecule to the excited states of the cation. The algorithm employs a recently proposed formula for nonadiabatic LZ transition probabilities derived from the adiabatic potential energy surfaces. The evolution of the populations of the ground state and the two lowest excited adiabatic states is calculated up to 200 fs. The results agree well with quantum simulations available for the first 100 fs based on the same potential energy surfaces. Three different time scales are detected formore » the nuclear dynamics: Ultrafast Jahn–Teller dynamics between the excited states on a 5 fs time scale; fast transitions between the excited state and the ground state within a time scale of 20 fs; and relatively slow partial conversion of a first-excited-state population to the ground state within a time scale of 100 fs. Beyond 100 fs, the adiabatic electronic populations are nearly constant due to a dynamic equilibrium between the three states. The ultrafast nonradiative decay of the excited-state populations provides a qualitative explanation of the experimental evidence that the ammonia cation is nonfluorescent.« less

Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes

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

Westlake, Brittany C.; Brennaman, Kyle M.; Concepcion, Javier J.

2011-05-24

The simultaneous, concerted transfer of electrons and protons—electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectralmore » measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H⁺ is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated ⁺H–B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.« less

Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes.

PubMed

Westlake, Brittany C; Brennaman, M Kyle; Concepcion, Javier J; Paul, Jared J; Bettis, Stephanie E; Hampton, Shaun D; Miller, Stephen A; Lebedeva, Natalia V; Forbes, Malcolm D E; Moran, Andrew M; Meyer, Thomas J; Papanikolas, John M

2011-05-24

The simultaneous, concerted transfer of electrons and protons--electron-proton transfer (EPT)--is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H(+) is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck-Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated (+)H ─ B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.

Comparison of Nerve Excitability Testing, Nerve Conduction Velocity, and Behavioral Observations for Acrylamide Induced Peripheral Neuropathy

EPA Science Inventory

Nerve excitability (NE) testing is a sensitive method to test for peripheral neurotoxicity in humans,and may be more sensitive than compound nerve action potential (CNAP) or nerve conduction velocity (NCV).We used acrylamide to compare the NE and CNAP/NCV methods. Behavioral test...

Ketogenic diet restores aberrant cortical motor maps and excitation-to-inhibition imbalance in the BTBR mouse model of autism spectrum disorder.

PubMed

Smith, Jacklyn; Rho, Jong M; Teskey, G Campbell

2016-05-01

Autism spectrum disorder (ASD) is an increasingly prevalent neurodevelopmental disorder characterized by deficits in sociability and communication, and restricted and/or repetitive motor behaviors. Amongst the diverse hypotheses regarding the pathophysiology of ASD, one possibility is that there is increased neuronal excitation, leading to alterations in sensory processing, functional integration and behavior. Meanwhile, the high-fat, low-carbohydrate ketogenic diet (KD), traditionally used in the treatment of medically intractable epilepsy, has already been shown to reduce autistic behaviors in both humans and in rodent models of ASD. While the mechanisms underlying these effects remain unclear, we hypothesized that this dietary approach might shift the balance of excitation and inhibition towards more normal levels of inhibition. Using high-resolution intracortical microstimulation, we investigated basal sensorimotor excitation/inhibition in the BTBR T+Itpr(tf)/J (BTBR) mouse model of ASD and tested whether the KD restores the balance of excitation/inhibition. We found that BTBR mice had lower movement thresholds and larger motor maps indicative of higher excitation/inhibition compared to C57BL/6J (B6) controls, and that the KD reversed both these abnormalities. Collectively, our results afford a greater understanding of cortical excitation/inhibition balance in ASD and may help expedite the development of therapeutic approaches aimed at improving functional outcomes in this disorder. Copyright © 2016 Elsevier B.V. All rights reserved.

Ground and excited states of CaSH through electron propagator calculations

NASA Astrophysics Data System (ADS)

Ortiz, J. V.

1990-05-01

Electron propagator calculations of electron affinities of CaSH + produce ground and excited state energies at the optimized, C s minimum of the neutral ground state and at a C ∞v geometry. Feynman-Dyson amplitudes (FDAs) describe the distribution of the least bound electron in various states. The neutral ground state differs from the cation by the occupation of a one-electron state dominated by Ca s functions. Described by FDAs with Ca-S π pseudosymmetry, corresponding excited states have unpaired electrons in orbitals displaying interference between Ca p and d functions. Above these lies a σ pseudosymmetry FDA with principal contributions from Ca d functions. Two FDAs with σ pseudosymmetry follow. Higher excited states exhibit considerable delocalization onto S.

A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems

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

Liu, Wenlan; Köhn, Andreas; InnovationLab GmbH, Speyerer St. 4, D-69115 Heidelberg

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 targetmore » 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.« less

Electron Impact Cross Sections for Molecular Lasers

DTIC Science & Technology

1984-04-27

range coumunication and surveillance, isotope separation, and controlled thermonuclear fussion . Among all kinds of lasers, the gaseous discharge...shape resonance of n symmetry (reviewed by Schulz, 1976). Like vibrational excitation from the ground state, such process from nuclear -excited states as...energy range specifically in the 1-4 eV resonant region. 4 - A. Vibrational Excitation of Nuclear -Excited N2 For vibrational excitation by

Search for excited states in 25O

NASA Astrophysics Data System (ADS)

Jones, M. D.; Fossez, K.; Baumann, T.; DeYoung, P. A.; Finck, J. E.; Frank, N.; Kuchera, A. N.; Michel, N.; Nazarewicz, W.; Rotureau, J.; Smith, J. K.; Stephenson, S. L.; Stiefel, K.; Thoennessen, M.; Zegers, R. G. T.

2017-11-01

Background: Theoretical calculations suggest the presence of low-lying excited states in 25O. Previous experimental searches by means of proton knockout on 26F produced no evidence for such excitations. Purpose: We search for excited states in 25O using the 24O(d ,p ) 25O reaction. The theoretical analysis of excited states in unbound O,2725 is based on the configuration interaction approach that accounts for couplings to the scattering continuum. Method: We use invariant-mass spectroscopy to measure neutron-unbound states in 25O. For the theoretical approach, we use the complex-energy Gamow Shell Model and Density Matrix Renormalization Group method with a finite-range two-body interaction optimized to the bound states and resonances of O-2623, assuming a core of 22O. We predict energies, decay widths, and asymptotic normalization coefficients. Results: Our calculations in a large s p d f space predict several low-lying excited states in 25O of positive and negative parity, and we obtain an experimental limit on the relative cross section of a possible Jπ=1/2 + state with respect to the ground state of 25O at σ1 /2 +/σg .s .=0 .25-0.25+1.0 . We also discuss how the observation of negative parity states in 25O could guide the search for the low-lying negative parity states in 27O. Conclusion: Previous experiments based on the proton knockout of 26F suffered from the low cross sections for the population of excited states in 25O because of low spectroscopic factors. In this respect, neutron transfer reactions carry more promise.

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

NASA Astrophysics Data System (ADS)

Mebel, Alexander M.; Lin, Sheng-Hsien

1997-03-01

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

Single crystal EPR study at 95 GHz of a large Fe based molecular nanomagnet: toward the structuring of magnetic nanoparticle properties.

PubMed

Castelli, L; Fittipaldi, M; Powell, A K; Gatteschi, D; Sorace, L

2011-08-28

A W-band single-crystal EPR study has been performed on a molecular cluster comprising 19 iron(III) ions bridged by oxo- hydroxide ions, Fe(19), in order to investigate magnetic nanosystems with a behavior in between the one of Magnetic NanoParticles (MNP) and that of Single Molecule Magnets (SMM). The Fe(19) has a disk-like shape: a planar Fe(7) core with a brucite (Mg(OH)(2)) structure enclosed in a "shell" of 12 Fe(III) ions. EPR and magnetic measurements revealed an S = 35/2 ground state with an S = 33/2 excited state lying ∼ 8 K above. The presence of other low-lying excited states was also envisaged. Rhombic Zero Field Splitting (ZFS) tensors were determined, the easy axes lying in the Fe(19) plane for both the multiplets. At particular temperatures and orientations, a partially resolved fine structure could be observed which could not be distinguished in powder spectra, due to orientation disorder. The similarities of the EPR behavior of Fe(19) and MNP, together with the accuracy of single crystal analysis, helped to shed light on spectral features observed in MNP spectra, that is a sharp line at g = 2 and a low intensity transition at g = 4. Moreover, a theoretical analysis has been used to estimate the contribution to the total magnetic anisotropy of core and surface; this latter is crucial in determining the easy axis-type anisotropy, alike that of MNP surface. This journal is © The Royal Society of Chemistry 2011

Electron Excitation Rate Coefficients for Transitions from the IS21S Ground State to the 1S2S1,3S and 1S2P1,3P0 Excited States of Helium

NASA Astrophysics Data System (ADS)

Aggarwal, K. M.; Kingston, A. E.; McDowell, M. R. C.

1984-03-01

The available experimental and theoretical electron impact excitation cross section data for the transitions from the 1s2 1S ground state to the 1s2s 1,3S and 1s2p 1,3P0 excited states of helium are assessed. Based on this assessed data, excitation rate coefficients are calculated over a wide electron temperature range below 3.0×106K. A comparison with other published results suggests that the rates used should be lower by a factor of 2 or more.

Excitation of vacuum ultraviolet spectra of krypton in a cooled gas discharge

NASA Astrophysics Data System (ADS)

Gerasimov, Gennadii N.; Krylov, Boris E.; Hallin, Reinhold

1995-08-01

Results are presented on the experimental study of VUV spectra of krypton excited by a dc discharge in a capillary tube with the wall cooled to the temperature of liquid nitrogen. We studied the 120-200 nm spectral region corresponding to the transitions between the dimer lowest excited states and the weakly bound ground state, 1u, 0u+ yields 0g+. Electron impact, transferring dimers from the ground state into the excited state, is shown to be an efficient excitation mechanism in the 50-650 Torr and the 10-50 mA pressure and current ranges. The spectra obtained and the calculations made corroborate the high rate of this process.

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.

Chaos in nuclei: Theory and experiment

NASA Astrophysics Data System (ADS)

Muñoz, L.; Molina, R. A.; Gómez, J. M. G.

2018-05-01

During the last three decades the quest for chaos in nuclei has been quite intensive, both with theoretical calculations using nuclear models and with detailed analyses of experimental data. In this paper we outline the concept and characteristics of quantum chaos in two different approaches, the random matrix theory fluctuations and the time series fluctuations. Then we discuss the theoretical and experimental evidence of chaos in nuclei. Theoretical calculations, especially shell-model calculations, have shown a strongly chaotic behavior of bound states in regions of high level density. The analysis of experimental data has shown a strongly chaotic behavior of nuclear resonances just above the one-nucleon emission threshold. For bound states, combining experimental data of a large number of nuclei, a tendency towards chaotic motion is observed in spherical nuclei, while deformed nuclei exhibit a more regular behavior associated to the collective motion. On the other hand, it had never been possible to observe chaos in the experimental bound energy levels of any single nucleus. However, the complete experimental spectrum of the first 151 states up to excitation energies of 6.20 MeV in the 208Pb nucleus have been recently identified and the analysis of its spectral fluctuations clearly shows the existence of chaotic motion.

Excited level populations and excitation kinetics of nonequilibrium ionizing argon discharge plasma of atmospheric pressure

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

Akatsuka, Hiroshi

2009-04-15

Population densities of excited states of argon atoms are theoretically examined for ionizing argon plasma in a state of nonequilibrium under atmospheric pressure from the viewpoint of elementary processes with collisional radiative model. The dependence of excited state populations on the electron and gas temperatures is discussed. Two electron density regimes are found, which are distinguished by the population and depopulation mechanisms for the excited states in problem. When the electron impact excitation frequency for the population or depopulation is lower than the atomic impact one, the electron density of the plasma is considered as low to estimate the populationmore » and depopulation processes. Some remarkable characteristics of population and depopulation mechanisms are found for the low electron density atmospheric plasma, where thermal relaxation by atomic collisions becomes the predominant process within the group of close-energy states in the ionizing plasma of atmospheric pressure, and the excitation temperature is almost the same as the gas temperature. In addition to the collisional relaxation by argon atoms, electron impact excitation from the ground state is also an essential population mechanism. The ratios of population density of the levels pairs, between which exists a large energy gap, include information on the electron collisional kinetics. For high electron density, the effect of atomic collisional relaxation becomes weak. For this case, the excitation mechanism is explained as electron impact ladderlike excitation similar to low-pressure ionizing plasma, since the electron collision becomes the dominant process for the population and depopulation kinetics.« less

THE PHOTOTOXOICITY OF POLYCYCLIC AROMATIC HYDROCARBONS: A THEORETICAL STUDY OF EXCITED STATES AND CORRELATION TO EXPERIMENT

EPA Science Inventory

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...

Coulomb displacement energies of excited states

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

Sherr, R.; Bertsch, G.

The Bansal--French--Zamick model is quite successful in accounting for the Coulomb displacement energies of excited particle--hole states in a variety of light nuclei. Level shifts are typically reproduced to within 50 keV. However, the model fails for certain excited 0$sup +$ states, and this remains a puzzle. (AIP)

Near-Edge X-ray Absorption Fine Structure within Multilevel Coupled Cluster Theory.

PubMed

Myhre, Rolf H; Coriani, Sonia; Koch, Henrik

2016-06-14

Core excited states are challenging to calculate, mainly because they are embedded in a manifold of high-energy valence-excited states. However, their locality makes their determination ideal for local correlation methods. In this paper, we demonstrate the performance of multilevel coupled cluster theory in computing core spectra both within the core-valence separated and the asymmetric Lanczos implementations of coupled cluster linear response theory. We also propose a visualization tool to analyze the excitations using the difference between the ground-state and excited-state electron densities.

The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C{sub 60} molecular triad

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

Olguin, Marco; Basurto, Luis; Zope, Rajendra R.

We present a detailed study of charge transfer (CT) excited states for a large number of configurations in a light-harvesting Carotenoid-diaryl-Porphyrin-C{sub 60} (CPC{sub 60}) molecular triad. The chain-like molecular triad undergoes photoinduced charge transfer process exhibiting a large excited state dipole moment, making it suitable for application to molecular-scale opto-electronic devices. An important consideration is that the structural flexibility of the CPC{sub 60} triad impacts its dynamics in solvents. Since experimentally measured dipole moments for the triad of ∼110 D and ∼160 D strongly indicate a range in structural variability in the excited state, studying the effect of structural changesmore » on the CT excited state energetics furthers the understanding of its charge transfer states. We have calculated the variation in the lowest CT excited state energies by performing a scan of possible variation in the structure of the triad. Some of these configurations were generated by incrementally scanning a 360° torsional (dihedral) twist at the C{sub 60}-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five different CPC{sub 60} conformations were studied to determine the effect of pi-conjugation and particle-hole Coulombic attraction on the CT excitation energies. Our calculations show that configurational changes in the triad induces a variation of ∼0.6 eV in CT excited state energies in the gas-phase. The corresponding calculated excited state dipoles show a range of 47 D–188 D. The absorption spectra and density of states of these structures show little variation except for the structures where the porphyrin and aryl conjugation is changed.« less

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

Nishitani, Junichi, E-mail: jnishitani@issp.u-tokyo.ac.jp; Lippmaa, Mikk; Suemoto, Tohru

The dynamics of photoexcited electrons in various excited d-states was investigated in a transition metal oxide MnO by tunable optical pump-terahertz probe measurements. Photoexcited electrons in the lowest excited d-state showed the longest relaxation time among the three excited d-states that are accessible in MnO at room temperature. The relaxation rate in the lowest excited d-state showed a drastic increase below the Neel temperature T{sub N} = 120 K in MnO. We conclude that this increase is caused by the appearance of a decay channel related to magnetic-excitation-assisted photoluminescence from self-trapped exciton (STE) states. The opening of relaxation channels to the STE statesmore » in an antiferromagnetic phase suggests that it may be possible to control photocarrier lifetime by magnetic order in transition metal oxides.« less

Dynamic study of excited state hydrogen-bonded complexes of harmane in cyclohexane-toluene mixtures.

PubMed

Carmona, Carmen; Balón, Manuel; Galán, Manuel; Guardado, Pilar; Muñoz, María A

2002-09-01

Photoinduced proton transfer reactions of harmane or 1-methyl-9H-pyrido[3,4-b]indole (HN) in the presence of the proton donor hexafluoroisopropanol (HFIP) in cyclohexane-toluene mixtures (CY-TL; 10% vol/vol of TL) have been studied. Three excited state species have been identified: a 1:2 hydrogen-bonded proton transfer complex (PTC), between the pyridinic nitrogen of the substrate and the proton donor, a hydrogen-bonded cation-like exciplex (CL*) with a stoichiometry of at least 1:3 and a zwitterionic exciplex (Z*). Time-resolved fluorescence measurements evidence that upon excitation of ground state PTC, an excited state equilibrium is established between PTC* and the cationlike exciplex, CL*, lambdaem approximately/= 390 nm. This excited state reaction is assisted by another proton donor molecule. Further reaction of CL* with an additional HFIP molecule produces the zwitterionic species, Z*, lambda(em) approximately/= 500 nm. From the analysis of the multiexponential decays, measured at different emission wavelengths and as a function of HFIP concentration, the mechanism of these excited state reactions has been established. Thus, three rate constants and three reciprocal lifetimes have been determined. The simultaneous study of 1,9-dimethyl-9H-pyrido[3,4-b]indole (MHN) under the same experimental conditions has helped to understand the excited state kinetics of these processes.

Hysteresis and change of transition temperature in thin films of Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2}, a new sublimable spin-crossover molecule

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

Davesne, V.; Gruber, M.; Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe

2015-05-21

Thin films of the spin-crossover (SCO) molecule Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2} (Fe-pyrz) were sublimed on Si/SiO{sub 2} and quartz substrates, and their properties investigated by X-ray absorption and photoemission spectroscopies, optical absorption, atomic force microscopy, and superconducting quantum interference device. Contrary to the previously studied Fe(phen){sub 2}(NCS){sub 2}, the films are not smooth but granular. The thin films qualitatively retain the typical SCO properties of the powder sample (SCO, thermal hysteresis, soft X-ray induced excited spin-state trapping, and light induced excited spin-state trapping) but present intriguing variations even in micrometer-thick films: the transition temperature decreases when the thickness is decreased,more » and the hysteresis is affected. We explain this behavior in the light of recent studies focusing on the role of surface energy in the thermodynamics of the spin transition in nano-structures. In the high-spin state at room temperature, the films have a large optical gap (∼5 eV), decreasing at thickness below 50 nm, possibly due to film morphology.« less

New styryl phenanthroline derivatives as model D-π-A-π-D materials for non-linear optics.

PubMed

Bonaccorso, Carmela; Cesaretti, Alessio; Elisei, Fausto; Mencaroni, Letizia; Spalletti, Anna; Fortuna, Cosimo Gianluca

2018-04-27

Four novel push-pull systems combining a central phenanthroline acceptor moiety and two substituted benzene rings, as a part of the conjugated π-system between the donor and the acceptor moieties, have been synthetized through a straightforward and efficient one-step synthetic procedure. The chromophores display high fluorescence and a peculiar fluorosolvatochromic behavior. Ultrafast investigation by means of state-of-the-art femtosecond-resolved transient absorption and fluorescence up-conversion spectroscopies allowed the role of intramolecular charge transfer (ICT) states to be evidenced, also revealing the crucial role played by both the polarity and proticity of the medium on the excited state dynamics of the chromophores. The ICT processes, responsible for the solvatochromism, also lead to interesting non-linear optical (NLO) properties: namely great two photon absorption cross-sections (hundreds of GM), investigated by the Two Photon Excited Fluorescence (TPEF) technique, and large second order hyperpolarizability coefficients, estimated through a convenient solvatochromic method. These features thus make the investigated styryl phenanthroline molecules model D-π-A-π-D compounds for non-linear optical applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gradual collapse of nuclear wave functions regulated by frequency tuned X-ray scattering.

PubMed

Ignatova, Nina; Cruz, Vinícius V; Couto, Rafael C; Ertan, Emelie; Zimin, Andrey; Guimarães, Freddy F; Polyutov, Sergey; Ågren, Hans; Kimberg, Victor; Odelius, Michael; Gel'mukhanov, Faris

2017-03-07

As is well established, the symmetry breaking by isotope substitution in the water molecule results in localisation of the vibrations along one of the two bonds in the ground state. In this study we find that this localisation may be broken in excited electronic states. Contrary to the ground state, the stretching vibrations of HDO are delocalised in the bound core-excited state in spite of the mass difference between hydrogen and deuterium. The reason for this effect can be traced to the narrow "canyon-like" shape of the potential of the state along the symmetric stretching mode, which dominates over the localisation mass-difference effect. In contrast, the localisation of nuclear motion to one of the HDO bonds is preserved in the dissociative core-excited state . The dynamics of the delocalisation of nuclear motion in these core-excited states is studied using resonant inelastic X-ray scattering of the vibrationally excited HDO molecule. The results shed light on the process of a wave function collapse. After core-excitation into the state of HDO the initial wave packet collapses gradually, rather than instantaneously, to a single vibrational eigenstate.

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

Shi, Jade; Nobrega, R. Paul; Schwantes, Christian

The dynamics of globular proteins can be described in terms of transitions between a folded native state and less-populated intermediates, or excited states, which can play critical roles in both protein folding and function. Excited states are by definition transient species, and therefore are difficult to characterize using current experimental techniques. We report an atomistic model of the excited state ensemble of a stabilized mutant of an extensively studied flavodoxin fold protein CheY. We employed a hybrid simulation and experimental approach in which an aggregate 42 milliseconds of all-atom molecular dynamics were used as an informative prior for the structuremore » of the excited state ensemble. The resulting prior was then refined against small-angle X-ray scattering (SAXS) data employing an established method (EROS). The most striking feature of the resulting excited state ensemble was an unstructured N-terminus stabilized by non-native contacts in a conformation that is topologically simpler than the native state. We then predict incisive single molecule FRET experiments, using these results, as a means of model validation. Our study demonstrates the paradigm of uniting simulation and experiment in a statistical model to study the structure of protein excited states and rationally design validating experiments.« less

Extended Lagrangian Excited State Molecular Dynamics

DOE PAGES

Bjorgaard, Josiah August; Sheppard, Daniel Glen; Tretiak, Sergei; ...

2018-01-09

In this work, an extended Lagrangian framework for excited state molecular dynamics (XL-ESMD) using time-dependent self-consistent field theory is proposed. The formulation is a generalization of the extended Lagrangian formulations for ground state Born–Oppenheimer molecular dynamics [Phys. Rev. Lett. 2008 100, 123004]. The theory is implemented, demonstrated, and evaluated using a time-dependent semiempirical model, though it should be generally applicable to ab initio theory. The simulations show enhanced energy stability and a significantly reduced computational cost associated with the iterative solutions of both the ground state and the electronically excited states. Relaxed convergence criteria can therefore be used both formore » the self-consistent ground state optimization and for the iterative subspace diagonalization of the random phase approximation matrix used to calculate the excited state transitions. In conclusion, the XL-ESMD approach is expected to enable numerically efficient excited state molecular dynamics for such methods as time-dependent Hartree–Fock (TD-HF), Configuration Interactions Singles (CIS), and time-dependent density functional theory (TD-DFT).« less

Extended Lagrangian Excited State Molecular Dynamics

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

Bjorgaard, Josiah August; Sheppard, Daniel Glen; Tretiak, Sergei

In this work, an extended Lagrangian framework for excited state molecular dynamics (XL-ESMD) using time-dependent self-consistent field theory is proposed. The formulation is a generalization of the extended Lagrangian formulations for ground state Born–Oppenheimer molecular dynamics [Phys. Rev. Lett. 2008 100, 123004]. The theory is implemented, demonstrated, and evaluated using a time-dependent semiempirical model, though it should be generally applicable to ab initio theory. The simulations show enhanced energy stability and a significantly reduced computational cost associated with the iterative solutions of both the ground state and the electronically excited states. Relaxed convergence criteria can therefore be used both formore » the self-consistent ground state optimization and for the iterative subspace diagonalization of the random phase approximation matrix used to calculate the excited state transitions. In conclusion, the XL-ESMD approach is expected to enable numerically efficient excited state molecular dynamics for such methods as time-dependent Hartree–Fock (TD-HF), Configuration Interactions Singles (CIS), and time-dependent density functional theory (TD-DFT).« less

Extended Lagrangian Excited State Molecular Dynamics.

PubMed

Bjorgaard, J A; Sheppard, D; Tretiak, S; Niklasson, A M N

2018-02-13

An extended Lagrangian framework for excited state molecular dynamics (XL-ESMD) using time-dependent self-consistent field theory is proposed. The formulation is a generalization of the extended Lagrangian formulations for ground state Born-Oppenheimer molecular dynamics [Phys. Rev. Lett. 2008 100, 123004]. The theory is implemented, demonstrated, and evaluated using a time-dependent semiempirical model, though it should be generally applicable to ab initio theory. The simulations show enhanced energy stability and a significantly reduced computational cost associated with the iterative solutions of both the ground state and the electronically excited states. Relaxed convergence criteria can therefore be used both for the self-consistent ground state optimization and for the iterative subspace diagonalization of the random phase approximation matrix used to calculate the excited state transitions. The XL-ESMD approach is expected to enable numerically efficient excited state molecular dynamics for such methods as time-dependent Hartree-Fock (TD-HF), Configuration Interactions Singles (CIS), and time-dependent density functional theory (TD-DFT).

Negative thermal expansion near two structural quantum phase transitions

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

Occhialini, Connor A.; Handunkanda, Sahan U.; Said, Ayman

Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a structural quantum phase transition, posing a question of fundamental interest as to whether this special circumstance is related to the anomalous behavior. To test this hypothesis, we report an elastic and inelastic x-ray scattering study of a second system Hg2I2 also tuned near a structural quantum phase transition while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant negative thermal expansion below 100 K formore » dimensions along the body-centered-tetragonal c axis, bolstering the connection between negative thermal expansion and zero-temperature structural transitions.We identify the common traits between these systems and propose a set of materials design principles that can guide discovery of newmaterials exhibiting negative thermal expansion« less

Negative thermal expansion near two structural quantum phase transitions

NASA Astrophysics Data System (ADS)

Occhialini, Connor A.; Handunkanda, Sahan U.; Said, Ayman; Trivedi, Sudhir; Guzmán-Verri, G. G.; Hancock, Jason N.

2017-12-01

Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a structural quantum phase transition, posing a question of fundamental interest as to whether this special circumstance is related to the anomalous behavior. To test this hypothesis, we report an elastic and inelastic x-ray scattering study of a second system Hg2I2 also tuned near a structural quantum phase transition while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant negative thermal expansion below 100 K for dimensions along the body-centered-tetragonal c axis, bolstering the connection between negative thermal expansion and zero-temperature structural transitions. We identify the common traits between these systems and propose a set of materials design principles that can guide discovery of new materials exhibiting negative thermal expansion.

A three-dimensional He-CO potential energy surface with improved long-range behavior

NASA Astrophysics Data System (ADS)

McBane, George C.

2016-12-01

A weakness of the "CBS + corr" He-CO potential energy surface (Peterson and McBane, 2005) has been rectified by constraining the potential to adopt accurate long-range behavior for He-CO distances well beyond 15a0 . The resulting surface is very similar to the original in the main part of the interaction. Comparison with accurately known bound-state energies indicates that the surface is slightly improved in the region sampled by the highest lying bound states. The positions of shape and Feshbach resonances within a few cm-1 of the j = 1 excitation threshold are essentially unchanged. The low-energy scattering lengths changed noticeably. The revised surface generates a small negative limiting scattering length for collisions with 4He, while the original surface gave a small positive one. Both surfaces yield scattering lengths quite different from the widely used surface of Heijmen et al. (1997) for both He isotopes.

Dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT formation and decay after picosecond pulsed X-ray excitation and femtosecond UV excitation.

PubMed

Zhao, Liyan; Odaka, Hideho; Ono, Hiroshi; Kajimoto, Shinji; Hatanaka, Koji; Hobley, Jonathan; Fukumura, Hiroshi

2005-01-01

The dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT state formation and decay were determined after femtosecond UV laser excitation and picosecond pulsed X-ray excitation, in an N,N-dimethylformamide (DMF) solution as well as in its solid form. At room temperature, after UV excitation, this MLCT excited state emits both in DMF solution and in the solid form. Transient absorption spectra were measured in solution at various delay times following excitation by a 160 fs, 390 nm laser pulse. There was a prompt absorption increase at around 460 nm occurring within the pump probe convolution (<1 ps), which was assigned to the formation of the 3MLCT state. This transient absorbance was constant over 100 ps. In contrast to the solution state, in the solid state, the emission maximum slightly red-shifts with increasing time after laser excitation. In both solid and solution the emission rises within the system response time. The solid sample exhibited a 1.4 ns emission decay that was not observed for the solution sample. The emission rise from a solid sample after 20 ps pulsed X-ray excitation was significantly slower than the system's time resolution. It is proposed that kinetically energetic electrons are ejected following X-ray induced ionisation, creating ionised tracks in which energetic cations and electrons take time to recombine yielding delayed 3MLCT states that emit.

Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid

PubMed Central

Yu, Deshui; Valado, María Martínez; Hufnagel, Christoph; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer

2016-01-01

Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa. PMID:27922087

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

Effect of xenon on the excited states of phototropic receptor flavin in corn seedlings

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

Vierstra, R.D.; Poff, K.L.; Walker, E.B.

1981-05-01

The chemically inert, water-soluble heavy atom gas, xenon, at millimolar concentrations specifically quenches the triplet excited state of flavin in solution without quenching the flavin singlet excited state. The preferential quenching of the flavin triplet over the singlet excited state by Xe has been established by showing that the flavin triplet-sensitized photooxidation of NADH is inhibited while the fluorescence intensity and lifetime of flavin are not affected by Xe. No significant inhibition of phototropism and geotropism by Xe was observed, suggesting that a flavin singlet state is more likely involved than the triplet state in the primary photoprocess of phototropismmore » in corn.« less

A new energy transfer channel from carotenoids to chlorophylls in purple bacteria.

PubMed

Feng, Jin; Tseng, Chi-Wei; Chen, Tingwei; Leng, Xia; Yin, Huabing; Cheng, Yuan-Chung; Rohlfing, Michael; Ma, Yuchen

2017-07-10

It is unclear whether there is an intermediate dark state between the S 2 and S 1 states of carotenoids. Previous two-dimensional electronic spectroscopy measurements support its existence and its involvement in the energy transfer from carotenoids to chlorophylls, but there is still considerable debate on the origin of this dark state and how it regulates the energy transfer process. Here we use ab initio calculations on excited-state dynamics and simulated two-dimensional electronic spectrum of carotenoids from purple bacteria to provide evidence supporting that the dark state may be assigned to a new A g + state. Our calculations also indicate that groups on the conjugation backbone of carotenoids may substantially affect the excited-state levels and the energy transfer process. These results contribute to a better understanding of carotenoid excited states.Carotenoids harvest energy from light and transfer it to chlorophylls during photosynthesis. Here, Feng et al. perform ab initio calculations on excited-state dynamics and simulated 2D electronic spectrum of carotenoids, supporting the existence of a new excited state in carotenoids.

Drosophila SLC5A11 Mediates Hunger by Regulating K(+) Channel Activity.

PubMed

Park, Jin-Yong; Dus, Monica; Kim, Seonil; Abu, Farhan; Kanai, Makoto I; Rudy, Bernardo; Suh, Greg S B

2016-08-08

Hunger is a powerful drive that stimulates food intake. Yet, the mechanism that determines how the energy deficits that result in hunger are represented in the brain and promote feeding is not well understood. We previously described SLC5A11-a sodium/solute co-transporter-like-(or cupcake) in Drosophila melanogaster, which is required for the fly to select a nutritive sugar over a sweeter nonnutritive sugar after periods of food deprivation. SLC5A11 acts on approximately 12 pairs of ellipsoid body (EB) R4 neurons to trigger the selection of nutritive sugars, but the underlying mechanism is not understood. Here, we report that the excitability of SLC5A11-expressing EB R4 neurons increases dramatically during starvation and that this increase is abolished in the SLC5A11 mutation. Artificial activation of SLC5A11-expresssing neurons is sufficient to promote feeding and hunger-driven behaviors; silencing these neurons has the opposite effect. Notably, SLC5A11 transcript levels in the brain increase significantly when flies are starved and decrease shortly after starved flies are refed. Furthermore, expression of SLC5A11 is sufficient for promoting hunger-driven behaviors and enhancing the excitability of SLC5A11-expressing neurons. SLC5A11 inhibits the function of the Drosophila KCNQ potassium channel in a heterologous expression system. Accordingly, a knockdown of dKCNQ expression in SLC5A11-expressing neurons produces hunger-driven behaviors even in fed flies, mimicking the overexpression of SLC5A11. We propose that starvation increases SLC5A11 expression, which enhances the excitability of SLC5A11-expressing neurons by suppressing dKCNQ channels, thereby conferring the hunger state. Copyright © 2016 Elsevier Ltd. All rights reserved.

Excitation energies of dissociating H2: A problematic case for the adiabatic approximation of time-dependent density functional theory

NASA Astrophysics Data System (ADS)

Gritsenko, O. V.; van Gisbergen, S. J. A.; Görling, A.; Baerends, E. J.

2000-11-01

Time-dependent density functional theory (TDDFT) is applied for calculation of the excitation energies of the dissociating H2 molecule. The standard TDDFT method of adiabatic local density approximation (ALDA) totally fails to reproduce the potential curve for the lowest excited singlet 1Σu+ state of H2. Analysis of the eigenvalue problem for the excitation energies as well as direct derivation of the exchange-correlation (xc) kernel fxc(r,r',ω) shows that ALDA fails due to breakdown of its simple spatially local approximation for the kernel. The analysis indicates a complex structure of the function fxc(r,r',ω), which is revealed in a different behavior of the various matrix elements K1c,1cxc (between the highest occupied Kohn-Sham molecular orbital ψ1 and virtual MOs ψc) as a function of the bond distance R(H-H). The effect of nonlocality of fxc(r,r') is modeled by using different expressions for the corresponding matrix elements of different orbitals. Asymptotically corrected ALDA (ALDA-AC) expressions for the matrix elements K12,12xc(στ) are proposed, while for other matrix elements the standard ALDA expressions are retained. This approach provides substantial improvement over the standard ALDA. In particular, the ALDA-AC curve for the lowest singlet excitation qualitatively reproduces the shape of the exact curve. It displays a minimum and approaches a relatively large positive energy at large R(H-H). ALDA-AC also produces a substantial improvement for the calculated lowest triplet excitation, which is known to suffer from the triplet instability problem of the restricted KS ground state. Failure of the ALDA for the excitation energies is related to the failure of the local density as well as generalized gradient approximations to reproduce correctly the polarizability of dissociating H2. The expression for the response function χ is derived to show the origin of the field-counteracting term in the xc potential, which is lacking in the local density and generalized gradient approximations and which is required to obtain a correct polarizability.

Producing coherent excitations in pumped Mott antiferromagnetic insulators

NASA Astrophysics Data System (ADS)

Wang, Yao; Claassen, Martin; Moritz, B.; Devereaux, T. P.

2017-12-01

Nonequilibrium dynamics in correlated materials has attracted attention due to the possibility of characterizing, tuning, and creating complex ordered states. To understand the photoinduced microscopic dynamics, especially the linkage under realistic pump conditions between transient states and remnant elementary excitations, we performed nonperturbative simulations of various time-resolved spectroscopies. We used the Mott antiferromagnetic insulator as a model platform. The transient dynamics of multiparticle excitations can be attributed to the interplay between Floquet virtual states and a modification of the density of states, in which interactions induce a spectral weight transfer. Using an autocorrelation of the time-dependent spectral function, we show that resonance of the virtual states with the upper Hubbard band in the Mott insulator provides the route towards manipulating the electronic distribution and modifying charge and spin excitations. Our results link transient dynamics to the nature of many-body excitations and provide an opportunity to design nonequilibrium states of matter via tuned laser pulses.

Vibrational frequencies and dephasing times in excited electronic states by femtosecond time-resolved four-wave mixing

NASA Astrophysics Data System (ADS)

Joo, Taiha; Albrecht, A. C.

1993-06-01

Time-resolved degenerate four-wave mixing (TRDFWM) for an electronically resonant system in a phase-matching configuration that measures population decay is reported. Because the spectral width of input light exceeds the vibrational Bohr frequency of a strong Raman active mode, the vibrational coherence produces strong oscillations in the TRDFWM signal together with the usual population decay from the excited electronic state. The data are analyzed in terms of a four-level system: ground and excited electronic states each split by a vibrational quantum of a Raman active mode. Absolute frequencies and their dephasing times of the vibrational modes at ≈590 cm -1 are obtained for the excited as well as the ground electronic state. The vibrational dephasing rate in the excited electronic state is about an order of magnitude faster than that in the ground state, the origin of which is speculated upon.

Excitation of atoms and ions in plasmas by ultra-short electromagnetic pulses

NASA Astrophysics Data System (ADS)

Astapenko, V. A.; Sakhno, S. V.; Svita, S. Yu; Lisitsa, V. S.

2017-02-01

The problem of atoms and ions diagnostics in rarefied and dense plasmas by ultrashort laser pulses (USP) is under consideration. The application of USP provides: 1) excitation from ground states due to their carrier frequency high enough, 2) penetration into optically dense media due to short pulses duration. The excitation from ground atomic states increases sharply populations of excited atomic states in contrast with standard laser induced fluorescence spectroscopy based on radiative transitions between excited atomic states. New broadening parameter in radiation absorption, namely inverse pulse duration time 1/τ appears in addition to standard line-shape width in the profile G(ω). The Lyman-beta absorption spectra for USP are calculated for Holtsmark static broadening mechanism. Excitation of highly charged H-like ions in hot plasmas is described by both Gaussian shapes for Doppler broadening and pulse spectrum resulting in analytical absorption line-shape. USP penetration into optically thick media and corresponding excitation probability are calculated. It is shown a great effect of USP duration on excitation probabilities in optically thick media. The typical situations for plasma diagnostics by USP are discussed in details.

Identification of Excited States in the N=Z Nucleus 82Nb

NASA Astrophysics Data System (ADS)

Caceres, L. S.; Gorska, M.; Jungclaus, A.; Regan, P. H.; Garnsworthy, A. B.; Pietri, S.; Podolyak, Zs.; Rudolph, D.; Steer, S. J.; Grawe, H.; Balabanski, D. L.; Becker, F.; Bednarczyk, P.; Benzoni, G.; Blank, B.; Brandau, C.; Bruce, A. M.; Camera, F.; Catford, W. N.; Cullen, I. J.; Dombradi, Zs.; Doornenbal, P.; Estevez, E.; Geissel, H.; Gelletly, W.; Gerl, J.; Grebosz, J.; Heinz, A.; Hoischen, R.; Ilie, G.; Jolie, J.; Jones, G. A.; Kmiecik, M.; Kojouharov, I.; Kondev, F. G.; Kurtukian-Nieto, T.; Kurz, N.; Lalkowski, S.; Liu, L.; Maj, A.; Myalski, S.; Montes, F.; Pfuetzner, M.; Prokopowicz, W.; Saito, T.; Schaffner, H.; Schwertel, S.; Shizuma, T.; Simons, A. J.; Tashenov, S.; Walker, P. M.; Werner-Malento, E.; Wieland, O.; Wollersheim, H. J.

2007-04-01

Information on the first excited states in the N=Z=41 nucleus 82Nb sheds light on the competition of isospin T=0 and T=1 states in the A sim 80 region. The measurement was performed at the GSI laboratory using fragmentation of a 107Ag primary beam at 750 MeV/u on a 4 g/cm2 9Be target. The fragments were separated and identified unambiguously in the FRagment Separator. Three excited states were observed and the half-life estimate for the isomeric state was extracted. A tentative spin assignment based on the isobaric analogue states systematics in the Tz=1 nucleus 82Zr, and transition probabilities indicate T=1 character of the first two excited states, and T=0 for the isomeric state.

Dopamine Neurons Change the Type of Excitability in Response to Stimuli

PubMed Central

Gutkin, Boris S.; Lapish, Christopher C.; Kuznetsov, Alexey

2016-01-01

The dynamics of neuronal excitability determine the neuron’s response to stimuli, its synchronization and resonance properties and, ultimately, the computations it performs in the brain. We investigated the dynamical mechanisms underlying the excitability type of dopamine (DA) neurons, using a conductance-based biophysical model, and its regulation by intrinsic and synaptic currents. Calibrating the model to reproduce low frequency tonic firing results in N-methyl-D-aspartate (NMDA) excitation balanced by γ-Aminobutyric acid (GABA)-mediated inhibition and leads to type I excitable behavior characterized by a continuous decrease in firing frequency in response to hyperpolarizing currents. Furthermore, we analyzed how excitability type of the DA neuron model is influenced by changes in the intrinsic current composition. A subthreshold sodium current is necessary for a continuous frequency decrease during application of a negative current, and the low-frequency “balanced” state during simultaneous activation of NMDA and GABA receptors. Blocking this current switches the neuron to type II characterized by the abrupt onset of repetitive firing. Enhancing the anomalous rectifier Ih current also switches the excitability to type II. Key characteristics of synaptic conductances that may be observed in vivo also change the type of excitability: a depolarized γ-Aminobutyric acid receptor (GABAR) reversal potential or co-activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) leads to an abrupt frequency drop to zero, which is typical for type II excitability. Coactivation of N-methyl-D-aspartate receptors (NMDARs) together with AMPARs and GABARs shifts the type I/II boundary toward more hyperpolarized GABAR reversal potentials. To better understand how altering each of the aforementioned currents leads to changes in excitability profile of DA neuron, we provide a thorough dynamical analysis. Collectively, these results imply that type I excitability in dopamine neurons might be important for low firing rates and fine-tuning basal dopamine levels, while switching excitability to type II during NMDAR and AMPAR activation may facilitate a transient increase in dopamine concentration, as type II neurons are more amenable to synchronization by mutual excitation. PMID:27930673

Memory trace replay: the shaping of memory consolidation by neuromodulation

PubMed Central

Atherton, Laura A.; Dupret, David; Mellor, Jack R.

2015-01-01

The consolidation of memories for places and events is thought to rely, at the network level, on the replay of spatially tuned neuronal firing patterns representing discrete places and spatial trajectories. This occurs in the hippocampal-entorhinal circuit during sharp wave ripple events (SWRs) that occur during sleep or rest. Here, we review theoretical models of lingering place cell excitability and behaviorally induced synaptic plasticity within cell assemblies to explain which sequences or places are replayed. We further provide new insights into how fluctuations in cholinergic tone during different behavioral states might shape the direction of replay and how dopaminergic release in response to novelty or reward can modulate which cell assemblies are replayed. PMID:26275935

Network Events on Multiple Space and Time Scales in Cultured Neural Networks and in a Stochastic Rate Model

PubMed Central

Gigante, Guido; Deco, Gustavo; Marom, Shimon; Del Giudice, Paolo

2015-01-01

Cortical networks, in-vitro as well as in-vivo, can spontaneously generate a variety of collective dynamical events such as network spikes, UP and DOWN states, global oscillations, and avalanches. Though each of them has been variously recognized in previous works as expression of the excitability of the cortical tissue and the associated nonlinear dynamics, a unified picture of the determinant factors (dynamical and architectural) is desirable and not yet available. Progress has also been partially hindered by the use of a variety of statistical measures to define the network events of interest. We propose here a common probabilistic definition of network events that, applied to the firing activity of cultured neural networks, highlights the co-occurrence of network spikes, power-law distributed avalanches, and exponentially distributed ‘quasi-orbits’, which offer a third type of collective behavior. A rate model, including synaptic excitation and inhibition with no imposed topology, synaptic short-term depression, and finite-size noise, accounts for all these different, coexisting phenomena. We find that their emergence is largely regulated by the proximity to an oscillatory instability of the dynamics, where the non-linear excitable behavior leads to a self-amplification of activity fluctuations over a wide range of scales in space and time. In this sense, the cultured network dynamics is compatible with an excitation-inhibition balance corresponding to a slightly sub-critical regime. Finally, we propose and test a method to infer the characteristic time of the fatigue process, from the observed time course of the network’s firing rate. Unlike the model, possessing a single fatigue mechanism, the cultured network appears to show multiple time scales, signalling the possible coexistence of different fatigue mechanisms. PMID:26558616

Plucking a hydrogen bond: A near infrared study of all four intermolecular modes in (DF)2

NASA Astrophysics Data System (ADS)

Davis, Scott; Anderson, David T.; Nesbitt, David J.

1996-10-01

The near ir combination band spectra of supersonically cooled (DF)2 in the 2900 to 3300 cm-1 region have been recorded with a high resolution slit jet spectrometer. Twelve vibration-rotation-tunneling (VRT) bands are observed, representing each of the four intermolecular modes (van der Waals stretch ν4, geared bend ν5, out-of-plane torsion ν6, and antigeared bend ν3) built as combination bands on either the ν1 (free) or ν2 (bound) DF stretches. Analysis of the rotationally resolved spectra provide spectroscopic constants, intermolecular frequencies, tunneling splittings, and predissociation rates as a function of both intra- and intermolecular excitation. The intermolecular frequencies demonstrate a small but systematic dependence on intramolecular mode, which is exploited to yield frequency predictions relevant to far-ir studies, as well as facilitate direct comparison with full 6-D quantum calculations on trial potential surfaces. The tunneling splittings demonstrate a much stronger dependence upon intermolecular mode, increasing by as much as an order of magnitude for geared bend excitation. Conversely, high resolution line shape analysis reveals that vibrational predissociation broadening is only modestly affected by intermolecular excitation, and instead exhibits mode specific behavior controlled predominantly by intramolecular excitation. Detailed H/D isotopic vibrational shifts are obtained by comparison with previous combination band studies of all four intermolecular modes in (HF)2. In contrast to the strong state mixing previously observed for (HF)2, the van der Waals stretch and geared bend degrees of freedom are largely decoupled in (DF)2, due to isotopically ``detuning'' of resonances between bend-stretch intermolecular vibrations. Four-dimensional quantum calculations of the (HF)2 and (DF)2 eigenfunctions indicate that the isotopic dependence of this bend-stretch resonance behavior is incorrectly predicted by current hydrogen bond potential surfaces.

Profilin2 contributes to synaptic vesicle exocytosis, neuronal excitability, and novelty-seeking behavior

PubMed Central

Pilo Boyl, Pietro; Di Nardo, Alessia; Mulle, Christophe; Sassoè-Pognetto, Marco; Panzanelli, Patrizia; Mele, Andrea; Kneussel, Matthias; Costantini, Vivian; Perlas, Emerald; Massimi, Marzia; Vara, Hugo; Giustetto, Maurizio; Witke, Walter

2007-01-01

Profilins are actin binding proteins essential for regulating cytoskeletal dynamics, however, their function in the mammalian nervous system is unknown. Here, we provide evidence that in mouse brain profilin1 and profilin2 have distinct roles in regulating synaptic actin polymerization with profilin2 preferring a WAVE-complex-mediated pathway. Mice lacking profilin2 show a block in synaptic actin polymerization in response to depolarization, which is accompanied by increased synaptic excitability of glutamatergic neurons due to higher vesicle exocytosis. These alterations in neurotransmitter release correlate with a hyperactivation of the striatum and enhanced novelty-seeking behavior in profilin2 mutant mice. Our results highlight a novel, profilin2-dependent pathway, regulating synaptic physiology, neuronal excitability, and complex behavior. PMID:17541406

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

Suhara, Tadahiro; Kanada-En'yo, Yoshiko

Structures of excited states in {sup 14}C are investigated with a method of {beta}-{gamma} constraint antisymmetrized molecular dynamics in combination with the generator coordinate method. Various excited states with the developed 3{alpha}-cluster core structures are suggested in positive- and negative-parity states. In the positive-parity states, triaxial deformed and linear-chain structures are found to construct excited bands. Interestingly, {sup 10}Be+{alpha} correlation is found in the cluster states above the {sup 10}Be+{alpha} threshold energy.

Asymptotics of quasi-classical localized states in 2D system of charged hard-core bosons

NASA Astrophysics Data System (ADS)

Panov, Yu. D.; Moskvin, A. S.

2018-05-01

The continuous quasi-classical two-sublattice approximation is constructed for the 2D system of charged hard-core bosons to explore metastable inhomogeneous states analogous to inhomogeneous localized excitations in magnetic systems. The types of localized excitations are determined by asymptotic analysis and compared with numerical results. Depending on the homogeneous ground state, the excitations are the ferro and antiferro type vortices, the skyrmion-like topological excitations or linear domain walls.

Entangled Biphoton Virtual-State Spectroscopy of the A(exp 2)Sigma(sup +)-X(exp 2)Pi System of OH

NASA Technical Reports Server (NTRS)

Kojima, Jun; Nguyen, Quang-Viet

2004-01-01

This Letter describes the first application of entanglement-induced virtual-state spectroscopy to a molecular system. Non-classical, non-monotonic behavior in a two-photon absorption cross section of the OH A-X system, induced by an entangled biphoton state is theoretically demonstrated. A Fourier transform analysis of the biphoton cross section permits access to the energy eigenvalues of intermediate rovibronic states with a fixed excitation photon energy. The dependence of the Fourier spectrum on the tuning range of the entanglement time (T(sub e)) and the relative path delay (tau(sub e)) is discussed. Our analysis reveals that the implementation of molecular virtual-state spectroscopy for the OH A-X system requires the tuning of tau(sub e) over a pico-second range with femto-second resolution.

Entangled Biphoton Virtual-State Spectroscopy of the A(exp 2)Sigma(+) - X(exp 2)Pi System of OH

NASA Technical Reports Server (NTRS)

Kojima, Jun; Nguyen, Quang-Viet

2004-01-01

This Letter describes the first application of entanglement-induced virtual-state spectroscopy to a molecular system. Non-classical, non-monotonic behavior in a two-photon absorption cross section of the OH A-X system, induced by an entangled biphoton state is theoretically demonstrated. A Fourier transform analysis of the biphoton cross section permits access to the energy eigenvalues of intermediate rovibronic states with a fixed excitation photon energy. The dependence of the Fourier spectrum on the tuning range of the entanglement time T(sub e), and the relative path delay tau(sub e) is discussed. Our analysis reveals that the implementation of molecular virtual-state spectroscopy for the OH A-X system requires the tuning of tau(sub e) over a pico-second range with femto-second resolution.

Intramolecular charge transfer and trans-cis isomerization of the DCM styrene dye in polar solvents. A CS INDO MRCI study

NASA Astrophysics Data System (ADS)

Marguet, S.; Mialocq, J. C.; Millie, P.; Berthier, G.; Momicchioli, F.

1992-03-01

The solvent-induced changes of trans-cis isomerization efficiency and electronic structure of the excited state of the DCM dye have been considered by means of CS INDO MRCI calculations. The potential energy curves, dipole moments and atomic charge densities as a function of two internal coordinates, namely the rotation angle about the central "double" bond and the twisting of the dimethylamino group, have been obtained for the ground state and the lowest excited states. The structural requirements for the existence of ICT (intramolecular charge transfer) excited states have been investigated by considering internal rotations about three single bonds. The reliability of the potential surfaces and of the solvation models has been discussed with reference to test-calculations on the DMABN molecule. In the first excited singlet state of DCM, the low-energy barrier for the trans-cis isomerization has been found unaffected by the solvent polarity. The only singlet excited state presenting a large ICT character has been found to be the S 2 state for a perpendicularly twisted conformation of the dimethylamino group (TICT state). The assumption of a deactivation of the trans-isomer in the locally excited state through the TICT funnel has been largely discussed with reference to the simplifications of the present theoretical approach.

Simulation of X-ray absorption spectra with orthogonality constrained density functional theory.

PubMed

Derricotte, Wallace D; Evangelista, Francesco A

2015-06-14

Orthogonality constrained density functional theory (OCDFT) [F. A. Evangelista, P. Shushkov and J. C. Tully, J. Phys. Chem. A, 2013, 117, 7378] is a variational time-independent approach for the computation of electronic excited states. In this work we extend OCDFT to compute core-excited states and generalize the original formalism to determine multiple excited states. Benchmark computations on a set of 13 small molecules and 40 excited states show that unshifted OCDFT/B3LYP excitation energies have a mean absolute error of 1.0 eV. Contrary to time-dependent DFT, OCDFT excitation energies for first- and second-row elements are computed with near-uniform accuracy. OCDFT core excitation energies are insensitive to the choice of the functional and the amount of Hartree-Fock exchange. We show that OCDFT is a powerful tool for the assignment of X-ray absorption spectra of large molecules by simulating the gas-phase near-edge spectrum of adenine and thymine.

Increase in cortical pyramidal cell excitability accompanies depression-like behavior in mice: a transcranial magnetic stimulation study.

PubMed

Sun, Peng; Wang, Furong; Wang, Li; Zhang, Yu; Yamamoto, Ryo; Sugai, Tokio; Zhang, Qing; Wang, Zhengda; Kato, Nobuo

2011-11-09

Clinical evidence suggests that cortical excitability is increased in depressives. We investigated its cellular basis in a mouse model of depression. In a modified version of forced swimming (FS), mice were initially forced to swim for 5 consecutive days and then were treated daily with repetitive transcranial magnetic stimulation (rTMS) or sham treatment for the following 4 weeks without swimming. On day 2 through day 5, the mice manifested depression-like behaviors. The next and last FS was performed 4 weeks later, which revealed a 4 week maintenance of depression-like behavior in the sham mice. In slices from the sham controls, excitability in cingulate cortex pyramidal cells was elevated in terms of membrane potential and frequencies of spikes evoked by current injection. Depolarized resting potential was shown to depend on suppression of large conductance calcium-activated potassium (BK) channels. This BK channel suppression was confirmed by measuring spike width, which depends on BK channels. Chronic rTMS treatment during the 4 week period significantly reduced the depression-like behavior. In slices obtained from the rTMS mice, normal excitability and BK channel activity were recovered. Expression of a scaffold protein Homer1a was reduced by the FS and reversed by rTMS in the cingulate cortex. Similar recovery in the same behavioral, electrophysiological, and biochemical features was observed after chronic imipramine treatment. The present study demonstrated that manifestation and disappearance of depression-like behavior are in parallel with increase and decrease in cortical neuronal excitability in mice and suggested that regulation of BK channels by Homer1a is involved in this parallelism.

Electron-Impact Cross Sections for Ground State to np Excitations of Sodium and Potassium.

PubMed

Stone, Philip M; Kim, Yong-Ki

2004-01-01

Cross sections for electron impact excitation of atoms are important for modeling of low temperature plasmas and gases. While there are many experimental and theoretical results for excitation to the first excited states, little information is available for excitation to higher states. We present here calculations of excitations from the ground state to the np levels of sodium (n = 3 through 11) and potassium (n = 4 through 12). We also present a calculation for a transition from the excited sodium level 3p to 3d to show the generality of the method. Scaling formulas developed earlier by Kim [Phys. Rev. A 64, 032713 (2001)] for plane-wave Born cross sections are used. These formulas have been shown to be remarkably accurate yet simple to use. We have used a core polarization potential in a Dirac-Fock wave function code to calculate target atom wave functions and a matching form of the dipole transition operator to calculate oscillator strengths and Born cross sections. The scaled Born results here for excitation to the first excited levels are in very good agreement with experimental and other theoretical data, and the results for excitation to the next few levels are in satisfactory agreement with the limited data available. The present results for excitation to the higher levels are believed to be the only data available.

Use of ultrafast dispersed pump-dump-probe and pump-repump-probe spectroscopies to explore the light-induced dynamics of peridinin in solution.

PubMed

Papagiannakis, Emmanouil; Vengris, Mikas; Larsen, Delmar S; van Stokkum, Ivo H M; Hiller, Roger G; van Grondelle, Rienk

2006-01-12

Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump-probe, pump-dump-probe, and pump-repump-probe transient absorption spectroscopy in the visible region. Dispersed pump-probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led to direct generation of the peridinin cation, observed for the first time in a transient absorption experiment. The excited and ground electronic states manifold of peridinin has been reconstructed using target analysis; this approach combined with the measured multipulse spectroscopic data allows us to estimate the spectra and time scales of the corresponding transient states.

Time-resolved photoelectron spectroscopy of adenosine and adenosine monophosphate photodeactivation dynamics in water microjets

NASA Astrophysics Data System (ADS)

Williams, Holly L.; Erickson, Blake A.; Neumark, Daniel M.

2018-05-01

The excited state relaxation dynamics of adenosine and adenosine monophosphate were studied at multiple excitation energies using femtosecond time-resolved photoelectron spectroscopy in a liquid water microjet. At pump energies of 4.69-4.97 eV, the lowest ππ* excited state, S1, was accessed and its decay dynamics were probed via ionization at 6.20 eV. By reversing the role of the pump and probe lasers, a higher-lying ππ* state was excited at 6.20 eV and its time-evolving photoelectron spectrum was monitored at probe energies of 4.69-4.97 eV. The S1 ππ* excited state was found to decay with a lifetime ranging from ˜210 to 250 fs in adenosine and ˜220 to 250 fs in adenosine monophosphate. This lifetime drops with increasing pump photon energy. Signal from the higher-lying ππ* excited state decayed on a time scale of ˜320 fs and was measureable only in adenosine monophosphate.

A pair natural orbital based implementation of CCSD excitation energies within the framework of linear response theory

NASA Astrophysics Data System (ADS)

Frank, Marius S.; Hättig, Christof

2018-04-01

We present a pair natural orbital (PNO)-based implementation of coupled cluster singles and doubles (CCSD) excitation energies that builds upon the previously proposed state-specific PNO approach to the excited state eigenvalue problem. We construct the excited state PNOs for each state separately in a truncated orbital specific virtual basis and use a local density-fitting approximation to achieve an at most quadratic scaling of the computational costs for the PNO construction. The earlier reported excited state PNO construction is generalized such that a smooth convergence of the results for charge transfer states is ensured for general coupled cluster methods. We investigate the accuracy of our implementation by applying it to a large and diverse test set comprising 153 singlet excitations in organic molecules. Already moderate PNO thresholds yield mean absolute errors below 0.01 eV. The performance of the implementation is investigated through the calculations on alkene chains and reveals an at most cubic cost-scaling for the CCSD iterations with the system size.

Ultrafast Dynamics of 1,3-Cyclohexadiene in Highly Excited States

DOE PAGES

Bühler, Christine C.; Minitti, Michael P.; Deb, Sanghamitra; ...

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

Measurement of picosecond lifetimes in neutron-rich Xe isotopes

NASA Astrophysics Data System (ADS)

Ilieva, S.; Kröll, Th.; Régis, J.-M.; Saed-Samii, N.; Blanc, A.; Bruce, A. M.; Fraile, L. M.; de France, G.; Hartig, A.-L.; Henrich, C.; Ignatov, A.; Jentschel, M.; Jolie, J.; Korten, W.; Köster, U.; Lalkovski, S.; Lozeva, R.; Mach, H.; Mǎrginean, N.; Mutti, P.; Paziy, V.; Regan, P. H.; Simpson, G. S.; Soldner, T.; Thürauf, M.; Ur, C. A.; Urban, W.; Warr, N.

2016-09-01

Background: Lifetimes of nuclear excited states in fission fragments have been studied in the past following isotope separation, thus giving access mainly to the fragments' daughters and only to long-lived isomeric states in the primary fragments. For the first time now, short-lived excited states in the primary fragments, produced in neutron-induced prompt fission of 235U and 241Pu, were studied within the EXILL&FATIMA campaign at the intense neutron-beam facility of the Institute Laue-Langevin in Grenoble. Purpose: We aim to investigate the quadrupole collective properties of neutron-rich even-even 138,140,142Xe isotopes lying between the double shell closure N =82 and Z =50 and a deformed region with octupole collectivity. Method: The γ rays emitted from the excited fragments were detected with a mixed array consisting of 8 HPGe EXOGAM Clover detectors (EXILL) and 16 LaBr3(Ce) fast scintillators (FATIMA). The detector system has the unique ability to select the interesting fragment making use of the high resolution of the HPGe detectors and determine subnanosecond lifetimes using the fast scintillators. For the analysis the generalized centroid difference method was used. Results: We show that quadrupole collectivity increases smoothly with increasing neutron number above the closed N =82 neutron shell. Our measurements are complemented by state-of-the-art theory calculations based on shell-model descriptions. Conclusions: The observed smooth increase in quadrupole collectivity is similar to the evolution seen in the measured masses of the xenon isotopic chain and is well reproduced by theory. This behavior is in contrast to higher Z even-even nuclei where abrupt change in deformation occurs around N =90 .

Vibrational energy transfer dynamics in ruthenium polypyridine transition metal complexes.

PubMed

Fedoseeva, Marina; Delor, Milan; Parker, Simon C; Sazanovich, Igor V; Towrie, Michael; Parker, Anthony W; Weinstein, Julia A

2015-01-21

Understanding the dynamics of the initial stages of vibrational energy transfer in transition metal complexes is a challenging fundamental question which is also of crucial importance for many applications, such as improving the performance of solar devices or photocatalysis. The present study investigates vibrational energy transport in the ground and the electronic excited state of Ru(4,4'-(COOEt)2-2,2-bpy)2(NCS)2, a close relative of the efficient "N3" dye used in dye-sensitized solar cells. Using the emerging technique of ultrafast two-dimensional infrared spectroscopy, we show that, similarly to other transition-metal complexes, the central Ru heavy atom acts as a "bottleneck" making the energy transfer from small ligands with high energy vibrational stretching frequencies less favorable and thereby affecting the efficiency of vibrational energy flow in the complex. Comparison of the vibrational relaxation times in the electronic ground and excited state of Ru(4,4'-(COOEt)2-2,2-bpy)2(NCS)2 shows that it is dramatically faster in the latter. We propose to explain this observation by the intramolecular electrostatic interactions between the thiocyanate group and partially oxidised Ru metal center, which increase the degree of vibrational coupling between CN and Ru-N modes in the excited state thus reducing structural and thermodynamic barriers that slow down vibrational relaxation and energy transport in the electronic ground state. As a very similar behavior was earlier observed in another transition-metal complex, Re(4,4'-(COOEt)2-2,2'-bpy)(CO)3Cl, we suggest that this effect in vibrational energy dynamics might be common for transition-metal complexes with heavy central atoms.

Transient spatiotemporal chaos in the Morris-Lecar neuronal ring network.

PubMed

Keplinger, Keegan; Wackerbauer, Renate

2014-03-01

Transient behavior is thought to play an integral role in brain functionality. Numerical simulations of the firing activity of diffusively coupled, excitable Morris-Lecar neurons reveal transient spatiotemporal chaos in the parameter regime below the saddle-node on invariant circle bifurcation point. The neighborhood of the chaotic saddle is reached through perturbations of the rest state, in which few initially active neurons at an effective spatial distance can initiate spatiotemporal chaos. The system escapes from the neighborhood of the chaotic saddle to either the rest state or to a state of pulse propagation. The lifetime of the chaotic transients is manipulated in a statistical sense through a singular application of a synchronous perturbation to a group of neurons.

Brain Activation in Motor Sequence Learning Is Related to the Level of Native Cortical Excitability

PubMed Central

Lissek, Silke; Vallana, Guido S.; Güntürkün, Onur; Dinse, Hubert; Tegenthoff, Martin

2013-01-01

Cortical excitability may be subject to changes through training and learning. Motor training can increase cortical excitability in motor cortex, and facilitation of motor cortical excitability has been shown to be positively correlated with improvements in performance in simple motor tasks. Thus cortical excitability may tentatively be considered as a marker of learning and use-dependent plasticity. Previous studies focused on changes in cortical excitability brought about by learning processes, however, the relation between native levels of cortical excitability on the one hand and brain activation and behavioral parameters on the other is as yet unknown. In the present study we investigated the role of differential native motor cortical excitability for learning a motor sequencing task with regard to post-training changes in excitability, behavioral performance and involvement of brain regions. Our motor task required our participants to reproduce and improvise over a pre-learned motor sequence. Over both task conditions, participants with low cortical excitability (CElo) showed significantly higher BOLD activation in task-relevant brain regions than participants with high cortical excitability (CEhi). In contrast, CElo and CEhi groups did not exhibit differences in percentage of correct responses and improvisation level. Moreover, cortical excitability did not change significantly after learning and training in either group, with the exception of a significant decrease in facilitatory excitability in the CEhi group. The present data suggest that the native, unmanipulated level of cortical excitability is related to brain activation intensity, but not to performance quality. The higher BOLD mean signal intensity during the motor task might reflect a compensatory mechanism in CElo participants. PMID:23613956

Electronic excitations in finite and infinite polyenes

NASA Astrophysics Data System (ADS)

Tavan, Paul; Schulten, Klaus

1987-09-01

We study electronic excitations in long polyenes, i.e., in one-dimensional strongly correlated electron systems which are neither infinite nor small. The excitations are described within Hubbard and Pariser-Parr-Pople (PPP) models by means of a multiple-reference double-excitation expansion [P. Tavan and K. Schulten, J. Chem. Phys. 85, 6602 (1986)]. We find that quantized ``transition'' momenta can be assigned to electronic excitations in finite chains. These momenta link excitation energies of finite chains to dispersion relations of infinite chains, i.e., they bridge the gap between finite and infinite systems. A key result is the following: Excitation energies E in polyenes with N carbon atoms are described very accurately by the formula Eβ=ΔEβ0+αβk(N)q, q=1,2,..., where β denotes the excitation class, ΔEβ0 the energy gap in the infinite system [αβk(N)>0], and k(N) the elementary transition momentum. The parameters ΔEβ0 and αβ are determined for covalent and ionic excitations in alternating and nonalternating polyenes. The covalent excitations are combinations of triplet excitations T, i.e., T, TT, TTT, . . . . The lowest singlet excitations in the infinite polyene, e.g., in polyacetylene or polydiacetylene, are TT states. Available evidence proves that these states can dissociate into separate triplets. The bond structure of TT states is that of a neutral soliton-antisoliton pair. The level density of TT states in long polyenes is high enough to allow dissociation into separate solitons.

Temporal analysis of nonresonant two-photon coherent control involving bound and dissociative molecular states

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

Su Jing; Chen Shaohao; Jaron-Becker, Agnieszka

We theoretically study the control of two-photon excitation to bound and dissociative states in a molecule induced by trains of laser pulses, which are equivalent to certain sets of spectral phase modulated pulses. To this end, we solve the time-dependent Schroedinger equation for the interaction of molecular model systems with an external intense laser field. Our numerical results for the temporal evolution of the population in the excited states show that, in the case of an excited dissociative state, control schemes, previously validated for the atomic case, fail due to the coupling of electronic and nuclear motion. In contrast, formore » excitation to bound states the two-photon excitation probability is controlled via the time delay and the carrier-envelope phase difference between two consecutive pulses in the train.« less

Transient diffraction grating measurements of molecular diffusion in the undergraduate laboratory

NASA Astrophysics Data System (ADS)

Spiegel, Daniel R.; Tuli, Santona

2011-07-01

Diffusion is a central process in many biological, chemical, and physical systems. We describe an experiment that employs the interference of laser beams to allow the measurement of molecular diffusion on submillimeter length scales. The interference fringes of two intersecting pump beams within a dye solution create a sinusoidal distribution of long-lived molecular excited states. A third probe beam is incident at a wavelength at which the indices of refraction of the ground and excited states are different, so the probe beam diffracts from the spatially periodic excited-state pattern. After the pump beams are switched off, the excited-state periodicity washes out as the system diffuses back to equilibrium. The molecular diffusion constant is obtained from the rate constant of the exponential decay of the diffracted beam. It is also possible to measure the excited-state lifetime.

Thermality and excited state Rényi entropy in two-dimensional CFT

NASA Astrophysics Data System (ADS)

Lin, Feng-Li; Wang, Huajia; Zhang, Jia-ju

2016-11-01

We evaluate one-interval Rényi entropy and entanglement entropy for the excited states of two-dimensional conformal field theory (CFT) on a cylinder, and examine their differences from the ones for the thermal state. We assume the interval to be short so that we can use operator product expansion (OPE) of twist operators to calculate Rényi entropy in terms of sum of one-point functions of OPE blocks. We find that the entanglement entropy for highly excited state and thermal state behave the same way after appropriate identification of the conformal weight of the state with the temperature. However, there exists no such universal identification for the Rényi entropy in the short-interval expansion. Therefore, the highly excited state does not look thermal when comparing its Rényi entropy to the thermal state one. As the Rényi entropy captures the higher moments of the reduced density matrix but the entanglement entropy only the average, our results imply that the emergence of thermality depends on how refined we look into the entanglement structure of the underlying pure excited state.

Ab initio study of the ground and excited electronic states of the methyl radical

PubMed Central

Zanchet, A.; Bañares, L.; Senent, M. L.; García-Vela, A.

2016-01-01

The ground and some excited electronic states of the methyl radical have been characterized by means of highly correlated ab intio techniques. The specific excited states investigated are those involved in the dissociation of the radical, namely the 3s and 3pz Rydberg states, and the A1 and B1 valence states crossing them, respectively. The C-H dissociative coordinate and the HCH bending angle were considered in order to generate the first two-dimensional ab initio representation of the potential surfaces of the above electronic states of CH3, along with the nonadiabatic couplings between them. Spectroscopic constants and frequencies calculated for the ground and bound excited states agree well with most of the available experimental data. Implications of the shape of the excited potential surfaces and couplings for the dissociation pathways of CH3 are discussed in the light of recent experimental results for dissociation from low-lying vibrational states of CH3. Based on the ab initio data some predictions are made regarding methyl photodissociation from higher initial vibrational states. PMID:27892569

All-optical quantum fluid spin beam splitter

NASA Astrophysics Data System (ADS)

Askitopoulos, A.; Nalitov, A. V.; Sedov, E. S.; Pickup, L.; Cherotchenko, E. D.; Hatzopoulos, Z.; Savvidis, P. G.; Kavokin, A. V.; Lagoudakis, P. G.

2018-06-01

We investigate the spin behavior of the first excited state of a polariton condensate in an optical trap by means of polarization resolved spectroscopy. The interplay between the repulsive polariton interactions and the gain saturation results in a nontrivial spontaneous switching between the two quasidegenerate spatial modes of the polariton condensate. As a result, the polarization pattern of the emitted light dramatically changes. Successful harnessing of this effect can lead to a spin-demultiplexing device for polariton-based optical integrated circuits.

A Quantum Electronics Approach to Optical Negative Index Metamaterials (NIMs): Homogeneous NIMs in the Solid State

DTIC Science & Technology

2012-03-12

index effect at ~ 27.8 µm. This effect was theoretically predicted earlier, and it is based on coexistence of the spin wave ( magnon ) mode with the...refractive index at ~ 150 GHz, based on analogous plasmon- magnon excitation mechanism. 2.1 Fabrication of Cr doped IO material system...film, that the non-magnetic film possesses no maximum in region 27-28 µm. Such behavior is expected, since the spin waves ( magnons ) which are

Experimental data and theoretical analysis of an operating 100 kW wind turbine

NASA Technical Reports Server (NTRS)

Linscott, B. S.; Glasgow, J. C.; Anderson, W. D.; Donham, R. E.

1978-01-01

Experimental test data are correlated with analyses of turbine loads and complete system behavior of the ERDA-NASA 100 kW Mod-0 wind turbine generator over a broad range of steady state conditions, as well as during transient conditions. The deficit in the ambient wind field due to the upwind tower turbine support structure is found to be very significant in exciting higher harmonic loads associated with the flapping response of the blade in bending.

"Bright" and "dark" excited states of an alternating at oligomer characterized by femtosecond broadband spectroscopy.

PubMed

Kwok, Wai-Ming; Ma, Chensheng; Phillips, David Lee

2009-08-20

The nature and dynamics of DNA excited states is of pivotal importance in determining both DNA ultraviolet photostability and its vulnerability toward photodamage. The complexity regarding the involvement of "bright" and "dark" excited states, their molecular origin, and the roles played by these states in the course of electronic energy relaxation constitute an active and contentious area in current research of DNA excited states. As a case study, we report here a combined broadband femtosecond time-resolved fluorescence (TRF) and transient absorption (TA) study on a self-complementary d(AT)(10) oligomer and a reference system of an equal molar mixture of the constituent bases represented by adenosine and thymidine (A+T). Comparison of the spectral character and temporal evolution of the TRF and TA data for 267 nm excited d(AT)(10) and A+T provides evidence for a base-localized excitation feature for an early (< approximately 50 fs) "bright" S(LE) state and its ensuing evolution within approximately 3 ps into a approximately 72 ps "dark" S(E) exciplex in d(AT)(10). Combined analysis of the d(AT)(10) TRF and TA results suggests the presence of a weakly fluorescent transient S(G) state that acts as a gateway to mediate the excitation transfer and energy elimination. A distinct base conformation-dependent model involving an ultrafast approximately 0.3 ps conversion of the S(LE) to S(G) that then evolves by approximately 3 ps into the S(E) has been proposed to account for the collective deactivation character of d(AT)(10). This presents a novel excited-state picture that can unify the seemingly conflicting time-resolved results reported previously for related AT DNAs. The direct spectral and dynamical data provided here contributes important photophysical parameters for the description of the excited states of AT oligomers. The possible connection between the energy transfer giving the S(E) and the photostability vs photodamage of A/T DNAs is briefly discussed.

Many-electron aspects of molecular promotion in ion-atom collisions - Production of core-excited states of Li in Li/+/-He collisions

NASA Technical Reports Server (NTRS)

Elston, S. B.; Vane, C. R.; Schumann, S.

1979-01-01

Production of core-excited autoionizing states of neutral Li having configurations of the form 1snln(prime)l(prime) has been observed over the impact-energy range from 10-50 keV. Although the results for production of all such states is remarkably consistent with a quasi-molecular-excitation model proposed by Stolterfoht and Leithaeuser (1976), production of individual lines in the observed spectra exhibits collision-velocity dependencies indicative of considerably more complex processes, including processes which appear to be inherently two-electron in nature. Excitation functions are presented for (1s2s/2/)/2/S, 1s(2s2p/3/P)/2/P, 1s(2s2p/1/P)/2/P, and (1s2p/2/)/2/D core-excited state of Li and for total core excitation.

Excited-State Conformational/Electronic Responses of Saddle-Shaped N,N'-Disubstituted-Dihydrodibenzo[a,c]phenazines: Wide-Tuning Emission from Red to Deep Blue and White Light Combination.

PubMed

Zhang, Zhiyun; Wu, Yu-Sin; Tang, Kuo-Chun; Chen, Chi-Lin; Ho, Jr-Wei; Su, Jianhua; Tian, He; Chou, Pi-Tai

2015-07-08

A tailored strategy is utilized to modify 5,10-dimethylphenazine (DMP) to donor-acceptor type N,N'-disubstituted-dihydrodibenzo[a,c]phenazines. The representative compounds DMAC (N,N'-dimethyl), DPAC (N,N'-diphenyl), and FlPAC (N-phenyl-N'-fluorenyl) reveal significant nonplanar distortions (i.e., a saddle shape) and remarkably large Stokes-shifted emission independent of the solvent polarity. For DPAC and FlPAC with higher steric hindrance on the N,N'-substituents, normal Stokes-shifted emission also appears, for which the peak wavelength reveals solvent-polarity dependence. These unique photophysical behaviors are rationalized by electronic configuration coupled conformation changes en route to the geometry planarization in the excited state. This proposed mechanism is different from the symmetry rule imposed to explain the anomalously long-wavelength emission for DMP and is firmly supported by polarity-, viscosity-, and temperature-dependent steady-state and nanosecond time-resolved spectroscopy. Together with femtosecond early dynamics and computational simulation of the reaction energy surfaces, the results lead us to establish a sequential, three-step kinetics. Upon electronic excitation of N,N'-disubstituted-dihydrodibenzo[a,c]phenazines, intramolecular charge-transfer takes place, followed by the combination of polarization stabilization and skeletal motion toward the planarization, i.e., elongation of the π-delocalization over the benzo[a,c]phenazines moiety. Along the planarization, DPAC and FlPAC encounter steric hindrance raised by the N,N'-disubstitutes, resulting in a local minimum state, i.e., the intermediate. The combination of initial charge-transfer state, intermediate, and the final planarization state renders the full spectrum of interest and significance in their anomalous photophysics. Depending on rigidity, the N,N'-disubstituted-dihydrodibenzo[a,c]phenazines exhibit multiple emissions, which can be widely tuned from red to deep blue and even to white light generation upon optimization of the surrounding media.

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.

{ital L}=1 Excitation in the Halo Nucleus {sup 11}Li

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

Korsheninnikov, A.; Fukuda, S.; Ito, S.

Collisions of {sup 11}Li+p at 68AMeV have been studied by correlational measurements. An excited state of {sup 11}Li at E{sup {asterisk}}{approx_equal}1.3MeV was observed. The measured angular distributions show the dipole nature of the excitation of the 1.3-MeV peak. The structure of the excited states and the ground state of {sup 11}Li is discussed. {copyright} {ital 1997} {ital The American Physical Society}

Exciplex Formation between Silver Ions and the Lowest MLCT Excited State of the Tris(Bipyrazine)Ruthenium(2) Cation

DTIC Science & Technology

1988-07-11

OFFICE OF NAVAL RESEARCH Contract N00014-84-G-0201 Task No. 0051-865 0 Technical Report #21 Exciplex Formation Between Silver Ions and the Lowest...ELEMENT NO-. NO NO ~ ACCESSION NO 11. TITLE (include Security Classification) Exciplex Formation Between Silver Ions and the Lowest MLCT Excited State of... eXCiplexes with upIV to six silver ions per excited Cation. Lifetime, wavelength data are presented as a function of the [Agi/[Ru] ratio. An excited state

Laser-muon spin spectroscopy in liquids - a technique to study the excited state chemistry of transients.

PubMed

Ghandi, Khashayar; Clark, Ian P; Lord, James S; Cottrell, Stephen P

2007-01-21

This study introduces laser-muon spin spectroscopy in the liquid phase, which extends muonium chemistry in liquids to the realm of excited states and enables the detection of muoniated molecules by their spin evolution after laser excitation. This leads to new opportunities to study the Kinetic Isotope Effects (KIEs) of muonium/atomic hydrogen reactions and to probe transient chemistry in radiolysis processes involved in muonium formation, as well as muoniated intermediates in excited states.

Theoretical study of photoacidity of HCN: the effect of complexation with water.

PubMed

Muchová, Eva; Spirko, Vladimir; Hobza, Pavel; Nachtigallová, Dana

2006-11-14

The character of the hydrogen bonding and the excited state proton transfer (ESPT) in the model system HCN...H(2)O is investigated. The PES of the two lowest excited states of the H(2)O...HCN complex was calculated using the CASPT2 method. The nonadiabatic coupling of the two states of the (pi-->pi*) and (pi-->sigma*) character is responsible for the excited state proton/hydrogen transfer. Compared to the ground state, the barrier for this process is significantly smaller. An increased number of water molecules in the complex with cyclic hydrogen-bonded network causes a large blue shift of the state of the (pi-->sigma*) character. The question of the dissociation of the complex in its excited state is also addressed.

Refinements in the description of excited VRT states of the water dimer

NASA Astrophysics Data System (ADS)

Harker, H. A.; Keutsch, F. N.; Leforestier, C.; Scribano, Y.; Han, J.-X.; Saykally, R. J.

2007-03-01

Extensive new spectroscopic measurements are combined with a global analysis of the ground state data in order to re-examine and to refine the description of the excited vibration rotation tunneling (VRT) states of the water dimer. Notably, six new 'donor torsion' subbands are analytically identified, current vibrational assignments of the Ka = 1 stacks are reassessed, the previously reported (H2O)2 donor torsion overtone (DT)2 and hydrogen bond stretch (S) data sets are augmented, and four new (S) subbands have been measured. Unusually large Coriolis effects are predicted, excited state E2 ↔ E1 assignments are reinforced, and possibilities of experimentally determining ground state AS splitting in (H2O)2 from excited state data are discussed.

Search for two-neutrino double-β decay of 96Zr to excited states of 96Mo

NASA Astrophysics Data System (ADS)

Finch, S. W.; Tornow, W.

2015-10-01

Background: Double-β decay is a rare second-order nuclear decay. The importance of this decay stems from the possibility of neutrinoless double-β decay and its applications to neutrino physics. Purpose: A search was conducted for the 2 ν β β decay of 96Zr to excited final states of the daughter nucleus, 96Mo. Measurements of this decay are important to test nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the neutrinoless double-β decay half-life. Method: Two coaxial high-purity germanium detectors were used in coincidence to detect γ rays produced by the daughter nucleus as it de-excited to the ground state. The experiment was carried out at the Kimballton Underground Research Facility and produced 685.7 d of data with a 17.91 g enriched sample. Results: No counts were seen above background. For the decay to the first excited 0+ state, a limit of T1 /2>3.1 ×1020 yr was produced. Limits to higher excited states are also reported. Conclusion: The new limits on double-β decay are an improvement over previous experiments by a factor of 2 to 5 for the various excited states. The nuclear matrix element for the double-β decay to the first excited 0+ state is found to be <0.13 .

Photophysics of Deoxycytidine and 5-Methyldeoxycytidine in Solution: A Comprehensive Picture by Quantum Mechanical Calculations and Femtosecond Fluorescence Spectroscopy.

PubMed

Martínez-Fernández, L; Pepino, A J; Segarra-Martí, J; Jovaišaitė, J; Vaya, I; Nenov, A; Markovitsi, D; Gustavsson, T; Banyasz, A; Garavelli, M; Improta, R

2017-06-14

The study concerns the relaxation of electronic excited states of the DNA nucleoside deoxycytidine (dCyd) and its methylated analogue 5-methyldeoxycytidine (5mdCyd), known to be involved in the formation of UV-induced lesions of the genetic code. Due to the existence of four closely lying and potentially coupled excited states, the deactivation pathways in these systems are particularly complex and have not been assessed so far. Here, we provide a complete mechanistic picture of the excited state relaxation of dCyd/5mdCyd in three solvents-water, acetonitrile, and tetrahydrofuran-by combining femtosecond fluorescence experiments, addressing the effect of solvent proticity on the relaxation dynamics of dCyd and 5mdCyd for the first time, and two complementary quantum mechanical approaches (CASPT2/MM and PCM/TD-CAM-B3LYP). The lowest energy ππ* state is responsible for the sub-picosecond lifetime observed for dCyd in all the solvents. In addition, computed excited state absorption and transient IR spectra allow one, for the first time, to assign the tens of picoseconds time constant, reported previously, to a dark state (n O π*) involving the carbonyl lone pair. A second low-lying dark state, involving the nitrogen lone pair (n N π*), does significantly participate in the excited state dynamics. The 267 nm excitation of dCyd leads to a non-negligible population of the second bright ππ* state, which affects the dynamics, acting mainly as a "doorway" state for the n O π* state. The solvent plays a key role governing the interplay between the different excited states; unexpectedly, water favors population of the dark states. In the case of 5mdCyd, an energy barrier present on the main nonradiative decay route explains the 6-fold lengthening of the excited state lifetime compared to that of dCyd, observed for all the examined solvents. Moreover, C5-methylation destabilizes both n O π* and n N π* dark states, thus preventing them from being populated.

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

Gu, L. L.; Guo, X. G., E-mail: xgguo@mail.sim.ac.cn; Fu, Z. L.

Strong and sharp photocurrent peak at longitudinal optical (LO) phonon frequency (8.87 THz) is found in GaAs/(Al,Ga)As terahertz quantum-well photodetectors (QWPs). Two mesa-structure terahertz QWPs with and without one-dimensional metal grating are fabricated to investigate the behavior of such photoresponse peak. The experimental and simulation results indicate that the photocurrent peak originates from a two-step process. First, at the LO phonon frequency, a large number of non-equilibrium LO phonons are excited by the incident electromagnetic field, and the electromagnetic energy is localized and enhanced in the thin multi-quantum-well layer. Second, through the Frohlich interaction, the localized electrons are excited tomore » continuum states by absorbing the non-equilibrium LO phonons, which leads to the strong photoresponse peak. This finding is useful for exploring strong light-matter interaction and realizing high sensitive terahertz photodetectors.« less

Spinon dynamics in quantum integrable antiferromagnets

NASA Astrophysics Data System (ADS)

Vlijm, R.; Caux, J.-S.

2016-05-01

The excitations of the Heisenberg antiferromagnetic spin chain in zero field are known as spinons. As pairwise-created fractionalized excitations, spinons are important in the understanding of inelastic neutron scattering experiments in (quasi-)one-dimensional materials. In the present paper, we consider the real space-time dynamics of spinons originating from a local spin flip on the antiferromagnetic ground state of the (an)isotropic Heisenberg spin-1/2 model and the Babujan-Takhtajan spin-1 model. By utilizing algebraic Bethe ansatz methods at finite system size to compute the expectation value of the local magnetization and spin-spin correlations, spinons are visualized as propagating domain walls in the antiferromagnetic spin ordering with anisotropy dependent behavior. The spin-spin correlation after the spin flip displays a light cone, satisfying the Lieb-Robinson bound for the propagation of correlations at the spinon velocity.

Nonadiabatic excited-state molecular dynamics: modeling photophysics in organic conjugated materials.

PubMed

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

2014-04-15

To design functional photoactive materials for a variety of technological applications, researchers need to understand their electronic properties in detail and have ways to control their photoinduced pathways. When excited by photons of light, organic conjugated materials (OCMs) show dynamics that are often characterized by large nonadiabatic (NA) couplings between multiple excited states through a breakdown of the Born-Oppenheimer (BO) approximation. Following photoexcitation, various nonradiative intraband relaxation pathways can lead to a number of complex processes. Therefore, computational simulation of nonadiabatic molecular dynamics is an indispensable tool for understanding complex photoinduced processes such as internal conversion, energy transfer, charge separation, and spatial localization of excitons. Over the years, we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework that efficiently and accurately describes photoinduced phenomena in extended conjugated molecular systems. We use the fewest-switches surface hopping (FSSH) algorithm to treat quantum transitions among multiple adiabatic excited state potential energy surfaces (PESs). Extended molecular systems often contain hundreds of atoms and involve large densities of excited states that participate in the photoinduced dynamics. We can achieve an accurate description of the multiple excited states using the configuration interaction single (CIS) formalism with a semiempirical model Hamiltonian. Analytical techniques allow the trajectory to be propagated "on the fly" using the complete set of NA coupling terms and remove computational bottlenecks in the evaluation of excited-state gradients and NA couplings. Furthermore, the use of state-specific gradients for propagation of nuclei on the native excited-state PES eliminates the need for simplifications such as the classical path approximation (CPA), which only uses ground-state gradients. Thus, the NA-ESMD methodology offers a computationally tractable route for simulating hundreds of atoms on ~10 ps time scales where multiple coupled excited states are involved. In this Account, we review recent developments in the NA-ESMD modeling of photoinduced dynamics in extended conjugated molecules involving multiple coupled electronic states. We have successfully applied the outlined NA-ESMD framework to study ultrafast conformational planarization in polyfluorenes where the rate of torsional relaxation can be controlled based on the initial excitation. With the addition of the state reassignment algorithm to identify instances of unavoided crossings between noninteracting PESs, NA-ESMD can now be used to study systems in which these so-called trivial unavoided crossings are expected to predominate. We employ this technique to analyze the energy transfer between poly(phenylene vinylene) (PPV) segments where conformational fluctuations give rise to numerous instances of unavoided crossings leading to multiple pathways and complex energy transfer dynamics that cannot be described using a simple Förster model. In addition, we have investigated the mechanism of ultrafast unidirectional energy transfer in dendrimers composed of poly(phenylene ethynylene) (PPE) chromophores and have demonstrated that differential nuclear motion favors downhill energy transfer in dendrimers. The use of native excited-state gradients allows us to observe this feature.

Atomistic structural ensemble refinement reveals non-native structure stabilizes a sub-millisecond folding intermediate of CheY

DOE PAGES

Shi, Jade; Nobrega, R. Paul; Schwantes, Christian; ...

2017-03-08

The dynamics of globular proteins can be described in terms of transitions between a folded native state and less-populated intermediates, or excited states, which can play critical roles in both protein folding and function. Excited states are by definition transient species, and therefore are difficult to characterize using current experimental techniques. We report an atomistic model of the excited state ensemble of a stabilized mutant of an extensively studied flavodoxin fold protein CheY. We employed a hybrid simulation and experimental approach in which an aggregate 42 milliseconds of all-atom molecular dynamics were used as an informative prior for the structuremore » of the excited state ensemble. The resulting prior was then refined against small-angle X-ray scattering (SAXS) data employing an established method (EROS). The most striking feature of the resulting excited state ensemble was an unstructured N-terminus stabilized by non-native contacts in a conformation that is topologically simpler than the native state. We then predict incisive single molecule FRET experiments, using these results, as a means of model validation. Our study demonstrates the paradigm of uniting simulation and experiment in a statistical model to study the structure of protein excited states and rationally design validating experiments.« less

Atomistic structural ensemble refinement reveals non-native structure stabilizes a sub-millisecond folding intermediate of CheY

NASA Astrophysics Data System (ADS)

Shi, Jade; Nobrega, R. Paul; Schwantes, Christian; Kathuria, Sagar V.; Bilsel, Osman; Matthews, C. Robert; Lane, T. J.; Pande, Vijay S.

2017-03-01

The dynamics of globular proteins can be described in terms of transitions between a folded native state and less-populated intermediates, or excited states, which can play critical roles in both protein folding and function. Excited states are by definition transient species, and therefore are difficult to characterize using current experimental techniques. Here, we report an atomistic model of the excited state ensemble of a stabilized mutant of an extensively studied flavodoxin fold protein CheY. We employed a hybrid simulation and experimental approach in which an aggregate 42 milliseconds of all-atom molecular dynamics were used as an informative prior for the structure of the excited state ensemble. This prior was then refined against small-angle X-ray scattering (SAXS) data employing an established method (EROS). The most striking feature of the resulting excited state ensemble was an unstructured N-terminus stabilized by non-native contacts in a conformation that is topologically simpler than the native state. Using these results, we then predict incisive single molecule FRET experiments as a means of model validation. This study demonstrates the paradigm of uniting simulation and experiment in a statistical model to study the structure of protein excited states and rationally design validating experiments.

Electronic quenching of OH A 2Σ + radicals in collisions with molecular hydrogen

NASA Astrophysics Data System (ADS)

Pollack, Ilana B.; Lei, Yuxiu; Stephenson, Thomas A.; Lester, Marsha I.

2006-04-01

Collisional quenching of electronically excited OH A 2Σ + radicals by molecular hydrogen introduces nonradiative pathways that rapidly remove OH population from the excited state, and result in a significantly decreased fluorescence lifetime. One of these pathways is shown to lead to ground state OH X 2Π products with ˜1 eV of internal excitation in both highly excited rotational levels of v = 1 and the lowest rotational levels of v = 2. This highly nonstatistical OH X 2Π product distribution reflects the passage of the HO-H 2 system through the conical intersection regions that couple the ground and excited state surfaces.

A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

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.

A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

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

Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it

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.

Structures and Binding Energies of the Naphthalene Dimer in Its Ground and Excited States.

PubMed

Dubinets, N O; Safonov, A A; Bagaturyants, A A

2016-05-05

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.

Optogenetic Excitation of Central Amygdala Amplifies and Narrows Incentive Motivation to Pursue One Reward Above Another

PubMed Central

Warlow, Shelley M.; Berridge, Kent C.

2014-01-01

Choosing one reward above another is important for achieving adaptive life goals. Yet hijacked into excessive intensity in disorders such as addiction, single-minded pursuit becomes maladaptive. Here, we report that optogenetic channelrhodopsin stimulation of neurons in central nucleus of amygdala (CeA), paired with earning a particular sucrose reward in rats, amplified and narrowed incentive motivation to that single reward target. Therefore, CeA rats chose and intensely pursued only the laser-paired sucrose reward while ignoring an equally good sucrose alternative. In contrast, reward-paired stimulation of basolateral amygdala did not hijack choice. In a separate measure of incentive motivation, CeA stimulation also increased the progressive ratio breakpoint or level of effort exerted to obtain sucrose reward. However, CeA stimulation by itself failed to support behavioral self-stimulation in the absence of any paired external food reward, suggesting that CeA photo-excitation specifically transformed the value of its external reward (rather than adding an internal reinforcement state). Nor did CeA stimulation by itself induce any aversive state that motivated escape. Finally, CeA stimulation also failed to enhance ‘liking’ reactions elicited by sucrose taste and did not simply increase the general motivation to eat. This pattern suggests that CeA photo-excitation specifically enhances and narrows incentive motivation to pursue an associated external reward at the expense of another comparable reward. PMID:25505310

[Sexuality in children 9-14 years old].

PubMed

Ballester Arnal, Rafael; Gil Llario, María Dolores

2006-02-01

The aim of this study was to analyze sexual behaviors and attitudes of children 9-14 years old in Spain. In this article we present data from 470 children of which 52% are boys and 48% girls. In order to evaluate the sample, Information, Attitudes and Behaviors related to Health Questionnaire (CIACS-II) was used. Results evidence that boys 9 years old already show behaviors that evidence their interest towards sexuality. 8% have sometimes masturbated and 9% have used pornography for becoming excited. 14% of children 11-12 years old have already had sexual relations and 38% state to have sexual fantasies. Girls start to masturbate and to have sexual relations later than boys and show a prevalence of sexual fantasies and use of pornography very lower. It is necessary sexual education programs to be implanted since early ages in schools.

Elucidating Neuronal Mechanisms Using Intracellular Recordings during Behavior.

PubMed

Lee, Albert K; Brecht, Michael

2018-06-01

Intracellular recording allows measurement and perturbation of the membrane potential of identified neurons with sub-millisecond and sub-millivolt precision. This gives intracellular recordings a unique capacity to provide rich information about individual cells (e.g., high-resolution characterization of inputs, outputs, excitability, and structure). Hence, such recordings can elucidate the mechanisms that underlie fundamental phenomena, such as brain state, sparse coding, gating, gain modulation, and learning. Technical developments have increased the range of behaviors during which intracellular recording methods can be employed, such as in freely moving animals and head-fixed animals actively performing tasks, including in virtual environments. Such advances, and the combination of intracellular recordings with genetic and imaging techniques, have enabled investigation of the mechanisms that underlie neural computations during natural and trained behaviors. Copyright © 2018 Elsevier Ltd. All rights reserved.

Disposal of Energy by UV-B Sunscreens

NASA Astrophysics Data System (ADS)

Nordlund, Thomas; Krishnan, Rajagopal

2008-03-01

Ideal sunscreens absorb dangerous UV light and dispose of the energy safely. ``Safe disposal'' usually means conversion to heat. However, efficient absorption entails a high radiative rate, which implies high energy-transfer and other rates, unless some process intervenes to ``defuse'' the excited state. We studied the excited-state kinetics of three UV-B (290-320 nm) sunscreens by absorption, steady-state and time-resolved fluorescence. Excited-state rate analysis suggests that some sunscreens have low radiative-rate ``dark'' states, in addition to normal excited states.* We deduce dark states when sunscreens of high extinction coefficient do not show lifetimes and total emission consistent with such high radiative rates. A high radiative rate, accompanied by efficient fluorescence emission and/or transfer, may be unfavorable for a sunscreen. In spite of its dark excited state, padimate O shows significant re-emission of light in the UV-A (320-400 nm) and energy transfer to a natural component of excised skin, probably collagen. * Krishnan, R. and T.M. Nordlund (2007) J. Fluoresc. DOI 10.1007/s10895-007-0264-3.

High Pressure Optical Studies of the Thallous Halides and of Charge-Transfer Complexes

NASA Astrophysics Data System (ADS)

Jurgensen, Charles Willard

High pressure was used to study the insulator -to-metal transition in sulfur and the thallous halides and to study the intermolecular interactions in charge -transfer complexes. The approach to the band overlap insulator -to-metal transition was studied in three thallous halides and sulfur by optical absorption measurements of the band gap as a function of pressure. The band gap of sulfur continuously decreases with pressure up to the insulator -to-metal transition which occurs between 450 and 485 kbars. The results on the thallous halides indicate that the indirect gap decreases more rapidly than the direct gap; the closing of the indirect gap is responsible for the observed insulator -to-metal transitions. High pressure electronic and vibrational spectroscopic measurements on the solid-state complexes of HMB-TCNE were used to study the intermolecular interactions of charge -transfer complexes. The vibrational frequency shifts indicate that the degree of charge transfer increases with pressure which is independently confirmed by an increase in the molar absorptivity of the electronic charge-transfer peak. Induction and dispersion forces contribute towards a red shift of the charge-transfer peak; however, charge-transfer resonance contributes toward a blue shift and this effect is dominant for the HMB-TCNE complexes. High pressure electronic spectra were used to study the effect of intermolecular interactions on the electronic states of TCNQ and its complexes. The red shifts with pressure of the electronic spectra of TCNQ and (TCNQ)(' -) in polymer media and of crystalline TCNQ can be understood in terms of Van der Waals interactions. None of the calculations which considered intradimer distance obtained the proper behavior for either the charge-transfer of the locally excited states of the complexes. The qualitative behavior of both states can be interpreted as the effect of increased mixing of the locally excited and charge transfer states.

Disordered Berezinskii-Kosterlitz-Thouless transition and superinsulation

DOE PAGES

Sankar, S.; Vinokur, V. M.; Tripathi, V.

2018-01-22

Here, we investigate the critical Berezinskii-Kosterlitz-Thouless (BKT) behavior of disordered two-dimensional Josephson-junction arrays (JJA) on the insulating side of the superconductor-insulator transition (SIT) taking into account the effect of hitherto ignored residual random dipole moments of the superconducting grains. We show that for weak Josephson coupling the model is equivalent to a Coulomb gas subjected to a disorder potential with logarithmic correlations. We demonstrate that strong enough disorder transforms the BKT divergence of the correlation length, ξ BKT ∝ exp (const / √T-T BKT), characterizing the average distance between the unbound topological excitations of the opposite signs, into a moremore » singular Vogel-Fulcher-Tamman (VFT) behavior, ξ VFT ∝ exp [const / (T-T VFT)] , which is viewed as a hallmark of glass transitions in glass-forming materials. We further show that the VFT criticality is a precursor of the transition into a nonergodic superinsulating state, while the BKT critical behavior implies freezing into an ergodic confined BKT state. Finally, our finding sheds light on the yet unresolved problem of the origin of the VFT criticality.« less

Spin Chirality of Cu3 and V3 Nanomagnets. 1. Rotation Behavior of Vector Chirality, Scalar Chirality, and Magnetization in the Rotating Magnetic Field, Magnetochiral Correlations.

PubMed

Belinsky, Moisey I

2016-05-02

The rotation behavior of the vector chirality κ, scalar chirality χ, and magnetization M in the rotating magnetic field H1 is considered for the V3 and Cu3 nanomagnets, in which the Dzialoshinsky-Moriya coupling is active. The polar rotation of the field H1 of the given strength H1 results in the energy spectrum characterized by different vector and scalar chiralities in the ground and excited states. The magnetochiral correlations between the vector and scalar chiralities, energy, and magnetization in the rotating field were considered. Under the uniform polar rotation of the field H1, the ground-state chirality vector κI performs sawtooth oscillations and the magnetization vector MI performs the sawtooth oscillating rotation that is accompanied by the correlated transformation of the scalar chirality χI. This demonstrates the magnetochiral effect of the joint rotation behavior and simultaneous frustrations of the spin chiralities and magnetization in the rotating field, which are governed by the correlation between the chiralities and magnetization.

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

Sankar, S.; Vinokur, V. M.; Tripathi, V.

Here, we investigate the critical Berezinskii-Kosterlitz-Thouless (BKT) behavior of disordered two-dimensional Josephson-junction arrays (JJA) on the insulating side of the superconductor-insulator transition (SIT) taking into account the effect of hitherto ignored residual random dipole moments of the superconducting grains. We show that for weak Josephson coupling the model is equivalent to a Coulomb gas subjected to a disorder potential with logarithmic correlations. We demonstrate that strong enough disorder transforms the BKT divergence of the correlation length, ξ BKT ∝ exp (const / √T-T BKT), characterizing the average distance between the unbound topological excitations of the opposite signs, into a moremore » singular Vogel-Fulcher-Tamman (VFT) behavior, ξ VFT ∝ exp [const / (T-T VFT)] , which is viewed as a hallmark of glass transitions in glass-forming materials. We further show that the VFT criticality is a precursor of the transition into a nonergodic superinsulating state, while the BKT critical behavior implies freezing into an ergodic confined BKT state. Finally, our finding sheds light on the yet unresolved problem of the origin of the VFT criticality.« less