Quantum speed limit for arbitrary initial states

PubMed Central

Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Cao, Jun-Peng; Fan, Heng

2014-01-01

The minimal time a system needs to evolve from an initial state to its one orthogonal state is defined as the quantum speed limit time, which can be used to characterize the maximal speed of evolution of a quantum system. This is a fundamental question of quantum physics. We investigate the generic bound on the minimal evolution time of the open dynamical quantum system. This quantum speed limit time is applicable to both mixed and pure initial states. We then apply this result to the damped Jaynes-Cummings model and the Ohimc-like dephasing model starting from a general time-evolution state. The bound of this time-dependent state at any point in time can be found. For the damped Jaynes-Cummings model, when the system starts from the excited state, the corresponding bound first decreases and then increases in the Markovian dynamics. While in the non-Markovian regime, the speed limit time shows an interesting periodic oscillatory behavior. For the case of Ohimc-like dephasing model, this bound would be gradually trapped to a fixed value. In addition, the roles of the relativistic effects on the speed limit time for the observer in non-inertial frames are discussed. PMID:24809395

Exact stochastic unraveling of an optical coherence dynamics by cumulant expansion

NASA Astrophysics Data System (ADS)

Olšina, Jan; Kramer, Tobias; Kreisbeck, Christoph; Mančal, Tomáš

2014-10-01

A numerically exact Monte Carlo scheme for calculation of open quantum system dynamics is proposed and implemented. The method consists of a Monte Carlo summation of a perturbation expansion in terms of trajectories in Liouville phase-space with respect to the coupling between the excited states of the molecule. The trajectories are weighted by a complex decoherence factor based on the second-order cumulant expansion of the environmental evolution. The method can be used with an arbitrary environment characterized by a general correlation function and arbitrary coupling strength. It is formally exact for harmonic environments, and it can be used with arbitrary temperature. Time evolution of an optically excited Frenkel exciton dimer representing a molecular exciton interacting with a charge transfer state is calculated by the proposed method. We calculate the evolution of the optical coherence elements of the density matrix and linear absorption spectrum, and compare them with the predictions of standard simulation methods.

Simulation of femtosecond two-dimensional electronic spectra of conical intersections

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

Krčmář, Jindřich; Gelin, Maxim F.; Domcke, Wolfgang

2015-08-21

We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed.

Observing Quantum State Diffusion by Heterodyne Detection of Fluorescence

NASA Astrophysics Data System (ADS)

Campagne-Ibarcq, P.; Six, P.; Bretheau, L.; Sarlette, A.; Mirrahimi, M.; Rouchon, P.; Huard, B.

2016-01-01

A qubit can relax by fluorescence, which prompts the release of a photon into its electromagnetic environment. By counting the emitted photons, discrete quantum jumps of the qubit state can be observed. The succession of states occupied by the qubit in a single experiment, its quantum trajectory, depends in fact on the kind of detector. How are the quantum trajectories modified if one measures continuously the amplitude of the fluorescence field instead? Using a superconducting parametric amplifier, we perform heterodyne detection of the fluorescence of a superconducting qubit. For each realization of the measurement record, we can reconstruct a different quantum trajectory for the qubit. The observed evolution obeys quantum state diffusion, which is characteristic of quantum measurements subject to zero-point fluctuations. Independent projective measurements of the qubit at various times provide a quantitative verification of the reconstructed trajectories. By exploring the statistics of quantum trajectories, we demonstrate that the qubit states span a deterministic surface in the Bloch sphere at each time in the evolution. Additionally, we show that when monitoring fluorescence field quadratures, coherent superpositions are generated during the decay from excited to ground state. Counterintuitively, measuring light emitted during relaxation can give rise to trajectories with increased excitation probability.

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.

Hyperspectral Probing of Exciton dynamics and Multiplication in PbSe Nanocrystals

NASA Astrophysics Data System (ADS)

Gdor, I.; Sachs, H.; Roitblat, A.; Strasfeld, D.; Bawendi, M. G.; Ruhman, S.

2013-03-01

Height time hyperspectral near IR probing providing broad-band coverage is employed on PbSe nanocrystals, uncovering spectral evolution following high energy photo-excitation due to hot exciton relaxation and recombination. Separation of single, double and triple exciton state contributions to these spectra is demonstrated, and the mechanisms underlying the course of spectral evolution are investigated. In addition no sign of MEG was detected in this sample up to a photon energy 3.7 times that of the band gap.

In-beam γ -ray spectroscopy of Mn 63

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

Baugher, T.; Gade, A.; Janssens, R. V. F.

2016-01-01

Background: Neutron-rich, even-mass chromium and iron isotopes approaching neutron number N = 40 have been important benchmarks in the development of shell-model effective interactions incorporating the effects of shell evolution in the exotic regime. Odd-mass manganese nuclei have received less attention, but provide important and complementary sensitivity to these interactions. Purpose: We report the observation of two new γ -ray transitions in 63 Mn , which establish the ( 9 / 2 - ) and ( 11 / 2 - ) levels on top of the previously known ( 7 / 2 - ) first-excited state. The lifetime for themore » ( 7 / 2 - ) and ( 9 / 2 - ) excited states were determined for the first time, while an upper limit could be established for the ( 11 / 2 - ) level. Method: Excited states in 63 Mn have been populated in inelastic scattering from a 9 Be target and in the fragmentation of 65 Fe . γ γ coincidence relationships were used to establish the decay level scheme. A Doppler line-shape analysis for the Doppler-broadened ( 7 / 2 - ) → 5 / 2 - , ( 9 / 2 - ) → ( 7 / 2 - ) , and ( 11 / 2 - ) → ( 9 / 2 - ) transitions was used to determine (limits for) the corresponding excited-state lifetimes. Results: The low-lying level scheme and the excited-state lifetimes were compared with large-scale shell-model calculations using different model spaces and effective interactions in order to isolate important aspects of shell evolution in this region of structural change. Conclusions: While the theoretical ( 7 / 2 - ) and ( 9 / 2 - ) excitation energies show little dependence on the model space, the calculated lifetime of the ( 7 / 2 - ) level and calculated energy of the ( 11 / 2 - ) level reveal the importance of including the neutron g 9 / 2 and d 5 / 2 orbitals in the model space. The LNPS effective shell-model interaction provides the best overall agreement with the new data.« less

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.

Real time observation of the excimer formation dynamics of a gas phase benzene dimer by picosecond pump-probe spectroscopy.

PubMed

Miyazaki, Mitsuhiko; Fujii, Masaaki

2015-10-21

We observed the real-time excimer (EXC) formation dynamics of a gas phase benzene dimer (Bz2) cluster after photo-excitation to the S1 state by applying an ionization detected picosecond transient absorption method for probing the visible EXC absorption for the first time. The time evolution of the EXC absorption from the S1 0(0) level shows a rise that is well fitted by a single exponential function with a time constant of 18 ± 2 ps. The structure of the Bz dimer has a T-shaped structure in the ground electronic state, and that in the EXC state is a parallel sandwich (SW) structure. Thus, the observed rise time corresponds to the structural change from the T to the SW structures, which directly shows the EXC formation. On the other hand, the EXC formation after excitation of the S1 6(1) vibrational level of the stem site showed a faster rise of the time constant of 10 ± 2 ps. Supposing equilibrium between the EXC and the local excited states, it followed that the intramolecular vibrational energy redistribution rate of the 6(1) level is largely enhanced and becomes faster than the EXC formation reaction.

Exploring Nuclear Photorelaxation of Pyranine in Aqueous Solution: an Integrated Ab-Initio Molecular Dynamics and Time Resolved Vibrational Analysis Approach.

PubMed

Chiariello, Maria Gabriella; Rega, Nadia

2018-03-22

Advances in time-resolved vibrational spectroscopy techniques provided a new stimulus for understanding the transient molecular dynamics triggered by the electronic excitation. The detailed interpretation of such time-dependent spectroscopic signals is a challenging task from both experimental and theoretical points of view. We simulated and analyzed the transient photorelaxation of the pyranine photoacid in aqueous solution, with special focus on structural parameters and low frequency skeleton modes that are possibly preparatory for the photoreaction occurring at later time, as suggested by experimental spectroscopic studies. To this aim, we adopted an accurate computational protocol that combines excited state ab initio molecular dynamics within an hybrid quantum mechanical/molecular mechanics framework and a time-resolved vibrational analysis based on the Wavelet transform. According to our results, the main nuclear relaxation on the excited potential energy surface is completed in about 500 fs, in agreement with experimental data. The rearrangement of C-C bonds occurs according to a complex vibrational dynamics, showing oscillatory patterns that are out of phase and modulated by modes below 200 cm -1 . We also analyzed in both the ground and the excited state the evolution of some structural parameters involved in excited state proton transfer reaction, namely, those involving the pyranine and the water molecule hydrogen bonded to the phenolic O-H group. Both the hydrogen bond distance and the intermolecular orientation are optimized in the excited state, resulting in a tighter proton donor-acceptor couple. Indeed, we found evidence that collective low frequency skeleton modes, such as the out of plane wagging at 108 cm -1 and the deformation at 280 cm -1 , are photoactivated by the ultrafast part of the relaxation and modulate the pyranine-water molecule rearrangement, favoring the preparatory step for the photoreactivity.

Dicke states in multiple quantum dots

NASA Astrophysics Data System (ADS)

Sitek, Anna; Manolescu, Andrei

2013-10-01

We present a theoretical study of the collective optical effects which can occur in groups of three and four quantum dots. We define conditions for stable subradiant (dark) states, rapidly decaying super-radiant states, and spontaneous trapping of excitation. Each quantum dot is treated like a two-level system. The quantum dots are, however, realistic, meaning that they may have different transition energies and dipole moments. The dots interact via a short-range coupling which allows excitation transfer across the dots, but conserves the total population of the system. We calculate the time evolution of single-exciton and biexciton states using the Lindblad equation. In the steady state the individual populations of each dot may have permanent oscillations with frequencies given by the energy separation between the subradiant eigenstates.

Dark and bright-state polaritons in triple- Λ EIT system

NASA Astrophysics Data System (ADS)

Selvan, Karthick

2018-04-01

Properties of polaritons in triple-Λ EIT system are investigated using Sawada-Brout-Chong method. The role of dark and bright-state polaritons in the dynamics of the system is studied in detail by including the decay of excited atomic levels. Time evolution of entanglement of single and three-photon EIT modes within the system is investigated to explain this study.

Deuteron Coulomb Excitation in Peripheral Collisions with a Heavy Ion

NASA Astrophysics Data System (ADS)

Du, Weijie; Yin, Peng; Li, Yang; Chen, Guangyao; Zuo, Wei; Zhao, Xingbo; Vary, James P.

2017-09-01

We develop an ab initio time-dependent Basis Function (tBF) method to solve non-perturbative and time-dependent problems in non-relativistic quantum mechanics. As a test problem, we apply this method to the Coulomb excitation of a deuteron by an impinging heavy ion. We employ wave functions for the bound and excited states of the deuterium system based on a realistic nucleon-nucleon interaction and study the evolution of the transition probability, the r.m.s. radius and the r.m.s. momentum of the system during the scattering process. The dependencies of these quantities on the external field strength and the bombarding energy are also analyzed and compared to corresponding results obtained from first-order perturbation theory. The time evolution of both the charge and the momentum distributions is shown. This work was supported in part by the U. S. Department of Energy (DOE) under Grants No. DESC0008485 (SciDAC/NUCLEI) and DE-FG02-87ER40371. W. Zuo and P. Yin are supported by the National Natural Science Foundation of China (11435014).

Spin-dependent evolution of collectivity in 112Te

NASA Astrophysics Data System (ADS)

Doncel, M.; Bäck, T.; Qi, C.; Cullen, D. M.; Hodge, D.; Cederwall, B.; Taylor, M. J.; Procter, M.; Giles, M.; Auranen, K.; Grahn, T.; Greenlees, P. T.; Jakobsson, U.; Julin, R.; Juutinen, S.; HerzáÅ, A.; Konki, J.; Pakarinen, J.; Partanen, J.; Peura, P.; Rahkila, P.; Ruotsalainen, P.; Sandzelius, M.; Sarén, J.; Scholey, C.; Sorri, J.; Stolze, S.; Uusitalo, J.

2017-11-01

The evolution of collectivity with spin along the yrast line in the neutron-deficient nucleus 112Te has been studied by measuring the reduced transition probability of excited states in the yrast band. In particular, the lifetimes of the 4+ and 6+ excited states have been determined by using the recoil distance Doppler-shift method. The results are discussed using both large-scale shell-model and total Routhian surface calculations.

Picosecond excite-and-probe absorption measurement of the intra-2E(g)E(3/2)-state vibrational relaxation time in Ti(3+):Al2O3

NASA Technical Reports Server (NTRS)

Gayen, S. K.; Wang, W. B.; Petricevic, V.; Yoo, K. M.; Alfano, R. R.

1987-01-01

The Ti(3+)-doped Al2O3 has been recently demonstrated to be a tunable solid-state laser system with Ti(3+) as the laser-active ion. In this paper, the kinetics of vibrational transitions in the 2E(g)E(3/2) electronic state of Ti(3+):Al2O3a (crucial for characterizing new host materials for the Ti ion) was investigated. A 527-nm 5-ps pulse was used to excite a band of higher vibrational levels of the 2E(g)E(3/2) state, and the subsequent growth of population in the zero vibrational level and lower vibrational levels was monitored by a 3.9-micron picosecond probe pulse. The time evolution curve in the excited 2E(g)E(3/2) state at room temperature was found to be characterized by a sharp rise followed by a long decay, the long lifetime decay reflecting the depopulation of the zero and the lower vibrational levels of the 2E(g)E(3/2) state via radiative transitions. An upper limit of 3.5 ps was estimated for intra-2E(g)E(3/2)-state vibrational relaxation time.

Entanglement and thermodynamics after a quantum quench in integrable systems.

PubMed

Alba, Vincenzo; Calabrese, Pasquale

2017-07-25

Entanglement and entropy are key concepts standing at the foundations of quantum and statistical mechanics. Recently, the study of quantum quenches revealed that these concepts are intricately intertwined. Although the unitary time evolution ensuing from a pure state maintains the system at zero entropy, local properties at long times are captured by a statistical ensemble with nonzero thermodynamic entropy, which is the entanglement accumulated during the dynamics. Therefore, understanding the entanglement evolution unveils how thermodynamics emerges in isolated systems. Alas, an exact computation of the entanglement dynamics was available so far only for noninteracting systems, whereas it was deemed unfeasible for interacting ones. Here, we show that the standard quasiparticle picture of the entanglement evolution, complemented with integrability-based knowledge of the steady state and its excitations, leads to a complete understanding of the entanglement dynamics in the space-time scaling limit. We thoroughly check our result for the paradigmatic Heisenberg chain.

Entanglement and thermodynamics after a quantum quench in integrable systems

NASA Astrophysics Data System (ADS)

Alba, Vincenzo; Calabrese, Pasquale

2017-07-01

Entanglement and entropy are key concepts standing at the foundations of quantum and statistical mechanics. Recently, the study of quantum quenches revealed that these concepts are intricately intertwined. Although the unitary time evolution ensuing from a pure state maintains the system at zero entropy, local properties at long times are captured by a statistical ensemble with nonzero thermodynamic entropy, which is the entanglement accumulated during the dynamics. Therefore, understanding the entanglement evolution unveils how thermodynamics emerges in isolated systems. Alas, an exact computation of the entanglement dynamics was available so far only for noninteracting systems, whereas it was deemed unfeasible for interacting ones. Here, we show that the standard quasiparticle picture of the entanglement evolution, complemented with integrability-based knowledge of the steady state and its excitations, leads to a complete understanding of the entanglement dynamics in the space-time scaling limit. We thoroughly check our result for the paradigmatic Heisenberg chain.

Entanglement and thermodynamics after a quantum quench in integrable systems

PubMed Central

Alba, Vincenzo; Calabrese, Pasquale

2017-01-01

Entanglement and entropy are key concepts standing at the foundations of quantum and statistical mechanics. Recently, the study of quantum quenches revealed that these concepts are intricately intertwined. Although the unitary time evolution ensuing from a pure state maintains the system at zero entropy, local properties at long times are captured by a statistical ensemble with nonzero thermodynamic entropy, which is the entanglement accumulated during the dynamics. Therefore, understanding the entanglement evolution unveils how thermodynamics emerges in isolated systems. Alas, an exact computation of the entanglement dynamics was available so far only for noninteracting systems, whereas it was deemed unfeasible for interacting ones. Here, we show that the standard quasiparticle picture of the entanglement evolution, complemented with integrability-based knowledge of the steady state and its excitations, leads to a complete understanding of the entanglement dynamics in the space–time scaling limit. We thoroughly check our result for the paradigmatic Heisenberg chain. PMID:28698379

Inverting pump-probe spectroscopy for state tomography of excitonic systems.

PubMed

Hoyer, Stephan; Whaley, K Birgitta

2013-04-28

We propose a two-step protocol for inverting ultrafast spectroscopy experiments on a molecular aggregate to extract the time-evolution of the excited state density matrix. The first step is a deconvolution of the experimental signal to determine a pump-dependent response function. The second step inverts this response function to obtain the quantum state of the system, given a model for how the system evolves following the probe interaction. We demonstrate this inversion analytically and numerically for a dimer model system, and evaluate the feasibility of scaling it to larger molecular aggregates such as photosynthetic protein-pigment complexes. Our scheme provides a direct alternative to the approach of determining all Hamiltonian parameters and then simulating excited state dynamics.

Room-temperature ultrafast nonlinear spectroscopy of a single molecule

NASA Astrophysics Data System (ADS)

Liebel, Matz; Toninelli, Costanza; van Hulst, Niek F.

2018-01-01

Single-molecule spectroscopy aims to unveil often hidden but potentially very important contributions of single entities to a system's ensemble response. Albeit contributing tremendously to our ever growing understanding of molecular processes, the fundamental question of temporal evolution, or change, has thus far been inaccessible, thus painting a static picture of a dynamic world. Here, we finally resolve this dilemma by performing ultrafast time-resolved transient spectroscopy on a single molecule. By tracing the femtosecond evolution of excited electronic state spectra of single molecules over hundreds of nanometres of bandwidth at room temperature, we reveal their nonlinear ultrafast response in an effective three-pulse scheme with fluorescence detection. A first excitation pulse is followed by a phase-locked de-excitation pulse pair, providing spectral encoding with 25 fs temporal resolution. This experimental realization of true single-molecule transient spectroscopy demonstrates that two-dimensional electronic spectroscopy of single molecules is experimentally within reach.

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.

Recombination dynamics of optically excited charge carriers in bulk MoS2

NASA Astrophysics Data System (ADS)

Völzer, Tim; Lütgens, Matthias; Fennel, Franziska; Lochbrunner, Stefan

2017-10-01

Transition metal dichalcogenides (TMDCs), such as MoS2, are promising candidates for optoelectronic or catalytic applications. On that account, a detailed characterization of the electronic dynamics in these materials is of pivotal importance. Here, we investigate the temporal evolution of an excited carrier population by all-optical pump-probe spectroscopy. On the sub-picosecond time scale we observe thermal relaxation of the excited carriers by electron-phonon coupling. The dynamics on the nanosecond time scale can be understood in terms of defect-assisted Auger recombination over a broad carrier density regime spanning more than one order of magnitude. Hence, our results emphasize the importance of defect states for electronic processes in TMDCs at room temperature.

Isomerization Intermediates In Solution Phase Photochemistry Of Stilbenes

NASA Astrophysics Data System (ADS)

Doany, F. E.; Hochstrasser, R. M.; Greene, B. I.

1985-04-01

Picosecond and subpicosecond spectroscopic studies have revealed evidence for an isomerization intermediate between cis and trans in the photoinduced isomerism of both stilbene and biindanyledene ("stiff" stilbene). In stiff stilbene, a transient absorption at 351 nm displays time evolution and viscosity dependence consistent with absorption by a twisted intermediate ("phantom" state) with a lOps lifetime. An analagous bottleneck state with a life-time of 4ps is also consistent with the ground state recovery dynamics of t-stilbene following excitation of c-stilbene when monitored with 0.1ps resolution.

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.

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

Resonance and decay phenomena lead to quantum mechanical time asymmetry

NASA Astrophysics Data System (ADS)

Bohm, A.; Bui, H. V.

2013-04-01

The states (Schrödinger picture) and observables (Heisenberg picture) in the standard quantum theory evolve symmetrically in time, given by the unitary group with time extending over -∞ < t < +∞. This time evolution is a mathematical consequence of the Hilbert space boundary condition for the dynamical differential equations. However, this unitary group evolution violates causality. Moreover, it does not solve an old puzzle of Wigner: How does one describe excited states of atoms which decay exponentially, and how is their lifetime τ related to the Lorentzian width Γ? These question can be answered if one replaces the Hilbert space boundary condition by new, Hardy space boundary conditions. These Hardy space boundary conditions allow for a distinction between states (prepared by a preparation apparatus) and observables (detected by a registration apparatus). The new Hardy space quantum theory is time asymmetric, i.e, the time evolution is given by the semigroup with t0 <= t < +∞, which predicts a finite "beginning of time" t0, where t0 is the ensemble of time at which each individual system has been prepared. The Hardy space axiom also leads to the new prediction: the width Γ and the lifetime τ are exactly related by τ = hslash/Γ.

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

Research on System Coherence Evolution of Different Environmental Models

NASA Astrophysics Data System (ADS)

Zhang, Si-Qi; Lu, Jing-Bin; Li, Hong; Liu, Ji-Ping; Zhang, Xiao-Ru; Liu, Han; Liang, Yu; Ma, Ji; Liu, Xiao-Jing; Wu, Xiang-Yao

2018-04-01

In this paper, we have studied the evolution curve of two-level atomic system that the initial state is excited state. At the different of environmental reservoir models, which include the single Lorentzian, ideal photon band-gap, double Lorentzian and square Lorentzian reservoir, we researched the influence of these environmental reservoir models on the evolution of energy level population. At static no modulation, comparing the four environmental models, the atomic energy level population oscillation of square Lorentzian reservoir model is fastest, and the atomic system decoherence is slowest. Under dynamic modulation, comparing the photon band-gap model with the single Lorentzian reservoir model, no matter what form of dynamic modulation, the time of atoms decay to the ground state is longer for the photonic band-gap model. These conclusions make the idea of using the environmental change to modulate the coherent evolution of atomic system become true.

Selective bond breaking mediated by state specific vibrational excitation in model HOD molecule through optimized femtosecond IR pulse: a simulated annealing based approach.

PubMed

Shandilya, Bhavesh K; Sen, Shrabani; Sahoo, Tapas; Talukder, Srijeeta; Chaudhury, Pinaki; Adhikari, Satrajit

2013-07-21

The selective control of O-H/O-D bond dissociation in reduced dimensionality model of HOD molecule has been explored through IR+UV femtosecond pulses. The IR pulse has been optimized using simulated annealing stochastic approach to maximize population of a desired low quanta vibrational state. Since those vibrational wavefunctions of the ground electronic states are preferentially localized either along the O-H or O-D mode, the femtosecond UV pulse is used only to transfer vibrationally excited molecule to the repulsive upper surface to cleave specific bond, O-H or O-D. While transferring from the ground electronic state to the repulsive one, the optimization of the UV pulse is not necessarily required except specific case. The results so obtained are analyzed with respect to time integrated flux along with contours of time evolution of probability density on excited potential energy surface. After preferential excitation from [line]0, 0> ([line]m, n> stands for the state having m and n quanta of excitations in O-H and O-D mode, respectively) vibrational level of the ground electronic state to its specific low quanta vibrational state ([line]1, 0> or [line]0, 1> or [line]2, 0> or [line]0, 2>) by using optimized IR pulse, the dissociation of O-D or O-H bond through the excited potential energy surface by UV laser pulse appears quite high namely, 88% (O-H ; [line]1, 0>) or 58% (O-D ; [line]0, 1>) or 85% (O-H ; [line]2, 0>) or 59% (O-D ; [line]0, 2>). Such selectivity of the bond breaking by UV pulse (if required, optimized) together with optimized IR one is encouraging compared to the normal pulses.

Observation of ultrafast temporal evolution of symmetry in short-pulsed laser induced transient states of matter (Conference Presentation)

NASA Astrophysics Data System (ADS)

Garnett, Joy; Krzyzanowska, Halina; Baydin, Andrey; Tolk, Norman H.

2017-02-01

In condensed matter physics, ultrafast photoexcitation has been shown to result in modification of macroscopic material properties, sometimes involving phase changes, on a subpicosecond time scale. In semiconductors, irreversible non-thermal solid-to-liquid structural transitions have been demonstrated at high laser fluences. In the pump-probe experiments reported here, we observe a striking continuously varying low-fluence pump-induced time-dependent structural symmetry modification in intrinsic gallium arsenide (GaAs) using a probe that produces femtosecond polarization-resolved second harmonic generation (f-PRSHG) data. SHG spectroscopy is particularly suited to monitor symmetry changes since its magnitude is governed by the nonlinear optical susceptibility tensor whose elements are determined by the underlying material symmetry. Conceptually, these experiments seek to provide insight into the details of the time evolution of symmetry arising from laser induced transient states of matter in GaAs. Overall, the basic explanation of these experimental observations is that as a result of the photoinduced electronic excitation, many electrons, including bond electrons are excited to higher states. This results in subpicosecond changes in the local anharmonic potential and produces a changing nonlinear polarization response thus accounting for the nonthermal time dependent symmetry changes. Clearly, our approach may be easily extended to many different crystalline materials with different levels of defects, dopants and stresses to fully characterize the time dependent behavior of laser induced transient states in material systems.

Shortcuts to adiabaticity using flow fields

NASA Astrophysics Data System (ADS)

Patra, Ayoti; Jarzynski, Christopher

2017-12-01

A shortcut to adiabaticity is a recipe for generating adiabatic evolution at an arbitrary pace. Shortcuts have been developed for quantum, classical and (most recently) stochastic dynamics. A shortcut might involve a counterdiabatic (CD) Hamiltonian that causes a system to follow the adiabatic evolution at all times, or it might utilize a fast-forward (FF) potential, which returns the system to the adiabatic path at the end of the process. We develop a general framework for constructing shortcuts to adiabaticity from flow fields that describe the desired adiabatic evolution. Our approach encompasses quantum, classical and stochastic dynamics, and provides surprisingly compact expressions for both CD Hamiltonians and FF potentials. We illustrate our method with numerical simulations of a model system, and we compare our shortcuts with previously obtained results. We also consider the semiclassical connections between our quantum and classical shortcuts. Our method, like the FF approach developed by previous authors, is susceptible to singularities when applied to excited states of quantum systems; we propose a simple, intuitive criterion for determining whether these singularities will arise, for a given excited state.

Complexity Reduction of Collisional-Radiative Kinetics for Atomic Plasma

DTIC Science & Technology

2013-12-23

through collisional and radiative interactions .4–6 The most accurate treatment for these non- equilibrium plasmas requires a state-to-state approach,7–13...CR system versus time, during con- stant-Te plasma evolution from a low -temperature ASDF and low electron number density; as excitation and...Collisional-radiative model in air for earth re-entry problems,” Phys. Plasmas 13, 043502 (2006). 9C. O. Laux, L. Pierrot, and R. J. Gessman, “State-to

Watching the Real-time Evolution of a Laser Modified Atom Using Attosecond Pulses

NASA Astrophysics Data System (ADS)

Shivaram, Niranjan; Timmers, Henry; Tong, Xiao-Min; Sandhu, Arvinder

2011-10-01

In the presence of even moderately strong laser fields, atomic states are heavily modified and develop rich structure. Such a laser dressed atom can be described using the Floquet theory in which the laser dressed states called Floquet states are composed of different Fourier components. In this work we use XUV attosecond pulses to excite a He atom from its ground state to near-infrared (NIR) laser dressed Floquet states, which are ionized by the dressing laser field. Quantum interferences between Fourier components of these Floquet states lead to oscillations in He ion yield as a function of time-delay between the XUV and NIR pulses. From the ion yield signal we measure the quantum phase difference between transition matrix elements to two different Fourier components as a function of both time-delay (instantaneous NIR intensity) and NIR pulse peak intensity. These measurements along with information from time-dependent Schrodinger equation simulations enable us to observe the real-time evolution of the laser modified atom as the dominant Floquet state mediating the ionization changes from the 5p Floquet state to the 2p Floquet state with increasing NIR intensity.

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

Fluence-dependent singlet exciton dynamics in length-sorted chirality-enriched single-walled carbon nanotubes.

PubMed

Park, Jaehong; Deria, Pravas; Olivier, Jean-Hubert; Therien, Michael J

2014-02-12

We utilize individualized, length-sorted (6,5)-chirality enriched single-walled carbon nanotubes (SWNTs) having dimensions of 200 and 800 nm, femtosecond transient absorption spectroscopy, and variable excitation fluences that modulate the exciton density per nanotube unit length, to interrogate nanotube exciton/biexciton dynamics. For pump fluences below 30 μJ/cm(2), transient absorption (TA) spectra of (6,5) SWNTs reveal the instantaneous emergence of the exciton to biexciton transition (E11 → E11,BX) at 1100 nm; in contrast, under excitation fluences exceeding 100 μJ/cm(2), this TA signal manifests a rise time (τ rise ∼ 250 fs), indicating that E11 state repopulation is required to produce this signal. Femtosecond transient absorption spectroscopic data acquired over the 900-1400 nm spectral region of the near-infrared (NIR) region for (6,5) SWNTs, as a function of nanotube length and exciton density, reveal that over time delays that exceed 200 fs exciton-exciton interactions do not occur over spatial domains larger than 200 nm. Furthermore, the excitation fluence dependence of the E11 → E11,BX transient absorption signal demonstrates that relaxation of the E11 biexciton state (E11,BX) gives rise to a substantial E11 state population, as increasing delay times result in a concomitant increase of E11 → E11,BX transition oscillator strength. Numerical simulations based on a three-state model are consistent with a mechanism whereby biexcitons are generated at high excitation fluences via sequential SWNT ground- and E11-state excitation that occurs within the 980 nm excitation pulse duration. These studies that investigate fluence-dependent TA spectral evolution show that SWNT ground → E11 and E11 → E11,BX excitations are coresonant and provide evidence that E11,BX → E11 relaxation constitutes a significant decay channel for the SWNT biexciton state over delay times that exceed 200 fs, a finding that runs counter to assumptions made in previous analyses of SWNT biexciton dynamical data where exciton-exciton annihilation has been assumed to play a dominant role.

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.

A wavelength dependent investigation of the indole photophysics via ionization and fragmentation pump-probe spectroscopies.

PubMed

Godfrey, T J; Yu, Hui; Biddle, Michael S; Ullrich, Susanne

2015-10-14

A wavelength dependent study investigating the low-lying (1)La and (1)Lb states, both possessing (1)ππ* character, and the (1)πσ* state in the deactivation process of indole is presented here. Relaxation dynamics following excitation at 241, 250, 260, 270, 273, and 282 nm are examined using three gas-phase, pump-probe spectroscopic techniques: (1) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), (2) time-resolved photoelectron spectroscopy (TR-PES), and (3) time-resolved ion yield (TR-IY). Applied in combination, a more complete picture of the indole relaxation dynamics may be gleaned. For instance, TR-PES experiments directly observe all relaxation pathways by probing the evolution of the excited states following photoexcitation; whereas, TR-KER measurements indirectly, yet specifically, probe for (1)πσ*-state activity through the detection of H-atoms eliminated along the indole nitrogen-hydrogen (N-H) stretch coordinate-a possible outcome of (1)πσ*-state relaxation in indole. In addition, mass information obtained via TR-IY monitors fragmentation dynamics that may occur within the neutral electronically excited and/or cationic states. The work herein assesses the onset and importance of the (1)πσ* state at various pump wavelengths by systematically tuning across the ultraviolet absorption spectrum of indole with a particular focus on those pump wavelengths longer than 263 nm, where the involvement of the (1)πσ* state is under current debate. As far as this experimental work is concerned, there does not appear to be any significant involvement by the (1)πσ* state in the indole relaxation processes following excitation at 270, 273, or 282 nm. This investigation also evaluates the primary orbital promotions contributing to the (1)La, (1)Lb, and (1)πσ* transitions based on ionization preferences observed in TR-PES spectra. Relaxation time constants associated with dynamics along these states are also reported for excitation at all of the aforementioned pump wavelengths and are used to pinpoint the origin of the discrepancies found in the literature. In this context, advantages and disadvantages of the three experimental techniques are discussed.

Internal Charmonium Evolution in the Quark-Gluon Plasma

NASA Astrophysics Data System (ADS)

Chen, Baoyi; Du, Xiaojian; Rapp, Ralf

2017-08-01

We employ a time-dependent Schrödinger equation to study the evolution of a c c ‾ dipole in a quark-gluon plasma (QGP). Medium effects on the heavy-quark potential in the QGP are found to significantly affect the timescales of the internal evolution of the dipole. Color-screening can enhance the overlap of the expanding wavepackage with excited states at high temperature, while it is reduced at lower temperatures where the dipole favors the formation of the charmonium ground state. We investigate the consequences of this mechanism on the double ratio of charmonium nuclear modification factors, RAAψ (2 S) /RAAJ/ψ, in heavy-ion collisions. The impact of the transition mechanisms on this ratio turns out to be rather sensitive to the attractive strength of the potential, and to its temperature dependence.

Evolution of Excited-State Dynamics in Periodic Au 28, Au 36, Au 44, and Au 52 Nanoclusters

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

Zhou, Meng; Zeng, Chenjie; Sfeir, Matthew Y.

An understanding of the correlation between the atomic structure and optical properties of gold nanoclusters is essential for exploration of their functionalities and applications involving light harvesting and electron transfer. We report the femto-nanosecond excited state dynamics of a periodic series of face-centered cubic (FCC) gold nanoclusters (including Au 28, Au 36, Au 44, and Au 52), which exhibit a set of unique features compared with other similar sized clusters. Molecular-like ultrafast S n → S 1 internal conversions (i.e., radiationless electronic transitions) are observed in the relaxation dynamics of FCC periodic series. Excited-state dynamics with near-HOMO–LUMO gap excitation lacksmore » ultrafast decay component, and only the structural relaxation dominates in the dynamical process, which proves the absence of core–shell relaxation. Interestingly, both the relaxation of the hot carriers and the band-edge carrier recombination become slower as the size increases. The evolution in excited-state properties of this FCC series offers new insight into the structure-dependent properties of metal nanoclusters, which will benefit their optical energy harvesting and photocatalytic applications.« less

Evolution of Excited-State Dynamics in Periodic Au 28, Au 36, Au 44, and Au 52 Nanoclusters

DOE PAGES

Zhou, Meng; Zeng, Chenjie; Sfeir, Matthew Y.; ...

2017-08-10

An understanding of the correlation between the atomic structure and optical properties of gold nanoclusters is essential for exploration of their functionalities and applications involving light harvesting and electron transfer. We report the femto-nanosecond excited state dynamics of a periodic series of face-centered cubic (FCC) gold nanoclusters (including Au 28, Au 36, Au 44, and Au 52), which exhibit a set of unique features compared with other similar sized clusters. Molecular-like ultrafast S n → S 1 internal conversions (i.e., radiationless electronic transitions) are observed in the relaxation dynamics of FCC periodic series. Excited-state dynamics with near-HOMO–LUMO gap excitation lacksmore » ultrafast decay component, and only the structural relaxation dominates in the dynamical process, which proves the absence of core–shell relaxation. Interestingly, both the relaxation of the hot carriers and the band-edge carrier recombination become slower as the size increases. The evolution in excited-state properties of this FCC series offers new insight into the structure-dependent properties of metal nanoclusters, which will benefit their optical energy harvesting and photocatalytic applications.« less

A multi-frequency fatigue testing method for wind turbine rotor blades

NASA Astrophysics Data System (ADS)

Eder, M. A.; Belloni, F.; Tesauro, A.; Hanis, T.

2017-02-01

Rotor blades are among the most delicate components of modern wind turbines. Reliability is a crucial aspect, since blades shall ideally remain free of failure under ultra-high cycle loading conditions throughout their designated lifetime of 20-25 years. Full-scale blade tests are the most accurate means to experimentally simulate damage evolution under operating conditions, and are therefore used to demonstrate that a blade type fulfils the reliability requirements to an acceptable degree of confidence. The state-of-the-art testing method for rotor blades in industry is based on resonance excitation where typically a rotating mass excites the blade close to its first natural frequency. During operation the blade response due to external forcing is governed by a weighted combination of its eigenmodes. Current test methodologies which only utilise the lowest eigenfrequency induce a fictitious damage where additional tuning masses are required to recover the desired damage distribution. Even with the commonly adopted amplitude upscaling technique fatigue tests remain a time-consuming and costly endeavour. The application of tuning masses increases the complexity of the problem by lowering the natural frequency of the blade and therefore increasing the testing time. The novel method presented in this paper aims at shortening the duration of the state-of-the-art fatigue testing method by simultaneously exciting the blade with a combination of two or more eigenfrequencies. Taking advantage of the different shapes of the excited eigenmodes, the actual spatial damage distribution can be more realistically simulated in the tests by tuning the excitation force amplitudes rather than adding tuning masses. This implies that in portions of the blade the lowest mode is governing the damage whereas in others higher modes contribute more significantly due to their higher cycle count. A numerical feasibility study based on a publicly available large utility rotor blade is used to demonstrate the ability of the proposed approach to outperform the state-of-the-art testing method without compromising fatigue test requirements. It will be shown that the novel method shortens the testing time and renders the damage evolution with a higher degree of fidelity.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission.

PubMed

Hart, Stephanie M; Silva, W Ruchira; Frontiera, Renee R

2018-02-07

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features. We hypothesize that these features arise from the formation of cationic and anionic species due to partial transfer of electron density from one pentacene molecule to a neighboring molecule. These observations provide experimental evidence for the role of states with significant charge-transfer character which facilitate the singlet fission process in pentacene. Our work both provides new insight into the singlet fission mechanism in pentacene and demonstrates the utility of structurally-sensitive time-resolved spectroscopic techniques in monitoring ultrafast processes.

Coherent exciton-vibrational dynamics and energy transfer in conjugated organics

DOE PAGES

Nelson, Tammie R.; Ondarse-Alvarez, Dianelys; Oldani, Nicolas; ...

2018-06-13

Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon is important when designing carrier transport in optoelectronic materials. Here, excited state dynamics simulations reveal a ubiquitous pattern in the evolution of photoexcitations for a broad range of molecular systems. Symmetries of the wavefunctions define a specific form of the non-adiabatic coupling that drives quantum transitions between excited states, leading to a collective asymmetric vibrational excitation coupled to the electronic system. This promotes periodic oscillatory evolution of the wavefunctions, preserving specific phase and amplitude relations across the ensemble ofmore » trajectories. The simple model proposed here explains the appearance of coherent exciton-vibrational dynamics due to non-adiabatic transitions, which is universal across multiple molecular systems. The observed relationships between electronic wavefunctions and the resulting functionalities allows us to understand, and potentially manipulate, excited state dynamics and energy transfer in molecular materials.« less

Coherent exciton-vibrational dynamics and energy transfer in conjugated organics

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

Nelson, Tammie R.; Ondarse-Alvarez, Dianelys; Oldani, Nicolas

Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon is important when designing carrier transport in optoelectronic materials. Here, excited state dynamics simulations reveal a ubiquitous pattern in the evolution of photoexcitations for a broad range of molecular systems. Symmetries of the wavefunctions define a specific form of the non-adiabatic coupling that drives quantum transitions between excited states, leading to a collective asymmetric vibrational excitation coupled to the electronic system. This promotes periodic oscillatory evolution of the wavefunctions, preserving specific phase and amplitude relations across the ensemble ofmore » trajectories. The simple model proposed here explains the appearance of coherent exciton-vibrational dynamics due to non-adiabatic transitions, which is universal across multiple molecular systems. The observed relationships between electronic wavefunctions and the resulting functionalities allows us to understand, and potentially manipulate, excited state dynamics and energy transfer in molecular materials.« less

Convective Excitation of Inertial Modes in Binary Neutron Star Mergers

NASA Astrophysics Data System (ADS)

De Pietri, Roberto; Feo, Alessandra; Font, José A.; Löffler, Frank; Maione, Francesco; Pasquali, Michele; Stergioulas, Nikolaos

2018-06-01

We present the first very long-term simulations (extending up to ˜140 ms after merger) of binary neutron star mergers with piecewise polytropic equations of state and in full general relativity. Our simulations reveal that, at a time of 30-50 ms after merger, parts of the star become convectively unstable, which triggers the excitation of inertial modes. The excited inertial modes are sustained up to several tens of milliseconds and are potentially observable by the planned third-generation gravitational-wave detectors at frequencies of a few kilohertz. Since inertial modes depend on the rotation rate of the star and they are triggered by a convective instability in the postmerger remnant, their detection in gravitational waves will provide a unique opportunity to probe the rotational and thermal state of the merger remnant. In addition, our findings have implications for the long-term evolution and stability of binary neutron star remnants.

Representing the thermal state in time-dependent density functional theory

DOE PAGES

Modine, N. A.; Hatcher, R. M.

2015-05-28

Classical molecular dynamics (MD) provides a powerful and widely used approach to determining thermodynamic properties by integrating the classical equations of motion of a system of atoms. Time-Dependent Density Functional Theory (TDDFT) provides a powerful and increasingly useful approach to integrating the quantum equations of motion for a system of electrons. TDDFT efficiently captures the unitary evolution of a many-electron state by mapping the system into a fictitious non-interacting system. In analogy to MD, one could imagine obtaining the thermodynamic properties of an electronic system from a TDDFT simulation in which the electrons are excited from their ground state bymore » a time-dependent potential and then allowed to evolve freely in time while statistical data are captured from periodic snapshots of the system. For a variety of systems (e.g., many metals), the electrons reach an effective state of internal equilibrium due to electron-electron interactions on a time scale that is short compared to electron-phonon equilibration. During the initial time-evolution of such systems following electronic excitation, electron-phonon interactions should be negligible, and therefore, TDDFT should successfully capture the internal thermalization of the electrons. However, it is unclear how TDDFT represents the resulting thermal state. In particular, the thermal state is usually represented in quantum statistical mechanics as a mixed state, while the occupations of the TDDFT wave functions are fixed by the initial state in TDDFT. Two key questions involve (1) reformulating quantum statistical mechanics so that thermodynamic expectations can be obtained as an unweighted average over a set of many-body pure states and (2) constructing a family of non-interacting (single determinant) TDDFT states that approximate the required many-body states for the canonical ensemble. In Section II, we will address these questions by first demonstrating that thermodynamic expectations can be evaluated by averaging over certain many-body pure states, which we will call thermal states, and then constructing TDDFT states that approximate these thermal states. In Section III, we will present some numerical tests of the resulting theory, and in Section IV, we will summarize our main results and discuss some possible future directions for this work.« less

Transient lattice contraction in the solid-to-plasma transition

PubMed Central

Ferguson, Ken R.; Bucher, Maximilian; Gorkhover, Tais; Boutet, Sébastien; Fukuzawa, Hironobu; Koglin, Jason E.; Kumagai, Yoshiaki; Lutman, Alberto; Marinelli, Agostino; Messerschmidt, Marc; Nagaya, Kiyonobu; Turner, Jim; Ueda, Kiyoshi; Williams, Garth J.; Bucksbaum, Philip H.; Bostedt, Christoph

2016-01-01

In condensed matter systems, strong optical excitations can induce phonon-driven processes that alter their mechanical properties. We report on a new phenomenon where a massive electronic excitation induces a collective change in the bond character that leads to transient lattice contraction. Single large van der Waals clusters were isochorically heated to a nanoplasma state with an intense 10-fs x-ray (pump) pulse. The structural evolution of the nanoplasma was probed with a second intense x-ray (probe) pulse, showing systematic contraction stemming from electron delocalization during the solid-to-plasma transition. These findings are relevant for any material in extreme conditions ranging from the time evolution of warm or hot dense matter to ultrafast imaging with intense x-ray pulses or, more generally, any situation that involves a condensed matter-to-plasma transition. PMID:27152323

Revisiting the relaxation dynamics of isolated pyrrole

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

Montero, Raúl; Ovejas, Virginia; Fernández-Fernández, Marta

Herein, the interpretation of the femtosecond-scale temporal evolution of the pyrrole ion signal, after excitation in the 267–217 nm interval, recently published by our group [R. Montero, A. Peralta Conde, V. Ovejas, M. Fernández-Fernández, F. Castaño, J. R. Vázquez de Aldana, and A. Longarte, J. Chem. Phys.137, 064317 (2012)] is re-visited. The observation of a shift in the pyrrole{sup +} transient respect to zero delay reference, initially attributed to ultrafast dynamics on the πσ{sup *} type state (3s a{sub 1} ← π 1a{sub 2}), is demonstrated to be caused by the existence of pump + probe populated states, along themore » ionization process. The influence of these resonances in pump-prone ionization experiments, when multi-photon probes are used, and the significance of a proper zero-time reference, is discussed. The possibility of preparing the πσ{sup *} state by direct excitation is investigated by collecting 1 + 1 photoelectron spectra, at excitation wavelengths ranging from 255 to 219 nm. No conclusive evidences of ionization through this state are found.« less

Double-Resonance Facilitated Decomposion of Emission Spectra

NASA Astrophysics Data System (ADS)

Kato, Ryota; Ishikawa, Haruki

2016-06-01

Emission spectra provide us with rich information about the excited-state processes such as proton-transfer, charge-transfer and so on. In the cases that more than one excited states are involved, emission spectra from different excited states sometimes overlap and a decomposition of the overlapped spectra is desired. One of the methods to perform a decomposition is a time-resolved fluorescence technique. It uses a difference in time evolutions of components involved. However, in the gas-phase, a concentration of the sample is frequently too small to carry out this method. On the other hand, double-resonance technique is a very powerful tool to discriminate or identify a common species in the spectra in the gas-phase. Thus, in the present study, we applied the double-resonance technique to resolve the overlapped emission spectra. When transient IR absorption spectra of the excited state are available, we can label the population of the certain species by the IR excitation with a proper selection of the IR wavenumbers. Thus, we can obtain the emission spectra of labeled species by subtracting the emission spectra with IR labeling from that without IR. In the present study, we chose the charge-transfer emission spectra of cyanophenyldisilane (CPDS) as a test system. One of us reported that two charge-transfer (CT) states are involved in the intramolecular charge-transfer (ICT) process of CPDS-water cluster and recorded the transient IR spectra. As expected, we have succeeded in resolving the CT emission spectra of CPDS-water cluster by the double resonance facilitated decomposion technique. In the present paper, we will report the details of the experimental scheme and the results of the decomposition of the emission spectra. H. Ishikawa, et al., Chem. Phys. Phys. Chem., 9, 117 (2007).

T sub 1-echo sequence: Protecting the State of a Qubit in the Presence of Coherent Interaction

DTIC Science & Technology

2012-09-25

memory is at energy m, and they are coupled with a coupling strength v⊥. We write the coupling in the rotating - wave approximation , assuming q,m...important for the time evolution. In the validity range of the rotating - wave approximation , the above Hamiltonian preserves the total number of...excited state) in total is involved in the dynamics, the underlying Jaynes - Cummings Hamiltonian will lead to the same results as the ones presented here

Many-body excitations and deexcitations in trapped ultracold bosonic clouds

NASA Astrophysics Data System (ADS)

Theisen, Marcus; Streltsov, Alexej I.

2016-11-01

We employ the multiconfigurational time-dependent Hartree for bosons (MCTDHB) method to study excited states of interacting Bose-Einstein condensates confined by harmonic and double-well trap potentials. Two approaches to access excitations, one static and the other dynamic, are investigated and contrasted. In static simulations the low-lying excitations are computed by utilizing a linear-response theory constructed on top of a static MCTDHB solution (LR-MCTDHB). Complimentarily, we propose two dynamic protocols that address excitations by propagating the MCTDHB wave function. In particular, we investigate dipolelike oscillations induced by shifting the origin of the confining potential and breathinglike excitations by quenching the frequency of a parabolic part of the trap. To contrast static predictions and dynamic results we compute the time evolution and regard the respective Fourier transform of several local and nonlocal observables. Namely, we study the expectation value of the position operator , its variance Var [x (t )] , and a local density computed at selected positions. We find that the variance is the most sensitive and informative quantity: Along with excitations it contains information about deexcitations even in a linear regime of the induced dynamics. The dynamic protocols are found to access the many-body excitations predicted by the static LR-MCTDHB approach.

Holonomic Quantum Control by Coherent Optical Excitation in Diamond.

PubMed

Zhou, Brian B; Jerger, Paul C; Shkolnikov, V O; Heremans, F Joseph; Burkard, Guido; Awschalom, David D

2017-10-06

Although geometric phases in quantum evolution are historically overlooked, their active control now stimulates strategies for constructing robust quantum technologies. Here, we demonstrate arbitrary single-qubit holonomic gates from a single cycle of nonadiabatic evolution, eliminating the need to concatenate two separate cycles. Our method varies the amplitude, phase, and detuning of a two-tone optical field to control the non-Abelian geometric phase acquired by a nitrogen-vacancy center in diamond over a coherent excitation cycle. We demonstrate the enhanced robustness of detuned gates to excited-state decoherence and provide insights for optimizing fast holonomic control in dissipative quantum systems.

Holonomic Quantum Control by Coherent Optical Excitation in Diamond

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

Zhou, Brian B.; Jerger, Paul C.; Shkolnikov, V. O.

Although geometric phases in quantum evolution are historically overlooked, their active control now stimulates strategies for constructing robust quantum technologies. Here, we demonstrate arbitrary singlequbit holonomic gates from a single cycle of nonadiabatic evolution, eliminating the need to concatenate two separate cycles. Our method varies the amplitude, phase, and detuning of a two-tone optical field to control the non-Abelian geometric phase acquired by a nitrogen-vacancy center in diamond over a coherent excitation cycle. We demonstrate the enhanced robustness of detuned gates to excited-state decoherence and provide insights for optimizing fast holonomic control in dissipative quantum systems.

On the strong and selective isotope effect in the UV excitation of N2 with implications toward the nebula and Martian atmosphere.

PubMed

Muskatel, B H; Remacle, F; Thiemens, Mark H; Levine, R D

2011-04-12

Isotopic effects associated with molecular absorption are discussed with reference to natural phenomena including early solar system processes, Titan and terrestrial atmospheric chemistry, and Martian atmospheric evolution. Quantification of the physicochemical aspects of the excitation and dissociation processes may lead to enhanced understanding of these environments. Here we examine a physical basis for an additional isotope effect during photolysis of molecular nitrogen due to the coupling of valence and Rydberg excited states. The origin of this isotope effect is shown to be the coupling of diabatic electronic states of different bonding nature that occurs after the excitation of these states. This coupling is characteristic of energy regimes where two or more excited states are nearly crossing or osculating. A signature of the resultant isotope effect is a window of rapid variation in the otherwise smooth distribution of oscillator strengths vs. frequency. The reference for the discussion is the numerical solution of the time dependent Schrödinger equation for both the electronic and nuclear modes with the light field included as part of the Hamiltonian. Pumping is to all extreme UV dipole-allowed, valence and Rydberg, excited states of N(2). The computed absorption spectra are convoluted with the solar spectrum to demonstrate the importance of including this isotope effect in planetary, interstellar molecular cloud, and nebular photochemical models. It is suggested that accidental resonance with strong discrete lines in the solar spectrum such as the CIII line at 97.703 nm can also have a marked effect.

Unraveling the Primary Isomerization Dynamics in Cyanobacterial Phytochrome Cph1 with Multi-pulse Manipulations.

PubMed

Kim, Peter W; Rockwell, Nathan C; Freer, Lucy H; Chang, Che-Wei; Martin, Shelley S; Lagarias, J Clark; Larsen, Delmar S

2013-07-20

The ultrafast mechanisms underlying the initial photoisomerization (P r → Lumi-R) in the forward reaction of the cyanobacterial photoreceptor Cph1 were explored with multipulse pump-dump-probe transient spectroscopy. A recently postulated multi-population model was used to fit the transient pump-dump-probe and dump-induced depletion signals. We observed dump-induced depletion of the Lumi-R photoproduct, demonstrating that photoisomerization occurs via evolution on both the excited- and ground-state electronic surfaces. Excited-state equilibrium was not observed, as shown via the absence of a dump-induced excited-state "Le Châtelier redistribution" of excited-state populations. The importance of incorporating the inhomogeneous dynamics of Cph1 in interpreting measured transient data is discussed.

Unraveling the Primary Isomerization Dynamics in Cyanobacterial Phytochrome Cph1 with Multi-pulse Manipulations

PubMed Central

Kim, Peter W.; Rockwell, Nathan C.; Freer, Lucy H.; Chang, Che-Wei; Martin, Shelley S.; Lagarias, J. Clark; Larsen, Delmar S.

2013-01-01

The ultrafast mechanisms underlying the initial photoisomerization (Pr → Lumi-R) in the forward reaction of the cyanobacterial photoreceptor Cph1 were explored with multipulse pump-dump-probe transient spectroscopy. A recently postulated multi-population model was used to fit the transient pump-dump-probe and dump-induced depletion signals. We observed dump-induced depletion of the Lumi-R photoproduct, demonstrating that photoisomerization occurs via evolution on both the excited- and ground-state electronic surfaces. Excited-state equilibrium was not observed, as shown via the absence of a dump-induced excited-state “Le Châtelier redistribution” of excited-state populations. The importance of incorporating the inhomogeneous dynamics of Cph1 in interpreting measured transient data is discussed. PMID:24143267

Optimal multi-type sensor placement for response and excitation reconstruction

NASA Astrophysics Data System (ADS)

Zhang, C. D.; Xu, Y. L.

2016-01-01

The need to perform dynamic response reconstruction always arises as the measurement of structural response is often limited to a few locations, especially for a large civil structure. Besides, it is usually very difficult, if not impossible, to measure external excitations under the operation condition of a structure. This study presents an algorithm for optimal placement of multi-type sensors, including strain gauges, displacement transducers and accelerometers, for the best reconstruction of responses of key structural components where there are no sensors installed and the best estimation of external excitations acting on the structure at the same time. The algorithm is developed in the framework of Kalman filter with unknown excitation, in which minimum-variance unbiased estimates of the generalized state of the structure and the external excitations are obtained by virtue of limited sensor measurements. The structural responses of key locations without sensors can then be reconstructed with the estimated generalized state and excitation. The asymptotic stability feature of the filter is utilized for optimal sensor placement. The number and spatial location of the multi-type sensors are determined by adding the optimal sensor which gains the maximal reduction of the estimation error of reconstructed responses. For the given mode number in response reconstruction and the given locations of external excitations, the optimal multi-sensor placement achieved by the proposed method is independent of the type and time evolution of external excitation. A simply-supported overhanging steel beam under multiple types of excitation is numerically studied to demonstrate the feasibility and superiority of the proposed method, and the experimental work is then carried out to testify the effectiveness of the proposed method.

Surface-Enhanced Impulsive Coherent Vibrational Spectroscopy

PubMed Central

Du, Juan; Harra, Juha; Virkki, Matti; Mäkelä, Jyrki M.; Leng, Yuxin; Kauranen, Martti; Kobayashi, Takayoshi

2016-01-01

Surface-enhanced Raman spectroscopy (SERS) has attracted a lot of attention in molecular sensing because of the remarkable ability of plasmonic metal nanostructures to enhance the weak Raman scattering process. On the other hand, coherent vibrational spectroscopy triggered by impulsive excitation using ultrafast laser pulses provides complete information about the temporal evolution of molecular vibrations, allowing dynamical processes in molecular systems to be followed in “real time”. Here, we combine these two concepts and demonstrate surface-enhanced impulsive vibrational spectroscopy. The vibrational modes of the ground and excited states of poly[2-methoxy-5-(2-ethylhexyloxy)−1,4-phenylenevinylene] (MEH-PPV), spin-coated on a substrate covered with monodisperse silver nanoparticles, are impulsively excited with a sub-10 fs pump pulse and characterized with a delayed broad-band probe pulse. The maximum enhancement in the spectrally and temporally resolved vibrational signatures averaged over the whole sample is about 4.6, while the real-time information about the instantaneous vibrational amplitude together with the initial vibrational phase is preserved. The phase is essential to determine the vibrational contributions from the ground and excited states. PMID:27812020

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.

Linear response of entanglement entropy from holography

NASA Astrophysics Data System (ADS)

Lokhande, Sagar F.; Oling, Gerben W. J.; Pedraza, Juan F.

2017-10-01

For time-independent excited states in conformal field theories, the entanglement entropy of small subsystems satisfies a `first law'-like relation, in which the change in entanglement is proportional to the energy within the entangling region. Such a law holds for time-dependent scenarios as long as the state is perturbatively close to the vacuum, but is not expected otherwise. In this paper we use holography to investigate the spread of entanglement entropy for unitary evolutions of special physical interest, the so-called global quenches. We model these using AdS-Vaidya geometries. We find that the first law of entanglement is replaced by a linear response relation, in which the energy density takes the role of the source and is integrated against a time-dependent kernel with compact support. For adiabatic quenches the standard first law is recovered, while for rapid quenches the linear response includes an extra term that encodes the process of thermalization. This extra term has properties that resemble a time-dependent `relative entropy'. We propose that this quantity serves as a useful order parameter to characterize far-from-equilibrium excited states. We illustrate our findings with concrete examples, including generic power-law and periodically driven quenches.

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.

Vibrational cooling dynamics of a [FeFe]-hydrogenase mimic probed by time-resolved infrared spectroscopy.

PubMed

Caplins, Benjamin W; Lomont, Justin P; Nguyen, Son C; Harris, Charles B

2014-12-11

Picosecond time-resolved infrared spectroscopy (TRIR) was performed for the first time on a dithiolate bridged binuclear iron(I) hexacarbonyl complex ([Fe₂(μ-bdt)(CO)₆], bdt = benzene-1,2-dithiolate) which is a structural mimic of the active site of the [FeFe]-hydrogenase enzyme. As these model active sites are increasingly being studied for their potential in photocatalytic systems for hydrogen production, understanding their excited and ground state dynamics is critical. In n-heptane, absorption of 400 nm light causes carbonyl loss with low quantum yield (<10%), while the majority (ca. 90%) of the parent complex is regenerated with biexponential kinetics (τ₁ = 21 ps and τ₂ = 134 ps). In order to understand the mechanism of picosecond bleach recovery, a series of UV-pump TRIR experiments were performed in different solvents. The long time decay (τ₂) of the transient spectra is seen to change substantially as a function of solvent, from 95 ps in THF to 262 ps in CCl₄. Broadband IR-pump TRIR experiments were performed for comparison. The measured vibrational lifetimes (T₁(avg)) of the carbonyl stretches were found to be in excellent correspondence to the observed τ₂ decays in the UV-pump experiments, signifying that vibrationally excited carbonyl stretches are responsible for the observed longtime decays. The fast spectral evolution (τ₁) was determined to be due to vibrational cooling of low frequency modes anharmonically coupled to the carbonyl stretches that were excited after electronic internal conversion. The results show that cooling of both low and high frequency vibrational modes on the electronic ground state give rise to the observed picosecond TRIR transient spectra of this compound, without the need to invoke electronically excited states.

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.

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.

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

Efficient Online Optimized Quantum Control for Adiabatic Quantum Computation

NASA Astrophysics Data System (ADS)

Quiroz, Gregory

Adiabatic quantum computation (AQC) relies on controlled adiabatic evolution to implement a quantum algorithm. While control evolution can take many forms, properly designed time-optimal control has been shown to be particularly advantageous for AQC. Grover's search algorithm is one such example where analytically-derived time-optimal control leads to improved scaling of the minimum energy gap between the ground state and first excited state and thus, the well-known quadratic quantum speedup. Analytical extensions beyond Grover's search algorithm present a daunting task that requires potentially intractable calculations of energy gaps and a significant degree of model certainty. Here, an in situ quantum control protocol is developed for AQC. The approach is shown to yield controls that approach the analytically-derived time-optimal controls for Grover's search algorithm. In addition, the protocol's convergence rate as a function of iteration number is shown to be essentially independent of system size. Thus, the approach is potentially scalable to many-qubit systems.

Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B 12

DOE PAGES

Miller, Nicholas A.; Deb, Aniruddha; Alonso-Mori, Roberto; ...

2017-01-30

Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B 12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV–visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributionsmore » and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co–CN bond and Co–N Im bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. In conclusion, these observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.« less

Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B 12

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

Miller, Nicholas A.; Deb, Aniruddha; Alonso-Mori, Roberto

Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B 12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV–visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributionsmore » and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co–CN bond and Co–N Im bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. In conclusion, these observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.« less

Real-time spectral interferometry probes the internal dynamics of femtosecond soliton molecules

NASA Astrophysics Data System (ADS)

Herink, G.; Kurtz, F.; Jalali, B.; Solli, D. R.; Ropers, C.

2017-04-01

Solitons, particle-like excitations ubiquitous in many fields of physics, have been shown to exhibit bound states akin to molecules. The formation of such temporal soliton bound states and their internal dynamics have escaped direct experimental observation. By means of an emerging time-stretch technique, we resolve the evolution of femtosecond soliton molecules in the cavity of a few-cycle mode-locked laser. We track two- and three-soliton bound states over hundreds of thousands of consecutive cavity roundtrips, identifying fixed points and periodic and aperiodic molecular orbits. A class of trajectories acquires a path-dependent geometrical phase, implying that its dynamics may be topologically protected. These findings highlight the importance of real-time detection in resolving interactions in complex nonlinear systems, including the dynamics of soliton bound states, breathers, and rogue waves.

Femtosecond pump-supercontinuum probe and transient lens spectroscopy of adonixanthin.

PubMed

Lenzer, Thomas; Schubert, Steffen; Ehlers, Florian; Lohse, Peter W; Scholz, Mirko; Oum, Kawon

2009-03-15

The ultrafast internal conversion (IC) dynamics of adonixanthin in organic solvents were studied by pump-supercontinuum probe (PSCP) and transient lens (TL) spectroscopy after photoexcitation to the S(2) state. Transient PSCP spectra in the range 344-768 nm provided the spectral evolution of the S(0)-->S(2) ground state bleach and S(1)-->S(n) excited state absorption. Time constants were tau(2) =115 and 111 fs for the S(2)-->S(1) IC and tau(1)=6.4 and 5.8 ps for the S(1)-->S(0) IC in acetone and methanol, respectively. There was only an insignificant polarity dependence of tau(1), underlining the negligible importance of intramolecular charge transfer (ICT) in the lowest-lying excited state of C(40) carotenoids with carbonyl substitution on the beta-ionone ring. A blueshift and a spectral narrowing of the S(1)-->S(n) ESA band, likely due to solvation dynamics, and formation of the adonixanthin radial cation at high pump energies via resonant two-photon ionization were found.

Transient infrared spectroscopy: a new approach to investigate valence tautomerism.

PubMed

Touceda, Patricia Tourón; Patricia, Tourón Touceda; Vázquez, Sandra Mosquera; Sandra, Mosquera Vázquez; Lima, Manuela; Manuela, Lima; Lapini, Andrea; Andrea, Lapini; Foggi, Paolo; Paolo, Foggi; Dei, Andrea; Andrea, Dei; Righini, Roberto; Roberto, Righini

2012-01-14

In this work we present, to our knowledge for the first time, the results of a transient infrared spectroscopic study of the photoinduced valence tautomerism process in cobalt-dioxolene complexes with sub-picosecond time resolution. The molecular systems investigated were [Co(tpa)(diox)]PF(6) (1) and [Co(Me(3)tpa)(diox)]PF(6) (2), where diox = 3,5-di-tert-butyl-1,2-dioxolene; tpa = tris(2-pyridylmethyl)amine and Me(3)tpa its 6-methylated analogue. Complex (1) is present in solution as ls-Co(III)(catecholate) (1-CAT), while (2) as hs-Co(II)(semiquinonate) (2-SQ). DFT calculation of the harmonic frequencies for (1) and (2) allowed us to identify the vibrational markers of catecholate and semiquinonate redox isomers. Irradiation with 405 and 810 nm pulses (~35 fs) of (1-CAT) induces the formation of an intermediate excited species from which the ground state population is recovered with a time constant of 1.5 ± 0.3 ns. Comparing the 1 ns transient infrared spectrum with the experimental difference spectrum FTIR(2-SQ)-FTIR(1-CAT) and with the calculated difference spectrum IR(c)(1-SQ)-IR(c)(1-CAT) we are able to unequivocally identify the long lived species as the semiquinonate redox isomer of (1). On the other hand, no evidence of photoconversion is observed upon irradiation of (2) with 405 nm. Temporal evolution of transient spectra was analyzed with the combined approach consisting of singular values decomposition and global fitting (global analysis). After 405 and 810 nm excitation of (1-CAT), the semiquinonate excited species is formed on an ultrafast time scale (<200 fs) and cools down within the first 50 ps. Excitation of (2-SQ) with 405 nm wavelength produces a short lived excited state in which the semiquinonate nature of dioxolene is preserved and the ground state recovery is completed within 30 ps.

Relaxation of photoexcitations in polaron-induced magnetic microstructures

NASA Astrophysics Data System (ADS)

Köhler, Thomas; Rajpurohit, Sangeeta; Schumann, Ole; Paeckel, Sebastian; Biebl, Fabian R. A.; Sotoudeh, Mohsen; Kramer, Stephan C.; Blöchl, Peter E.; Kehrein, Stefan; Manmana, Salvatore R.

2018-06-01

We investigate the evolution of a photoexcitation in correlated materials over a wide range of time scales. The system studied is a one-dimensional model of a manganite with correlated electron, spin, orbital, and lattice degrees of freedom, which we relate to the three-dimensional material Pr1 -xCaxMnO3 . The ground-state phases for the entire composition range are determined and rationalized by a coarse-grained polaron model. At half doping a pattern of antiferromagnetically coupled Zener polarons is realized. Using time-dependent density-matrix renormalization group (tDMRG), we treat the electronic quantum dynamics following the excitation. The emergence of quasiparticles is addressed, and the relaxation of the nonequilibrium quasiparticle distribution is investigated via a linearized quantum-Boltzmann equation. Our approach shows that the magnetic microstructure caused by the Zener polarons leads to an increase of the relaxation times of the excitation.

Condensation of collective charge ordering in chromium

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

Singer, A.; Marsh, M. J.; Dietze, S. H.

2015-03-01

We report on the dynamics of the structural order parameter in a chromium film using synchrotron radiation in response to photoinduced ultrafast excitations. Following transient optical excitations the effective lattice temperature of the film rises close to the Neel temperature and the charge-density wave (CDW) amplitude is reduced but does not appear to ever be fully destroyed. The persistence of the CDW diffraction signal demonstrates that the CDW, if destroyed by the laser pulse, must be reestablished within the 100-ps time resolution of the synchrotron x-ray pulses. Furthermore, at all times after photoexcitation, the CDW retains its low-temperature periodicity, rathermore » than regenerating with its high-temperature period shortly after photoexcitation. The long-term evolution shows that the CDW reverts to its ground state on a time scale of 370 +/- 40 ps. We attribute the apparent persistence of the CDW to the long-lived periodic lattice displacement in chromium. This study highlights the fundamental role of the lattice distortion and its impact on the recondensation dynamics of the charge ordered state in strongly correlated materials.« less

Time evolution, Lamb shift, and emission spectra of spontaneous emission of two identical atoms

NASA Astrophysics Data System (ADS)

Wang, Da-Wei; Li, Zheng-Hong; Zheng, Hang; Zhu, Shi-Yao

2010-04-01

A unitary transformation method is used to investigate the dynamic evolution of two multilevel atoms, in the basis of symmetric and antisymmetric states, with one atom being initially prepared in the first excited state and the other in the ground state. The unitary transformation guarantees that our calculations are based on the ground state of the atom-field system and the self-energy is subtracted at the beginning. The total Lamb shifts of the symmetric and antisymmetric states are divided into transformed shift and dynamic shift. The transformed shift is due to emitting and reabsorbing of virtual photons, by a single atom (nondynamic single atomic shift) and between the two atoms (quasi-static shift). The dynamic shift is due to the emitting and reabsorbing of real photons, by a single atom (dynamic single atomic shift) and between the two atoms (dynamic interatomic shift). The emitting and reabsorbing of virtual and real photons between the two atoms result in the interatomic shift, which does not exist for the one-atom case. The spectra at the long-time limit are calculated. If the distance between the two atoms is shorter than or comparable to the wavelength, the strong coupling between the two atoms splits the spectrum into two peaks, one from the symmetric state and the other from the antisymmetric state. The origin of the red or blue shifts for the symmetric and antisymmetric states mainly lies in the negative or positive interaction energy between the two atoms. In the investigation of the short time evolution, we find the modification of the effective density of states by the interaction between two atoms can modulate the quantum Zeno and quantum anti-Zeno effects in the decays of the symmetric and antisymmetric states.

Effects of Shannon entropy and electric field on polaron in RbCl triangular quantum dot

NASA Astrophysics Data System (ADS)

M, Tiotsop; A, J. Fotue; S, C. Kenfack; N, Issofa; H, Fotsin; L, C. Fai

2016-04-01

In this paper, the time evolution of the quantum mechanical state of a polaron is examined using the Pekar type variational method on the condition of the electric-LO-phonon strong-coupling and polar angle in RbCl triangular quantum dot. We obtain the eigenenergies, and the eigenfunctions of the ground state, and the first excited state respectively. This system in a quantum dot can be treated as a two-level quantum system qubit and the numerical calculations are performed. The effects of Shannon entropy and electric field on the polaron in the RbCl triangular quantum dot are also studied.

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.

Energy-resolved coherent diffraction from laser-driven electronic motion in atoms

NASA Astrophysics Data System (ADS)

Shao, Hua-Chieh; Starace, Anthony F.

2017-10-01

We investigate theoretically the use of energy-resolved ultrafast electron diffraction to image laser-driven electronic motion in atoms. A chirped laser pulse is used to transfer the valence electron of the lithium atom from the ground state to the first excited state. During this process, the electronic motion is imaged by 100-fs and 1-fs electron pulses in energy-resolved diffraction measurements. Simulations show that the angle-resolved spectra reveal the time evolution of the energy content and symmetry of the electronic state. The time-dependent diffraction patterns are further interpreted in terms of the momentum transfer. For the case of incident 1-fs electron pulses, the rapid 2 s -2 p quantum beat motion of the target electron is imaged as a time-dependent asymmetric oscillation of the diffraction pattern.

Variational study of fermionic and bosonic systems with non-Gaussian states: Theory and applications

NASA Astrophysics Data System (ADS)

Shi, Tao; Demler, Eugene; Ignacio Cirac, J.

2018-03-01

We present a new variational method for investigating the ground state and out of equilibrium dynamics of quantum many-body bosonic and fermionic systems. Our approach is based on constructing variational wavefunctions which extend Gaussian states by including generalized canonical transformations between the fields. The key advantage of such states compared to simple Gaussian states is presence of non-factorizable correlations and the possibility of describing states with strong entanglement between particles. In contrast to the commonly used canonical transformations, such as the polaron or Lang-Firsov transformations, we allow parameters of the transformations to be time dependent, which extends their regions of applicability. We derive equations of motion for the parameters characterizing the states both in real and imaginary time using the differential structure of the variational manifold. The ground state can be found by following the imaginary time evolution until it converges to a steady state. Collective excitations in the system can be obtained by linearizing the real-time equations of motion in the vicinity of the imaginary time steady-state solution. Our formalism allows us not only to determine the energy spectrum of quasiparticles and their lifetime, but to obtain the complete spectral functions and to explore far out of equilibrium dynamics such as coherent evolution following a quantum quench. We illustrate and benchmark this framework with several examples: a single polaron in the Holstein and Su-Schrieffer-Heeger models, non-equilibrium dynamics in the spin-boson and Kondo models, the superconducting to charge density wave phase transitions in the Holstein model.

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.

Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

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

Chen, Lin X.; Shelby, Megan L.; Lestrange, Patrick J.

2016-01-01

This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(II) tetramesitylporphyrin (NiTMP) were successfully measured for optically excited state at a timescale from 100 fs to 50 ps, providing insight into its sub-ps electronic and structural relaxation processes. Importantly, a transient reduced state Ni(I) (π, 3dx2-y2) electronic state is captured through the interpretation of a short-lived excited state absorption on the low-energy shoulder of the edge, which is aidedmore » by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of electronic configuration on specific metal orbital energies. A strong influence of the valence orbital occupation on the inner shell orbital energies indicates that one should not use the transition energy from 1s to other orbitals to draw conclusions about the d-orbital energies. For photocatalysis, a transient electronic configuration could influence d-orbital energies up to a few eV and any attempt to steer the reaction pathway should account for this to ensure that external energies can be used optimally in driving desirable processes. NiTMP structural evolution and the influence of the porphyrin macrocycle conformation on relaxation kinetics can be likewise inferred from this study.« less

Temporal resistance variation of the second generation HTS tape during superconducting-to-normal state transition.

PubMed

Malginov, Vladimir A; Malginov, Andrey V; Fleishman, Leonid S

2013-01-01

The quench process in high-temperature superconducting (HTS) wires plays an important role in superconducting power devices, such as fault current limiters, magnets, cables, etc. The superconducting device should survive after the overheating due to quench. We studied the evolution of the resistance of the YBCO tape wire during the quench process with 1 ms time resolution for various excitation voltages. The resistive normal zone was found to be located in a domain of about 1-4 cm long. The normal state nucleation begins in 40-60 ms after voltage is applied across the HTS tape. In subsequent 200-300 ms other normal state regions appear. The normal domain heating continues in the following 5-10s that results in a factor of 2-3 increase of its resistance. Formation of the normal domain during the quench process follows the same stages for different excitation voltages. Characteristic domain sizes, lifetimes and temperatures are determined for all stages.

Coherent photoluminescence excitation spectroscopy of semicrystalline polymeric semiconductors

NASA Astrophysics Data System (ADS)

Silva, Carlos; Grégoire, Pascal; Thouin, Félix

In polymeric semiconductors, the competition between through-bond (intrachain) and through-space (interchain) electronic coupling determines two-dimensional spatial coherence of excitons. The balance of intra- and interchain excitonic coupling depends very sensitively on solid-state microstructure of the polymer film (polycrystalline, semicrystalline with amorphous domains, etc.). Regioregular poly(3-hexylthiophene) has emerged as a model material because its photoluminescence (PL) spectral lineshape reveals intricate information on the magnitude of excitonic coupling, the extent of energetic disorder, and on the extent to which the disordered energy landscape is correlated. I discuss implementation of coherent two-dimensional electronic spectroscopy. We identify cross peaks between 0-0 and 0-1 excitation peaks, and we measure their time evolution, which we interpret within the context of a hybrid HJ aggregate model. By measurement of the homogeneous linewidth in diverse polymer microstructures, we address the nature of optical transitions within such hynbrid aggregate model. These depend strongly on sample processing, and I discuss the relationship between microstructure, steady-state absorption and PL spectral lineshape, and 2D coherent PL excitation spectral lineshapes.

Nova V2362 Cygni (Nova Cygni 2006): Spitzer, Swift, and Ground-Based Spectral Evolution

NASA Technical Reports Server (NTRS)

Lynch, David K.; Venturini, Catherine C.; Mazuk, S.; Woodward, Charles; Gehrz, Robert; Rayner, John; Helton, L.A.; Ness, Jan-Uwe; Starrfield, Sumner; Rudy, Richard J.;

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.

Electron-mediated relaxation following ultrafast pumping of strongly correlated materials: model evidence of a correlation-tuned crossover between thermal and nonthermal states.

PubMed

Moritz, B; Kemper, A F; Sentef, M; Devereaux, T P; Freericks, J K

2013-08-16

We examine electron-electron mediated relaxation following ultrafast electric field pump excitation of the fermionic degrees of freedom in the Falicov-Kimball model for correlated electrons. The results reveal a dichotomy in the temporal evolution of the system as one tunes through the Mott metal-to-insulator transition: in the metallic regime relaxation can be characterized by evolution toward a steady state well described by Fermi-Dirac statistics with an increased effective temperature; however, in the insulating regime this quasithermal paradigm breaks down with relaxation toward a nonthermal state with a complicated electronic distribution as a function of momentum. We characterize the behavior by studying changes in the energy, photoemission response, and electronic distribution as functions of time. This relaxation may be observable qualitatively on short enough time scales that the electrons behave like an isolated system not in contact with additional degrees of freedom which would act as a thermal bath, especially when using strong driving fields and studying materials whose physics may manifest the effects of correlations.

[Excitation and relaxation of metastable state NaK(1 3Pi) at high vibrational levels].

PubMed

Luan, Nan-Nan; Cai, Qin; Zhang, Li-Ping; Dai, Kang; Shen, Yi-Fan

2011-11-01

The authors have investigated collision vibrational energy transfer rate constants in NaK[1 3Pi(v)] and He system. Pump laser excitation of the spin-forbidden band was used to produce very highly vibrationally excited metastable state NaK[1 3Pi (v = 22, 21, 20)]. The probe laser was used to excite the 1 3Pi (v = 22, 21, 20) to 5 3Pi(v'). Laser induced fluorescence (LIF) from 5 3Pi --> 1 3Sigma+ transition was used to follow the collision dynamics. The semilog plots of time-resolved LIF was obtained. The slopes yielded the effective lifetimes. From such data several Stern-Volmer plots could be constructed and the relaxation rate constants could be extracted for the sum of all processes that give rise to the decay of the prepared vibrational state. The rate constants (in units of 10(-11) cm3 x s(-1)) for v being 22, 21 and 20 are 1.4 +/- 0.1, 1.2 +/- 0.1 and 1.0 +/- 0.1, respectively. The vibrational relaxation rate is increasing with vibrational quantum number. In order to determine the importance of multiquantum relaxation, it is necessary to measure the relative population of both the prepared state and collisionally populated states. By the kinetic equations governing up to Delta(v) = 2 transitions, the time dependence of populations of the vibrational states were obtained. With the help of the integrating the population equations over all time, the importance of the two-quantum relaxation could be studied experimentally. By varying the delay between the pump and the probe laser, the He pressure dependent vibrational state specific decay could be measured. The time evolutions and relative intensities of the three states v = 22, 21 and 20 by preparing v = 22 were obtained. Using experimental data the rate constants (in units of 10(-11) cm3 x s(-1)) for v = 22 --> 21 and v = 22 --> 20 are 0.67 +/- 0.15 and 0.49 +/- 0.12, respectively. The single quantum relaxation accounts for only about 48% of the total relaxation out of v = 22. Multi-quantum relaxation (Delta(v) > 1) was found to be important at high vibrational states.

Ab Initio Study of Electronic Excitation Effects on SrTiO 3

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

Zhao, Shijun; Zhang, Yanwen; Weber, William J.

Interaction of energetic ions or lasers with solids often induces electronic excitations that may modify material properties significantly. In this study, effects of electronic excitations on strontium titanate SrTiO 3 (STO) are investigated based on first-principles calculations. The lattice structure, electronic properties, lattice vibrational frequencies, and dynamical stabilities are studied in detail. The results suggest that electronic excitation induces charge redistribution that is mainly observed in Ti–O bonds. The electronic band gap increases with increasing electronic excitation, as excitation mainly induces depopulation of Ti 3d states. Phonon analysis indicates that there is a large phonon band gap induced by electronicmore » excitation because of the changes in the vibrational properties of Ti and O atoms. In addition, a new peak appears in the phonon density of states with imaginary frequencies, an indication of lattice instability. Further dynamics simulations confirm that STO undergoes transition to an amorphous structure under strong electronic excitations. In conclusion, the optical properties of STO under electronic excitation are consistent with the evolution of atomic and electronic structures, which suggests a possibility to probe the properties of STO in nonequilibrium state using optical measurement.« less

Ab Initio Study of Electronic Excitation Effects on SrTiO 3

DOE PAGES

Zhao, Shijun; Zhang, Yanwen; Weber, William J.

2017-11-14

Interaction of energetic ions or lasers with solids often induces electronic excitations that may modify material properties significantly. In this study, effects of electronic excitations on strontium titanate SrTiO 3 (STO) are investigated based on first-principles calculations. The lattice structure, electronic properties, lattice vibrational frequencies, and dynamical stabilities are studied in detail. The results suggest that electronic excitation induces charge redistribution that is mainly observed in Ti–O bonds. The electronic band gap increases with increasing electronic excitation, as excitation mainly induces depopulation of Ti 3d states. Phonon analysis indicates that there is a large phonon band gap induced by electronicmore » excitation because of the changes in the vibrational properties of Ti and O atoms. In addition, a new peak appears in the phonon density of states with imaginary frequencies, an indication of lattice instability. Further dynamics simulations confirm that STO undergoes transition to an amorphous structure under strong electronic excitations. In conclusion, the optical properties of STO under electronic excitation are consistent with the evolution of atomic and electronic structures, which suggests a possibility to probe the properties of STO in nonequilibrium state using optical measurement.« less

Ultrafast surface carrier dynamics in the topological insulator Bi₂Te₃.

PubMed

Hajlaoui, M; Papalazarou, E; Mauchain, J; Lantz, G; Moisan, N; Boschetto, D; Jiang, Z; Miotkowski, I; Chen, Y P; Taleb-Ibrahimi, A; Perfetti, L; Marsi, M

2012-07-11

We discuss the ultrafast evolution of the surface electronic structure of the topological insulator Bi(2)Te(3) following a femtosecond laser excitation. Using time and angle-resolved photoelectron spectroscopy, we provide a direct real-time visualization of the transient carrier population of both the surface states and the bulk conduction band. We find that the thermalization of the surface states is initially determined by interband scattering from the bulk conduction band, lasting for about 0.5 ps; subsequently, few picoseconds are necessary for the Dirac cone nonequilibrium electrons to recover a Fermi-Dirac distribution, while their relaxation extends over more than 10 ps. The surface sensitivity of our measurements makes it possible to estimate the range of the bulk-surface interband scattering channel, indicating that the process is effective over a distance of 5 nm or less. This establishes a correlation between the nanoscale thickness of the bulk charge reservoir and the evolution of the ultrafast carrier dynamics in the surface Dirac cone.

Spatial Imaging of Strongly Interacting Rydberg Atoms

NASA Astrophysics Data System (ADS)

Thaicharoen, Nithiwadee

The strong interactions between Rydberg excitations can result in spatial correlations between the excitations. The ability to control the interaction strength and the correlations between Rydberg atoms is applicable in future technological implementations of quantum computation. In this thesis, I investigates how both the character of the Rydberg-Rydberg interactions and the details of the excitation process affect the nature of the spatial correlations and the evolution of those correlations in time. I first describes the experimental apparatus and methods used to perform high-magnification Rydberg-atom imaging, as well as three experiments in which these methods play an important role. The obtained Rydberg-atom positions reveal the correlations in the many-body Rydberg-atom system and their time dependence with sub-micron spatial resolution. In the first experiment, atoms are excited to a Rydberg state that experiences a repulsive van der Waals interaction. The Rydberg excitations are prepared with a well-defined initial separation, and the effect of van der Waals forces is observed by tracking the interatomic distance between the Rydberg atoms. The atom trajectories and thereby the interaction coefficient C6 are extracted from the pair correlation functions of the Rydberg atom positions. In the second experiment, the Rydberg atoms are prepared in a highly dipolar state by using adiabatic state transformation. The atom-pair kinetics that follow from the strong dipole-dipole interactions are observed. The pair correlation results provide the first direct visualization of the electric-dipole interaction and clearly exhibit its anisotropic nature. In both the first and the second experiment, results of semi-classical simulations of the atom-pair trajectories agree well with the experimental data. In the analysis, I use energy conservation and measurements of the initial positions and the terminal velocities of the atom pairs to extract the C6 and C 3 interaction coefficients. The final experiment demonstrates the ability to enhance or suppress the degree of spatial correlation in a system of Rydberg excitations, using a rotary-echo excitation process in concert with particular excitation laser detunings. The work in this thesis demonstrates an ability to control long-range interactions between Rydberg atoms, which paves the way towards preparing and studying increasingly complex many-body systems.

Extracting third order optical nonlinearities of Mn(III)-Phthalocyanine chloride using high repetition rate femtosecond pulses

NASA Astrophysics Data System (ADS)

Makhal, Krishnandu; Mathur, Paresh; Maurya, Sidharth; Goswami, Debabrata

2017-02-01

Third order nonlinearities of Mn(III)-Phthalocyanine chloride in dimethyl-sulphoxide under 50 fs pulses, operating at 94 MHz, by eliminating cumulative thermal effects have been investigated and reported by us. Modifications were done in data acquisition during Z-scan experiment, which included recording of time evolution waveform traces in an oscilloscope and not collection of Z versus transmission and utilization of a chopper of a suitable duty cycle. Time evolution traces were further processed analytically through MatLab® programming, which yielded Z-scan traces similar to what was obtained with single shot 50 fs pulse. We observed reverse saturable absorption at 800 nm owing to excited state absorption. We show that the nonlinear refractive index (γ) and nonlinear absorption coefficient (β) are over estimated almost 100 times, when MHz pulses are used compared to a situation, where thermo-optical nonlinearities are accounted. Illumination and dark periods are carefully set in a way, so that the sample is able to completely recover its initial temperature before arrival of the next pulse. Magnitudes of γ and β were found to be -(6.5-4.9) × 10-16 m2/W and (5.4-6.2) × 10-10 m/W under the MHz condition, whereas they were -(0.18-2.2) × 10-18 m2/W and (9.5-15) × 10-12 m/W under the thermally managed condition, respectively. To reveal the associated fast nonlinearity, femtosecond transient absorption experiment was performed, which inferred excited state absorption and ground state bleaching across the 450-780 nm region. Dynamics associated with these processes are reported along with fluorescence lifetime obtained through the TCSPC technique. Structure optimization using TDDFT calculations and HOMO-LUMO gaps with orbital pictures are also shown.

Collisional Removal of OH (X (sup 2)Pi, nu=7) by O2, N2, CO2, and N2O

NASA Technical Reports Server (NTRS)

Knutsen, Karen; Dyer, Mark J.; Copeland, Richard A.

1996-01-01

Collisional removal rate constants for the OH (X 2PI, nu = 7) radical are measured for the colliders O2, CO2, and N2O, and an upper limit is established for N2. OH(nu = 4) molecules, generated in a microwave discharge flow cell by the reaction of hydrogen atoms with ozone, are excited to v = 7 by the output of a pulsed infrared laser via direct vibrational overtone excitation. The temporal evolution of the P = 7 population is probed as a function of the collider gas partial pressure by a time-delayed pulsed ultraviolet laser. Fluorescence from the B 21 + state is detected in the visible spectral region.

Nuclear shapes studied with low-energy Coulomb excitation

NASA Astrophysics Data System (ADS)

Zielińska, Magda; Hadyńska-Klȩk, Katarzyna

2018-05-01

Coulomb excitation is one of the rare methods available to obtain information on static electromagnetic moments of short-lived excited nuclear states, including collective non-yrast levels. It is thus an ideal tool to study shape coexistence and shape evolution throughout the nuclear chart. Historically, these experiments were limited to stable isotopes, however the advent of new facilities, providing intense beams of short-lived radioactive species, has opened the possibility to apply this powerful technique to a much wider range of nuclei. Here, we present some recent complex Coulomb-excitation studies and use the example of superdeformed states in 42Ca to demonstrate the sensitivity of the method to second-order effects such as relative signs of electromagnetic matrix elements and quadrupole moments.

Evolution of the Magnetic Excitations in NaOsO3 through its Metal-Insulator Transition

NASA Astrophysics Data System (ADS)

Vale, J. G.; Calder, S.; Donnerer, C.; Pincini, D.; Shi, Y. G.; Tsujimoto, Y.; Yamaura, K.; Sala, M. Moretti; van den Brink, J.; Christianson, A. D.; McMorrow, D. F.

2018-06-01

The temperature dependence of the excitation spectrum in NaOsO3 through its metal-to-insulator transition (MIT) at 410 K has been investigated using resonant inelastic x-ray scattering at the Os L3 edge. High-resolution (Δ E ˜56 meV ) measurements show that the well-defined, low-energy magnons in the insulating state weaken and dampen upon approaching the metallic state. Concomitantly, a broad continuum of excitations develops which is well described by the magnetic fluctuations of a nearly antiferromagnetic Fermi liquid. By revealing the continuous evolution of the magnetic quasiparticle spectrum as it changes its character from itinerant to localized, our results provide unprecedented insight into the nature of the MIT in NaOsO3 [J. G. Vale, S. Calder, C. Donnerer, D. Pincini, Y. G. Shi, Y. Tsujimoto, K. Yamaura, M. M. Sala, J. van den Brink, A. D. Christianson, and D. F. McMorrow, Phys. Rev. B 97, 184429 (2018), 10.1103/PhysRevB.97.184429].

Time evolution of two holes in t - J chains with anisotropic couplings

NASA Astrophysics Data System (ADS)

Manmana, Salvatore R.; Thyen, Holger; Köhler, Thomas; Kramer, Stephan C.

Using time-dependent Matrix Product State (MPS) methods we study the real-time evolution of hole-excitations in t-J chains close to filling n = 1 . The dynamics in 'standard' t - J chains with SU(2) invariant spin couplings is compared to the one when introducing anisotropic, XXZ-type spin interactions as realizable, e.g., by ultracold polar molecules on optical lattices. The simulations are performed with MPS implementations based on the usual singular value decompositions (SVD) as well as ones using the adaptive cross approximation (ACA) instead. The ACA can be seen as an iterative approach to SVD which is often used, e.g., in the context of finite-element-methods, leading to a substantial speedup. A comparison of the performance of both algorithms in the MPS context is discussed. Financial support via DFG through CRC 1073 (''Atomic scale control of energy conversion''), project B03 is gratefully acknowledged.

Quench of non-Markovian coherence in the deep sub-Ohmic spin–boson model: A unitary equilibration scheme

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

Yao, Yao, E-mail: yaoyao@fudan.edu.cn

The deep sub-Ohmic spin–boson model shows a longstanding non-Markovian coherence at low temperature. Motivating to quench this robust coherence, the thermal effect is unitarily incorporated into the time evolution of the model, which is calculated by the adaptive time-dependent density matrix renormalization group algorithm combined with the orthogonal polynomials theory. Via introducing a unitary heating operator to the bosonic bath, the bath is heated up so that a majority portion of the bosonic excited states is occupied. It is found in this situation the coherence of the spin is quickly quenched even in the coherent regime, in which the non-Markovianmore » feature dominates. With this finding we come up with a novel way to implement the unitary equilibration, the essential term of the eigenstate-thermalization hypothesis, through a short-time evolution of the model.« less

Time dependent Schrödinger equation for black hole evaporation: No information loss

NASA Astrophysics Data System (ADS)

Corda, Christian

2015-02-01

In 1976 S. Hawking claimed that "Because part of the information about the state of the system is lost down the hole, the final situation is represented by a density matrix rather than a pure quantum state".1 In a series of papers, together with collaborators, we naturally interpreted BH quasi-normal modes (QNMs) in terms of quantum levels discussing a model of excited BH somewhat similar to the historical semi-classical Bohr model of the structure of a hydrogen atom. Here we explicitly write down, for the same model, a time dependent Schrödinger equation for the system composed by Hawking radiation and BH QNMs. The physical state and the correspondent wave function are written in terms of a unitary evolution matrix instead of a density matrix. Thus, the final state results to be a pure quantum state instead of a mixed one. Hence, Hawking's claim is falsified because BHs result to be well defined quantum mechanical systems, having ordered, discrete quantum spectra, which respect 't Hooft's assumption that Schrödinger equations can be used universally for all dynamics in the universe. As a consequence, information comes out in BH evaporation in terms of pure states in a unitary time dependent evolution. In Section 4 of this paper we show that the present approach permits also to solve the entanglement problem connected with the information paradox.

Coherence Evolution and Transfer Supplemented by Sender's Initial-State Restoring

NASA Astrophysics Data System (ADS)

Fel'dman, E. B.; Zenchuk, A. I.

2017-12-01

The evolution of quantum coherences comes with a set of conservation laws provided that the Hamiltonian governing this evolution conserves the spin-excitation number. At that, coherences do not intertwist during the evolution. Using the transmission line and the receiver in the initial ground state we can transfer the coherences to the receiver without interaction between them, although the matrix elements contributing to each particular coherence intertwist in the receiver's state. Therefore we propose a tool based on the unitary transformation at the receiver side to untwist these elements and thus restore (at least partially) the structure of the sender's initial density matrix. A communication line with two-qubit sender and receiver is considered as an example of implementation of this technique.

New insights into the nonadiabatic state population dynamics of model proton-coupled electron transfer reactions from the mixed quantum-classical Liouville approach

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

Shakib, Farnaz A.; Hanna, Gabriel, E-mail: gabriel.hanna@ualberta.ca

In a previous study [F. A. Shakib and G. Hanna, J. Chem. Phys. 141, 044122 (2014)], we investigated a model proton-coupled electron transfer (PCET) reaction via the mixed quantum-classical Liouville (MQCL) approach and found that the trajectories spend the majority of their time on the mean of two coherently coupled adiabatic potential energy surfaces. This suggested a need for mean surface evolution to accurately simulate observables related to ultrafast PCET processes. In this study, we simulate the time-dependent populations of the three lowest adiabatic states in the ET-PT (i.e., electron transfer preceding proton transfer) version of the same PCET modelmore » via the MQCL approach and compare them to the exact quantum results and those obtained via the fewest switches surface hopping (FSSH) approach. We find that the MQCL population profiles are in good agreement with the exact quantum results and show a significant improvement over the FSSH results. All of the mean surfaces are shown to play a direct role in the dynamics of the state populations. Interestingly, our results indicate that the population transfer to the second-excited state can be mediated by dynamics on the mean of the ground and second-excited state surfaces, as part of a sequence of nonadiabatic transitions that bypasses the first-excited state surface altogether. This is made possible through nonadiabatic transitions between different mean surfaces, which is the manifestation of coherence transfer in MQCL dynamics. We also investigate the effect of the strength of the coupling between the proton/electron and the solvent coordinate on the state population dynamics. Drastic changes in the population dynamics are observed, which can be understood in terms of the changes in the potential energy surfaces and the nonadiabatic couplings. Finally, we investigate the state population dynamics in the PT-ET (i.e., proton transfer preceding electron transfer) and concerted versions of the model. The PT-ET results confirm the participation of all of the mean surfaces, albeit in different proportions compared to the ET-PT case, while the concerted results indicate that the mean of the ground- and first-excited state surfaces only plays a role, due to the large energy gaps between the ground- and second-excited state surfaces.« less

Evolution of collectivity near mid-shell from excited-state lifetime measurements in rare earth nuclei

NASA Astrophysics Data System (ADS)

Werner, V.; Cooper, N.; Régis, J.-M.; Rudigier, M.; Williams, E.; Jolie, J.; Cakirli, R. B.; Casten, R. F.; Ahn, T.; Anagnostatou, V.; Berant, Z.; Bonett-Matiz, M.; Elvers, M.; Heinz, A.; Ilie, G.; Radeck, D.; Savran, D.; Smith, M. K.

2016-03-01

The B (E 2 ) excitation strength of the first excited 2+ state in even-even nuclei should directly correlate with the size of the valence space and maximize at mid-shell. A previously found saturation of B (E 2 ) strengths in well-deformed rotors at mid-shell is tested through high-precision measurements of the lifetimes of the lowest-lying 2+ states of the 168Hf and 174W rare earth isotopes. Measurements were performed using fast LaBr3 scintillation detectors. Combined with the recently remeasured B (E 2 ;21+→01+) values for Hf and W isotopes the new data remove discrepancies observed in the differentials of B (E 2 ) values for these isotopes.

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.

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

Avetissian, H. K.; Avchyan, B. R.; Mkrtchian, G. F.

The multiphoton resonant excitation of three-level atoms by the two laser fields of different frequencies is investigated. The time evolution of the system and analytical solutions expressing Rabi oscillations of the probability amplitudes at the two-color multiphoton resonant excitation are found using a nonperturbative resonant approach. The specific examples for experimental implementation of two-color multiphoton resonant excitation of hydrogen atoms are considered.

Chemical evolution via beta decay: a case study in strontium-90

NASA Astrophysics Data System (ADS)

Marks, N. A.; Carter, D. J.; Sassi, M.; Rohl, A. L.; Sickafus, K. E.; Uberuaga, B. P.; Stanek, C. R.

2013-02-01

Using 90Sr as a representative isotope, we present a framework for understanding beta decay within the solid state. We quantify three key physical and chemical principles, namely momentum-induced recoil during the decay event, defect creation due to physical displacement, and chemical evolution over time. A fourth effect, that of electronic excitation, is also discussed, but this is difficult to quantify and is strongly material dependent. The analysis is presented for the specific cases of SrTiO3 and SrH2. By comparing the recoil energy with available threshold displacement data we show that in many beta-decay situations defects such as Frenkel pairs will not be created during decay as the energy transfer is too low. This observation leads to the concept of chemical evolution over time, which we quantify using density functional theory. Using a combination of Bader analysis, phonon calculations and cohesive energy calculations, we show that beta decay leads to counter-intuitive behavior that has implications for nuclear waste storage and novel materials design.

Chemical evolution via beta decay: a case study in strontium-90.

PubMed

Marks, N A; Carter, D J; Sassi, M; Rohl, A L; Sickafus, K E; Uberuaga, B P; Stanek, C R

2013-02-13

Using (90)Sr as a representative isotope, we present a framework for understanding beta decay within the solid state. We quantify three key physical and chemical principles, namely momentum-induced recoil during the decay event, defect creation due to physical displacement, and chemical evolution over time. A fourth effect, that of electronic excitation, is also discussed, but this is difficult to quantify and is strongly material dependent. The analysis is presented for the specific cases of SrTiO(3) and SrH(2). By comparing the recoil energy with available threshold displacement data we show that in many beta-decay situations defects such as Frenkel pairs will not be created during decay as the energy transfer is too low. This observation leads to the concept of chemical evolution over time, which we quantify using density functional theory. Using a combination of Bader analysis, phonon calculations and cohesive energy calculations, we show that beta decay leads to counter-intuitive behavior that has implications for nuclear waste storage and novel materials design.

Time-synchronized continuous wave laser-induced fluorescence on an oscillatory xenon discharge.

PubMed

MacDonald, N A; Cappelli, M A; Hargus, W A

2012-11-01

A novel approach to time-synchronizing laser-induced fluorescence measurements to an oscillating current in a 60 Hz xenon discharge lamp using a continuous wave laser is presented. A sample-hold circuit is implemented to separate out signals at different phases along a current cycle, and is followed by a lock-in amplifier to pull out the resulting time-synchronized fluorescence trace from the large background signal. The time evolution of lower state population is derived from the changes in intensity of the fluorescence excitation line shape resulting from laser-induced fluorescence measurements of the 6s(')[1/2](1)(0)-6p(')[3/2](2) xenon atomic transition at λ = 834.68 nm. Results show that the lower state population oscillates at twice the frequency of the discharge current, 120 Hz.

Polarized photon scattering of 52Cr: Determining the parity of dipole states

NASA Astrophysics Data System (ADS)

Krishichayan, Fnu; Bhike, M.; Tornow, W.

2014-03-01

Observation of dipole states in nuclei are important because they provide information on various collective and single-particle nuclear excitation modes, e.g., pygmy dipole resonance (PDR) and spin-flip M1 resonance. The PDR has been extensively studied in the higher and medium mass region, whereas not much information is available around the low mass (A ~ 50) region where, apparently,the PDR starts to form. The present photoresponse of 52Cr has been investigated to test the evolution of the PDR in a nucleus with a small number of excess neutrons as well as to look for spin-flip M1 resonance excitation mode. Spin-1 states in 52Cr between 5.0 to 9.5 MeV excitation energy were excited by exploiting fully polarized photons using the (γ ,γ') nuclear resonance fluorescence technique, a completely model-independent electromagnetic method. The de-excitation γ-rays were detected using a HPGe array. The experiment was carried out using the HIGS facility at TUNL. Results of unambiguous parity determinations of dipole states in 52Cr will be presented.

Mid-infrared picosecond pump-dump-probe and pump-repump-probe experiments to resolve a ground-state intermediate in cyanobacterial phytochrome Cph1.

PubMed

van Wilderen, Luuk J G W; Clark, Ian P; Towrie, Michael; van Thor, Jasper J

2009-12-24

Multipulse picosecond mid-infrared spectroscopy has been used to study photochemical reactions of the cyanobacterial phytochrome photoreceptor Cph1. Different photophysical schemes have been discussed in the literature to describe the pathways after photoexcitation, particularly, to identify reaction phases that are linked to photoisomerisation and electronic decay in the 1566-1772 cm(-1) region that probes C=C and C=O stretching modes of the tetrapyrrole chromophore. Here, multipulse spectroscopy is employed, where, compared to conventional visible pump-mid-infrared probe spectroscopy, an additional visible pulse is incorporated that interacts with populations that are evolving on the excited- and ground-state potential energy surfaces. The time delays between the pump and the dump pulse are chosen such that the dump pulse interacts with different phases in the reaction process. The pump and dump pulses are at the same wavelength, 640 nm, and are resonant with the Pr ground state as well as with the excited state and intermediates. Because the dump pulse additionally pumps the remaining, partially recovered, and partially oriented ground-state population, theory is developed for estimating the fraction of excited-state molecules. The calculations take into account the model-dependent ground-state recovery fraction, the angular dependence of the population transfer resulting from the finite bleach that occurs with linearly polarized intense femtosecond optical excitation, and the partially oriented population for the dump field. Distinct differences between the results from the experiments that use a 1 or a 14 ps dump time favor a branching evolution from S1 to an excited state or reconfigured chromophore and to a newly identified ground-state intermediate (GSI). Optical dumping at 1 ps shows the instantaneous induced absorption of a delocalized C=C stretching mode at 1608 cm(-1), where the increased cross section is associated with the electronic ground-state structure of the ZZZ configuration of the linear tetrapyrrole chromophore. The dump-induced absorption decays with time constants of 5 and 19 ps to the Pr ground state. Employing a dump pulse at 14 ps results in an instantaneous decrease of the absorption of the 1608 cm(-1) band, indicating repumping of the GSI. The dump-induced absorption recovers back to the GSI with a 6 ps lifetime. A spectral similarity is observed between the 6 ps phase in the dump experiment and the 3 ps component found in the two-pulse pump-probe measurement. Combined with the dominance of ground-state absorption bands in the dump-induced spectrum, this indicates the presence of a GSI, which is additionally characterized by previously unidentified induced absorption at 1710 and 1570-80 cm(-1). The metastable photoproduct Lumi-R, which is in the electronic ground state and populated at 500 ps after excitation of Pr, is highly efficiently repumped into the Pr ground state with the power density used. After repumping, Lumi-R is not recovered on the 500 ps time scale of the experiment and is distinct from the GSI of Pr since it is not associated with its characteristic induced absorption at 1710 and 1570-80 cm(-1).

Quasiperiodic energy dependence of exciton relaxation kinetics in the sexithiophene crystal.

PubMed

Petelenz, Piotr; Zak, Emil

2014-10-16

Femtosecond kinetics of fluorescence rise in the sexithiophene crystal is studied on a microscopic model of intraband relaxation, where exciton energy is assumed to be dissipated by phonon-accompanied scattering, with the rates calculated earlier. The temporal evolution of the exciton population is described by a set of kinetic equations, solved numerically to yield the population buildup at the band bottom. Not only the time scale but also the shape of the rise curves is found to be unusually sensitive to excitation energy, exhibiting unique quasiperiodic dependence thereon, which is rationalized in terms of the underlying model. Further simulations demonstrate that the main conclusions are robust with respect to experimental factors such as finite temperature and inherent spectral broadening of the exciting pulse, while the calculated fluorescence rise times are found to be in excellent agreement with experimental data available to date. As the rise profiles are composed of a number of exponential contributions, which varies with excitation energy, the common practice of characterizing the population buildup in the emitting state by a single value of relaxation time turns out to be an oversimplification. New experiments giving further insight into the kinetics and mechanism of intraband exciton relaxation are suggested.

Linear entropy and collapse–revival phenomenon for a general formalism N-type four-level atom interacting with a single-mode field

NASA Astrophysics Data System (ADS)

Eied, A. A.

2018-05-01

In this paper, the linear entropy and collapse-revival phenomenon through the relation (< {\\hat{a}}+{\\hat{a}} > -{\\bar{n}}) in a system of N-configuration four-level atom interacting with a single-mode field with additional forms of nonlinearities of both the field and the intensity-dependent atom-field coupling functional are investigated. A factorization of the initial density operator is assumed, considering the field to be initially in a squeezed coherent states and the atom initially in its most upper excited state. The dynamical behavior of the linear entropy and the time evolution of (< {\\hat{a}}+ {\\hat{a}} > -{\\bar{n}}) are analyzed. In particular, the effects of the mean photon number, detuning, Kerr-like medium and the intensity-dependent coupling functional on the entropy and the evolution of (< {\\hat{a}}+ {\\hat{a}} > -{\\bar{n}}) are examined.

Deciphering excited state evolution in halorhodopsin with stimulated emission pumping.

PubMed

Bismuth, Oshrat; Komm, Pavel; Friedman, Noga; Eliash, Tamar; Sheves, Mordechai; Ruhman, Sanford

2010-03-04

The primary photochemical dynamics of Hb. pharaonis Halorhodopsin (pHR) are investigated by femtosecond visible pump-near IR dump-hyperspectral probe spectroscopy. The efficiency of excited state depletion is deduced from transient changes in absorption, recorded with and without stimulated emission pumping (SEP), as a function of the dump delay. The concomitant reduction of photocycle population is assessed by probing the "K" intermediate difference spectrum. Results show that the cross section for stimulating emission is nearly constant throughout the fluorescent state lifetime. Probing "K" demonstrates that dumping produces a proportionate reduction in photocycle yields. We conclude that, despite its nonexponential internal conversion (IC) kinetics, the fluorescent state in pHR constitutes a single intermediate in the photocycle. This contrasts with conclusions drawn from the study of primary events in the related chloride pump from Hb. salinarum (sHR), believed to produce the "K" intermediate from a distinct short-lived subpopulation in the excited state. Our discoveries concerning internal conversion dynamics in pHR are discussed in light of recent expectations for similar excited state dynamics in both proteins.

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.

The observation of ultrafast excited-state dynamical evolution in B800- partially or completely released LH2 of Rhodobacter sphaeroides 601 at room temperature.

PubMed

Liu, Weimin; Liu, Yuan; Yan, Yongli; Liu, Kangjun; Guo, Lijun; Xu, Chunhe; Qian, Shixiong

2006-04-01

Photodynamics of two kinds of peripheral antenna complexes (LH2 of Rhodobacter sphaeroides, native LH2 (RS601) and B800-released LH2 where B800-BChls were partially or completely removed with different pH treatments), were studied using femtosecond pump-probe technique at different laser wavelengths. The obtained results for these samples with different B800/B850 ratios demonstrated that under the excitation around B800 nm, the photoabsorption and photobleaching dynamics were caused by the direct excitation of upper excitonic levels of B850 and excited state of B800 pigments, respectively. Furthermore, the removal of B800 pigments had little effect on the energy transfer processes of B850 interband/intraband transfer.

Evolution from Rydberg gas to ultracold plasma in a supersonic atomic beam of Xe

NASA Astrophysics Data System (ADS)

Hung, J.; Sadeghi, H.; Schulz-Weiling, M.; Grant, E. R.

2014-08-01

A Rydberg gas of xenon, entrained in a supersonic atomic beam, evolves slowly to form an ultracold plasma. In the early stages of this evolution, when the free-electron density is low, Rydberg atoms undergo long-range \\ell -mixing collisions, yielding states of high orbital angular momentum. The development of high-\\ell states promotes dipole-dipole interactions that help to drive Penning ionization. The electron density increases until it reaches the threshold for avalanche. Ninety μs after the production of a Rydberg gas with the initial state, {{n}_{0}}{{\\ell }_{0}}=42d, a 432 V cm-1 electrostatic pulse fails to separate charge in the excited volume, an effect which is ascribed to screening by free electrons. Photoexcitation cross sections, observed rates of \\ell -mixing, and a coupled-rate-equation model simulating the onset of the electron-impact avalanche point consistently to an initial Rydberg gas density of 5\\times {{10}^{8}}\\;c{{m}^{-3}}.

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).

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.

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.

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.

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

Early time excited-state structural evolution of pyranine in methanol revealed by femtosecond stimulated Raman spectroscopy.

PubMed

Wang, Yanli; Liu, Weimin; Tang, Longteng; Oscar, Breland; Han, Fangyuan; Fang, Chong

2013-07-25

To understand chemical reactivity of molecules in condensed phase in real time, a structural dynamics technique capable of monitoring molecular conformational motions on their intrinsic time scales, typically on femtoseconds to picoseconds, is needed. We have studied a strong photoacid pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, HPTS, pK(a)* ≈ 0) in pure methanol and observed that excited-state proton transfer (ESPT) is absent, in sharp contrast with our previous work on HPTS in aqueous solutions wherein ESPT prevails following photoexcitation. Two transient vibrational marker bands at ~1477 (1454) and 1532 (1528) cm(-1) appear in CH3OH (CD3OD), respectively, rising within the instrument response time of ~140 fs and decaying with 390-470 (490-1400) fs and ~200 ps time constants in CH3OH (CD3OD). We attribute the mode onset to small-scale coherent proton motion along the pre-existing H-bonding chain between HPTS and methanol, and the two decay stages to the low-frequency skeletal motion-modulated Franck-Condon relaxation within ~1 ps and subsequent rotational diffusion of H-bonding partners in solution before fluorescence. The early time kinetic isotope effect (KIE) of ~3 upon methanol deuteration argues active proton motions particularly within the first few picoseconds when coherent skeletal motions are underdamped. Pronounced quantum beats are observed for high-frequency modes consisting of strong phenolic COH rocking (1532 cm(-1)) or H-out-of-plane wagging motions (952 cm(-1)) due to anharmonic coupling to coherent low-frequency modes impulsively excited at ca. 96, 120, and 168 cm(-1). The vivid illustration of atomic motions of HPTS in varying H-bonding geometry with neighboring methanol molecules unravels the multidimensional energy relaxation pathways immediately following photoexcitation, and provides compelling evidence that, in lieu of ESPT, the photoacidity of HPTS promptly activates characteristic low-frequency skeletal motions to search phase space mainly concerning the phenolic end and to efficiently dissipate vibrational energy via skeletal deformation and proton shuttling motions within the intermediate, relatively confined excited-state HPTS-methanol complex on a solvent-dependent dynamic potential energy surface.

Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212.

PubMed

Ino, Akihiro; Anzai, Hiroaki; Arita, Masashi; Namatame, Hirofumi; Taniguchi, Masaki; Ishikado, Motoyuki; Fujita, Kazuhiro; Ishida, Shigeyuki; Uchida, Shinichi

2013-12-05

: The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-Tc cuprate, Bi2Sr2CaCu2 O8+δ (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening.

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

Lackner, Florian; Chatterley, Adam S.; Pemmaraju, C. D.

Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C 4H 4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (~58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field inducedmore » ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se + ions within an overall time scale of approximately 170 fs. In this study, we propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ 1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se + and ring-open cations within an additional τ 2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. In conclusion, the findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural rearrangements.« less

Direct observation of ring-opening dynamics in strong-field ionized selenophene using femtosecond inner-shell absorption spectroscopy

DOE PAGES

Lackner, Florian; Chatterley, Adam S.; Pemmaraju, C. D.; ...

2016-12-21

Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C 4H 4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (~58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field inducedmore » ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se + ions within an overall time scale of approximately 170 fs. In this study, we propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ 1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se + and ring-open cations within an additional τ 2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. In conclusion, the findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural rearrangements.« less

Photoelectron imaging of autoionizing states of xenon: Effect of external electric fields

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

Shubert, V. Alvin; Pratt, Stephen T.

Velocity map photoelectron imaging was used to study the photoelectron angular distributions of autoionizing Stark states of atomic xenon excited just below the Xe{sup +} {sup 2} P{sub 1/2}{sup o} threshold at fields ranging from 50 to 700 V/cm. Two-color, two-photon resonant, three-photon excitation via the 6p{sup '}[1/2]{sub 0} level was used to probe the region of interest. The wavelength scans show a similar evolution of structure to that observed in single-photon excitation [Ernst et al., Phys. Rev. A 37, 4172 (1988)]. The photoelectron angular distributions following autoionization of the Stark states provide information on the decay of excited statesmore » in electron fields. In the present experiments, the large autoionization width of the ({sup 2} P{sub 1/2}{sup o})nd[3/2]{sub 1}{sup o} series dominates the decay processes, and thus controls the angular distributions. However, the angular distributions of the Stark states also indicate the presence of other decay channels contributing to the decay of these states.« less

Optical pump terahertz probe studies of semiconducting polymers

NASA Astrophysics Data System (ADS)

Cunningham, Paul D.

Optical-pump terahertz-probe spectroscopy (OPTP) has been applied to study charge generation, transport and the evolution of the photo-induced excited states in thin film organic semiconductors, with emphasis on their relevance to photovoltaic technology. In these experiments the response of the photoexcited material to the AC electric field of a terahertz (THz) pulse was measured. From this response, the evolution of the complex conductivity in the far-infrared was monitored. OPTP presents advantages over other techniques by being an all-optical probe of the complex conductivity over nanometer scale distances with sub-picosecond resolution and exhibits particular sensitivity to carrier scattering rates, which typically lay in the THz range. Conductivity models were applied to the extracted conductivity curves in order to determine technologically relevant quantities like the charge carrier mobility and external quantum yield of charge carrier generation. We observed charge carriers generated on a subpicosecond time scale in thin films of polyhexylthiophene (P3HT). Through application of the Drude-Smith model (DSM) over the 0-2 THz band, we determined a room temperature intrinsic mobility of about 30 cm2/Vs. The temperature dependence of the conductivity dynamics showed signs of thermally activated polaron hopping influenced by torsional disorder. Both above and below gap excitation resulted in similar dynamics, showing that the majority of carriers recombine within 1 ps. We were able to observe charge transfer occurring on a sub-ps timescale to the soluble fullerene, PCBM, for both excited states, demonstrating that narrow gap polymers can be blended with PCBM for photovoltaic applications. We observed charge carrier generated on a sub-ps time scale in thin amorphous films of metalated polymers. The time evolution of the conductivity showed that charge carriers recombine and only excitons persist after 100 ps. This characteristic appears to be common to amorphous systems. An intrinsic mobility of 20 cm2/Vs was found for the most promising material. Broadband (0-6 THz) studies of the photoconductivity in P3HT suggest that the hole mobility is lower than initially determined. They also bring into question whether the DSM can describe the conductivity effectively or whether delocalized polaron transitions at higher frequencies are the origin of the observed features.

Discharge mode transition and temporal-spatial evolution of an air-water plasma jet generated by pulsating DC power

NASA Astrophysics Data System (ADS)

Lei, J.; Geng, Y.; Liu, K.; Zhu, W.; Zheng, Z.; Hu, H.

2017-12-01

In this paper, pulsating direct current air-water plasma jet, which can increase the production of •OH and decrease the temperature, is studied. The results show that the discharge mode changes in one cycle from corona discharge with steep Trichel current pulse to glow-like discharge. It is unknown whether the different discharge modes and water ratio have an effect on the transient process of the excited O and •OH production and the mechanism of plasma propagation. So, a series of experiments are done in this paper. The results show that the changing rules of both the excited state O and the discharge current reach their two peak values synchronously. And its maximum appears at the time of the first peak current value in corona mode. However, the change of the excited state •OH is different. It increases to its maximum at the time of the second peak current value in glow-like mode. Besides, the intensified charge coupled device photographs show that the luminous intensity of the discharge zone at the first peak current value in corona mode is stronger than the second peak current value in glow-like mode. At the same time, the discharge area of the former is larger than the latter. Nevertheless, with the increase in water ratio, the discharge area change reversed. Additionally, the air plasma plume propagation depends on the gas flow. The initial propagation velocity decreases with the increase in water ratio.

Evolution of deformation in neutron-rich Ba isotopes up to A =150

NASA Astrophysics Data System (ADS)

Licǎ, R.; Benzoni, G.; Rodríguez, T. R.; Borge, M. J. G.; Fraile, L. M.; Mach, H.; Morales, A. I.; Madurga, M.; Sotty, C. O.; Vedia, V.; De Witte, H.; Benito, J.; Bernard, R. N.; Berry, T.; Bracco, A.; Camera, F.; Ceruti, S.; Charviakova, V.; Cieplicka-Oryńczak, N.; Costache, C.; Crespi, F. C. L.; Creswell, J.; Fernandez-Martínez, G.; Fynbo, H.; Greenlees, P. T.; Homm, I.; Huyse, M.; Jolie, J.; Karayonchev, V.; Köster, U.; Konki, J.; Kröll, T.; Kurcewicz, J.; Kurtukian-Nieto, T.; Lazarus, I.; Lund, M. V.; Mǎrginean, N.; Mǎrginean, R.; Mihai, C.; Mihai, R. E.; Negret, A.; Orduz, A.; Patyk, Z.; Pascu, S.; Pucknell, V.; Rahkila, P.; Rapisarda, E.; Regis, J. M.; Robledo, L. M.; Rotaru, F.; Saed-Samii, N.; Sánchez-Tembleque, V.; Stanoiu, M.; Tengblad, O.; Thuerauf, M.; Turturica, A.; Van Duppen, P.; Warr, N.; IDS Collaboration

2018-02-01

The occurrence of octupolar shapes in the Ba isotopic chain was recently established experimentally up to N =90 . To further extend the systematics, the evolution of shapes in the most neutron-rich members of the Z =56 isotopic chain accessible at present, Ba,150148, has been studied via β decay at the ISOLDE Decay Station. This paper reports on the first measurement of the positive- and negative-parity low-spin excited states of 150Ba and presents an extension of the β -decay scheme of 148Cs. Employing the fast timing technique, half-lives for the 21+ level in both nuclei have been determined, resulting in T1 /2=1.51 (1 ) ns for 148Ba and T1 /2=3.4 (2 ) ns for 150Ba. The systematics of low-spin states, together with the experimental determination of the B (E 2 :2+→0+) transition probabilities, indicate an increasing collectivity in Ba-150148, towards prolate deformed shapes. The experimental data are compared to symmetry conserving configuration mixing (SCCM) calculations, confirming an evolution of increasingly quadrupole deformed shapes with a definite octupolar character.

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.

Ultrafast measurements of chlorine dioxide photochemistry

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

Ludowise, P.D.

Time-resolved mass spectrometry and time-resolved photoelectron spectroscopy are used to study the ultrafast photodissociation dynamics of chlorine dioxide, an important constituent in stratospheric ozone depletion. Chapter 1 introduces these pump/probe techniques, in which a femtosecond pump pulse excites a molecule to a dissociative state. At a later time, a second femtosecond probe pulse ionizes the molecule. The resulting mass and photoelectron spectra are acquired as a function of the delay between the pump and probe pulses, which follows the evolution of the molecule on the excited state. A comparison to other techniques used to study reaction dynamics is discussed. Chaptermore » 2 includes a detailed description of the design and construction of the experimental apparatus, which consists of a femtosecond laser system, a molecular beam time-of-flight spectrometer, and a data acquisition system. The time-of-flight spectrometer is specifically designed to have a short flight distance to maximize the photoelectron collection efficiency without degrading the resolution, which is limited by the bandwidth of the femtosecond laser system. Typical performance of the apparatus is demonstrated in a study of the time-resolved photoelectron spectroscopy of nitric oxide. The results of the time-resolved mass spectrometry experiments of chlorine dioxide are presented in Chapter 3. Upon excitation to the A {sup 2}A{sub 2} state near 3.2 eV, the molecule dissociates through an indirect two-step mechanism. The direct dissociation channel has been predicted to be open, but is not observed. A quantum beat is observed in the OClO{sup +} species, which is described as a vibrational coherence of the optically prepared A {sup 2}A{sub 2} state. Chapter 4 presents the results of the time-resolved photoelectron experiments of chlorine dioxide. At short delay time, the quantum beat of the OClO{sup +} species is observed in the X {sup 1}A{sub 1} state of the ion. At infinite delay, the signal is dominated by the ClO{sup +} ion, observed in a variety of electronic states. The photoelectron data is shown to support the indirect two-step dissociation mechanism derived from the mass results. Conclusions of the mass and photoelectron results are discussed in context of the stratospheric ozone depletion problem.« less

SEMICONDUCTOR PHYSICS: Properties of the two- and three-dimensional quantum dot qubit

NASA Astrophysics Data System (ADS)

Shihua, Chen

2010-05-01

On the condition of electric-longitudinal-optical (LO) phonon strong coupling in both two- and three-dimensional parabolic quantum dots (QDs), we obtain the eigenenergies of the ground state (GS) and the first excited state (ES), the eigenfunctions of the GS and the first ES by using a variational method of Pekar type. This system in QD may be employed as a quantum system-quantum bit (qubit). When the electron is in the superposition state of the GS and the first ES, we obtain the time evolution of the electron density. The relations of both the electron probability density and the period of oscillation with the electric-LO phonon coupling strength and confinement length are discussed.

Higher spin gravitational couplings: Ghosts in the Yang-Mills detour complex

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

Gover, A. R.; Hallowell, K.; Waldron, A.

2007-01-15

Gravitational interactions of higher spin fields are generically plagued by inconsistencies. There exists however, a simple framework that couples higher spins to a broad class of gravitational backgrounds (including Ricci flat and Einstein) consistently at the classical level. The model is the simplest example of a Yang-Mills detour complex and has broad mathematical applications, especially to conformal geometry. Even the simplest version of the theory, which couples gravitons, vectors and scalar fields in a flat background is rather rich, providing an explicit setting for detailed analysis of ghost excitations. Its asymptotic scattering states consist of a physical massless graviton, scalar,more » and massive vector along with a degenerate pair of zero norm photon excitations. Coherent states of the unstable sector do have positive norms, but their evolution is no longer unitary and amplitudes grow with time. The class of models proposed is extremely general and of considerable interest for ghost condensation and invariant theory.« less

Holography and thermalization in optical pump-probe spectroscopy

NASA Astrophysics Data System (ADS)

Bagrov, A.; Craps, B.; Galli, F.; Keränen, V.; Keski-Vakkuri, E.; Zaanen, J.

2018-04-01

Using holography, we model experiments in which a 2 +1 D strange metal is pumped by a laser pulse into a highly excited state, after which the time evolution of the optical conductivity is probed. We consider a finite-density state with mildly broken translation invariance and excite it by oscillating electric field pulses. At zero density, the optical conductivity would assume its thermalized value immediately after the pumping has ended. At finite density, pulses with significant dc components give rise to slow exponential relaxation, governed by a vector quasinormal mode. In contrast, for high-frequency pulses the amplitude of the quasinormal mode is strongly suppressed, so that the optical conductivity assumes its thermalized value effectively instantaneously. This surprising prediction may provide a stimulus for taking up the challenge to realize these experiments in the laboratory. Such experiments would test a crucial open question faced by applied holography: are its predictions artifacts of the large N limit or do they enjoy sufficient UV independence to hold at least qualitatively in real-world systems?

Direct detection of time-resolved Rabi oscillations in a single quantum dot via resonance fluorescence

NASA Astrophysics Data System (ADS)

Schaibley, J. R.; Burgers, A. P.; McCracken, G. A.; Steel, D. G.; Bracker, A. S.; Gammon, D.; Sham, L. J.

2013-03-01

Optical Rabi oscillations are coherent population oscillations of a two-level system coupled by an electric dipole transition when driven by a strong nearly resonant optical field. In quantum dot structures, these measurements have typically been performed as a function of the total pulse area ∫Ω0(t)dt where the pulse area varies as a function of Rabi frequency. Here, we report direct detection of the time-resolved coherent transient response of the resonance fluorescence to measure the time evolution of the optical Rabi oscillations in a single charged InAs quantum dot. We extract a decoherence rate consistent with the limit from the excited state lifetime.

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.

Vibrational energy transfer in OH X 2Pi(i), v = 2 and 1

NASA Technical Reports Server (NTRS)

Raiche, George A.; Jeffries, Jay B.; Rensberger, Karen J.; Crosley, David R.

1990-01-01

Using an IR-pump/UV-probe method in a flow discharge cell, vibrational energy transfer in OH X 2Pi(i) has been studied. OH is prepared in v = 2 by overtone excitation, and the time evolution of population in v = 2 and 1 monitored by laser-induced fluorescence. Rate constants for vibrational relaxation by the colliders H2O, NH3, CO2, and CH4 were measured. Ratios of rate constants for removal from the two states, k2/k1, range from two to five.

Auger heating of carriers in {GaAs}/{AlAs} heterostructures

NASA Astrophysics Data System (ADS)

Borri, P.; Ceccherini, S.; Gurioli, M.; Bogani, F.

1997-07-01

The photoluminescence of {GaAs}/{AlAs} multiple quantum wells structures under optical ps excitation is investigated for carrier densities in the range 10 18-4 × 10 19 cm -3 with frequency and time-resolved spectroscopic techniques. The measurements give a direct evidence of the occurrence in the sample of carrier heating. This energy up-conversion gives rise to photoluminescence from the states near the Fermi level whose intensity and time evolution depend on the carrier density in a strongly non-linear way. The observed behaviour can be explained introducing in the carrier dynamics an up-conversion mechanism due to Auger-like processes.

Coulomb Correlations Intertwined with Spin and Orbital Excitations in LaCoO_{3}.

PubMed

Tomiyasu, K; Okamoto, J; Huang, H Y; Chen, Z Y; Sinaga, E P; Wu, W B; Chu, Y Y; Singh, A; Wang, R-P; de Groot, F M F; Chainani, A; Ishihara, S; Chen, C T; Huang, D J

2017-11-10

We carried out temperature-dependent (20-550 K) measurements of resonant inelastic x-ray scattering on LaCoO_{3} to investigate the evolution of its electronic structure across the spin-state crossover. In combination with charge-transfer multiplet calculations, we accurately quantified the renomalized crystal-field excitation energies and spin-state populations. We show that the screening of the effective on-site Coulomb interaction of 3d electrons is orbital selective and coupled to the spin-state crossover in LaCoO_{3}. The results establish that the gradual spin-state crossover is associated with a relative change of Coulomb energy versus bandwidth, leading to a Mott-type insulator-to-metal transition.

Nonlinear Evolution of Counter-Propagating Whistler Mode Waves Excited by Anisotropic Electrons Within the Equatorial Source Region: 1-D PIC Simulations

NASA Astrophysics Data System (ADS)

Chen, Huayue; Gao, Xinliang; Lu, Quanming; Sun, Jicheng; Wang, Shui

2018-02-01

Nonlinear physical processes related to whistler mode waves are attracting more and more attention for their significant role in reshaping whistler mode spectra in the Earth's magnetosphere. Using a 1-D particle-in-cell simulation model, we have investigated the nonlinear evolution of parallel counter-propagating whistler mode waves excited by anisotropic electrons within the equatorial source region. In our simulations, after the linear phase of whistler mode instability, the strong electrostatic standing structures along the background magnetic field will be formed, resulting from the coupling between excited counter-propagating whistler mode waves. The wave numbers of electrostatic standing structures are about twice those of whistler mode waves generated by anisotropic hot electrons. Moreover, these electrostatic standing structures can further be coupled with either parallel or antiparallel propagating whistler mode waves to excite high-k modes in this plasma system. Compared with excited whistler mode waves, these high-k modes typically have 3 times wave number, same frequency, and about 2 orders of magnitude smaller amplitude. Our study may provide a fresh view on the evolution of whistler mode waves within their equatorial source regions in the Earth's magnetosphere.

Beta-decay rates of FP shell nuclei with A greater than 60 in massive stars at the presupernova stage

NASA Astrophysics Data System (ADS)

Kar, K.; Ray, A.; Sarkar, S.

1994-10-01

Beta decay and electron capture on a number of neutron-rich nuclei with A greater than 60 at the presupernova stage may play an important role in determining the hydrostatic core structure of massive presupernova stars and, through this, affect the subsequent evolution during the gravitational collapse and supernova explosion phases. In particular, some isotopes of cobalt and copper can make a substantial contribution to the overall changes in the lepton fraction and entropy of the stellar core during its very late stage of evolution. In the stellar evolution calculations to date, many of these nuclei could not be appropriately tracked in the reaction network, since reliable rates for these have not been available so far. We describe a model to calculate the beta-decay rates using an average beta strength function and an electron phase-space factor evaluated for typical presupernova matter density (rho = 3 x 107-3 x 109 g/cu cm) and temperature (T = (2-5) x 109 K). For the Gamnow-Teller (GT) strength function we use a sum rule calculated by the spectral distribution theory, and the centroid of the distribution is obtained from experimental data on (p, n) reactions. The width sigma of the GT strength function has two parts (sigma2 = (sigmaN exp 2 + (sigmaC exp 2, with sigmaC = 0.157ZA-1/3). The parameter sigmaN is fixed by a best fit to the observed half-lives for the free decays of a number of A greater than 60 nuclei. In the calculation of rates we include contributions from the excited states of the mother nucleus wherever they are known experimentally. For the excited states one uses the same form of the GT strength function, but shifted in energy using the extended isobaric analog state argument. The method is particularly suited for calculating contributions from the excited states important at high temperatures relevant at the presupernova stellar evolution phase. We also include the contributions to the transition rates from the Gamow-Teller resonance states (e.g., the GTR+ state) in the mother nucleus, which may be thermally populated. The beta-decay rates for nuclei having A greater than 60 reported here can be inputs for presupernova stellar evolution and nucleosynthesis calculations employing detailed nuclear reaction networks relevant in the advanced phases of hydrostatic nuclear burning.

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.

Compilation of giant electric dipole resonances built on excited states

NASA Astrophysics Data System (ADS)

Schiller, A.; Thoennessen, M.

2007-07-01

Giant Electric Dipole Resonance (GDR) parameters for γ decay to excited states with finite spin and temperature are compiled. Over 100 original works have been reviewed and from some 70 of them, about 350 sets of hot GDR parameters for different isotopes, excitation energies, and spin regions have been extracted. All parameter sets have been brought onto a common footing by calculating the equivalent Lorentzian parameters. The current compilation is complementary to an earlier compilation by Samuel S. Dietrich and Barry L. Berman (At. Data Nucl. Data Tables 38 (1988) 199-338) on ground-state photo-neutron and photo-absorption cross sections and their Lorentzian parameters. A comparison of the two may help shed light on the evolution of GDR parameters with temperature and spin. The present compilation is current as of July 2006.

Collisional Removal of O2 (c(sup 1) Sigma(sup-)(sub u), nu=9) by O2, N2, and He

NASA Technical Reports Server (NTRS)

Copeland, Richard A.; Knutsen, Karen; Onishi, Marc E.; Yalcin, Talat

1996-01-01

The collisional removal Of 02 molecules in selected vibrational levels of the c state is studied using a two-laser double-resonance technique. The output of the first laser excites the 02 to nu = 9 or 10 of the c Sigma - state, and the ultraviolet output of the second laser monitors specific rovibrational levels via resonance-enhanced ionization. The temporal evolution of the c Sigma u state vibrational level is observed by scanning the time delay between the two pulsed lasers. As the rate constants for 02 and N2 are similar in magnitude, N2 collisions dominate the removal rate in the earth's atmosphere. For v= 10 colliding with 02, we find a removal rate constant that is 2-5 times that for v=9 and that single quantum collision cascade is an important pathway for removal.

Access to long-term optical memories using photon echoes retrieved from electron spins in semiconductor quantum wells

NASA Astrophysics Data System (ADS)

Poltavtsev, S. V.; Langer, L.; Yugova, I. A.; Salewski, M.; Kapitonov, Y. V.; Yakovlev, D. R.; Karczewski, G.; Wojtowicz, T.; Akimov, I. A.; Bayer, M.

2016-10-01

We use spontaneous (two-pulse) and stimulated (three-pulse) photon echoes for studying the coherent evolution of optically excited ensemble of trions which are localized in semiconductor CdTe/CdMgTe quantum well. Application of transverse magnetic field leads to the Larmor precession of the resident electron spins, which shuffles optically induced polarization between optically accessible and inaccessible states. This results in several spectacular phenomena. First, magnetic field induces oscillations of spontaneous photon echo amplitude. Second, in three-pulse excitation scheme, the photon echo decay is extended by several orders of magnitude. In this study, short-lived optical excitation which is created by the first pulse is coherently transferred into a long-lived electron spin state using the second optical pulse. This coherent spin state of electron ensemble persists much longer than any optical excitation in the system, preserving information on initial optical field, which can be retrieved as a photon echo by means of third optical pulse.

Planar pyrochlore: A strong-coupling analysis

NASA Astrophysics Data System (ADS)

Brenig, Wolfram; Honecker, Andreas

2002-04-01

Recent investigations of the two-dimensional spin-1/2 checkerboard lattice favor a valence bond crystal with long-range quadrumer order [J.-B. Fouet, M. Mambrini, P. Sindzingre, and C. Lhuillier, cond-mat/0108070 (unpublished)]. Starting from the limit of isolated quadrumers, we perform a complementary analysis of the evolution of the spectrum as a function of the interquadrumer coupling j using both exact diagonalization (ED) and series expansion (SE) by continuous unitary transformation. We compute (i) the ground-state energy, (ii) the elementary triplet excitations, and (iii) singlet excitations on finite systems and find very good agreement between SE and ED. In the thermodynamic limit we find a ground-state energy substantially lower than that documented in the literature. The elementary triplet excitation is shown to be gapped and almost dispersionless, whereas the singlet sector contains strongly dispersive modes. Evidence is presented for the low energy singlet excitations in the spin gap in the vicinity of j=1 to result from a large downward renormalization of local high-energy states.

Nonlinear electronic excitations in crystalline solids using meta-generalized gradient approximation and hybrid functional in time-dependent density functional theory

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

Sato, Shunsuke A.; Taniguchi, Yasutaka; Department of Medical and General Sciences, Nihon Institute of Medical Science, 1276 Shimogawara, Moroyama-Machi, Iruma-Gun, Saitama 350-0435

2015-12-14

We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functionalmore » which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.« 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.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission† †Electronic supplementary information (ESI) available: Actinic pump spectrum, discussion on ground state addition process, peak fitting procedure, transient absorption data, power dependence measurements, etalon pulse shaping, TIPS-pentacene FSRS data, and optimized geometry and frequency calculation results. See DOI: 10.1039/c7sc03496b

PubMed Central

Hart, Stephanie M.; Silva, W. Ruchira

2017-01-01

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features. We hypothesize that these features arise from the formation of cationic and anionic species due to partial transfer of electron density from one pentacene molecule to a neighboring molecule. These observations provide experimental evidence for the role of states with significant charge-transfer character which facilitate the singlet fission process in pentacene. Our work both provides new insight into the singlet fission mechanism in pentacene and demonstrates the utility of structurally-sensitive time-resolved spectroscopic techniques in monitoring ultrafast processes. PMID:29675170

The Electronic Structure of the Cs/ n-GaN(0001) Nano-Interface

NASA Astrophysics Data System (ADS)

Benemanskaya, G. V.; Lapushkin, M. N.; Marchenko, D. E.; Timoshnev, S. N.

2018-03-01

Electronic structures of the n-GaN(0001) surface and Cs/ n-GaN(0001) interface with submonolayer Cs coverages were studied for the first time in situ by the photoelectron spectroscopy (PES) method. The spectra of photoemission from the valence band, surface electron states, and core levels (Ga 3 d, Cs 4 d, Cs 5 p) under synchrotron excitation were measured in a range of photon energies within 50-150 eV. Evolution of the spectrum of surface states near the valence-band maximum was revealed by PES during the adsorption of Cs atoms. A metallic character of the Cs/ n-GaN(0001) nano-interface is demonstrated.

Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212

PubMed Central

2013-01-01

The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-Tc cuprate, Bi2Sr2CaCu2 O8+δ (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening. PMID:24314035

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

On the Origin of Wind Line Variability in O Stars

NASA Astrophysics Data System (ADS)

Massa, D.; Prinja, R. K.

2015-08-01

We analyze 10 UV time series for five stars that fulfill specific sampling and spectral criteria to constrain the origin of large-scale wind structure in O stars. We argue that excited state lines must arise close to the stellar surface and are an excellent diagnostic complement to resonance lines which, due to radiative transfer effects, rarely show variability at low velocity. Consequently, we splice dynamic spectra of the excited state line N iv λ1718 at low velocity with those of Si iv λ λ 1400 at high velocity in order to examine the temporal evolution of wind line features. These spliced time series reveal that nearly all of the features observed in the time series originate at or very near the stellar surface. Furthermore, we positively identify the observational signature of equatorial corotating interaction regions in two of the five stars and possibly two others. In addition, we see no evidence of features originating further out in the wind. We use our results to confirm the fact that the features seen in dynamic spectra must be huge in order to remain in the line of sight for days, persisting to very large velocity, and that the photospheric footprint of the features must also be quite large, ˜15%-20% of the stellar diameter.

Quantum non-barking dogs

NASA Astrophysics Data System (ADS)

Imari Walker, Sara; Davies, Paul C. W.; Samantray, Prasant; Aharonov, Yakir

2014-06-01

Quantum weak measurements with states both pre- and post-selected offer a window into a hitherto neglected sector of quantum mechanics. A class of such systems involves time dependent evolution with transitions possible. In this paper we explore two very simple systems in this class. The first is a toy model representing the decay of an excited atom. The second is the tunneling of a particle through a barrier. The post-selection criteria are chosen as follows: at the final time, the atom remains in its initial excited state for the first example and the particle remains behind the barrier for the second. We then ask what weak values are predicted in the physical environment of the atom (to which no net energy has been transferred) and in the region beyond the barrier (to which the particle has not tunneled). Thus, just as the dog that didn't bark in Arthur Conan Doyle's story Silver Blaze gave Sherlock Holmes meaningful information about the dog's non-canine environment, here we probe whether the particle that has not decayed or has not tunneled can provide measurable information about physical changes in the environment. Previous work suggests that very large weak values might arise in these regions for long durations between pre- and post-selection times. Our calculations reveal some distinct differences between the two model systems.

Dynamics of Scroll Wave in a Three-Dimensional System with Changing Gradient.

PubMed

Yuan, Xiao-Ping; Chen, Jiang-Xing; Zhao, Ye-Hua; Liu, Gui-Quan; Ying, He-Ping

2016-01-01

The dynamics of a scroll wave in an excitable medium with gradient excitability is studied in detail. Three parameter regimes can be distinguished by the degree of gradient. For a small gradient, the system reaches a simple rotating synchronization. In this regime, the rigid rotating velocity of spiral waves is maximal in the layers with the highest filament twist. As the excitability gradient increases, the scroll wave evolutes into a meandering synchronous state. This transition is accompanied by a variation in twisting rate. Filament twisting may prevent the breakup of spiral waves in the bottom layers with a low excitability with which a spiral breaks in a 2D medium. When the gradient is large enough, the twisted filament breaks up, which results in a semi-turbulent state where the lower part is turbulent while the upper part contains a scroll wave with a low twisting filament.

Exploring coherent electron excitation and migration dynamics by electron diffraction with ultrashort X-ray pulses.

PubMed

Yuan, Kai-Jun; Bandrauk, André D

2017-10-04

Exploring ultrafast charge migration is of great importance in biological and chemical reactions. We present a scheme to monitor attosecond charge migration in molecules by electron diffraction with spatial and temporal resolutions from ab initio numerical simulations. An ultraviolet pulse creates a coherent superposition of electronic states, after which a time-delayed attosecond X-ray pulse is used to ionize the molecule. It is found that diffraction patterns in the X-ray photoelectron spectra show an asymmetric structure, which is dependent on the time delay between the pump-probe pulses, encoding the information of molecular orbital symmetry and chemical bonding. We describe these phenomena by developing an electronic time-dependent ultrafast molecular photoionization model of a coherent superposition state. The periodical distortion of electron diffraction patterns illustrates the evolution of the electronic coherence, providing a tool for attosecond imaging of ultrafast molecular reaction processes.

Deformation dependence of proton decay rates and angular distributions in a time-dependent approach

NASA Astrophysics Data System (ADS)

Carjan, N.; Talou, P.; Strottman, D.

1998-12-01

A new, time-dependent, approach to proton decay from axially symmetric deformed nuclei is presented. The two-dimensional time-dependent Schrödinger equation for the interaction between the emitted proton and the rest of the nucleus is solved numerically for well defined initial quasi-stationary proton states. Applied to the hypothetical proton emission from excited states in deformed nuclei of 208Pb, this approach shows that the problem cannot be reduced to one dimension. There are in general more than one directions of emission with wide distributions around them, determined mainly by the quantum numbers of the initial wave function rather than by the potential landscape. The distribution of the "residual" angular momentum and its variation in time play a major role in the determination of the decay rate. In a couple of cases, no exponential decay was found during the calculated time evolution (2×10-21 sec) although more than half of the wave function escaped during that time.

Multiple Decay Mechanisms and 2D‐UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine‐Uracil Monophosphate

PubMed Central

Li, Quansong; Giussani, Angelo; Segarra‐Martí, Javier; Nenov, Artur; Rivalta, Ivan; Voityuk, Alexander A.; Mukamel, Shaul; Roca‐Sanjuán, Daniel

2016-01-01

Abstract The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D‐UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine 1La state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine 1Lb and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter‐base hydrogen transfer and decay to the ground state through a conical intersection, or it can yield a long‐lived minimum stabilized by a hydrogen bond between the two ribose rings. This suggests that the 1Lb, S(U) and CT states of the stacked conformer may all contribute to the experimental lifetimes of 18 and 240 ps. We have also simulated the time evolution of the 2D‐UV spectra and provide the specific fingerprint of each species in a recommended probe window between 25 000 and 38 000 cm−1 in which decongested, clearly distinguishable spectra can be obtained. This is expected to allow the mechanistic scenarios to be discerned in the near future with the help of the corresponding experiments. Our results reveal the complexity of the photophysics of the relatively small ApU system, and the potential of 2D‐UV spectroscopy to disentangle the photophysics of multichromophoric systems. PMID:27113273

Multiple Decay Mechanisms and 2D-UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine-Uracil Monophosphate.

PubMed

Li, Quansong; Giussani, Angelo; Segarra-Martí, Javier; Nenov, Artur; Rivalta, Ivan; Voityuk, Alexander A; Mukamel, Shaul; Roca-Sanjuán, Daniel; Garavelli, Marco; Blancafort, Lluís

2016-05-23

The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D-UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine (1) La state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine (1) Lb and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter-base hydrogen transfer and decay to the ground state through a conical intersection, or it can yield a long-lived minimum stabilized by a hydrogen bond between the two ribose rings. This suggests that the (1) Lb , S(U) and CT states of the stacked conformer may all contribute to the experimental lifetimes of 18 and 240 ps. We have also simulated the time evolution of the 2D-UV spectra and provide the specific fingerprint of each species in a recommended probe window between 25 000 and 38 000 cm(-1) in which decongested, clearly distinguishable spectra can be obtained. This is expected to allow the mechanistic scenarios to be discerned in the near future with the help of the corresponding experiments. Our results reveal the complexity of the photophysics of the relatively small ApU system, and the potential of 2D-UV spectroscopy to disentangle the photophysics of multichromophoric systems. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Time Scale for Adiabaticity Breakdown in Driven Many-Body Systems and Orthogonality Catastrophe

NASA Astrophysics Data System (ADS)

Lychkovskiy, Oleg; Gamayun, Oleksandr; Cheianov, Vadim

2017-11-01

The adiabatic theorem is a fundamental result in quantum mechanics, which states that a system can be kept arbitrarily close to the instantaneous ground state of its Hamiltonian if the latter varies in time slowly enough. The theorem has an impressive record of applications ranging from foundations of quantum field theory to computational molecular dynamics. In light of this success it is remarkable that a practicable quantitative understanding of what "slowly enough" means is limited to a modest set of systems mostly having a small Hilbert space. Here we show how this gap can be bridged for a broad natural class of physical systems, namely, many-body systems where a small move in the parameter space induces an orthogonality catastrophe. In this class, the conditions for adiabaticity are derived from the scaling properties of the parameter-dependent ground state without a reference to the excitation spectrum. This finding constitutes a major simplification of a complex problem, which otherwise requires solving nonautonomous time evolution in a large Hilbert space.

On the theory of the type III burst exciter

NASA Technical Reports Server (NTRS)

Smith, R. A.; Goldstein, M. L.; Papadopoulos, K.

1976-01-01

In situ satellite observations of type III burst exciters at 1 AU show that the beam does not evolve into a plateau in velocity space, contrary to the prediction of quasilinear theory. The observations can be explained by a theory that includes mode coupling effects due to excitation of the parametric oscillating two-stream instability and its saturation by anomalous resistivity. The time evolution of the beam velocity distribution is included in the analysis.

Electron-impact vibrational relaxation in high-temperature nitrogen

NASA Technical Reports Server (NTRS)

Lee, Jong-Hun

1992-01-01

Vibrational relaxation process of N2 molecules by electron-impact is examined for the future planetary entry environments. Multiple-quantum transitions from excited states to higher/lower states are considered for the electronic ground state of the nitrogen molecule N2 (X 1Sigma-g(+)). Vibrational excitation and deexcitation rate coefficients obtained by computational quantum chemistry are incorporated into the 'diffusion model' to evaluate the time variations of vibrational number densities of each energy state and total vibrational energy. Results show a non-Boltzmann distribution of number densities at the earlier stage of relaxation, which in turn suppresses the equilibrium process but affects little the time variation of total vibrational energy. An approximate rate equation and a corresponding relaxation time from the excited states, compatible with the system of flow conservation equations, are derived. The relaxation time from the excited states indicates the weak dependency of the initial vibrational temperature. The empirical curve-fit formula for the improved e-V relaxation time is obtained.

The excitation of spiral density waves through turbulent fluctuations in accretion discs - II. Numerical simulations with MRI-driven turbulence

NASA Astrophysics Data System (ADS)

Heinemann, T.; Papaloizou, J. C. B.

2009-07-01

We present fully three-dimensional local simulations of compressible magneto-rotational instability (MRI) turbulence with the object of studying and elucidating the excitation of the non-axisymmetric spiral density waves that are observed to always be present in such simulations. They are potentially important for affecting protoplanetary migration through the action of associated stochastic gravitational forces and producing residual transport in MHD inactive regions through which they may propagate. The simulations we perform are with zero net flux and produce mean activity levels corresponding to the Shakura & Syunyaev α ~ 5 × 10-3, being at the lower end of the range usually considered in accretion disc modelling. We reveal the nature of the mechanism responsible for the excitation of these waves by determining the time-dependent evolution of the Fourier transforms of the participating state variables. The dominant waves are found to have no vertical structure and to be excited during periodically repeating swings in which they change from leading to trailing. The initial phase of the evolution of such a swing is found to be in excellent agreement with that expected from the WKBJ theory developed in a preceding paper by Heinemann & Papaloizou. However, shortly after the attainment of the expected maximum wave amplitude, the waves begin to be damped on account of the formation of weak shocks. As expected from the theory, the waves are seen to shorten in radial wavelength as they propagate. This feature enables non-linear dissipation to continue in spite of amplitude decrease. As a consequence, the waves are almost always seen to be in the non-linear regime. We demonstrate that the important source terms causing excitation of the waves are related to a quantity that reduces to the potential vorticity for small perturbations from the background state with no vertical dependence. We find that the root mean square density fluctuations associated with the waves are positively correlated with both this quantity and the general level of hydromagnetic turbulence. The mean angular momentum transport associated with spiral density waves generated in our simulations is estimated to be a significant fraction of that associated with the turbulent Reynolds stress.

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

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.

Mesoscopic structural phase progression in photo-excited VO 2 revealed by time-resolved x-ray diffraction microscopy

DOE PAGES

Zhu, Yi; Cai, Zhonghou; Chen, Pice; ...

2016-02-26

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO 2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation ismore » initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO 2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO 2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.« less

Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

NASA Astrophysics Data System (ADS)

Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

2016-02-01

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy.

PubMed

Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J; Jung, Il Woong; Walko, Donald A; Dufresne, Eric M; Jeong, Jaewoo; Samant, Mahesh G; Parkin, Stuart S P; Freeland, John W; Evans, Paul G; Wen, Haidan

2016-02-26

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

Space and time renormalization in phase transition dynamics

DOE PAGES

Francuz, Anna; Dziarmaga, Jacek; Gardas, Bartłomiej; ...

2016-02-18

Here, when a system is driven across a quantum critical point at a constant rate, its evolution must become nonadiabatic as the relaxation time τ diverges at the critical point. According to the Kibble-Zurek mechanism (KZM), the emerging post-transition excited state is characterized by a finite correlation length ξˆ set at the time tˆ=τˆ when the critical slowing down makes it impossible for the system to relax to the equilibrium defined by changing parameters. This observation naturally suggests a dynamical scaling similar to renormalization familiar from the equilibrium critical phenomena. We provide evidence for such KZM-inspired spatiotemporal scaling by investigatingmore » an exact solution of the transverse field quantum Ising chain in the thermodynamic limit.« less

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.

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.

Extinction time of a stochastic predator-prey model by the generalized cell mapping method

NASA Astrophysics Data System (ADS)

Han, Qun; Xu, Wei; Hu, Bing; Huang, Dongmei; Sun, Jian-Qiao

2018-03-01

The stochastic response and extinction time of a predator-prey model with Gaussian white noise excitations are studied by the generalized cell mapping (GCM) method based on the short-time Gaussian approximation (STGA). The methods for stochastic response probability density functions (PDFs) and extinction time statistics are developed. The Taylor expansion is used to deal with non-polynomial nonlinear terms of the model for deriving the moment equations with Gaussian closure, which are needed for the STGA in order to compute the one-step transition probabilities. The work is validated with direct Monte Carlo simulations. We have presented the transient responses showing the evolution from a Gaussian initial distribution to a non-Gaussian steady-state one. The effects of the model parameter and noise intensities on the steady-state PDFs are discussed. It is also found that the effects of noise intensities on the extinction time statistics are opposite to the effects on the limit probability distributions of the survival species.

Stimulated resonant x-ray Raman scattering with incoherent radiation

NASA Astrophysics Data System (ADS)

Weninger, Clemens; Rohringer, Nina

2013-11-01

We present a theoretical study on stimulated electronic Raman scattering in neon by resonant excitation with an x-ray free electron laser (XFEL). This study is in support of the recent experimental demonstration [C. Weninger , Phys. Rev. Lett. (to be published)] of stimulated x-ray Raman scattering. Focusing the broadband XFEL pulses into a cell of neon gas at atmospheric pressure a strong inelastic x-ray scattering signal in the forward direction was observed, as the x-ray energy was varied across the region of core-excited Rydberg states and the K edge. The broadband and intrinsically incoherent x-ray pulses from the XFEL lead to a rich, structured line shape of the scattered radiation. We present a generalized Maxwell-Liouville-von Neumann approach to self-consistently solve for the amplification of the scattered radiation along with the time evolution of the density matrix of the atomic and residual ionic system. An in-depth analysis of the evolution of the emission spectra as a function of the Raman gain is presented. Furthermore, we propose the use of statistical methods to obtain high-resolution scattering data beyond the lifetime broadening despite pumping with incoherent x-ray pulses.

Three types of membrane excitations in the marine diatom Coscinodiscus wailesii.

PubMed

Gradmann, D; Boyd, C M

2000-05-15

Three types of electrical excitation have been investigated in the marine diatom Coscinodiscus wailesii. I: Depolarization-triggered, transient Cl(-) conductance, G(Cl)(t), followed by a transient, voltage-gated K(+) conductance, G(K), with an active state a and two inactive states i(1) and i(2) in series (a-i(1)-i(2)). II: Similar G(Cl)(t) as in Type-I but triggered by hyperpolarization; a subsequent increase of G(K) in this type is indicated but not analyzed in detail. III: Hyperpolarization-induced transient of a voltage-gated activity of an electrogenic pump (i(2)-a-i(2)), followed by G(Cl)(t) as in Type-II excitations. Type-III with pump gating is novel as such. G(Cl)(t) in all types seems to reflect the mechanism of InsP(-)(3) and Ca(2+)-mediated G(Cl)(t) in the action potential in Chara (Biskup et al., 1999). The nonlinear current-voltage-time relationships of Type-I and Type-III excitations have been recorded under voltage-clamp using single saw-tooth command voltages (voltage range: -200 to +50 mV, typical slope: +/-1 Vs(-1)). Fits of the corresponding models to the experimental data provided numerical values of the model parameters. The statistical significance of these solutions is investigated. We suggest that the original function of electrical excitability of biological membranes is related to osmoregulation which has persisted through evolution in plants, whereas the familiar and osmotically neutral action potentials in animals have evolved later towards the novel function of rapid transmission of information over long distances.

Uncovering Highly-Excited State Mixing in Acetone Using Ultrafast VUV Pulses and Coincidence Imaging Techniques

DOE PAGES

Couch, David E.; Kapteyn, Henry C.; Murnane, Margaret M.; ...

2017-03-17

Here, understanding the ultrafast dynamics of highly-excited electronic states of small molecules is critical for a better understanding of atmospheric and astrophysical processes, as well as for designing coherent control strategies for manipulating chemical dynamics. In highly excited states, nonadiabatic coupling, electron-electron interactions, and the high density of states govern dynamics. However, these states are computationally and experimentally challenging to access. Fortunately, new sources of ultrafast vacuum ultraviolet pulses, in combination with electron-ion coincidence spectroscopies, provide new tools to unravel the complex electronic landscape. Here we report time-resolved photoelectron-photoion coincidence experiments using 8 eV pump photons to study the highlymore » excited states of acetone. We uncover for the first time direct evidence that the resulting excited state consists of a mixture of both n y → 3p and π → π* character, which decays with a time constant of 330 fs. In the future, this approach can inform models of VUV photochemistry and aid in designing coherent control strategies for manipulating chemical reactions.« less

Uncovering Highly-Excited State Mixing in Acetone Using Ultrafast VUV Pulses and Coincidence Imaging Techniques

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

Couch, David E.; Kapteyn, Henry C.; Murnane, Margaret M.

Here, understanding the ultrafast dynamics of highly-excited electronic states of small molecules is critical for a better understanding of atmospheric and astrophysical processes, as well as for designing coherent control strategies for manipulating chemical dynamics. In highly excited states, nonadiabatic coupling, electron-electron interactions, and the high density of states govern dynamics. However, these states are computationally and experimentally challenging to access. Fortunately, new sources of ultrafast vacuum ultraviolet pulses, in combination with electron-ion coincidence spectroscopies, provide new tools to unravel the complex electronic landscape. Here we report time-resolved photoelectron-photoion coincidence experiments using 8 eV pump photons to study the highlymore » excited states of acetone. We uncover for the first time direct evidence that the resulting excited state consists of a mixture of both n y → 3p and π → π* character, which decays with a time constant of 330 fs. In the future, this approach can inform models of VUV photochemistry and aid in designing coherent control strategies for manipulating chemical reactions.« less

Time-resolved and steady-state fluorescence studies of excited-state proton-transfer reactions of proflavine

NASA Astrophysics Data System (ADS)

De Silvestri, S.; Laporta, P.

1984-01-01

Time-resolved and steady-state fluorescence studies of proflavine in aqueous solution are presented. The observation of a monoexponential fluorescence decay with a time constant decreasing with increasing pH and the presence of an anomalous red-shift in the fluorescence spectrum as a function of pH indicate the existence of a complex proton-transfer mechanism in the excited state. A reaction scheme is proposed and the corresponding proton-transfer rates are evaluated. An excited-state pK value of 12.85 is obtained for the equilibrium between the cationic form of proflavine and the same form dissociated at an amino group.

Photoresponse of 60Ni below 10-MeV excitation energy: Evolution of dipole resonances in fp-shell nuclei near N=Z

NASA Astrophysics Data System (ADS)

Scheck, M.; Ponomarev, V. Yu.; Fritzsche, M.; Joubert, J.; Aumann, T.; Beller, J.; Isaak, J.; Kelley, J. H.; Kwan, E.; Pietralla, N.; Raut, R.; Romig, C.; Rusev, G.; Savran, D.; Schorrenberger, L.; Sonnabend, K.; Tonchev, A. P.; Tornow, W.; Weller, H. R.; Zilges, A.; Zweidinger, M.

2013-10-01

Background: Within the last decade, below the giant dipole resonance the existence of a concentration of additional electric dipole strength has been established. This accumulation of low-lying E1 strength is commonly referred to as pygmy dipole resonance (PDR).Purpose: The photoresponse of 60Ni has been investigated experimentally and theoretically to test the evolution of the PDR in a nucleus with only a small neutron excess. Furthermore, the isoscalar and isovector M1 resonances were investigated.Method: Spin-1 states were excited by exploiting the (γ,γ') nuclear resonance fluorescence technique with unpolarized continuous bremsstrahlung as well as with fully linearly polarized, quasimonochromatic, Compton-backscattered laser photons in the entrance channel of the reaction.Results: Up to 10 MeV a detailed picture of J=1 levels was obtained. For the preponderant number of the individual levels spin and parity were firmly assigned. Furthermore, branching ratios, transition widths, and reduced B(E1) or B(M1) excitation probability were calculated from the measured scattering cross sections. A comparison with theoretical results obtained within the quasiparticle phonon model allows an insight into the microscopic structure of the observed states.Conclusions: Below 10 MeV the directly observed E1 strength [∑B(E1)↑=(153.8±9.5) e2(fm)2] exhausts 0.5% of the Thomas-Reiche-Kuhn sum rule. This value increases to 0.8% of the sum rule [∑B(E1)↑=(250.9±31.1) e2(fm)2] when indirectly observed branches to lower-lying levels are considered. Two accumulations of M1 excited spin-1 states near 8 and 9 MeV excitation energy are identified as isoscalar and isovector M1 resonances dominated by proton and neutron f7/2→f5/2 spin-flip excitations. The B(M1)↑ strength of these structures accumulates to 3.94(27)μN2.

Recovery of photoinduced reversible dark States utilized for molecular diffusion measurements.

PubMed

Chmyrov, Andriy; Sandén, Tor; Widengren, Jerker

2010-12-15

For a spatially restricted excitation volume, the effective modulation of the excitation in time is influenced by the passage times of the molecules through the excitation volume. By applying an additional time-modulated excitation, the buildup of photoinduced reversible dark states in fluorescent molecules can be made to vary significantly with their passage times through the excitation volume. The variations in the dark state populations are reflected by the time-averaged fluorescence intensity, which thus can be used to characterize the mobilities of the molecules. The concept was experimentally verified by measuring the fluorescence response of freely diffusing cyanine fluorophores (Cy5), undergoing trans-cis isomerization when subject to time-modulated excitation in a focused laser beam. From the fluorescence response, and by applying a simple photodynamic model, the transition times of the Cy5 molecules could be well reproduced when applying different laminar flow speeds through the detection volume. The presented approach puts no constraints on sample concentration, no requirements for high time resolution or sensitivity in the detection, nor requires a high fluorescence brightness of the characterized molecules. This can make the concept useful for a broad range of biomolecular mobility studies.

Mean-field studies of time reversal breaking states in super-heavy nuclei with the Gogny force

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

Robledo, L. M., E-mail: luis.robledo@uam.es

2015-10-15

Recent progress on the description of time reversal breaking (odd mass and multi-quasiparticle excitation) states in super-heavy nuclei within a mean field framework and using several flavors of the Gogny interaction is reported. The study includes ground and excited states in selected odd mass isotopes of nobelium and mendelevium as well as high K isomeric states in {sup 254}No. These are two and four-quasiparticle excitations that are treated in the same self-consistent HFB plus blocking framework as the odd mass states.

Vortex-soliton complexes in coupled nonlinear Schrödinger equations with unequal dispersion coefficients.

PubMed

Charalampidis, E G; Kevrekidis, P G; Frantzeskakis, D J; Malomed, B A

2016-08-01

We consider a two-component, two-dimensional nonlinear Schrödinger system with unequal dispersion coefficients and self-defocusing nonlinearities, chiefly with equal strengths of the self- and cross-interactions. In this setting, a natural waveform with a nonvanishing background in one component is a vortex, which induces an effective potential well in the second component, via the nonlinear coupling of the two components. We show that the potential well may support not only the fundamental bound state, but also multiring excited radial state complexes for suitable ranges of values of the dispersion coefficient of the second component. We systematically explore the existence, stability, and nonlinear dynamics of these states. The complexes involving the excited radial states are weakly unstable, with a growth rate depending on the dispersion of the second component. Their evolution leads to transformation of the multiring complexes into stable vortex-bright solitons ones with the fundamental state in the second component. The excited states may be stabilized by a harmonic-oscillator trapping potential, as well as by unequal strengths of the self- and cross-repulsive nonlinearities.

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.

Ultrafast photo-initiated molecular quantum dynamics in the DNA dinucleotide d(ApG) revealed by broadband transient absorption spectroscopy.

PubMed

Stuhldreier, Mayra C; Temps, Friedrich

2013-01-01

The ultrafast photo-initiated quantum dynamics of the adenine-guanine dinucleotide d(ApG) in aqueous solution (pH 7) has been studied by femtosecond time-resolved spectroscopy after excitation at lambda = 260 nm. The results reveal a hierarchy of processes on time scales from tau < 100 fs to tau > 100 ps. Characteristic spectro-temporal signatures are observed indicating the transformation of the molecules in the electronic relaxation from the photo-excited state to a long-lived exciplex. In particular, broadband UV/VIS excited-state absorption (ESA) measurements detected a distinctive absorption by the excited dinucleotide around lambda = 335 nm, approximately 0.5 eV to the blue compared to the maximum of the broad and unstructured ESA spectrum after excitation of an equimolar mixture of the mononucleotides dAMP and dGMP. A similar feature has been identified as signature of the excimer in the dynamics of the adenine dinucleotide d(ApA). The lifetime of the d(ApG) exciplex was found to be tau = 124 +/- 4 ps both from the ESA decay time and from the ground-state recovery time, far longer than the sub-picosecond lifetimes of excited dAMP or dGMP. Fluorescence-time profiles measured by the up-conversion technique indicate that the exciplex state is reached around approximately 6 ps after excitation. Very weak residual fluorescence at longer times red-shifted to the emission from the photo-excited state shows that the exciplex is almost optically dark, but still has enough oscillator strength to give rise to the dual fluorescence of the dinucleotide in the static fluorescence spectrum.

Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study

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

Bhattacherjee, Aditi, E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu; Attar, Andrew R., E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu; Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720

2016-03-28

Femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy based on a high-harmonic generation source is used to study the 266 nm induced A-band photodissociation dynamics of allyl iodide (CH{sub 2} =CHCH{sub 2}I). The photolysis of the C—I bond at this wavelength produces iodine atoms both in the ground ({sup 2}P{sub 3/2}, I) and spin-orbit excited ({sup 2}P{sub 1/2}, I*) states, with the latter as the predominant channel. Using XUV absorption at the iodine N{sub 4/5} edge (45–60 eV), the experiments constitute a direct probe of not only the long-lived atomic iodine reaction products but also the fleeting transition state region ofmore » the repulsive n{sub I}σ{sup ∗}{sub C—I} excited states. Specifically, three distinct features are identified in the XUV transient absorption spectrum at 45.3 eV, 47.4 eV, and 48.4 eV (denoted transients A, B, and C, respectively), which arise from the repulsive valence-excited nσ{sup ∗} states and project onto the high-lying core-excited states of the dissociating molecule via excitation of 4d(I) core electrons. Transients A and B originate from 4d(I) → n(I) core-to-valence transitions, whereas transient C is best assigned to a 4d(I) →σ{sup ∗}(C—I) transition. The measured differential absorbance of these new features along with the I/I* branching ratios known from the literature is used to suggest a more definitive assignment, albeit provisional, of the transients to specific dissociative states within the A-band manifold. The transients are found to peak around 55 fs–65 fs and decay completely by 145 fs–185 fs, demonstrating the ability of XUV spectroscopy to map the evolution of reactants into products in real time. The similarity in the energies of transients A and B with analogous features observed in methyl iodide [Attar et al. J. Phys. Chem. Lett. 6, 5072, (2015)] together with the new observation of transient C in the present work provides a more complete picture of the valence electronic structure in the transition state region. The results provide a benchmark for theoretical calculations on the nature of core-excited states in halogenated hydrocarbons, especially in the transition state region along the C—I reaction coordinate.« less

Secular orbital evolution of Jupiter family comets

NASA Astrophysics Data System (ADS)

Rickman, H.; Gabryszewski, R.; Wajer, P.; Wiśniowski, T.; Wójcikowski, K.; Szutowicz, S.; Valsecchi, G. B.; Morbidelli, A.

2017-02-01

Context. The issue of the long term dynamics of Jupiter family comets (JFCs) involves uncertain assumptions about the physical evolution and lifetimes of these comets. Contrary to what is often assumed, real effects of secular dynamics cannot be excluded and therefore merit investigation. Aims: We use a random sample of late heavy bombardment cometary projectiles to study the long-term dynamics of JFCs by a Monte Carlo approach. In a steady-state picture of the Jupiter family, we investigate the orbital distribution of JFCs, including rarely visited domains like retrograde orbits or orbits within the outer parts of the asteroid main belt. Methods: We integrate 100 000 objects over a maximum of 100 000 orbital revolutions including the Sun, a comet, and four giant planets. Considering the steady-state number of JFCs to be proportional to the total time spent in the respective orbital domain, we derive the capture rate based on observed JFCs with small perihelia and large nuclei. We consider a purely dynamical model and one where the nuclei are eroded by ice sublimation. Results: The JFC inclination distribution is incompatible with our erosional model. This may imply that a new type of comet evolution model is necessary. Considering that comets may live for a long time, we show that JFCs can evolve into retrograde orbits as well as asteroidal orbits in the outer main belt or Cybele regions. The steady-state capture rate into the Jupiter family is consistent with 1 × 109 scattered disk objects with diameters D > 2 km. Conclusions: Our excited scattered disk makes it difficult to explain the JFC inclination distribution, unless the physical evolution of JFCs is more intricate than assumed in standard, erosional models. Independent of this, the population size of the Jupiter family is consistent with a relatively low-mass scattered disk.

Optical determination of charge transfer times from indoline dyes to ZnO in solid state dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Meyenburg, I.; Hofeditz, N.; Ruess, R.; Rudolph, M.; Schlettwein, D.; Heimbrodt, W.

2018-05-01

We studied the electron transfer at the interface of organic-inorganic hybrids consisting of indoline derivatives (D149 and D131) on ZnO substrates using a new optical method. We revealed the electron transfer times from the excited dye, e.g. the excitons formed in the dye aggregates to the ZnO substrate by analyzing the photoluminescence transients of the excitons after femtosecond excitation and applying kinetic model calculations. We reveal the changes of the electron transfer times by applying electrical bias. Pushing the Fermi energy of the ZnO substrate towards the excited dye level the transfer time gets longer and eventually the electron transfer is suppressed. The level alignment between the excited dye state and the ZnO Fermi-level is estimated. The excited state of D131 is about 100 meV higher than the respective state of D149 compared to the ZnO conduction band. This leads to shorter electron transfer times and eventually to higher quantum efficiencies of the solar cells.

Electron doping evolution of the magnetic excitations in NaFe 1-xCo xAs

DOE PAGES

Carr, Scott V.; Zhang, Chenglin; Song, Yu; ...

2016-06-13

We use time-of-flight (TOF) inelastic neutron scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe 1-xCo xAs with x = 0, 0.0175, 0.0215, 0.05, and 0.11. The effect of electron-doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden and suppress low energy (E 80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high energy (E > 80 meV) spin excitations are weakly Co-doping dependent. Integration of the local spin dynamic susceptibility "(!) of NaFe 1-xCo xAs reveals a total fluctuating moment ofmore » 3.6 μ2 B/Fe and a small but systematic reduction with electron doping. The presence of a large spin gap in the Cooverdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel Ni-doping evolution of spin excitations in BaFe 2-xNi xAs 2, confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping dependent high-energy spin excitations result from localized moments.« less

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.

Electronic structure and dynamics of thin Ge/GaAs(110) heterostructures

NASA Astrophysics Data System (ADS)

Haight, R.; Silberman, J. A.

1990-10-01

Using angle-resolved picosecond laser photoemission we have investigated both occupied and transiently excited empty states at the surface of Ge grown epitaxially on GaAs(110). We observe a normally unoccupied, Ge layer derived state whose separation from the valence-band maximum of the system is 700±50 meV at six monolayers Ge coverage. The evolution of the electronic structure is followed as a function of coverage and correlated with low-energy electron diffraction. The time dependence of the transiently occupied Ge signal is compared with that of the clean GaAs(110) surface and shows that electrons are prevented from diffusing into the GaAs bulk by the conduction-band offset of 330±40 meV.

Optical spectroscopy of excited exciton states in MoS2 monolayers in van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Robert, C.; Semina, M. A.; Cadiz, F.; Manca, M.; Courtade, E.; Taniguchi, T.; Watanabe, K.; Cai, H.; Tongay, S.; Lassagne, B.; Renucci, P.; Amand, T.; Marie, X.; Glazov, M. M.; Urbaszek, B.

2018-01-01

The optical properties of MoS2 monolayers are dominated by excitons, but for spectrally broad optical transitions in monolayers exfoliated directly onto SiO2 substrates detailed information on excited exciton states is inaccessible. Encapsulation in hexagonal boron nitride (hBN) allows approaching the homogenous exciton linewidth, but interferences in the van der Waals heterostructures make direct comparison between transitions in optical spectra with different oscillator strength more challenging. Here we reveal in reflectivity and in photoluminescence excitation spectroscopy the presence of excited states of the A exciton in MoS2 monolayers encapsulated in hBN layers of calibrated thickness, allowing us to extrapolate an exciton binding energy of ≈220 meV. We theoretically reproduce the energy separations and oscillator strengths measured in reflectivity by combining the exciton resonances calculated for a screened two-dimensional Coulomb potential with transfer matrix calculations of the reflectivity for the van der Waals structure. Our analysis shows a very different evolution of the exciton oscillator strength with principal quantum number for the screened Coulomb potential as compared to the ideal two-dimensional hydrogen model.

Self-consistent predictor/corrector algorithms for stable and efficient integration of the time-dependent Kohn-Sham equation

NASA Astrophysics Data System (ADS)

Zhu, Ying; Herbert, John M.

2018-01-01

The "real time" formulation of time-dependent density functional theory (TDDFT) involves integration of the time-dependent Kohn-Sham (TDKS) equation in order to describe the time evolution of the electron density following a perturbation. This approach, which is complementary to the more traditional linear-response formulation of TDDFT, is more efficient for computation of broad-band spectra (including core-excited states) and for systems where the density of states is large. Integration of the TDKS equation is complicated by the time-dependent nature of the effective Hamiltonian, and we introduce several predictor/corrector algorithms to propagate the density matrix, one of which can be viewed as a self-consistent extension of the widely used modified-midpoint algorithm. The predictor/corrector algorithms facilitate larger time steps and are shown to be more efficient despite requiring more than one Fock build per time step, and furthermore can be used to detect a divergent simulation on-the-fly, which can then be halted or else the time step modified.

Molecular alignment effect on the photoassociation process via a pump-dump scheme.

PubMed

Wang, Bin-Bin; Han, Yong-Chang; Cong, Shu-Lin

2015-09-07

The photoassociation processes via the pump-dump scheme for the heternuclear (Na + H → NaH) and the homonuclear (Na + Na → Na2) molecular systems are studied, respectively, using the time-dependent quantum wavepacket method. For both systems, the initial atom pair in the continuum of the ground electronic state (X(1)Σ(+)) is associated into the molecule in the bound states of the excited state (A(1)Σ(+)) by the pump pulse. Then driven by a time-delayed dumping pulse, the prepared excited-state molecule can be transferred to the bound states of the ground electronic state. It is found that the pump process can induce a superposition of the rovibrational levels |v, j〉 on the excited state, which can lead to the field-free alignment of the excited-state molecule. The molecular alignment can affect the dumping process by varying the effective coupling intensity between the two electronic states or by varying the population transfer pathways. As a result, the final population transferred to the bound states of the ground electronic state varies periodically with the delay time of the dumping pulse.

Molecular alignment effect on the photoassociation process via a pump-dump scheme

NASA Astrophysics Data System (ADS)

Wang, Bin-Bin; Han, Yong-Chang; Cong, Shu-Lin

2015-09-01

The photoassociation processes via the pump-dump scheme for the heternuclear (Na + H → NaH) and the homonuclear (Na + Na → Na2) molecular systems are studied, respectively, using the time-dependent quantum wavepacket method. For both systems, the initial atom pair in the continuum of the ground electronic state (X1Σ+) is associated into the molecule in the bound states of the excited state (A1Σ+) by the pump pulse. Then driven by a time-delayed dumping pulse, the prepared excited-state molecule can be transferred to the bound states of the ground electronic state. It is found that the pump process can induce a superposition of the rovibrational levels |v, j> on the excited state, which can lead to the field-free alignment of the excited-state molecule. The molecular alignment can affect the dumping process by varying the effective coupling intensity between the two electronic states or by varying the population transfer pathways. As a result, the final population transferred to the bound states of the ground electronic state varies periodically with the delay time of the dumping pulse.

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.

Measurements of population densities of metastable and resonant levels of argon using laser induced fluorescence

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

Nikolić, M.; Newton, J.; Sukenik, C. I.

2015-01-14

We present a new approach to measure population densities of Ar I metastable and resonant excited states in low temperature Ar plasmas at pressures higher than 1 Torr. This approach combines the time resolved laser induced fluorescence technique with the kinetic model of Ar. The kinetic model of Ar is based on calculating the population rates of metastable and resonant levels by including contributions from the processes that affect population densities of Ar I excited states. In particular, we included collisional quenching processes between atoms in the ground state and excited states, since we are investigating plasma at higher pressures. Wemore » also determined time resolved population densities of Ar I 2 p excited states by employing optical emission spectroscopy technique. Time resolved Ar I excited state populations are presented for the case of the post-discharge of the supersonic flowing microwave discharge at pressures of 1.7 and 2.3 Torr. The experimental set-up consists of a pulsed tunable dye laser operating in the near infrared region and a cylindrical resonance cavity operating in TE{sub 111} mode at 2.45 GHz. Results show that time resolved population densities of Ar I metastable and resonant states oscillate with twice the frequency of the discharge.« less

Transient nutation electron spin resonance spectroscopy on spin-correlated radical pairs: A theoretical analysis on hyperfine-induced nuclear modulations

NASA Astrophysics Data System (ADS)

Weber, Stefan; Kothe, Gerd; Norris, James R.

1997-04-01

The influence of anisotropic hyperfine interaction on transient nutation electron paramagnetic resonance (EPR) of light-induced spin-correlated radical pairs is studied theoretically using the density operator formalism. Analytical expressions for the time evolution of the transient EPR signal during selective microwave excitation of single transitions are derived for a model system comprised of a weakly coupled radical pair and one hyperfine-coupled nucleus with I=1/2. Zero-quantum electron coherence and single-quantum nuclear coherence are created as a result of the sudden light-induced generation of the radical pair state from a singlet-state precursor. Depending on the relative sizes of the nuclear Zeeman frequency and the secular and pseudo-secular parts of the hyperfine coupling, transitions between levels with different nuclear spin orientations are predicted to modulate the time-dependent EPR signal. These modulations are in addition to the well-known transient nutations and electron zero-quantum precessions. Our calculations provide insight into the mechanism of recent experimental observations of coherent nuclear modulations in the time-resolved EPR signals of doublets and radical pairs. Two distinct mechanisms of the modulations are presented for various microwave magnetic field strengths. The first modulation scheme arises from electron and nuclear coherences initiated by the laser excitation pulse and is "read out" by the weak microwave magnetic field. While the relative modulation depth of these oscillations with respect to the signal intensity is independent of the Rabi frequency, ω1, the frequencies of this coherence phenomenon are modulated by the effective microwave amplitude and determined by the nuclear Zeeman interaction and hyperfine coupling constants as well as the electron-electron spin exchange and dipolar interactions between the two radical pair halves. In a second mechanism the modulations are both created and detected by the microwave radiation. Here, the laser pulse merely defines the beginning of the microwave-induced coherent time evolution. This second mechanism appears the most consistent with current experimental observations.

Time dependent Schrödinger equation for black hole evaporation: No information loss

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

Corda, Christian, E-mail: cordac.galilei@gmail.com

2015-02-15

In 1976 S. Hawking claimed that “Because part of the information about the state of the system is lost down the hole, the final situation is represented by a density matrix rather than a pure quantum state”. This was the starting point of the popular “black hole (BH) information paradox”. In a series of papers, together with collaborators, we naturally interpreted BH quasi-normal modes (QNMs) in terms of quantum levels discussing a model of excited BH somewhat similar to the historical semi-classical Bohr model of the structure of a hydrogen atom. Here we explicitly write down, for the same model,more » a time dependent Schrödinger equation for the system composed by Hawking radiation and BH QNMs. The physical state and the correspondent wave function are written in terms of a unitary evolution matrix instead of a density matrix. Thus, the final state results to be a pure quantum state instead of a mixed one. Hence, Hawking’s claim is falsified because BHs result to be well defined quantum mechanical systems, having ordered, discrete quantum spectra, which respect ’t Hooft’s assumption that Schrödinger equations can be used universally for all dynamics in the universe. As a consequence, information comes out in BH evaporation in terms of pure states in a unitary time dependent evolution. In Section 4 of this paper we show that the present approach permits also to solve the entanglement problem connected with the information paradox.« less

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.

An examination of energy transfers and kinetic mechanisms in argon and in an argon-hydrogen medium excited by an electron beam Application in research on new lasers

NASA Astrophysics Data System (ADS)

Puech, V.

Experimental results on a Ar-H laser pumped by an electron gun are presented, along with a kinetic model of the evolution of states in Ar lasers with additives. Data from trials with the Ar-H laser are provided to confirm model predictions of the electron energy transfer. The electron densities and temperatures evolving on a nanosecond scale in the laser are quantified. A solution is found for the Boltzmann equation for the collisional processes characterizing the electron distribution of interactions between the pumping electrons and the various excited molecular states. The electron distribution function is assumed to be Maxwellian, and the distribution is shown to converge within a few picoseconds when the excitation is above the ionization energy.

Femtosecond solvation and the bandshape of polar dyes

NASA Astrophysics Data System (ADS)

Ernsting, N. P.; Eilers-König, N.; Kemeter, K.; Kovalenko, S.; Ruthmann, J.

1996-04-01

The bandwidth of gain spectra for the dye DASPI in polar solvents and its evolution is described by Brownian oscillators with different frequencies for the ground- and excited electronic states. Comparison with experiments reveals a fast relaxation process which is assigned to vibrational redistribution.

Type II shell evolution in A = 70 isobars from the N ≥ 40 island of inversion

NASA Astrophysics Data System (ADS)

Morales, A. I.; Benzoni, G.; Watanabe, H.; Tsunoda, Y.; Otsuka, T.; Nishimura, S.; Browne, F.; Daido, R.; Doornenbal, P.; Fang, Y.; Lorusso, G.; Patel, Z.; Rice, S.; Sinclair, L.; Söderström, P.-A.; Sumikama, T.; Wu, J.; Xu, Z. Y.; Yagi, A.; Yokoyama, R.; Baba, H.; Avigo, R.; Bello Garrote, F. L.; Blasi, N.; Bracco, A.; Camera, F.; Ceruti, S.; Crespi, F. C. L.; de Angelis, G.; Delattre, M.-C.; Dombradi, Zs.; Gottardo, A.; Isobe, T.; Kojouharov, I.; Kurz, N.; Kuti, I.; Matsui, K.; Melon, B.; Mengoni, D.; Miyazaki, T.; Modamio-Hoybjor, V.; Momiyama, S.; Napoli, D. R.; Niikura, M.; Orlandi, R.; Sakurai, H.; Sahin, E.; Sohler, D.; Schaffner, H.; Taniuchi, R.; Taprogge, J.; Vajta, Zs.; Valiente-Dobón, J. J.; Wieland, O.; Yalcinkaya, M.

2017-02-01

The level structures of 70Co and 70Ni, populated from the β decay of 70Fe, have been investigated using β-delayed γ-ray spectroscopy following in-flight fission of a 238U beam. The experimental results are compared to Monte-Carlo Shell-Model calculations including the pf +g9/2 +d5/2 orbitals. The strong population of a (1+) state at 274 keV in 70Co is at variance with the expected excitation energy of ∼1 MeV from near spherical single-particle estimates. This observation indicates a dominance of prolate-deformed intruder configurations in the low-lying levels, which coexist with the normal near spherical states. It is shown that the β decay of the neutron-rich A = 70 isobars from the new island of inversion to the Z = 28 closed-shell regime progresses in accordance with a newly reported type of shell evolution, the so-called Type II, which involves many particle-hole excitations across energy gaps.

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.

Electron kinetics dependence on gas pressure in laser-induced oxygen plasma experiment: Theoretical analysis

NASA Astrophysics Data System (ADS)

Gamal, Yosr E. E.-D.; Abdellatif, Galila

2017-08-01

A study is performed to investigate the dependency of threshold intensity on gas pressure observed in the measurements of the breakdown of molecular oxygen that carried out by Phuoc (2000) [1]. In this experiment, the breakdown was induced by 532 nm laser radiation of pulse width 5.5 ns and spot size of 8.5 μm, in oxygen over a wide pressure range (190-3000 Torr). The analysis aimed to explore the electron kinetic reliance on gas pressure for the separate contribution of each of the gain and loss processes encountered in this study. The investigation is based on an electron cascade model applied previously in Gamal and Omar (2001) [2] and Gaabour et al. (2013) [3]. This model solves numerically a differential equation designates the time evolution of the electron energy distribution, and a set of rate equations that describe the change of excited states population. The numerical examination of the electron energy distribution function and its parameters revealed that photo-ionization of the excited molecules plays a significant role in enhancing the electron density growth rate over the whole tested gas pressure range. This process is off set by diffusion of electrons out of the focal volume in the low-pressure regime. At atmospheric pressure electron, collisional processes dominate and act mainly to populate the excited states. Hence photo-ionization becomes efficient and compete with the encountered loss processes (electron diffusion, vibrational excitation of the ground state molecules as well as two body attachments). At high pressures ( 3000 Torr) three body attachments are found to be the primary cause of losses which deplete the electron density and hence results in the slow decrease of the threshold intensity.

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.

Phase-resolved and time-averaged puff motions of an excited stack-issued transverse jet

NASA Astrophysics Data System (ADS)

Hsu, C. M.; Huang, R. F.

2013-07-01

The dynamics of puff motions in an excited stack-issued transverse jet were studied experimentally in a wind tunnel. The temporal and spatial evolution processes of the puffs induced by acoustic excitation were examined using the smoke flow visualization method and high-speed particle image velocimetry. The temporal and spatial evolutions of the puffs were examined using phase-resolved ensemble-averaged velocity fields and the velocity, length scales, and vorticity characteristics of the puffs were studied. The time-averaged velocity fields were calculated to analyze the velocity distributions and vorticity contours. The results show that a puff consists of a pair of counter-rotating vortex rings. An initial vortex ring was formed due to a concentration of vorticity at the lee side of the issuing jet at the instant of the mid-oscillation cycle. A vortex ring rotating in the opposite direction to that of the initial vortex ring was subsequently formed at the upwind side of the issuing jet. These two counter-rotating vortex rings formed a "mushroom" vortex pair, which was deflected by the crossflow and traveled downstream along a time-averaged trajectory of zero vorticity. The trajectory was situated far above the time-averaged streamline evolving from the leading edge of the tube. The velocity magnitudes of the vortex rings at the upwind and the lee side decreased with time evolution as the puffs traveled downstream due to momentum dissipation and entrainment effects. The puffs traveling along the trajectory of zero vorticity caused large velocities to appear above the leading-edge streamline.

Exciting an Initially Cold Asteroid Belt Through a Planetary Instability

NASA Astrophysics Data System (ADS)

Deienno, Rogerio; Izidoro, Andre; Morbidelli, Alessandro; Gomes, Rodney; Nesvorny, David; Raymond, Sean N.

2018-04-01

The main asteroid belt (MB) is low in mass but dynamically excited, with much larger eccentricities and inclinations than the planets. In recent years, the Grand Tack model has been the predominant model capable of reconciling the formation of the terrestrial planets with a depleted but excited MB. Despite this success, the Grand Tack is still not generally accepted because of uncertainties in orbital migration. It was recently proposed that chaotic early evolution of Jupiter and Saturn could excite the initially cold MB. However, hydrodynamical simulations predict that the giant planets should generally emerge from the gas disk phase on orbits characterized by resonant and regular motion. Here we propose a new mechanism to excite the MB during the giant planets' ('Nice model') instability, which is expected to have included repeated close encounters between Jupiter and one or more ice giants ('Jumping Jupiter' -- JJ). We show that when Jupiter temporarily reaches a high enough level of excitation, both in eccentricity and inclination, it induces strong forced vectors of eccentricity and inclination within the MB region. Because during the JJ instability Jupiter's orbit 'jumps' around, forced vectors keep changing both in magnitude and phase throughout the whole MB region. The entire cold primordial MB can thus be excited as a natural outcome of the JJ instability. Furthermore, we show that the subsequent evolution of the Solar System is capable of reshaping the resultant MB to its present day orbital state, and that a strong mass depletion is always associated to the JJ instability phase.

Excited cosmic strings with superconducting currents

NASA Astrophysics Data System (ADS)

Hartmann, Betti; Michel, Florent; Peter, Patrick

2017-12-01

We present a detailed analysis of excited cosmic string solutions that possess superconducting currents. These currents can be excited inside the string core, and—if the condensate is large enough—can lead to the excitations of the Higgs field. Next to the case with global unbroken symmetry, we discuss also the effects of the gauging of this symmetry and show that excited condensates persist when coupled to an electromagnetic field. The space-time of such strings is also constructed by solving the Einstein equations numerically and we show how the local scalar curvature is modified by the excitation. We consider the relevance of our results on the cosmic string network evolution as well as observations of primordial gravitational waves and cosmic rays.

Producing coherent excitations in pumped Mott antiferromagnetic insulators

DOE PAGES

Wang, Yao; Claassen, Martin; Moritz, B.; ...

2017-12-15

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 multi-particle 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 showmore » 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. In conclusion, 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.« less

Dynamics and Steady States in Excitable Mobile Agent Systems

NASA Astrophysics Data System (ADS)

Peruani, Fernando; Sibona, Gustavo J.

2008-04-01

We study the spreading of excitations in 2D systems of mobile agents where the excitation is transmitted when a quiescent agent keeps contact with an excited one during a nonvanishing time. We show that the steady states strongly depend on the spatial agent dynamics. Moreover, the coupling between exposition time (ω) and agent-agent contact rate (CR) becomes crucial to understand the excitation dynamics, which exhibits three regimes with CR: no excitation for low CR, an excited regime in which the number of quiescent agents (S) is inversely proportional to CR, and, for high CR, a novel third regime, model dependent, where S scales with an exponent ξ-1, with ξ being the scaling exponent of ω with CR.

Solvent effects in time-dependent self-consistent field methods. I. Optical response calculations

DOE PAGES

Bjorgaard, J. A.; Kuzmenko, V.; Velizhanin, K. A.; ...

2015-01-22

In this study, we implement and examine three excited state solvent models in time-dependent self-consistent field methods using a consistent formalism which unambiguously shows their relationship. These are the linear response, state specific, and vertical excitation solvent models. Their effects on energies calculated with the equivalent of COSMO/CIS/AM1 are given for a set of test molecules with varying excited state charge transfer character. The resulting solvent effects are explained qualitatively using a dipole approximation. It is shown that the fundamental differences between these solvent models are reflected by the character of the calculated excitations.

Some remarks on the early evolution of Enceladus

NASA Astrophysics Data System (ADS)

Czechowski, Leszek

2014-12-01

Thermal history of Enceladus is investigated from the beginning of accretion to formation of its core (~400 My). We consider model with solid state convection (in a solid layer) as well as liquid state convection (in molten parts of the satellite). The numerical model of convection uses full conservative finite difference method. The roles of two modes of convection are considered using the parameterized theory of convection. The following heat sources are included: short lived and long lived radioactive isotopes, accretion, serpentinization, and phase changes. Heat transfer processes are: conduction, solid state convection, and liquid state convection. It is found that core formation was completed only when liquid state convection had slowed down. Eventually, the porous core with pores filled with water was formed. Recent data concerning gravity field of Enceladus confirm low density of the core. We investigated also thermal history for different values of the following parameters: time of beginning of accretion tini, duration of accretion tacr, viscosity of ice close to the melting point ηm, activation energy in formula for viscosity E, thermal conductivity of silicate component ksil, ammonia content XNH3, and energy of serpentinization cserp. All these parameters are important for evolution, but not dramatic differences are found for realistic values. Moreover, the hypothesis of proto-Enceladus (stating that initially Enceladus was substantially larger) is considered and thermal history of such body is calculated. The last subject is the Mimas-Enceladus paradox. Comparison of thermal models of Mimas and Enceladus indicates that period favorable for 'excited path of evolution' was significantly shorter for Mimas than for Enceladus.

Deterministic entanglement of superconducting qubits by parity measurement and feedback.

PubMed

Ristè, D; Dukalski, M; Watson, C A; de Lange, G; Tiggelman, M J; Blanter, Ya M; Lehnert, K W; Schouten, R N; DiCarlo, L

2013-10-17

The stochastic evolution of quantum systems during measurement is arguably the most enigmatic feature of quantum mechanics. Measuring a quantum system typically steers it towards a classical state, destroying the coherence of an initial quantum superposition and the entanglement with other quantum systems. Remarkably, the measurement of a shared property between non-interacting quantum systems can generate entanglement, starting from an uncorrelated state. Of special interest in quantum computing is the parity measurement, which projects the state of multiple qubits (quantum bits) to a state with an even or odd number of excited qubits. A parity meter must discern the two qubit-excitation parities with high fidelity while preserving coherence between same-parity states. Despite numerous proposals for atomic, semiconducting and superconducting qubits, realizing a parity meter that creates entanglement for both even and odd measurement results has remained an outstanding challenge. Here we perform a time-resolved, continuous parity measurement of two superconducting qubits using the cavity in a three-dimensional circuit quantum electrodynamics architecture and phase-sensitive parametric amplification. Using postselection, we produce entanglement by parity measurement reaching 88 per cent fidelity to the closest Bell state. Incorporating the parity meter in a feedback-control loop, we transform the entanglement generation from probabilistic to fully deterministic, achieving 66 per cent fidelity to a target Bell state on demand. These realizations of a parity meter and a feedback-enabled deterministic measurement protocol provide key ingredients for active quantum error correction in the solid state.

FIBER AND INTEGRAL OPTICS: Mode composition of radiation in graded-index waveguides with random microbending of the axis

NASA Astrophysics Data System (ADS)

Valyaev, A. B.; Krivoshlykov, S. G.

1989-06-01

It is shown that the problem of investigating the mode composition of a partly coherent radiation beam in a randomly inhomogeneous medium can be reduced to a study of evolution of the energy of individual modes and of the coefficients of correlations between the modes. General expressions are obtained for the coupling coefficients of modes in a parabolic waveguide with a random microbending of the axis and an analysis is made of their evolution as a function of the excitation conditions. An estimate is obtained of the distance in which a steady-state energy distribution between the modes is established. Explicit expressions are obtained for the correlation function in the case when a waveguide is excited by off-axial Gaussian beams or Gauss-Hermite modes.

Two dimensional kinetic analysis of electrostatic harmonic plasma waves

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

Fonseca-Pongutá, E. C.; Ziebell, L. F.; Gaelzer, R.

2016-06-15

Electrostatic harmonic Langmuir waves are virtual modes excited in weakly turbulent plasmas, first observed in early laboratory beam-plasma experiments as well as in rocket-borne active experiments in space. However, their unequivocal presence was confirmed through computer simulated experiments and subsequently theoretically explained. The peculiarity of harmonic Langmuir waves is that while their existence requires nonlinear response, their excitation mechanism and subsequent early time evolution are governed by essentially linear process. One of the unresolved theoretical issues regards the role of nonlinear wave-particle interaction process over longer evolution time period. Another outstanding issue is that existing theories for these modes aremore » limited to one-dimensional space. The present paper carries out two dimensional theoretical analysis of fundamental and (first) harmonic Langmuir waves for the first time. The result shows that harmonic Langmuir wave is essentially governed by (quasi)linear process and that nonlinear wave-particle interaction plays no significant role in the time evolution of the wave spectrum. The numerical solutions of the two-dimensional wave spectra for fundamental and harmonic Langmuir waves are also found to be consistent with those obtained by direct particle-in-cell simulation method reported in the literature.« less

Optically dark excitonic states mediated exciton and biexciton valley dynamics in monolayer WSe2

NASA Astrophysics Data System (ADS)

Zhang, Minghua; Fu, Jiyong; Dias, A. C.; Qu, Fanyao

2018-07-01

We present a theory to address the photoluminescence (PL) intensity and valley polarization (VP) dynamics in monolayer WSe2, under the impact of excitonic dark states of both excitons and biexcitons. We find that the PL intensity of all excitonic channels including intravalley exciton (Xb), intravalley biexciton (XXk,k) and intervalley biexciton (XX) in particular for the XXk,k PL is enhanced by laser excitation fluence. In addition, our results indicate the anomalous temperature dependence of PL, i.e. increasing with temperature, as a result of favored phonon assisted dark-to-bright scatterings at high temperatures. Moreover, we observe that the PL is almost immune to intervalley scatterings, which trigger the exchange of excitonic states between the two valleys. As far as the valley polarization is concerned, we find that the VP of Xb shrinks as temperature increases, exhibiting opposite temperature response to PL, while the intravalley XXk,k VP is found almost independent of temperature. In contrast to both Xb and XXk,k, the intervalley XX VP identically vanishes, because of equal populations of excitons in the K and valleys bounded to form intervalley biexcitons. Notably, it is found that the Xb VP much more strongly depends on bright–dark scattering than that of XXk,k, making dark state act as a robust reservoir for valley polarization against intervalley scatterings for Xb at strong bright–dark scatterings, but not for XXk,k. Dark excitonic states enabled enhancement of VP benefits quantum technology for information processing based on the valley degree of freedom in valleytronic devices. Furthermore, the VP has strong dependence on intervalley scattering but maintains essentially constant with excitation fluence. Finally, the dependence of time evolution of PL and VP on temperature and excitation fluence is discussed.

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.

Guest concentration, bias current, and temperature-dependent sign inversion of magneto-electroluminescence in thermally activated delayed fluorescence devices

NASA Astrophysics Data System (ADS)

Deng, Junquan; Jia, Weiyao; Chen, Yingbing; Liu, Dongyu; Hu, Yeqian; Xiong, Zuhong

2017-03-01

Non-emissive triplet excited states in devices that undergo thermally activated delayed fluorescence (TADF) can be up-converted to singlet excited states via reverse intersystem crossing (RISC), which leads to an enhanced electroluminescence efficiency. Exciton-based fluorescence devices always exhibit a positive magneto-electroluminescence (MEL) because intersystem crossing (ISC) can be suppressed effectively by an external magnetic field. Conversely, TADF devices should exhibit a negative MEL because RISC is suppressed by the external magnetic field. Intriguingly, we observed a positive MEL in TADF devices. Moreover, the sign of the MEL was either positive or negative, and depended on experimental conditions, including doping concentration, current density and temperature. The MEL observed from our TADF devices demonstrated that ISC in the host material and RISC in the guest material coexisted. These competing processes were affected by the experimental conditions, which led to the sign change of the MEL. This work gives important insight into the energy transfer processes and the evolution of excited states in TADF devices.

Ab initio study of potential ultrafast internal conversion routes in oxybenzone, caffeic acid, and ferulic acid: implications for sunscreens.

PubMed

Karsili, Tolga N V; Marchetti, Barbara; Ashfold, Michael N R; Domcke, Wolfgang

2014-12-26

Oxybenzone (OB) and ferulic acid (FA) both find use in commercial sunscreens; caffeic acid (CA) differs from FA by virtue of an -OH group in place of a -OCH3 group on the aromatic ring. We report the results of ab initio calculations designed to explore the excited state nonradiative relaxation pathways that provide photostability to these molecules and the photoprotection they offer toward UV-A and UV-B radiation. In the case of OB, internal conversion (IC) is deduced to occur on ultrafast time scales, via a barrierless electron-driven H atom transfer pathway from the S1(1(1)nπ*) state to a conical intersection (CI) with the ground (S0) state potential energy surface (PES). The situation with respect to CA and FA is somewhat less clear-cut, with low energy CIs identified by linking excited states to the S0 state following photoexcitation and subsequent evolution along (i) a ring centered out-of-plane deformation coordinate, (ii) the E/Z isomerism coordinate and, in the case of CA, (iii) an O-H stretch coordinate. Analogy with catechol suggests that the last of these processes (if active) would lead to radical formation (and thus potential phototoxicity), encouraging a suggestion that FA might be superior to CA as a sunscreen ingredient.

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.

Molecular alignment effect on the photoassociation process via a pump-dump scheme

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

Wang, Bin-Bin; Han, Yong-Chang, E-mail: ychan@dlut.edu.cn; Cong, Shu-Lin

The photoassociation processes via the pump-dump scheme for the heternuclear (Na + H → NaH) and the homonuclear (Na + Na → Na{sub 2}) molecular systems are studied, respectively, using the time-dependent quantum wavepacket method. For both systems, the initial atom pair in the continuum of the ground electronic state (X{sup 1}Σ{sup +}) is associated into the molecule in the bound states of the excited state (A{sup 1}Σ{sup +}) by the pump pulse. Then driven by a time-delayed dumping pulse, the prepared excited-state molecule can be transferred to the bound states of the ground electronic state. It is found thatmore » the pump process can induce a superposition of the rovibrational levels |v, j〉 on the excited state, which can lead to the field-free alignment of the excited-state molecule. The molecular alignment can affect the dumping process by varying the effective coupling intensity between the two electronic states or by varying the population transfer pathways. As a result, the final population transferred to the bound states of the ground electronic state varies periodically with the delay time of the dumping pulse.« less

Analytical second derivatives of excited-state energy within the time-dependent density functional theory coupled with a conductor-like polarizable continuum model.

PubMed

Liu, Jie; Liang, WanZhen

2013-01-14

This work extends our previous works [J. Liu and W. Z. Liang, J. Chem. Phys. 135, 014113 (2011); J. Liu and W. Z. Liang, J. Chem. Phys. 135, 184111 (2011)] on analytical excited-state Hessian within the framework of time-dependent density functional theory (TDDFT) to couple with a conductor-like polarizable continuum model (CPCM). The formalism, implementation, and application of analytical first and second energy derivatives of TDDFT/CPCM excited state with respect to the nuclear and electric perturbations are presented. Their performances are demonstrated by the calculations of excitation energies, excited-state geometries, and harmonic vibrational frequencies for a number of benchmark systems. The calculated results are in good agreement with the corresponding experimental data or other theoretical calculations, indicating the reliability of the current computer implementation of the developed algorithms. Then we made some preliminary applications to calculate the resonant Raman spectrum of 4-hydroxybenzylidene-2,3-dimethyl-imidazolinone in ethanol solution and the infrared spectra of ground and excited states of 9-fluorenone in methanol solution.

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.

Humans and robots: hand in grip.

PubMed

Hubbard, G Scott

2005-01-01

As we move boldly forward into the 21st century, there has rarely been a more exciting time in which to contemplate the future of space exploration. The President of the United States has made a new and ambitious commitment to exploration of the solar system and beyond. Robotic partners will play a vital role in ensuring that the Vision is truly "sustainable and affordable". Relevant science and technology will be discussed with particular emphasis on expertise from NASA Ames Research Center of which the author is Director. The likely evolution of the balance between human explorers and robotic explorers will be addressed. c2005 Published by Elsevier Ltd.

Lifetime Measurements in Neutron-Rich Xe Isotopes — Evolution of Quadrupole Collectivity Beyond 132Sn

NASA Astrophysics Data System (ADS)

Ilieva, S.; Bönig, S.; Hartig, A.-L.; Henrich, C.; Ignatov, A.; Kröll, Th.; Thürauf, M.; Jolie, J.; Régis, J.-M.; Saed-Samii, N.; Blanc, A.; de France, G.; Jentschel, M.; Köster, U.; Mutti, P.; Simpson, G. S.; Soldner, T.; Urban, W.; Mǎrginean, N.; Ur, C. A.; Mach, H.; Fraile, L. M.; Paziy, V.; Regan, P. H.; Bruce, A. M.; Lalkovski, S.; Korten, W.

Picosecond lifetimes of excited states in neutron-rich Xe isotopes were measured at the Institut Laue-Langevin via γ-ray spectroscopy of fission fragments from neutron-induced fission of 235U and 241Pu targets. The data collected with the recently installed fast timing array FATIMA in combination with the EXOGAM Ge array were analysed using the new generalized centroid difference method. Our aim is to study the quadrupole and octupole collectivity, arising in the mass region beyond the doubly magic 132Sn, by means of transition probabilities. These can be calculated from the directly measured lifetimes.

Coherent dynamics of localized excitons and trions in ZnO/(Zn,Mg)O quantum wells studied by photon echoes

NASA Astrophysics Data System (ADS)

Solovev, I. A.; Poltavtsev, S. V.; Kapitonov, Yu. V.; Akimov, I. A.; Sadofev, S.; Puls, J.; Yakovlev, D. R.; Bayer, M.

2018-06-01

We study optically the coherent evolution of trions and excitons in a δ -doped 3.5-nm-thick ZnO/Zn0.91Mg0.09O multiple quantum well by means of time-resolved four-wave mixing at a temperature of 1.5 K. Employing spectrally narrow picosecond laser pulses in the χ(3 ) regime allows us to address differently localized trion and exciton states, thereby avoiding many-body interactions and excitation-induced dephasing. The signal in the form of photon echoes from the negatively charged A excitons (TA, trions) decays with coherence times varying from 8 up to 60 ps, depending on the trion energy: more strongly localized trions reveal longer coherence dynamics. The localized neutral excitons decay on the picosecond time scale with coherence times up to T2=4.5 ps. The coherent dynamics of the XB exciton and TB trion are very short (T2<1 ps), which is attributed to the fast energy relaxation from the trion and exciton B states to the respective A states. The trion population dynamics is characterized by the decay time T1, rising from 30 to 100 ps with decreasing trion energy.

Generalized quantum Fokker-Planck equation for photoinduced nonequilibrium processes with positive definiteness condition

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

Jang, Seogjoo, E-mail: sjang@qc.cuny.edu

2016-06-07

This work provides a detailed derivation of a generalized quantum Fokker-Planck equation (GQFPE) appropriate for photo-induced quantum dynamical processes. The path integral method pioneered by Caldeira and Leggett (CL) [Physica A 121, 587 (1983)] is extended by utilizing a nonequilibrium influence functional applicable to different baths for the ground and the excited electronic states. Both nonequilibrium and non-Markovian effects are accounted for consistently by expanding the paths in the exponents of the influence functional up to the second order with respect to time. This procedure results in approximations involving only single time integrations for the exponents of the influence functionalmore » but with additional time dependent boundary terms that have been ignored in previous works. The boundary terms complicate the derivation of a time evolution equation but do not affect position dependent physical observables or the dynamics in the steady state limit. For an effective density operator with the boundary terms factored out, a time evolution equation is derived, through short time expansion of the effective action and Gaussian integration in analytically continued complex domain of space. This leads to a compact form of the GQFPE with time dependent kernels and additional terms, which renders the resulting equation to be in the Dekker form [Phys. Rep. 80, 1 (1981)]. Major terms of the equation are analyzed for the case of Ohmic spectral density with Drude cutoff, which shows that the new GQFPE satisfies the positive definiteness condition in medium to high temperature limit. Steady state limit of the GQFPE is shown to approach the well-known expression derived by CL in the high temperature and Markovian bath limit and also provides additional corrections due to quantum and non-Markovian effects of the bath.« less

Generalized quantum Fokker-Planck equation for photoinduced nonequilibrium processes with positive definiteness condition

NASA Astrophysics Data System (ADS)

Jang, Seogjoo

2016-06-01

This work provides a detailed derivation of a generalized quantum Fokker-Planck equation (GQFPE) appropriate for photo-induced quantum dynamical processes. The path integral method pioneered by Caldeira and Leggett (CL) [Physica A 121, 587 (1983)] is extended by utilizing a nonequilibrium influence functional applicable to different baths for the ground and the excited electronic states. Both nonequilibrium and non-Markovian effects are accounted for consistently by expanding the paths in the exponents of the influence functional up to the second order with respect to time. This procedure results in approximations involving only single time integrations for the exponents of the influence functional but with additional time dependent boundary terms that have been ignored in previous works. The boundary terms complicate the derivation of a time evolution equation but do not affect position dependent physical observables or the dynamics in the steady state limit. For an effective density operator with the boundary terms factored out, a time evolution equation is derived, through short time expansion of the effective action and Gaussian integration in analytically continued complex domain of space. This leads to a compact form of the GQFPE with time dependent kernels and additional terms, which renders the resulting equation to be in the Dekker form [Phys. Rep. 80, 1 (1981)]. Major terms of the equation are analyzed for the case of Ohmic spectral density with Drude cutoff, which shows that the new GQFPE satisfies the positive definiteness condition in medium to high temperature limit. Steady state limit of the GQFPE is shown to approach the well-known expression derived by CL in the high temperature and Markovian bath limit and also provides additional corrections due to quantum and non-Markovian effects of the bath.

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.

Excited-state quantum phase transitions in systems with two degrees of freedom: Level density, level dynamics, thermal properties

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

Stránský, Pavel; Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510, México, D.F.; Macek, Michal

2014-06-15

Quantum systems with a finite number of freedom degrees f develop robust singularities in the energy spectrum of excited states as the system’s size increases to infinity. We analyze the general form of these singularities for low f, particularly f=2, clarifying the relation to classical stationary points of the corresponding potential. Signatures in the smoothed energy dependence of the quantum state density and in the flow of energy levels with an arbitrary control parameter are described along with the relevant thermodynamical consequences. The general analysis is illustrated with specific examples of excited-state singularities accompanying the first-order quantum phase transition. --more » Highlights: •ESQPTs found in infinite-size limit of systems with low numbers of freedom degrees f. •ESQPTs related to non-analytical evolutions of classical phase–space properties. •ESQPT signatures analyzed for general f, particularly f=2, extending known case f=1. •ESQPT signatures identified in smoothened density and flow of energy spectrum. •ESQPTs shown to induce a new type of thermodynamic anomalies.« less

Temperature dependence of the hydrated electron's excited-state relaxation. I. Simulation predictions of resonance Raman and pump-probe transient absorption spectra of cavity and non-cavity models

NASA Astrophysics Data System (ADS)

Zho, Chen-Chen; Farr, Erik P.; Glover, William J.; Schwartz, Benjamin J.

2017-08-01

We use one-electron non-adiabatic mixed quantum/classical simulations to explore the temperature dependence of both the ground-state structure and the excited-state relaxation dynamics of the hydrated electron. We compare the results for both the traditional cavity picture and a more recent non-cavity model of the hydrated electron and make definite predictions for distinguishing between the different possible structural models in future experiments. We find that the traditional cavity model shows no temperature-dependent change in structure at constant density, leading to a predicted resonance Raman spectrum that is essentially temperature-independent. In contrast, the non-cavity model predicts a blue-shift in the hydrated electron's resonance Raman O-H stretch with increasing temperature. The lack of a temperature-dependent ground-state structural change of the cavity model also leads to a prediction of little change with temperature of both the excited-state lifetime and hot ground-state cooling time of the hydrated electron following photoexcitation. This is in sharp contrast to the predictions of the non-cavity model, where both the excited-state lifetime and hot ground-state cooling time are expected to decrease significantly with increasing temperature. These simulation-based predictions should be directly testable by the results of future time-resolved photoelectron spectroscopy experiments. Finally, the temperature-dependent differences in predicted excited-state lifetime and hot ground-state cooling time of the two models also lead to different predicted pump-probe transient absorption spectroscopy of the hydrated electron as a function of temperature. We perform such experiments and describe them in Paper II [E. P. Farr et al., J. Chem. Phys. 147, 074504 (2017)], and find changes in the excited-state lifetime and hot ground-state cooling time with temperature that match well with the predictions of the non-cavity model. In particular, the experiments reveal stimulated emission from the excited state with an amplitude and lifetime that decreases with increasing temperature, a result in contrast to the lack of stimulated emission predicted by the cavity model but in good agreement with the non-cavity model. Overall, until ab initio calculations describing the non-adiabatic excited-state dynamics of an excess electron with hundreds of water molecules at a variety of temperatures become computationally feasible, the simulations presented here provide a definitive route for connecting the predictions of cavity and non-cavity models of the hydrated electron with future experiments.

Time Evolution of Charge Carriers & Phonons after Photo-Excitation by an Ultra-Short Light Pulse in Bulk Germanium

NASA Astrophysics Data System (ADS)

Fahy, Stephen; Murphy-Armando, Felipe; Trigo, Mariano; Savic, Ivana; Murray, Eamonn; Reis, David

We have calculated the time-evolution of carriers and generated phonons in Ge after ultrafast photo-excitation above the direct band-gap. The relevant electron-phonon and anharmonic phonon scattering rates are obtained from first-principles electronic structure calculations. Measurements of the x-ray diffuse scattering after excitation near the L point in the Brillouin zone find a relatively slow (5 ps, compared to the typical electron-phonon energy relaxation of the Gamma-L phonon) increase of the phonon population. We find this is due to emission caused by the scattering of electrons between the Delta and L valleys, after the initial depopulation of the Gamma valley. The relative slowness of this process is due to a combination of causes: (i) the finite time for the initial depopulation of the conduction Gamma valley; (ii) the associated electron-phonon coupling is relatively weaker (compared to Gamma-L, Gamma-Delta and Delta-Delta couplings) ; (iii) the TA associated phonon has a long lifetime and (iv) the depopulation of the Delta valley suppresses the phonon emission. Supported by Science Foundation Ireland, Grant 12/1A/1601.

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.

Epidemic Dynamics in Open Quantum Spin Systems

NASA Astrophysics Data System (ADS)

Pérez-Espigares, Carlos; Marcuzzi, Matteo; Gutiérrez, Ricardo; Lesanovsky, Igor

2017-10-01

We explore the nonequilibrium evolution and stationary states of an open many-body system that displays epidemic spreading dynamics in a classical and a quantum regime. Our study is motivated by recent experiments conducted in strongly interacting gases of highly excited Rydberg atoms where the facilitated excitation of Rydberg states competes with radiative decay. These systems approximately implement open quantum versions of models for population dynamics or disease spreading where species can be in a healthy, infected or immune state. We show that in a two-dimensional lattice, depending on the dominance of either classical or quantum effects, the system may display a different kind of nonequilibrium phase transition. We moreover discuss the observability of our findings in laser driven Rydberg gases with particular focus on the role of long-range interactions.

Relaxation and collective excitations of cluster nano-plasmas

NASA Astrophysics Data System (ADS)

Reinholz, Heidi; Röpke, Gerd; Broda, Ingrid; Morozov, Igor; Bystryi, Roman; Lavrinenko, Yaroslav

2018-01-01

Nano-plasmas produced, for example, in clusters after short-pulse laser irradiation, can show collective excitations, as derived from the time evolution of fluctuations in thermodynamic equilibrium. Molecular dynamical simulations are performed for various cluster sizes. New data are obtained for the minimum value of the stationary cluster charge. The bi-local autocorrelation function gives the spatial structure of the eigenmodes, for which energy eigenvalues are obtained. By varying the cluster size, starting from a few-particle cluster, the emergence of macroscopic properties such as collective excitations is shown.

Evolution from quasivibrational to quasirotational structure in 155Tm and yrast 27 /2- to 25 /2- energy anomaly in the A ≈150 mass region

NASA Astrophysics Data System (ADS)

Liu, L.; Wang, S. Y.; Wang, S.; Hua, H.; Zhang, S. Q.; Meng, J.; Bark, R. A.; Wyngaardt, S. M.; Qi, B.; Sun, D. P.; Liu, C.; Li, Z. Q.; Jia, H.; Li, X. Q.; Xu, C.; Li, Z. H.; Sun, J. J.; Zhu, L. H.; Jones, P.; Lawrie, E. A.; Lawrie, J. J.; Wiedeking, M.; Bucher, T. D.; Dinoko, T.; Makhathini, L.; Majola, S. N. T.; Noncolela, S. P.; Shirinda, O.; Gál, J.; Kalinka, G.; Molnár, J.; Nyakó, B. M.; Timár, J.; Juhász, K.; Arogunjo, M.

2018-04-01

Excited states in 155Tm have been populated via the reaction 144Sm(16O, p 4 n )155Tm at a beam energy of 118 MeV. The ground-state band has been extended and a new side band of the ground-state band is identified. E-GOS curves and potential energy surface calculations are employed to discuss the structure evolution of the ground-state band. The newly observed side band in 155Tm is discussed based on the spin/energy systematics. In particular, the phenomenon of seniority inversion is proposed in 155Tm, and a systematic study of this phenomenon in the A ≈150 mass region is performed.

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.

Near-Field Spectroscopy and Imaging of Subwavelength Plasmonic Terahertz Resonators

DOE PAGES

Mitrofanov, Oleg; Khromova, Irina; Siday, Thomas; ...

2016-04-22

We describe the temporal evolution of the terahertz (THz) field leading to the excitation of plasmonic resonances in carbon microfibers. The field evolution is mapped in space and time for the 3/2 wavelength resonance using a subwavelength aperture THz near-field probe with an embedded THz photoconductive detector. The excitation of surface waves at the fiber tips leads to the formation of a standing wave along the fiber. Local THz time-domain spectroscopy at one of the standing wave crests shows a clear third-order resonance peak at 1.65 THz, well described by the Lorentz model. Lastly, this application of the subwavelength aperturemore » THz near-field microscopy for mode mapping and local spectroscopy demonstrates the potential of near-field methods for studies of subwavelength plasmonic THz resonators.« 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.

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.

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

Guldi, D.M.; Torres-Garcia, G.; Mattay, J.

Excited-state properties of three different pyrazine derivatives 4--6 were probed by emission and transient absorption spectroscopy. They display emission maxima at 464 (4), 417 (5), and 515 nm (6) that are red-shifted with respect to their strong UV ground-state absorption and formed with overall quantum yields ({Phi}) of 0.156, 0.22, and 0.13, respectively. Once photoexcited, these triplet excited pyrazines undergo rapid intermolecular energy transfer to a monofunctionalized fullerene derivative (7) with bimolecular rate constants ranging from 3.64 {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1} (6) to 1.1 {times} 10{sup 10} M{sup {minus}1} s{sup {minus}1} (4). The product of these bimolecularmore » energy-transfer reactions is in all cases the fullerene triplet excited state. Functionalization of pristine C{sub 60} with the investigated pyrazine derivatives promotes the UV-vis absorption characteristics and, in turn, improves the light-harvesting efficiency of the resulting dyads 1--3 relative to pristine C{sub 60}. Photoexcitation of the pyrazine moieties in dyads 1--3 leads to the formation of their singlet excited states. In contrast to the pyrazine models, photoexcitation of dyad 1--3 is followed by rapid intramolecular deactivation processes of the latter via energy transfer to the fullerene ground state with half-lives between 37 and 100 ps. In turn, energy transfer transforms the short-lived and moderately redox-active singlet excited states of pyrazine into the highly reactive fullerene triplet excited state. The latter is found to produce effectively singlet oxygen ({sup 1}O{sub 2}) with quenching rate constants for 1--3 of (1--1.5) {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1}. Similarly, reductive quenching of the triplet excited states in dyads 1--3 via electron transfer with diazabicyclooctane (DABCO) occurs with rate constants of 5.2--9.4 {times} 10{sup 7} M{sup {minus}1} s{sup {minus}1}.« less

Efficient photoassociation of ultracold cesium atoms with picosecond pulse laser

NASA Astrophysics Data System (ADS)

Hai, Yang; Hu, Xue-Jin; Li, Jing-Lun; Cong, Shu-Lin

2017-08-01

We investigate theoretically the formation of ultracold Cs2 molecules via photoassociation (PA) with three kinds of pulses (the Gaussian pulse, the asymmetric shaped laser pulse SL1 with a large rising time and a small falling time and the asymmetric shaped laser pulse SL2 with a small rising time and a large falling time). For the three kinds of pulses, the final population on vibrational levels from v‧ = 120 to 175 of the excited state displays a regular oscillation change with pulse width and interaction strength, and a high PA efficiency can be achieved with optimised parameters. The PA efficiency in the excited state steered by the SL1-pulse (SL2-pulse) train with optimised parameters which is composed of four SL1 (SL2) pulses is 1.74 times as much as that by the single SL1 (SL2) pulse due to the population accumulation effect. Moreover, a dump laser is employed to transfer the excited molecules from the excited state to the vibrational level v″ = 12 of the ground state to obtain stable molecules.

Study of collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings

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

Kozlov, D. N., E-mail: dnk@kapella.gpi.ru; Kobtsev, V. D.; Stel'makh, O. M.

2013-07-15

Collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H{sub 2}/O{sub 2} mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b{sup 1}{Sigma}{sub g}{sup +} state of O{sub 2} molecules deactivation rates are measured in a 4.3more » vol % H{sub 2} mixture at the number density of 2 amg in the temperature range 291-850 K. The physical deactivation is shown to dominate in the collisions of H{sub 2} with O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) and O{sub 2}(a{sup 1}{Delta}{sub g}) up to temperatures of 780-790 K at time delays up to 10 {mu}s after the excitation pulse. The parameters of the obtained temperature dependence of the (b{sup 1}{Sigma}{sub g}{sup +} state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200-400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H{sub 2}O molecules which appear as the mixture, as the result of the dark gross reaction with O{sub 2} molecules in the ground state, O{sub 2} + 2H{sub 2} {yields} 2H{sub 2}O. The measurements show that this reaction results in complete transformation of H{sub 2} into H{sub 2}O at temperatures of 790-810 K.« less

The excitation of a primordial cold asteroid belt as a natural outcome of the planetary instability

NASA Astrophysics Data System (ADS)

Deienno, Rogerio; Izidoro, André; Gomes, Rodney S.; Morbidelli, Alessandro; Nesvorny, David

2017-10-01

The initial dynamical state of the main asteroid belt (MB) always puzzled astronomers and it is still a hot subject under debate. For years, the currently well known Grand Tack model was considered to be the only capable of reconciling the formation of the terrestrial planets together with a well dynamically excited MB. This model, despite its success, is still not generally accepted given that it implies an invasion of Jupiter within the terrestrial region, passing through the MB twice. Other models for the terrestrial planet formation, on the other hand, always end up with a fully or partially cold MB formed. It was recently proposed that a chaotic evolution for Jupiter and Saturn before the planetary instability of the Solar System could excite an initially cold MB. However, hydrodynamical simulations predict that the orbits of those planets at the end of the gas disk phase should be characterized by resonant and regular motion. Therefore, the origin of this chaotic evolution is not fully understood. Here, assuming initial resonant and regular motion for Jupiter and Saturn, we propose a different mechanism capable of exciting a primordial cold MB during the planetary instability. For this, we assume that the planetary instability was of the jumping-Jupiter (JJ) type, and that it accounts for all the constraints already placed. Our results, which also possibly can explain the pathway to the chaotic evolution of Jupiter and Saturn, show that when Jupiter gets a temporary large enough level of excitation, both in eccentricity and inclination, it induces strong forced vectors of eccentricity and inclination within the MB region. Then, because in the JJ instability Jupiter is jumping around, such forced vectors keep changing both in magnitude and phase throughout the whole MB region. Thus, depending on the evolution of Jupiter during the JJ instability, the excitation of a primordial cold MB can indeed be achieved as a natural outcome of the planetary instability for any initial planetary configuration. Acknowledgment FAPESP 2014/02013-5.

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.

Shell Evolution towards 78Ni: Low-Lying States in 77Cu

NASA Astrophysics Data System (ADS)

Sahin, E.; Bello Garrote, F. L.; Tsunoda, Y.; Otsuka, T.; de Angelis, G.; Görgen, A.; Niikura, M.; Nishimura, S.; Xu, Z. Y.; Baba, H.; Browne, F.; Delattre, M.-C.; Doornenbal, P.; Franchoo, S.; Gey, G.; Hadyńska-KlÈ©k, K.; Isobe, T.; John, P. R.; Jung, H. S.; Kojouharov, I.; Kubo, T.; Kurz, N.; Li, Z.; Lorusso, G.; Matea, I.; Matsui, K.; Mengoni, D.; Morfouace, P.; Napoli, D. R.; Naqvi, F.; Nishibata, H.; Odahara, A.; Sakurai, H.; Schaffner, H.; Söderström, P.-A.; Sohler, D.; Stefan, I. G.; Sumikama, T.; Suzuki, D.; Taniuchi, R.; Taprogge, J.; Vajta, Z.; Watanabe, H.; Werner, V.; Wu, J.; Yagi, A.; Yalcinkaya, M.; Yoshinaga, K.

2017-06-01

The level structure of the neutron-rich 77Cu nucleus is investigated through β -delayed γ -ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of 77Ni are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in 77Cu are identified for the first time by correlating γ rays with the β decay of 77Ni, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale Monte Carlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near 78Ni and suggests a single-particle nature for both the 5 /21- and 3 /21- states in 77Cu, leading to doubly magic 78Ni.

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

NASA Astrophysics Data System (ADS)

Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

2011-07-01

The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

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.

Molecular reorganization of selected quinoline derivatives in the ground and excited states—Investigations via static DFT

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

Błaziak, Kacper; Panek, Jarosław J.; Jezierska, Aneta, E-mail: aneta.jezierska@chem.uni.wroc.pl

2015-07-21

Quinoline derivatives are interesting objects to study internal reorganizations due to the observed excited-state-induced intramolecular proton transfer (ESIPT). Here, we report on computations for selected 12 quinoline derivatives possessing three kinds of intramolecular hydrogen bonds. Density functional theory was employed for the current investigations. The metric and electronic structure simulations were performed for the ground state and first excited singlet and triplet states. The computed potential energy profiles do not show a spontaneous proton transfer in the ground state, whereas excited states exhibit this phenomenon. Atoms in Molecules (AIM) theory was applied to study the nature of hydrogen bonding, whereasmore » Harmonic Oscillator Model of aromaticity index (HOMA) provided data of aromaticity evolution as a derivative of the bridge proton position. The AIM-based topological analysis confirmed the presence of the intramolecular hydrogen bonding. In addition, using the theory, we were able to provide a quantitative illustration of bonding transformation: from covalent to the hydrogen. On the basis of HOMA analysis, we showed that the aromaticity of both rings is dependent on the location of the bridge proton. Further, the computed results were compared with experimental data available. Finally, ESIPT occurrence was compared for the three investigated kinds of hydrogen bridges, and competition between two bridges in one molecule was studied.« less

Excited state non-adiabatic dynamics of pyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study

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

Wu, Guorong; State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026

The dynamics of pyrrole excited at wavelengths in the range 242-217 nm are studied using a combination of time-resolved photoelectron spectroscopy and wavepacket propagations performed using the multi-configurational time-dependent Hartree method. Excitation close to the origin of pyrrole’s electronic spectrum, at 242 and 236 nm, is found to result in an ultrafast decay of the system from the ionization window on a single timescale of less than 20 fs. This behaviour is explained fully by assuming the system to be excited to the A{sub 2}(πσ{sup ∗}) state, in accord with previous experimental and theoretical studies. Excitation at shorter wavelengths hasmore » previously been assumed to result predominantly in population of the bright A{sub 1}(ππ{sup ∗}) and B{sub 2}(ππ{sup ∗}) states. We here present time-resolved photoelectron spectra at a pump wavelength of 217 nm alongside detailed quantum dynamics calculations that, together with a recent reinterpretation of pyrrole’s electronic spectrum [S. P. Neville and G. A. Worth, J. Chem. Phys. 140, 034317 (2014)], suggest that population of the B{sub 1}(πσ{sup ∗}) state (hitherto assumed to be optically dark) may occur directly when pyrrole is excited at energies in the near UV part of its electronic spectrum. The B{sub 1}(πσ{sup ∗}) state is found to decay on a timescale of less than 20 fs by both N-H dissociation and internal conversion to the A{sub 2}(πσ{sup ∗}) state.« less

Temperature dependent of IVR investigated by steady-state and time-frequency resolved CARS for liquid nitrobenzene and nitromethane

NASA Astrophysics Data System (ADS)

Yang, Yanqiang; Zhu, Gangbei; Yan, Lin; Liu, Xiaosong; Yang's Ultrafast Spectroscopy Group Team

2017-06-01

Intramolecular vibrational energy redistribution (IVR) is important process in thermal decomposition, shock chemistry and photochemistry. Anti-Stokes Raman scattering is sensitive to the vibrational population in excited states because only vibrational excited states are responsible to the anti-Stokes Raman scattering, does not vibrational ground states. In this report, steady-state anti-Stokes Raman spectroscopy and broad band ultrafast coherent anti-Stokes Raman scattering (CARS) are performed. The steady-state anti-Stokes Raman spectroscopy shows temperature dependent of vibrational energy redistribution in vibrational excited-state molecule, and reveal that, in liquid nitrobenzene, with temperature increasing, vibrational energy is mainly redistributed in NO2 symmetric stretching mode, and phenyl ring stretching mode of νCC. For liquid nitromethane, it is found that, with temperature increasing, vibrational energy concentrate in CN stretching mode and methyl umbrella vibrational mode. In the broad band ultrafast CARS experiment, multiple vibrational modes are coherently excited to vibrational excited states, and the time-frequency resolved CARS spectra show the coincident IVR processes. This work is supported by the National Natural Science Foundation of China (Grant Numbers 21673211 and 11372053), and the Science Challenging Program (Grant Number JCKY2016212A501).

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

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.

Electron correlation in real time.

PubMed

Sansone, Giuseppe; Pfeifer, Thomas; Simeonidis, Konstantinos; Kuleff, Alexander I

2012-02-01

Electron correlation, caused by the interaction among electrons in a multielectron system, manifests itself in all states of matter. A complete theoretical description of interacting electrons is challenging; different approximations have been developed to describe the fundamental aspects of the correlation that drives the evolution of simple (few-electron systems in atoms/molecules) as well as complex (multielectron wave functions in atoms, molecules, and solids) systems. Electron correlation plays a key role in the relaxation mechanisms that characterize excited states of neutral or ionized atoms and molecules populated by absorption of extreme ultraviolet (XUV) or X-ray radiation. The dynamics of these states can lead to different processes such as Fano resonance and Auger decay in atoms or interatomic Coulombic decay or charge migration in molecules and clusters. Many of these relaxation mechanisms are ubiquitous in nature and characterize the interaction of complex systems, such as biomolecules, adsorbates on surfaces, and hydrogen-bonded clusters, with XUV light. These mechanisms evolve typically on the femtosecond (1 fs=10(-15) s) or sub-femtosecond timescale. The experimental availability of few-femtosecond and attosecond (1 as=10(-18) s) XUV pulses achieved in the last 10 years offers, for the first time, the opportunity to excite and probe in time these dynamics giving the possibility to trace and control multielectron processes. The generation of ultrashort XUV radiation has triggered the development and application of spectroscopy techniques that can achieve time resolution well into the attosecond domain, thereby offering information on the correlated electronic motion and on the correlation between electron and nuclear motion. A deeper understanding of how electron correlation works could have a large impact in several research fields, such as biochemistry and biology, and trigger important developments in the design and optimization of electronic devices. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Equilibration in one-dimensional quantum hydrodynamic systems

NASA Astrophysics Data System (ADS)

Sotiriadis, Spyros

2017-10-01

We study quench dynamics and equilibration in one-dimensional quantum hydrodynamics, which provides effective descriptions of the density and velocity fields in gapless quantum gases. We show that the information content of the large time steady state is inherently connected to the presence of ballistically moving localised excitations. When such excitations are present, the system retains memory of initial correlations up to infinite times, thus evading decoherence. We demonstrate this connection in the context of the Luttinger model, the simplest quantum hydrodynamic model, and in the quantum KdV equation. In the standard Luttinger model, memory of all initial correlations is preserved throughout the time evolution up to infinitely large times, as a result of the purely ballistic dynamics. However nonlinear dispersion or interactions, when separately present, lead to spreading and delocalisation that suppress the above effect by eliminating the memory of non-Gaussian correlations. We show that, for any initial state that satisfies sufficient clustering of correlations, the steady state is Gaussian in terms of the bosonised or fermionised fields in the dispersive or interacting case respectively. On the other hand, when dispersion and interaction are simultaneously present, a semiclassical approximation suggests that localisation is restored as the two effects compensate each other and solitary waves are formed. Solitary waves, or simply solitons, are experimentally observed in quantum gases and theoretically predicted based on semiclassical approaches, but the question of their stability at the quantum level remains to a large extent an open problem. We give a general overview on the subject and discuss the relevance of our findings to general out of equilibrium problems. Dedicated to John Cardy on the occasion of his 70th birthday.

S-154 in the Large Magellanic Cloud - Spectral evolution from a luminous Fe II variable to a symbiotic-like star

NASA Technical Reports Server (NTRS)

Remillard, R. A.; Rosenthal, E.; Tuohy, I. R.; Schwartz, D. A.; Buckley, D. A. H.; Brissenden, R. J. V.

1992-01-01

The evolution of the emission-line Star S-154, between February and December 1988, from a low-excitation 'Fe II star' into a high-excitation state that resembles symbiotic stars, is traced. It is inferred that the spectral type of central stars do not always dominate the physical conditions in the circumstellar material and thereby determine the nebular classification. The membership of S-154 in the LMC was confirmed with a radial velocity measurement of +274 km/s. The historical light curve (1880-1990) obtained from 346 photograph plates of the Harvard Plate Library exhibits about 4 mag of variations, with an MB range of -6 to -2. No evidence was found for coherent modulations that would represent the orbital period of a symbiotic binary.

Luminescence studies and infrared emission of erbium-doped calcium zirconate phosphor.

PubMed

Tiwari, Neha; Dubey, Vikas

2016-05-01

The near-infrared-to-visible upconversion luminescence behaviour of Er(3+)-doped CaZrO3 phosphor is discussed in this manuscript. The phosphor was prepared by a combustion synthesis technique that is suitable for less-time-taking techniques for nanophosphors. The starting materials used for sample preparation were Ca(NO3)2.4H2O, Zr(NO3)4 and Er(NO3)2, and urea was used as a fuel. The prepared sample was characterized by X-ray diffraction (XRD). The surface morphology of prepared phosphor was determined by field emission gun scanning electron microscopy (FEGSEM). The functional group analysis was determined by Fourier transform infrared (FTIR) spectroscopy. All prepared phosphors with variable Er(3+) concentrations (0.5-2.5 mol%) were studied by photoluminescence analysis. It was found that the excitation spectra of the prepared phosphor showed a sharp excitation peak centred at 980 nm. The emission spectra with variable Er(3+) concentrations showed strong peaks in the 555 nm and 567 nm range, with a dominant peak at 555 nm due to the ((2)H(11/2),(4)S(3/2)) transition and a weaker transition at 567 nm associated with 527 nm. Spectrophotometric determination of the peak was evaluated by the Commission Internationale de I'Eclairage (CIE) method These upconverted emissions were attributed to a two-photon process. The excitation wavelength dependence of the upconverted luminescence, together with its time evolution after infrared pulsed excitation, suggested that energy transfer upconversion processes were responsible for the upconversion luminescence. The upconversion mechanisms were studied in detail through laser power dependence. Excited state absorption and energy transfer processes were discussed as possible upconversion mechanisms. The cross-relaxation process in Er(3+) was also investigated. Copyright © 2015 John Wiley & Sons, Ltd.

Self-pulsations and excitability in optically injected quantum-dot lasers: Impact of the excited states and spontaneous emission noise

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

Olejniczak, Lukasz; SUPELEC, OPTEL, and LMOPS EA 4423; Panajotov, Krassimir

2010-08-15

We study the dynamics of an optically injected quantum-dot laser accounting for excited states. Mapping of the bifurcations in the plane frequency detuning vs. injection strength shows that the relaxation rate scales the regions of locking and single- and double-period solutions, while the capture rate has a minor effect. Within the regions of time-periodic solutions, close to the saddle-node bifurcation boundary, we identify subregions where the output signal resembles excitable pulses as a result of the bottleneck phenomenon. We show that such emission is determined mainly by fluctuations in the occupation of the excited states. The interpulse time follows anmore » inverse square root scaling law as a function of the detuning. In a deterministic system the pulses are periodic regardless of the detuning, but in the presence of noise, close to the locking region, the interpulse time follows a positively skewed normal distribution. For a fixed frequency detuning, increasing the noise strength can shift the mean of the interpulse time distribution and make the pulsations more periodic.« less

Coulomb Excitation of the 64Ni Nucleus and Application of Inverse Kinematics

NASA Astrophysics Data System (ADS)

Greaves, Beau; Muecher, Dennis; Ali, Fuad A.; Drake, Tom; Bildstein, Vinzenz; Berner, Christian; Gernhaeuser, Roman; Nowak, K.; Hellgartner, S.; Lutter, R.; Reichert, S.

2017-09-01

In this contribution, we present new data on the semi-magic 64Ni nucleus, close to the N =40 harmonic oscillator shell gap. Recent studies suggest a complicated existence of shape coexistence in 68Ni, likely caused by type-II shell evolutions. The region studied here thus might define the ``shore'' of the region of more deformed nuclei in the Island of Inversion below 68Ni. At the Maier-Leibnitz-Laboratory (MLL) in Munich, a beam of 64Ni was excited using Coulomb excitation. The high-granularity MINIBALL HPGe array and a segmented silicon strip detector were used to identify gamma decays in 64Ni. Doppler-shifted attenuation method (DSAM) analysis was applied to the experimental data acquired to resolve the low-lying excited states and acquire a lifetime measurement based on Geant4 simulations of the first excited 2 + state, clarifying the previously conflicting results. Furthermore, we show DSAM data following transfer reactions in inverse kinematics. This new method has the potential to provide insight into tests of ab-initio shell model calculations in the sd-pf shell and for the study of nuclear reaction rates. Supported under NSERC SAPIN-2016-00030.

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

Low-lying excited states by constrained DFT

NASA Astrophysics Data System (ADS)

Ramos, Pablo; Pavanello, Michele

2018-04-01

Exploiting the machinery of Constrained Density Functional Theory (CDFT), we propose a variational method for calculating low-lying excited states of molecular systems. We dub this method eXcited CDFT (XCDFT). Excited states are obtained by self-consistently constraining a user-defined population of electrons, Nc, in the virtual space of a reference set of occupied orbitals. By imposing this population to be Nc = 1.0, we computed the first excited state of 15 molecules from a test set. Our results show that XCDFT achieves an accuracy in the predicted excitation energy only slightly worse than linear-response time-dependent DFT (TDDFT), but without incurring into problems of variational collapse typical of the more commonly adopted ΔSCF method. In addition, we selected a few challenging processes to test the limits of applicability of XCDFT. We find that in contrast to TDDFT, XCDFT is capable of reproducing energy surfaces featuring conical intersections (azobenzene and H3) with correct topology and correct overall energetics also away from the intersection. Venturing to condensed-phase systems, XCDFT reproduces the TDDFT solvatochromic shift of benzaldehyde when it is embedded by a cluster of water molecules. Thus, we find XCDFT to be a competitive method among single-reference methods for computations of excited states in terms of time to solution, rate of convergence, and accuracy of the result.

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.

A long-range-corrected density functional that performs well for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states.

PubMed

Rohrdanz, Mary A; Martins, Katie M; Herbert, John M

2009-02-07

We introduce a hybrid density functional that asymptotically incorporates full Hartree-Fock exchange, based on the long-range-corrected exchange-hole model of Henderson et al. [J. Chem. Phys. 128, 194105 (2008)]. The performance of this functional, for ground-state properties and for vertical excitation energies within time-dependent density functional theory, is systematically evaluated, and optimal values are determined for the range-separation parameter, omega, and for the fraction of short-range Hartree-Fock exchange. We denote the new functional as LRC-omegaPBEh, since it reduces to the standard PBEh hybrid functional (also known as PBE0 or PBE1PBE) for a certain choice of its two parameters. Upon optimization of these parameters against a set of ground- and excited-state benchmarks, the LRC-omegaPBEh functional fulfills three important requirements: (i) It outperforms the PBEh hybrid functional for ground-state atomization energies and reaction barrier heights; (ii) it yields statistical errors comparable to PBEh for valence excitation energies in both small and medium-sized molecules; and (iii) its performance for charge-transfer excitations is comparable to its performance for valence excitations. LRC-omegaPBEh, with the parameters determined herein, is the first density functional that satisfies all three criteria. Notably, short-range Hartree-Fock exchange appears to be necessary in order to obtain accurate ground-state properties and vertical excitation energies using the same value of omega.

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 .

Attosecond XUV absorption spectroscopy of doubly excited states in helium atoms dressed by a time-delayed femtosecond infrared laser

NASA Astrophysics Data System (ADS)

Yang, Z. Q.; Ye, D. F.; Ding, Thomas; Pfeifer, Thomas; Fu, L. B.

2015-01-01

In the present paper, we investigate the time-resolved transient absorption spectroscopy of doubly excited states of helium atoms by solving the time-dependent two-electron Schrödinger equation numerically based on a one-dimensional model. The helium atoms are subjected to an extreme ultraviolet (XUV) attosecond pulse and a time-delayed infrared (IR) few-cycle laser pulse. A superposition of doubly excited states populated by the XUV pulse is identified, which interferes with the direct ionization pathway leading to Fano resonance profiles in the photoabsorption spectrum. In the presence of an IR laser, however, the Fano line profiles are strongly modified: A shifting, splitting, and broadening of the original absorption lines is observed when the XUV attosecond pulse and infrared few-cycle laser pulse overlap in time, which is in good agreement with recent experimental results. At certain time delays, we observe symmetric Lorentz, inverted Fano profiles, and even negative absorption cross sections indicating that the XUV light can be amplified during the interaction with atoms. We further prove that the above pictures are general for different doubly excited states by suitably varying the frequency of the IR field to coherently couple the corresponding states.

Real-Time Time-Frequency Two-Dimensional Imaging of Ultrafast Transient Signals in Solid-State Organic Materials

PubMed Central

Takeda, Jun; Ishida, Akihiro; Makishima, Yoshinori; Katayama, Ikufumi

2010-01-01

In this review, we demonstrate a real-time time-frequency two-dimensional (2D) pump-probe imaging spectroscopy implemented on a single shot basis applicable to excited-state dynamics in solid-state organic and biological materials. Using this technique, we could successfully map ultrafast time-frequency 2D transient absorption signals of β-carotene in solid films with wide temporal and spectral ranges having very short accumulation time of 20 ms per unit frame. The results obtained indicate the high potential of this technique as a powerful and unique spectroscopic tool to observe ultrafast excited-state dynamics of organic and biological materials in solid-state, which undergo rapid photodegradation. PMID:22399879

Neutron knockout from 68,70Ni ground and isomeric states.

NASA Astrophysics Data System (ADS)

Recchia, F.; Weisshaar, D.; Gade, A.; Tostevin, J. A.; Janssens, R. V. F.; Albers, M.; Bader, V. M.; Baugher, T.; Bazin, D.; Berryman, J. S.; Brown, B. A.; Campbell, C. M.; Carpenter, M. P.; Chen, J.; Chiara, C. J.; Crawford, H. L.; Hoffman, C. R.; Kondev, F. G.; Korichi, A.; Langer, C.; Lauritsen, T.; Liddick, S. N.; Lunderberg, E.; Noji, S.; Prokop, C.; Stroberg, S. R.; Suchyta, S.; Wimmer, K.; Zhu, S.

2018-02-01

Neutron-rich isotopes are an important source of new information on nuclear physics. Specifically, the spin-isospin components in the nucleon-nucleon (NN) interaction, e.g., the proton-neutron tensor force, are expected to modify shell structure in exotic nuclei. These potential changes in the intrinsic shell structure are of fundamental interest. The study of the excitation energy of states corresponding to specific configurations in even-even isotopes, together with the single-particle character of the first excited states of odd-A, neutron-rich Ni isotopes, probes the evolution of the neutron orbitals around the Fermi surface as a function of the neutron number a step forward in the understanding of the region and the nature of the NN interaction at large N/Z ratios. In an experiment carried out at the National Superconducting Cyclotron Laboratory [1], new spectroscopic information was obtained for 68Ni and the distribution of single-particle strengths in 67,69Ni was characterized by means of single-neutron knockout from 68,70Ni secondary beams. The spectroscopic strengths, deduced from the measured partial cross sections to the individual states tagged by their de-exciting gamma rays, is used to identify and quantify configurations that involve neutron excitations across the N = 40 harmonic oscillator shell closure. The de-excitation γ rays were measured with the GRETINA tracking array [2]. The results challenge the validity of the most current shell-model Hamiltonians and effective interactions, highlighting shortcomings that cannot yet be explained. These results suggest that our understanding of the low-energy states in such nuclei is not complete and requires further investigation.

Chromophore twisting in the excited state of a photoswitchable fluorescent protein captured by time-resolved serial femtosecond crystallography

NASA Astrophysics Data System (ADS)

Coquelle, Nicolas; Sliwa, Michel; Woodhouse, Joyce; Schirò, Giorgio; Adam, Virgile; Aquila, Andrew; Barends, Thomas R. M.; Boutet, Sébastien; Byrdin, Martin; Carbajo, Sergio; de La Mora, Eugenio; Doak, R. Bruce; Feliks, Mikolaj; Fieschi, Franck; Foucar, Lutz; Guillon, Virginia; Hilpert, Mario; Hunter, Mark S.; Jakobs, Stefan; Koglin, Jason E.; Kovacsova, Gabriela; Lane, Thomas J.; Lévy, Bernard; Liang, Mengning; Nass, Karol; Ridard, Jacqueline; Robinson, Joseph S.; Roome, Christopher M.; Ruckebusch, Cyril; Seaberg, Matthew; Thepaut, Michel; Cammarata, Marco; Demachy, Isabelle; Field, Martin; Shoeman, Robert L.; Bourgeois, Dominique; Colletier, Jacques-Philippe; Schlichting, Ilme; Weik, Martin

2018-01-01

Chromophores absorb light in photosensitive proteins and thereby initiate fundamental biological processes such as photosynthesis, vision and biofluorescence. An important goal in their understanding is the provision of detailed structural descriptions of the ultrafast photochemical events that they undergo, in particular of the excited states that connect chemistry to biological function. Here we report on the structures of two excited states in the reversibly photoswitchable fluorescent protein rsEGFP2. We populated the states through femtosecond illumination of rsEGFP2 in its non-fluorescent off state and observed their build-up (within less than one picosecond) and decay (on the several picosecond timescale). Using an X-ray free-electron laser, we performed picosecond time-resolved crystallography and show that the hydroxybenzylidene imidazolinone chromophore in one of the excited states assumes a near-canonical twisted configuration halfway between the trans and cis isomers. This is in line with excited-state quantum mechanics/molecular mechanics and classical molecular dynamics simulations. Our new understanding of the structure around the twisted chromophore enabled the design of a mutant that displays a twofold increase in its off-to-on photoswitching quantum yield.

Chromophore twisting in the excited state of a photoswitchable fluorescent protein captured by time-resolved serial femtosecond crystallography

DOE PAGES

Coquelle, Nicolas; Sliwa, Michel; Woodhouse, Joyce; ...

2017-09-11

Chromophores absorb light in photosensitive proteins and thereby initiate fundamental biological processes such as photosynthesis, vision and biofluorescence. An important goal in their understanding is the provision of detailed structural descriptions of the ultrafast photochemical events that they undergo, in particular of the excited states that connect chemistry to biological function. Here in this paper we report on the structures of two excited states in the reversibly photoswitchable fluorescent protein rsEGFP2. We populated the states through femtosecond illumination of rsEGFP2 in its non-fluorescent off state and observed their build-up (within less than one picosecond) and decay (on the several picosecondmore » timescale). Using an X-ray free-electron laser, we performed picosecond time-resolved crystallography and show that the hydroxybenzylidene imidazolinone chromophore in one of the excited states assumes a near-canonical twisted configuration halfway between the trans and cis isomers. This is in line with excited-state quantum mechanics/molecular mechanics and classical molecular dynamics simulations. Our new understanding of the structure around the twisted chromophore enabled the design of a mutant that displays a twofold increase in its off-to-on photoswitching quantum yield.« less

Chromophore twisting in the excited state of a photoswitchable fluorescent protein captured by time-resolved serial femtosecond crystallography

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

Coquelle, Nicolas; Sliwa, Michel; Woodhouse, Joyce

Chromophores absorb light in photosensitive proteins and thereby initiate fundamental biological processes such as photosynthesis, vision and biofluorescence. An important goal in their understanding is the provision of detailed structural descriptions of the ultrafast photochemical events that they undergo, in particular of the excited states that connect chemistry to biological function. Here in this paper we report on the structures of two excited states in the reversibly photoswitchable fluorescent protein rsEGFP2. We populated the states through femtosecond illumination of rsEGFP2 in its non-fluorescent off state and observed their build-up (within less than one picosecond) and decay (on the several picosecondmore » timescale). Using an X-ray free-electron laser, we performed picosecond time-resolved crystallography and show that the hydroxybenzylidene imidazolinone chromophore in one of the excited states assumes a near-canonical twisted configuration halfway between the trans and cis isomers. This is in line with excited-state quantum mechanics/molecular mechanics and classical molecular dynamics simulations. Our new understanding of the structure around the twisted chromophore enabled the design of a mutant that displays a twofold increase in its off-to-on photoswitching quantum yield.« less

The Evolution and Stability of Massive Stars

NASA Astrophysics Data System (ADS)

Shiode, Joshua Hajime

Massive stars are the ultimate source for nearly all the elements necessary for life. The first stars forge these elements from the sparse set of ingredients supplied by the Big Bang, and distribute enriched ashes throughout their galactic homes via their winds and explosive deaths. Subsequent generations follow suit, assembling from the enriched ashes of their predecessors. Over the last several decades, the astrophysics community has developed a sophisticated theoretical picture of the evolution of these stars, but it remains an incomplete accounting of the rich set of observations. Using state of the art models of massive stars, I have investigated the internal processes taking place throughout the life-cycles of stars spanning those from the first generation ("Population III") to the present-day ("Population I"). I will argue that early-generation stars were not highly unstable to perturbations, contrary to a host of past investigations, if a correct accounting is made for the viscous effect of convection. For later generations, those with near solar metallicity, I find that this very same convection may excite gravity-mode oscillations that produce observable brightness variations at the stellar surface when the stars are near the main sequence. If confirmed with modern high-precision monitoring experiments, like Kepler and CoRoT, the properties of observed gravity modes in massive stars could provide a direct probe of the poorly constrained physics of gravity mode excitation by convection. Finally, jumping forward in stellar evolutionary time, I propose and explore an entirely new mechanism to explain the giant eruptions observed and inferred to occur during the final phases of massive stellar evolution. This mechanism taps into the vast nuclear fusion luminosity, and accompanying convective luminosity, in the stellar core to excite waves capable of carrying a super-Eddington luminosity out to the stellar envelope. This energy transfer from the core to the envelope has the potential to unbind a significant amount of mass in close proximity to a star's eventual explosion as a core collapse supernova.

Two-color vibrational, femtosecond, fully resonant electronically enhanced CARS (FREE-CARS) of gas-phase nitric oxide.

PubMed

Stauffer, Hans U; Roy, Sukesh; Schmidt, Jacob B; Wrzesinski, Paul J; Gord, James R

2016-09-28

A resonantly enhanced, two-color, femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) approach is demonstrated and used to explore the nature of the frequency- and time-dependent signals produced by gas-phase nitric oxide (NO). Through careful selection of the input pulse wavelengths, this fully resonant electronically enhanced CARS (FREE-CARS) scheme allows rovibronic-state-resolved observation of time-dependent rovibrational wavepackets propagating on the vibrationally excited ground-state potential energy surface of this diatomic species. Despite the use of broadband, ultrafast time-resolved input pulses, high spectral resolution of gas-phase rovibronic transitions is observed in the FREE-CARS signal, dictated by the electronic dephasing timescales of these states. Analysis and computational simulation of the time-dependent spectra observed as a function of pump-Stokes and Stokes-probe delays provide insight into the rotationally resolved wavepacket motion observed on the excited-state and vibrationally excited ground-state potential energy surfaces of NO, respectively.

Pulsed photoacoustic detection of flash-induced oxygen evolution from intact leaves and its oscillations

PubMed Central

Canaani, Ora; Malkin, Shmuel; Mauzerall, David

1988-01-01

Photoacoustic signals from intact leaves, produced upon excitation with single-turnover flashes, were shown to be dependent on their position in the flash sequence. Compared to the signal obtained from the first flash, all the others were time-shifted and had increased amplitudes. The signal from the third flash had the largest deviation, whereas that from the second flash deviated only minimally. The amplitude difference of the signals relative to that from the first flash was measured at a convenient time point (5 ms) and showed oscillations of period 4, similar to the O2-evolution pattern from algae. These oscillations were strongly damped, tending to a steady state from about the seventh flash on. The extra photoacoustic signal (relative to the first flash) was shown to be inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, heat treatment, or water infiltration. Its change with flash number, its saturation with increasing flash energy, and the above inhibition criteria indicate that it originates in pulsed O2 evolution. The sound wave produced by the first flash, however, arose by a photothermal mechanism only, as shown by its linear dependence on the flash intensity and insensitivity to the above treatments. The above flash pattern demonstrates that the photocycle of the S states (i.e., positive charge accumulation before two water molecules can be oxidized in a concerted way to produce molecular oxygen) occurs in intact leaves. It proves the applicability of the photoacoustic method for mechanistic studies of O2 evolution in leaves under physiological conditions. Water content of leaves is readily measured by this method. Images PMID:16593952

Autoresonant excitation of Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Batalov, S. V.; Shagalov, A. G.; Friedland, L.

2018-03-01

Controlling the state of a Bose-Einstein condensate driven by a chirped frequency perturbation in a one-dimensional anharmonic trapping potential is discussed. By identifying four characteristic time scales in this chirped-driven problem, three dimensionless parameters P1 ,2 ,3 are defined describing the driving strength, the anharmonicity of the trapping potential, and the strength of the particles interaction, respectively. As the driving frequency passes the linear resonance in the problem, and depending on the location in the P1 ,2 ,3 parameter space, the system may exhibit two very different evolutions, i.e., the quantum energy ladder climbing (LC) and the classical autoresonance (AR). These regimes are analyzed both in theory and simulations with the emphasis on the effect of the interaction parameter P3. In particular, the transition thresholds on the driving parameter P1 and their width in P1 in both the AR and LC regimes are discussed. Different driving protocols are also illustrated, showing efficient control of excitation and deexcitation of the condensate.

Characterization of High-Frequency Excitation of a Wake by Simulation

NASA Technical Reports Server (NTRS)

Cain, Alan B.; Rogers, Michael M.; Kibens, Valdis; Mansour, Nagi (Technical Monitor)

2003-01-01

Insights into the effects of high-frequency forcing on free shear layer evolution are gained through analysis of several direct numerical simulations. High-frequency forcing of a fully turbulent plane wake results in only a weak transient effect. On the other hand, significant changes in the developed turbulent state may result when high-frequency forcing is applied to a transitional wake. The impacts of varying the characteristics of the high-frequency forcing are examined, particularly, the streamwise wavenumber band in which forcing is applied and the initial amplitude of the forcing. The high-frequency excitation is found to increase the dissipation rate of turbulent kinetic energy, to reduce the turbulent kinetic energy production rate, and to reduce the turbulent kinetic energy suppression increases with forcing amplitude once a threshold level has been reached. For a given initial forcing energy, the largest reduction in turbulent kinetic energy density was achieved by forcing wavenumbers that are about two to three times the neutral wavenumber determined from linear stability theory.

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

Zhang, Hailong; Vibration Control Lab, School of Electrical and Automation Engineering, Nanjing Normal University, Nanjing 210042; Zhang, Ning

Magneto-rheological (MR) damper possesses inherent hysteretic characteristics. We investigate the resulting nonlinear behaviors of a two degree-of-freedom (2-DoF) MR vibration isolation system under harmonic external excitation. A MR damper is identified by employing the modified Bouc-wen hysteresis model. By numerical simulation, we characterize the nonlinear dynamic evolution of period-doubling, saddle node bifurcating and inverse period-doubling using bifurcation diagrams of variations in frequency with a fixed amplitude of the harmonic excitation. The strength of chaos is determined by the Lyapunov exponent (LE) spectrum. Semi-physical experiment on the 2-DoF MR vibration isolation system is proposed. We trace the time history and phasemore » trajectory under certain values of frequency of the harmonic excitation to verify the nonlinear dynamical evolution of period-doubling bifurcations to chaos. The largest LEs computed with the experimental data are also presented, confirming the chaotic motion in the experiment. We validate the chaotic motion caused by the hysteresis of the MR damper, and show the transitions between distinct regimes of stable motion and chaotic motion of the 2-DoF MR vibration isolation system for variations in frequency of external excitation.« less

Ultrafast Excited-State Dynamics of Cytosine Aza-Derivative and Analogues.

PubMed

Zhou, Zhongneng; Zhou, Xueyao; Wang, Xueli; Jiang, Bin; Li, Yongle; Chen, Jinquan; Xu, Jianhua

2017-04-13

Excited state dynamics of 5-azacytosine (5-AC), 2,4-diamino-1,3,5-triazine (2,4-DT), and 2-amino-1,3,5-triazine (2-AT) were comprehensively investigated by steady state absorption, fluorescence, and femtosecond transient absorption measurements. Time-dependent density functional theory (TDDFT) calculations were performed to help assign the absorption bands and understand the excited state decay mechanisms. The experimental results of excited singlet state dynamics for 5-AC, 2,4-DT, and 2-AT with femtosecond time resolution were reported for the first time. Two distinct decay pathways, with ∼1 ps and tens of picosecond lifetimes, were observed in 5-AC. Only one decay pathway with 17 ps lifetime was observed in 2,4-DT while an emissive state was found in 2-AT. TDDFT calculations suggest that 5-AC has a dark nπ* (S 1 ) state below the first allowed ππ* (S 2 ) state, which leads to the ultrafast decay of the ππ* state. In 2,4-DT, there is no dark nπ* state below the bright ππ* (S 1 ) state and the 17 ps lifetime is assigned to the relaxation from the ππ* (S 1 ) state to ground state. Two dark nπ* states (S 1 and S 2 ) were found in 2-AT, which exhibits much more complex excited state dynamics compared with the other two. Photoluminescence in 2-AT has been confirmed to be fluorescence emission from its bright ππ* (S 3 ) state. Our results strongly suggest that electronic structures are very sensitive to the substitution on the triazine ring and that the photophysical properties of nucleic acid analogues depend highly on their molecular structures.

Ultrafast formation of the benzoic acid triplet upon ultraviolet photolysis and its sequential photodissociation in solution

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

Yang Chunfan; Su Hongmei; Sun Xuezhong

2012-05-28

Time-resolved infrared (TR-IR) absorption spectroscopy in both the femtosecond and nanosecond time domain has been applied to examine the photolysis of benzoic acid in acetonitrile solution following either 267 nm or 193 nm excitation. By combining the ultrafast and nanosecond TR-IR measurements, both the excited states and the photofragments have been detected and key mechanistic insights were obtained. We show that the solvent interaction modifies the excited state relaxation pathways and thus the population dynamics, leading to different photolysis behavior in solution from that observed in the gas phase. Vibrational energy transfer to solvents dissipates excitation energy efficiently, suppressing themore » photodissociation and depopulating the excited S{sub 2} or S{sub 3} state molecules to the lowest T{sub 1} state with a rate of {approx}2.5 ps after a delayed onset of {approx}3.7 ps. Photolysis of benzoic acid using 267 nm excitation is dominated by the formation of the T{sub 1} excited state and no photofragments could be detected. The results from TR-IR experiments using higher energy of 193 nm indicate that photodissociation proceeds more rapidly than the vibrational energy transfer to solvents and C-C bond fission becomes the dominant relaxation pathway in these experiments as featured by the prominent observation of the COOH photofragments and negligible yield of the T{sub 1} excited state. The measured ultrafast formation of T{sub 1} excited state supports the existence of the surface intersections of S{sub 2}/S{sub 1}, S{sub 2}/T{sub 2}, and S{sub 1}/T{sub 1}/T{sub 2}, and the large T{sub 1} quantum yield of {approx}0.65 indicates the importance of the excited state depopulation to triplet manifold as the key factor affecting the photophysical and photochemical behavior of the monomeric benzoic acid.« less

The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

NASA Astrophysics Data System (ADS)

Song, Yin; Hellmann, Christoph; Stingelin, Natalie; Scholes, Gregory D.

2015-06-01

Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets ( S ( λ 1 , T ˜ 2 , λ 3 ) ) along the population time ( T ˜ 2 ) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps ( S ( λ 1 , ν ˜ 2 , λ 3 ) ). We found that the vibrational coherence from pure excited electronic states appears at positive frequency ( + ν ˜ 2 ) in the rephasing beating map and at negative frequency ( - ν ˜ 2 ) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.

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.

Trapping Dynamics in Photosystem I-Light Harvesting Complex I of Higher Plants Is Governed by the Competition Between Excited State Diffusion from Low Energy States and Photochemical Charge Separation.

PubMed

Molotokaite, Egle; Remelli, William; Casazza, Anna Paola; Zucchelli, Giuseppe; Polli, Dario; Cerullo, Giulio; Santabarbara, Stefano

2017-10-26

The dynamics of excited state equilibration and primary photochemical trapping have been investigated in the photosystem I-light harvesting complex I isolated from spinach, by the complementary time-resolved fluorescence and transient absorption approaches. The combined analysis of the experimental data indicates that the excited state decay is described by lifetimes in the ranges of 12-16 ps, 32-36 ps, and 64-77 ps, for both detection methods, whereas faster components, having lifetimes of 550-780 fs and 4.2-5.2 ps, are resolved only by transient absorption. A unified model capable of describing both the fluorescence and the absorption dynamics has been developed. From this model it appears that the majority of excited state equilibration between the bulk of the antenna pigments and the reaction center occurs in less than 2 ps, that the primary charge separated state is populated in ∼4 ps, and that the charge stabilization by electron transfer is completed in ∼70 ps. Energy equilibration dynamics associated with the long wavelength absorbing/emitting forms harbored by the PSI external antenna are also characterized by a time mean lifetime of ∼75 ps, thus overlapping with radical pair charge stabilization reactions. Even in the presence of a kinetic bottleneck for energy equilibration, the excited state dynamics are shown to be principally trap-limited. However, direct excitation of the low energy chlorophyll forms is predicted to lengthen significantly (∼2-folds) the average trapping time.

X-ray spectroscopy studies of nonradiative energy transfer processes in luminescent lanthanide materials

NASA Astrophysics Data System (ADS)

Pacold, Joseph I.

Luminescent materials play important roles in energy sciences, through solid state lighting and possible applications in solar energy utilization, and in biomedical research and applications, such as in immunoassays and fluorescence microscopy. The initial excitation of a luminescent material leads to a sequence of transitions between excited states, ideally ending with the emission of one or more optical-wavelength photons. It is essential to understand the microscopic physics of this excited state cascade in order to rationally design materials with high quantum efficiencies or with other fine-tuning of materials response. While optical-wavelength spectroscopies have unraveled many details of the energy transfer pathways in luminescent materials, significant questions remain open for many lanthanide-based luminescent materials. For organometallic dyes in particular, quantum yields remain limited in comparison with inorganic phosphors. This dissertation reports on a research program of synchrotron x-ray studies of the excited state electronic structure and energy-relaxation cascade in trivalent lanthanide phosphors and dyes. To this end, one of the primary results presented here is the first time-resolved x-ray absorption near edge spectroscopy studies of the transient 4f excited states in lanthanide-activated luminescent dyes and phosphors. This is a new application of time-resolved x-ray absorption spectroscopy that makes it possible to directly observe and, to some extent, quantify intramolecular nonradiative energy transfer processes. We find a transient increase in 4f spectral weight associated with an excited state confined to the 4f shell of trivalent Eu. This result implies that it is necessary to revise the current theoretical understanding of 4f excitation in trivalent lanthanide activators: either transient 4f-5d mixing effects are much stronger than previously considered, or else the lanthanide 4f excited state has an unexpectedly large contribution having a strong charge-transfer character. A second primary result comes from an an x-ray excited optical luminescence (XEOL) study that demonstrates, for the first time, that the high flux of modern synchrotron light sources can induce high fractional populations of excited states in trivalent lanthanide phosphors. In this work we have identified the leading-order nonlinear-response mechanism by drawing on strong similarities between XEOL and cathodoluminescence. These results establish the groundwork for studies that would allow deeper inquiry into energy-transfer mechanisms through time-resolved x-ray pump/optical-probe spectroscopies, through time-resolved x-ray emission spectroscopy, or through quantifying of higher-order nonlinear effects at further-enhanced fractional excitation levels. The above scientific results are augmented by a supporting effort in instrumental methodology. This includes the development of high-efficiency x-ray emission spectrometers and their use in collaborations to study pressure-induced changes in f-electron physics and to characterize the intermediate states that occur after photoexcitation of the photosystem-II protein.

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.

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

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.

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.

Temperature peaking at beginning of breakdown in 2.45 GHz pulsed off-resonance electron cyclotron resonance ion source hydrogen plasma

NASA Astrophysics Data System (ADS)

Cortázar, O. D.; Megía-Macías, A.; Vizcaíno-de-Julián, A.

2012-10-01

An experimental study of temperature and density evolution during breakdown in off-resonance ECR hydrogen plasma is presented. Under square 2.45 GHz microwave excitation pulses with a frequency of 50 Hz and relative high microwave power, unexpected transient temperature peaks that reach 18 eV during 20 μs are reported at very beginning of plasma breakdown. Decays of such peaks reach final stable temperatures of 5 eV at flat top microwave excitation pulse. Evidence of interplay between incoming power and duty cycle giving different kind of plasma parameters evolutions engaged to microwave coupling times is observed. Under relative high power conditions where short microwave coupling times are recorded, high temperature peaks are measured. However, for lower incoming powers and longer coupling times, temperature evolves gradually to a higher final temperature without peaking. On the other hand, the early instant where temperature peaks are observed also suggest a possible connection with preglow processes during breakdown in ECRIS plasmas.

Strong-Field Control of Laser Filamentation Mechanisms

NASA Astrophysics Data System (ADS)

Levis, Robert; Romanov, Dmitri; Filin, Aleskey; Compton, Ryan

2008-05-01

The propagation of short strong-file laser pulses in gas and solution phases often result in formation of filaments. This phenomenon involves many nonlinear processes including Kerr lensing, group velocity dispersion, multi-photon ionization, plasma defocusing, intensity clamping, and self-steepening. Of these, formation and dynamics of pencil-shape plasma areas plays a crucial role. The fundamental understanding of these laser-induced plasmas requires additional effort, because the process is highly nonlinear and complex. We studied the ultrafast laser-generated plasma dynamics both experimentally and theoretically. Ultrafast plasma dynamics was probed using Coherent Anti-Stokes Raman Scattering. The measurements were made in a room temperature gas maintained at 1 atm in a flowing cell. The time dependent scattering was measured by delaying the CARS probe with respect to the intense laser excitation pulse. A general trend is observed between the spacing of the ground state and the first allowed excited state with the rise time for the noble gas series and the molecular gases. This trend is consistent with our theoretical model, which considers the ultrafast dynamics of the strong field generated plasma as a three-step process; (i) strong-field ionization followed by the electron gaining considerable kinetic energy during the pulse; (ii) immediate post-pulse dynamics: fast thermalization, impact-ionization-driven electron multiplication and cooling; (iii) ensuing relaxation: evolution to electron-ion equilibrium and eventual recombination.

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

Analytical excited state forces for the time-dependent density-functional tight-binding method.

PubMed

Heringer, D; Niehaus, T A; Wanko, M; Frauenheim, Th

2007-12-01

An analytical formulation for the geometrical derivatives of excitation energies within the time-dependent density-functional tight-binding (TD-DFTB) method is presented. The derivation is based on the auxiliary functional approach proposed in [Furche and Ahlrichs, J Chem Phys 2002, 117, 7433]. To validate the quality of the potential energy surfaces provided by the method, adiabatic excitation energies, excited state geometries, and harmonic vibrational frequencies were calculated for a test set of molecules in excited states of different symmetry and multiplicity. According to the results, the TD-DFTB scheme surpasses the performance of configuration interaction singles and the random phase approximation but has a lower quality than ab initio time-dependent density-functional theory. As a consequence of the special form of the approximations made in TD-DFTB, the scaling exponent of the method can be reduced to three, similar to the ground state. The low scaling prefactor and the satisfactory accuracy of the method makes TD-DFTB especially suitable for molecular dynamics simulations of dozens of atoms as well as for the computation of luminescence spectra of systems containing hundreds of atoms. (c) 2007 Wiley Periodicals, Inc.

Application of the Real-Time Time-Dependent Density Functional Theory to Excited-State Dynamics of Molecules and 2D Materials

NASA Astrophysics Data System (ADS)

Miyamoto, Yoshiyuki; Rubio, Angel

2018-04-01

We review our recent developments in the ab initio simulation of excited-state dynamics within the framework of time-dependent density functional theory (TDDFT). Our targets range from molecules to 2D materials, although the methods are general and can be applied to any other finite and periodic systems. We discuss examples of excited-state dynamics obtained by real-time TDDFT coupled with molecular dynamics (MD) and the Ehrenfest approximation, including photoisomerization in molecules, photoenhancement of the weak interatomic attraction of noble gas atoms, photoenhancement of the weak interlayer interaction of 2D materials, pulse-laser-induced local bond breaking of adsorbed atoms on 2D sheets, modulation of UV light intensity by graphene nanoribbons at terahertz frequencies, and collision of high-speed ions with the 2D material to simulate the images taken by He ion microscopy. We illustrate how the real-time TDDFT approach is useful for predicting and understanding non-equilibrium dynamics in condensed matter. We also discuss recent developments that address the excited-state dynamics of systems out of equilibrium and future challenges in this fascinating field of research.

The signatures of the parental cluster on field planetary systems

NASA Astrophysics Data System (ADS)

Cai, Maxwell Xu; Portegies Zwart, Simon; van Elteren, Arjen

2018-03-01

Due to the high stellar densities in young clusters, planetary systems formed in these environments are likely to have experienced perturbations from encounters with other stars. We carry out direct N-body simulations of multiplanet systems in star clusters to study the combined effects of stellar encounters and internal planetary dynamics. These planetary systems eventually become part of the Galactic field population as the parental cluster dissolves, which is where most presently known exoplanets are observed. We show that perturbations induced by stellar encounters lead to distinct signatures in the field planetary systems, most prominently, the excited orbital inclinations and eccentricities. Planetary systems that form within the cluster's half-mass radius are more prone to such perturbations. The orbital elements are most strongly excited in the outermost orbit, but the effect propagates to the entire planetary system through secular evolution. Planet ejections may occur long after a stellar encounter. The surviving planets in these reduced systems tend to have, on average, higher inclinations and larger eccentricities compared to systems that were perturbed less strongly. As soon as the parental star cluster dissolves, external perturbations stop affecting the escaped planetary systems, and further evolution proceeds on a relaxation time-scale. The outer regions of these ejected planetary systems tend to relax so slowly that their state carries the memory of their last strong encounter in the star cluster. Regardless of the stellar density, we observe a robust anticorrelation between multiplicity and mean inclination/eccentricity. We speculate that the `Kepler dichotomy' observed in field planetary systems is a natural consequence of their early evolution in the parental cluster.

Highly excited and exotic meson spectrum from dynamical lattice QCD.

PubMed

Dudek, Jozef J; Edwards, Robert G; Peardon, Michael J; Richards, David G; Thomas, Christopher E

2009-12-31

Using a new quark-field construction algorithm and a large variational basis of operators, we extract a highly excited isovector meson spectrum on dynamical anisotropic lattices. We show how carefully constructed operators can be used to reliably identify the continuum spin of extracted states, overcoming the reduced cubic symmetry of the lattice. Using this method we extract, with confidence, excited states, states with exotic quantum numbers (0+-, 1-+, and 2+-), and states of high spin, including, for the first time in lattice QCD, spin-four states.

Fluorescence Spectroscopic Properties of Normal and Abnormal Biomedical Materials

NASA Astrophysics Data System (ADS)

Pradhan, Asima

Steady state and time-resolved optical spectroscopy and native fluorescence is used to study the physical and optical properties occurring in diseased and non-diseased biological human tissue, in particular, cancer of the human breast, artery and the dynamics of a photosensitizer useful in photodynamic therapy. The main focus of the research is on the optical properties of cancer and atherosclerotic tissues as compared to their normal counterparts using the different luminescence based spectroscopic techniques such as steady state fluorescence, time-resolved fluorescence, excitation spectroscopy and phosphorescence. The excitation and steady-state spectroscopic fluorescence using visible excitation wavelength displays a difference between normal and malignant tissues. This difference is attributed to absorption of the emission by hemoglobin in normal tissues. This method using 488nm fails to distinguish neoplastic tissue such as benign tissues and tumors from malignant tumors. The time-resolved fluorescence at visible, near -uv and uv excitation wavelengths display non-exponential profiles which are significantly different for malignant tumors as compared to non-malignant tissues only with uv excitation. The differences observed with visible and near-uv excitation wavelengths are not as significant. The non-exponential profiles are interpreted as due to a combination of fluorophores along with the action of non-radiative processes. Low temperature luminescence studies confirm the occurrence of non-radiative decay processes while temporal studies of various relevant biomolecules indicate the probable fluorophores responsible for the observed signal in tissues. Phosphorescence from human tissues have been observed for the first time and lifetimes of a few hundred nanoseconds are measured for malignant and benign tissues. Time-resolved fluorescence studies of normal artery and atherosclerotic plaque have shown that a combination of two excitation wavelengths can distinguish fibrous and calcified atherosclerotic plaque from normal artery. A minor effort of the study involves the high intensity effects on the optical properties of the dye, doxycycline (a particular photosensitizer of the tetracycline group) occurring during relaxation when excited at different laser intensities. This study has been performed by observing the fluorescence lifetimes and quantum yields of DOTC at different excitation intensities. The results obtained support the sequential excited state absorption model.

Probing Thermomechanics at the Nanoscale: Impulsively Excited Pseudosurface Acoustic Waves in Hypersonic Phononic Crystals

PubMed Central

2011-01-01

High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system’s initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system’s excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths. PMID:21910426

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.

Ultrafast time-resolved pump-probe spectroscopy of PYP by a sub-8 fs pulse laser at 400 nm.

PubMed

Liu, Jun; Yabushita, Atsushi; Taniguchi, Seiji; Chosrowjan, Haik; Imamoto, Yasushi; Sueda, Keiichi; Miyanaga, Noriaki; Kobayashi, Takayoshi

2013-05-02

Impulsive excitation of molecular vibration is known to induce wave packets in both the ground state and excited state. Here, the ultrafast dynamics of PYP was studied by pump-probe spectroscopy using a sub-8 fs pulse laser at 400 nm. The broadband spectrum of the UV pulse allowed us to detect the pump-probe signal covering 360-440 nm. The dependence of the vibrational phase of the vibrational mode around 1155 cm(-1) on the probe photon energy was observed for the first time to our knowledge. The vibrational mode coupled to the electronic transition observed in the probe spectral ranges of 2.95-3.05 and 3.15-3.35 eV was attributed to the wave packets in the ground state and the excited state, respectively. The frequencies in the ground state and excited state were determined to be 1155 ± 1 and 1149 ± 1 cm(-1), respectively. The frequency difference is due to change after photoexcitation. This means a reduction of the bond strength associated with π-π* excitation, which is related to the molecular structure change associated with the primary isomerization process in the photocycle in PYP. Real-time vibrational modes at low frequency around 138, 179, 203, 260, and 317 cm(-1) were also observed and compared with the Raman spectrum for the assignment of the vibrational wave packet.

Pump-shaped dump optimal control reveals the nuclear reaction pathway of isomerization of a photoexcited cyanine dye.

PubMed

Dietzek, Benjamin; Brüggemann, Ben; Pascher, Torbjörn; Yartsev, Arkady

2007-10-31

Using optimal control as a spectroscopic tool we decipher the details of the molecular dynamics of the essential multidimensional excited-state photoisomerization - a fundamental chemical reaction of key importance in biology. Two distinct nuclear motions are identified in addition to the overall bond-twisting motion: Initially, the reaction is dominated by motion perpendicular to the torsion coordinate. At later times, a second optically active vibration drives the system along the reaction path to the bottom of the excited-state potential. The time scales of the wavepacket motion on a different part of the excited-state potential are detailed by pump-shaped dump optimal control. This technique offers new means to control a chemical reaction far from the Franck-Condon point of absorption and to map details of excited-state reaction pathways revealing unique insights into the underlying reaction mechanism.

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.

Low-lying excited states by constrained DFT.

PubMed

Ramos, Pablo; Pavanello, Michele

2018-04-14

Exploiting the machinery of Constrained Density Functional Theory (CDFT), we propose a variational method for calculating low-lying excited states of molecular systems. We dub this method eXcited CDFT (XCDFT). Excited states are obtained by self-consistently constraining a user-defined population of electrons, N c , in the virtual space of a reference set of occupied orbitals. By imposing this population to be N c = 1.0, we computed the first excited state of 15 molecules from a test set. Our results show that XCDFT achieves an accuracy in the predicted excitation energy only slightly worse than linear-response time-dependent DFT (TDDFT), but without incurring into problems of variational collapse typical of the more commonly adopted ΔSCF method. In addition, we selected a few challenging processes to test the limits of applicability of XCDFT. We find that in contrast to TDDFT, XCDFT is capable of reproducing energy surfaces featuring conical intersections (azobenzene and H 3 ) with correct topology and correct overall energetics also away from the intersection. Venturing to condensed-phase systems, XCDFT reproduces the TDDFT solvatochromic shift of benzaldehyde when it is embedded by a cluster of water molecules. Thus, we find XCDFT to be a competitive method among single-reference methods for computations of excited states in terms of time to solution, rate of convergence, and accuracy of the result.

Fundamental molecules of life are pigments which arose and evolved to dissipate the solar spectrum

NASA Astrophysics Data System (ADS)

Michaelian, K.; Simeonov, A.

2015-02-01

The driving force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate. In the upper atmosphere of today, oxygen and ozone derived from life processes are performing the short wavelength UVC and UVB dissipation. On Earth's surface, water and organic pigments in water facilitate the near UV and visible photon dissipation. The first organic pigments probably formed, absorbed, and dissipated at those photochemically active wavelengths in the UVC that could have reached Earth's surface during the Archean. Proliferation of these pigments can be understood as an autocatalytic photochemical process obeying non-equilibrium thermodynamic directives related to increasing solar photon dissipation rate. Under these directives, organic pigments would have evolved over time to increase the global photon dissipation rate by; (1) increasing the ratio of their effective photon cross sections to their physical size, (2) decreasing their electronic excited state life times, (3) quenching radiative de-excitation channels (e.g. fluorescence), (4) covering ever more completely the prevailing solar spectrum, and (5) proliferating and dispersing to cover an ever greater surface area of Earth. From knowledge of the evolution of the spectrum of G-type stars, and considering the most probable history of the transparency of Earth's atmosphere, we construct the most probable Earth surface solar spectrum as a function of time and compare this with the history of molecular absorption maxima obtained from the available data in the literature. This comparison supports the conjecture that many fundamental molecules of life are pigments which arose and evolved to dissipate the solar spectrum, supports the thermodynamic dissipation theory for the origin of life, constrains models for Earth's early atmosphere, and sheds some new light on the origin of photosynthesis.

Pure-phase selective excitation in fast-relaxing systems.

PubMed

Zangger, K; Oberer, M; Sterk, H

2001-09-01

Selective pulses have been used frequently for small molecules. However, their application to proteins and other macromolecules has been limited. The long duration of shaped-selective pulses and the short T(2) relaxation times in proteins often prohibited the use of highly selective pulses especially on larger biomolecules. A very selective excitation can be obtained within a short time by using the selective excitation sequence presented in this paper. Instead of using a shaped low-intensity radiofrequency pulse, a cluster of hard 90 degrees pulses, delays of free precession, and pulsed field gradients can be used to selectively excite a narrow chemical shift range within a relatively short time. Thereby, off-resonance magnetization, which is allowed to evolve freely during the free precession intervals, is destroyed by the gradient pulses. Off-resonance excitation artifacts can be removed by random variation of the interpulse delays. This leads to an excitation profile with selectivity as well as phase and relaxation behavior superior to that of commonly used shaped-selective pulses. Since the evolution of scalar coupling is inherently suppressed during the double-selective excitation of two different scalar-coupled nuclei, the presented pulse cluster is especially suited for simultaneous highly selective excitation of N-H and C-H fragments. Experimental examples are demonstrated on hen egg white lysozyme (14 kD) and the bacterial antidote ParD (19 kD). Copyright 2001 Academic Press.

Ultrafast Nonradiative Decay and Excitation Energy Transfer by Carotenoids in Photosynthetic Light-Harvesting Proteins

NASA Astrophysics Data System (ADS)

Ghosh, Soumen

This dissertation investigates the photophysical and structural dynamics that allow carotenoids to serve as efficient excitation energy transfer donor to chlorophyll acceptors in photosynthetic light harvesting proteins. Femtosecond transient grating spectroscopy with optical heterodyne detection has been employed to follow the nonradiative decay pathways of carotenoids and excitation energy transfer to chlorophylls. It was found that the optically prepared S2 (11Bu+) state of beta-carotene decays in 12 fs fs to populate an intermediate electronic state, Sx, which then decays nonradiatively to the S 1 state. The ultrafast rise of the dispersion component of the heterodyne transient grating signal reports the formation of Sx intermediate since the rise of the dispersion signal is controlled by the loss of stimulated emission from the S2 state. These findings were extended to studies of peridinin, a carbonyl substituted carotenoid that serves as a photosynthetic light-harvesting chromophore in dinoflagellates. Numerical simulations using nonlinear response formalism and the multimode Brownian oscillator model assigned the Sx intermediate to a torsionally distorted structure evolving on the S2 potential surface. The decay of the Sx state is promoted by large amplitude out-of-plane torsional motions and is significantly retarded by solvent friction owing to the development of an intramolecular charge transfer character in peridinin. The slowing of the nonradiative decay allows the Sx state to transfer significant portion of the excitation energy to chlorophyll a acceptors in the peridinin-chlorophyll a protein. The results of heterodyne transient grating study on peridinin-chlorophyll a protein suggests two distinct energy transfer channels from peridinin to chlorophyll a: a 30 fs process involving quantum coherence and delocalized peridinin-Chl states and an incoherent, 2.5 ps process involving the distorted S2 state of peridinin. The torsional evolution on the S2 state is accompanied by the formation of an ICT character and dynamic exciton localization, which controls the mechanism of excitation energy transfer to chlorophyll a acceptors in the peridinin-chlorophyll a protein.

Quantum versus classical dynamics in the optical centrifuge

NASA Astrophysics Data System (ADS)

Armon, Tsafrir; Friedland, Lazar

2017-09-01

The interplay between classical and quantum-mechanical evolution in the optical centrifuge (OC) is discussed. The analysis is based on the quantum-mechanical formalism starting from either the ground state or a thermal ensemble. Two resonant mechanisms are identified, i.e., the classical autoresonance and the quantum-mechanical ladder climbing, yielding different dynamics and rotational excitation efficiencies. The rotating-wave approximation is used to analyze the two resonant regimes in the associated dimensionless two-parameter space and calculate the OC excitation efficiency. The results show good agreement between numerical simulations and theory and are relevant to existing experimental setups.

New excitations in Ba 142 and Ce 144 : Evolution of γ bands in the N = 86 isotones

DOE PAGES

Naidja, H.; Nowacki, F.; Bounthong, B.; ...

2017-06-02

New excited states in 142Ba and 144Ce are investigated by means of prompt γ-ray spectroscopy of the radiation following spontaneous fission of 252Cf. Measurements of angular correlations and the observed branchings allowed the assignment of spins and parities with confidence. The new measurements are reinforced by shell-model calculations where energy levels, electric transitions, and magnetic moments are consistent with experimental data. Lastly, the presence of collectivity in the N = 86 isotones is confirmed by clear signatures of soft triaxial γ bands in both nuclei.

Existence of a new emitting singlet state of proflavine: femtosecond dynamics of the excited state processes and quantum chemical studies in different solvents.

PubMed

Kumar, Karuppannan Senthil; Selvaraju, Chellappan; Malar, Ezekiel Joy Padma; Natarajan, Paramasivam

2012-01-12

Proflavine (3,6-diaminoacridine) shows fluorescence emission with lifetime, 4.6 ± 0.2 ns, in all the solvents irrespective of the solvent polarity. To understand this unusual photophysical property, investigations were carried out using steady state and time-resolved fluorescence spectroscopy in the pico- and femtosecond time domain. Molecular geometries in the ground and low-lying excited states of proflavine were examined by complete structural optimization using ab initio quantum chemical computations at HF/6-311++G** and CIS/6-311++G** levels. Time dependent density functional theory (TDDFT) calculations were performed to study the excitation energies in the low-lying excited states. The steady state absorption and emission spectral details of proflavine are found to be influenced by solvents. The femtosecond fluorescence decay of the proflavine in all the solvents follows triexponential function with two ultrafast decay components (τ(1) and τ(2)) in addition to the nanosecond component. The ultrafast decay component, τ(1), is attributed to the solvation dynamics of the particular solvent used. The second ultrafast decay component, τ(2), is found to vary from 50 to 215 ps depending upon the solvent. The amplitudes of the ultrafast decay components vary with the wavelength and show time dependent spectral shift in the emission maximum. The observation is interpreted that the time dependent spectral shift is not only due to solvation dynamics but also due to the existence of more than one emitting state of proflavine in the solvent used. Time resolved area normalized emission spectral (TRANES) analysis shows an isoemissive point, indicating the presence of two emitting states in homogeneous solution. Detailed femtosecond fluorescence decay analysis allows us to isolate the two independent emitting components of the close lying singlet states. The CIS and TDDFT calculations also support the existence of the close lying emitting states. The near constant lifetime observed for proflavine in different solvents is suggested to be due to the similar dipole moments of the ground and the evolved emitting singlet state of the dye from the Franck-Condon excited state.

Identification of analog states in the T=1/2 A=27 mirror system from low excitation energies to the region of hydrogen burning in the {sup 26}Al{sup g,m}(p,{gamma}){sup 27}Si reactions

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

Lotay, G.; Woods, P. J.; Seweryniak, D.

2011-09-15

The reactions {sup 26}Al{sup g}(p, {gamma}){sup 27}Si and {sup 26}Al{sup m}(p, {gamma}){sup 27}Si are important for influencing the galactic abundance of the cosmic {gamma}-ray emitter {sup 26}Al{sup g} and for the excess abundance of {sup 26}Mg found in presolar grains, respectively. Precise excitation energies and spin assignments of states from the ground state to the region of astrophysical interest in {sup 27}Si, including the identification and pairing of key astrophysical resonances with analog states in the mirror nucleus {sup 27}Al, are reported using {gamma} rays observed in the {sup 12}C + {sup 16}O fusion reaction. The detailed evolution of Coulombmore » energy differences between the states in {sup 27}Si and {sup 27}Al is explored, including the region above the astrophysical reaction thresholds.« less

A cardiac electrical activity model based on a cellular automata system in comparison with neural network model.

PubMed

Khan, Muhammad Sadiq Ali; Yousuf, Sidrah

2016-03-01

Cardiac Electrical Activity is commonly distributed into three dimensions of Cardiac Tissue (Myocardium) and evolves with duration of time. The indicator of heart diseases can occur randomly at any time of a day. Heart rate, conduction and each electrical activity during cardiac cycle should be monitor non-invasively for the assessment of "Action Potential" (regular) and "Arrhythmia" (irregular) rhythms. Many heart diseases can easily be examined through Automata model like Cellular Automata concepts. This paper deals with the different states of cardiac rhythms using cellular automata with the comparison of neural network also provides fast and highly effective stimulation for the contraction of cardiac muscles on the Atria in the result of genesis of electrical spark or wave. The specific formulated model named as "States of automaton Proposed Model for CEA (Cardiac Electrical Activity)" by using Cellular Automata Methodology is commonly shows the three states of cardiac tissues conduction phenomena (i) Resting (Relax and Excitable state), (ii) ARP (Excited but Absolutely refractory Phase i.e. Excited but not able to excite neighboring cells) (iii) RRP (Excited but Relatively Refractory Phase i.e. Excited and able to excite neighboring cells). The result indicates most efficient modeling with few burden of computation and it is Action Potential during the pumping of blood in cardiac cycle.

Use of non-adiabatic geometric phase for quantum computing by NMR.

PubMed

Das, Ranabir; Kumar, S K Karthick; Kumar, Anil

2005-12-01

Geometric phases have stimulated researchers for its potential applications in many areas of science. One of them is fault-tolerant quantum computation. A preliminary requisite of quantum computation is the implementation of controlled dynamics of qubits. In controlled dynamics, one qubit undergoes coherent evolution and acquires appropriate phase, depending on the state of other qubits. If the evolution is geometric, then the phase acquired depend only on the geometry of the path executed, and is robust against certain types of error. This phenomenon leads to an inherently fault-tolerant quantum computation. Here we suggest a technique of using non-adiabatic geometric phase for quantum computation, using selective excitation. In a two-qubit system, we selectively evolve a suitable subsystem where the control qubit is in state |1, through a closed circuit. By this evolution, the target qubit gains a phase controlled by the state of the control qubit. Using the non-adiabatic geometric phase we demonstrate implementation of Deutsch-Jozsa algorithm and Grover's search algorithm in a two-qubit system.

A program to compute the two-step excitation of mesospheric sodium atoms for the Polychromatic Laser Guide Star Project

NASA Astrophysics Data System (ADS)

Bellanger, Véronique; Courcelle, Arnaud; Petit, Alain

2004-09-01

A program to compute the two-step excitation of sodium atoms ( 3S→3P→4D) using the density-matrix formalism is presented. The BEACON program calculates population evolution and the number of photons emitted by fluorescence from the 3P, 4D, 4P, 4S levels. Program summaryTitle of program: BEACON Catalogue identifier:ADSX Program Summary URL:http://cpc.cs.qub.ac.uk/cpc/summaries/ADSX Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: none Operating systems under which the program has been tested: Win; Unix Programming language used: FORTRAN 77 Memory required to execute with typical data: 1 Mw Number of bits in a word: 32 Number of processors used: 1 (a parallel version of this code is also available and can be obtained on request) Number of lines in distributed program, including test data, etc.: 29 287 Number of bytes in distributed program, including test data, etc.: 830 331 Distribution format: tar.gz CPC Program Library subprograms used: none Nature of physical problem: Resolution of the Bloch equations in the case of the two-step laser excitation of sodium atoms. Method of solution: The program BEACON calculates the evolution of level population versus time using the density-matrix formalism. The number of photons emitted from the 3P, 4D and 4P levels is calculated using the branching ratios and the level lifetimes. Restriction on the complexity of the problem: Since the backscatter emission is calculated after the excitation process, excitation with laser pulse duration longer than the 4D level lifetime cannot be rigorously treated. Particularly, cw laser excitation cannot be calculated with this code. Typical running time:12 h

Extreme ultraviolet probing of nonequilibrium dynamics in high energy density germanium

NASA Astrophysics Data System (ADS)

Principi, E.; Giangrisostomi, E.; Mincigrucci, R.; Beye, M.; Kurdi, G.; Cucini, R.; Gessini, A.; Bencivenga, F.; Masciovecchio, C.

2018-05-01

Intense femtosecond infrared laser pulses induce a nonequilibrium between thousands of Kelvin hot valence electrons and room-temperature ions in a germanium sample foil. The evolution of this exotic state of matter is monitored with time-resolved extreme ultraviolet absorption spectroscopy across the Ge M2 ,3 edge (≃30 eV ) using the FERMI free-electron laser. We analyze two distinct regimes in the ultrafast dynamics in laser-excited Ge: First, on a subpicosecond time scale, the electron energy distribution thermalizes to an extreme temperature unreachable in equilibrium solid germanium; then, during the following picoseconds, the lattice reacts strongly altering the electronic structure and resulting in melting to a metallic state alongside a breakdown of the local atomic order. Data analysis, based on a hybrid approach including both numerical and analytical calculations, provides an estimation of the electron and ion temperatures, the electron density of states, the carrier-phonon relaxation time, as well as the carrier density and lattice heat capacity under those extreme nonequilibrium conditions. Related structural anomalies, such as the occurrence of a transient low-density liquid phase and the possible drop in lattice heat capacity are discussed.

Exotic and excited-state radiative transitions in charmonium from lattice QCD

DOE PAGES

Dudek, Jozef J.; Edwards, Robert G.; Thomas, Christopher E.

2009-05-01

We compute, for the first time using lattice QCD methods, radiative transition rates involving excited charmonium states, states of high spin and exotics. Utilizing a large basis of interpolating fields we are able to project out various excited state contributions to three-point correlators computed on quenched anisotropic lattices. In the first lattice QCD calculation of the exoticmore » $$1^{-+}$$ $$\\eta_{c1}$$ radiative decay, we find a large partial width $$\\Gamma(\\eta_{c1} \\to J/\\psi \\gamma) \\sim 100 \\,\\mathrm{keV}$$. We find clear signals for electric dipole and magnetic quadrupole transition form factors in $$\\chi_{c2} \\to J/\\psi \\gamma$$, calculated for the first time in this framework, and study transitions involving excited $$\\psi$$ and $$\\chi_{c1,2}$$ states. We calculate hindered magnetic dipole transition widths without the sensitivity to assumptions made in model studies and find statistically significant signals, including a non-exotic vector hybrid candidate $Y_{\\mathrm{hyb?}} \\to \\et« less

Absorption Spectra and Photoreactivity of p-Aminobenzophenone by Time-dependent Density Functional Theory

NASA Astrophysics Data System (ADS)

Cheng, Xue-mei; Huang, Yao; Ma, Jian-yi; Li, Xiang-yuan

2007-06-01

The absorption spectral properties of para-aminobenzophenone (p-ABP) were investigated in gas phase and in solution by time-dependent density functional theory. Calculations suggest that the singlet states vary greatly with the solvent polarities. In various polar solvents, including acetonitrile, methanol, ethanol, dimethyl sulfoxide, and dimethyl formamide, the excited S1 states with charge transfer character result from π → π* transitions. However, in nonpolar solvents, cyclohexane, and benzene, the S1 states are the result of n → π* transitions related to local excitation in the carbonyl group. The excited T1 states were calculated to have ππ* character in various solvents. From the variation of the calculated excited states, the band due to π → π* transition undergoes a redshift with an increase in solvent polarity, while the band due to n → π* transition undergoes a blueshift with an increase in solvent polarity. In addition, the triplet yields and the photoreactivities of p-ABP in various solvents are discussed.

Model for spontaneous frequency sweeping of an Alfvén wave in a toroidal plasma

NASA Astrophysics Data System (ADS)

Wang, Ge; Berk, H. L.

2012-05-01

We study the frequency chirping signals arising from spontaneously excited toroidial Alfvén eigenmode (TAE) waves that are being driven by an inverted energetic particle distribution whose free energy is tapped from the generic particle/wave resonance interaction. Initially a wave is excited inside the Alfvén gap with a frequency determined from the linear tip model of Rosenbluth, Berk and Van dam (RBV) [1]. Hole/clumps structures are formed and are observed to chirp towards lower energy states. We find that the chirping signals from clump enter the Alfvén continuum which eventually produce more rapid chirping signals. The accuracy of the adiabatic approximation for the mode evolution is tested and verified by demonstrating that a WKB-like decomposition of the time response for the field phase and amplitude agree with the data. Plots of the phase space structure correlate well with the chirping dependent shape of the separatrix structure. A novel aspect of the simulation is that it performed close to the wave frame of the phase space structure, which enables the numerical time step to remain the same during the simulation, independent of the rest frame frequency.

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Ultrafast excited-state dynamics of RNA and DNA C tracts

NASA Astrophysics Data System (ADS)

Cohen, Boiko; Larson, Matthew H.; Kohler, Bern

2008-06-01

The excited-state dynamics of the RNA homopolymer of cytosine and of the 18-mer (dC) 18 were studied by steady-state and time-resolved absorption and emission spectroscopy. At pH 6.8, excitation of poly(rC) by a femtosecond UV pump pulse produces excited states that decay up to one order of magnitude more slowly than the excited states formed in the mononucleotide cytidine 5'-monophosphate under the same conditions. Even slower relaxation is observed for the hemiprotonated, self-associated form of poly(rC), which is stable at acidic pH. Transient absorption and time-resolved fluorescence signals for (dC) 18 at pH 6.8 are similar to ones observed for poly(rC) near pH 4, indicating that hemiprotonated structures are found in DNA C tracts at neutral pH. In both systems, there is evidence for two kinds of emitting states with lifetimes of ˜100 ps and slightly more than 1 ns. The former states are responsible for the bulk of emission from the hemiprotonated structures. Evidence suggests that slow electronic relaxation in these self-complexes is the result of vertical base stacking. The similar signals from RNA and DNA C tracts suggest a common base-stacked structure, which may be identical with that of i-motif DNA.

Giant spin gap and magnon localization in the disordered Heisenberg antiferromagnet Sr 2 Ir 1 - x Ru x O 4

DOE PAGES

Cao, Yue; Liu, X.; Xu, Wenhu; ...

2017-03-06

Here, we study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr 2Ir 1–xRuxO 4. The maximum energy of the magnetic excitation remains robust up to x = 0.77, with a gap opening at low dopings and increasing to over 150 meV at x = 0.77. At these higher Ru concentrations, the dispersive magnetic excitations in Sr 2IrO 4 are rendered essentially momentum independent. Up to a Ru concentration of x = 0.77, both experiments and first-principles calculations show the Ir J eff = 1/2 state remains intact. The magnetic gap arises from the local interaction anisotropy inmore » the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest-neighbor ferromagnetic coupling.« less

LAD Dissertation Prize Talk: Molecular Collisional Excitation in Astrophysical Environments

NASA Astrophysics Data System (ADS)

Walker, Kyle M.

2017-06-01

While molecular excitation calculations are vital in determining particle velocity distributions, internal state distributions, abundances, and ionization balance in gaseous environments, both theoretical calculations and experimental data for these processes are lacking. Reliable molecular collisional data with the most abundant species - H2, H, He, and electrons - are needed to probe material in astrophysical environments such as nebulae, molecular clouds, comets, and planetary atmospheres. However, excitation calculations with the main collider, H2, are computationally expensive and therefore various approximations are used to obtain unknown rate coefficients. The widely-accepted collider-mass scaling approach is flawed, and alternate scaling techniques based on physical and mathematical principles are presented here. The most up-to-date excitation data are used to model the chemical evolution of primordial species in the Recombination Era and produce accurate non-thermal spectra of the molecules H2+, HD, and H2 in a primordial cloud as it collapses into a first generation star.

Giant spin gap and magnon localization in the disordered Heisenberg antiferromagnet Sr2Ir1 -xRuxO4

NASA Astrophysics Data System (ADS)

Cao, Yue; Liu, X.; Xu, Wenhu; Yin, Wei-Guo; Meyers, D.; Kim, Jungho; Casa, Diego; Upton, M. H.; Gog, Thomas; Berlijn, Tom; Alvarez, Gonzalo; Yuan, Shujuan; Terzic, Jasminka; Tranquada, J. M.; Hill, John P.; Cao, Gang; Konik, Robert M.; Dean, M. P. M.

2017-03-01

We study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr2Ir1 -xRuxO4 . The maximum energy of the magnetic excitation remains robust up to x =0.77 , with a gap opening at low dopings and increasing to over 150 meV at x =0.77 . At these higher Ru concentrations, the dispersive magnetic excitations in Sr2IrO4 are rendered essentially momentum independent. Up to a Ru concentration of x =0.77 , both experiments and first-principles calculations show the Ir Jeff=1 /2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest-neighbor ferromagnetic coupling.

Direct time-domain observation of attosecond final-state lifetimes in photoemission from solids

DOE PAGES

Tao, Z.; Chen, C.; Szilvasi, T.; ...

2016-06-01

Attosecond spectroscopic techniques have made it possible to measure differences in transport times for photoelectrons from localized core levels and delocalized valence bands in solids. Here, we report the application of attosecond pulse trains to directly and unambiguously measure the difference in lifetimes between photoelectrons born into free electron–like states and those excited into unoccupied excited states in the band structure of nickel (111). An enormous increase in lifetime of 212 ± 30 attoseconds occurs when the final state coincides with a short-lived excited state. Moreover, a strong dependence of this lifetime on emission angle is directly related to themore » final-state band dispersion as a function of electron transverse momentum. Our finding underscores the importance of the material band structure in determining photoelectron lifetimes and corresponding electron escape depths.« less

Femtosecond Study of Self-Trapped Vibrational Excitons in Crystalline Acetanilide

NASA Astrophysics Data System (ADS)

Edler, J.; Hamm, P.; Scott, A. C.

2002-02-01

Femtosecond IR spectroscopy of delocalized NH excitations of crystalline acetanilide confirms that self-trapping in hydrogen-bonded peptide units exists and does stabilize the excitation. Two phonons with frequencies of 48 and 76 cm -1 are identified as the major degrees of freedom that mediate self-trapping. After selective excitation of the free exciton, self-trapping occurs within a few 100 fs. Excitation of the self-trapped states disappears from the spectral window of this investigation on a 1 ps time scale, followed by a slow ground state recovery of the hot ground state within 18 ps.

Femtosecond study of self-trapped vibrational excitons in crystalline acetanilide.

PubMed

Edler, J; Hamm, P; Scott, A C

2002-02-11

Femtosecond IR spectroscopy of delocalized NH excitations of crystalline acetanilide confirms that self-trapping in hydrogen-bonded peptide units exists and does stabilize the excitation. Two phonons with frequencies of 48 and 76 cm (-1) are identified as the major degrees of freedom that mediate self-trapping. After selective excitation of the free exciton, self-trapping occurs within a few 100 fs. Excitation of the self-trapped states disappears from the spectral window of this investigation on a 1 ps time scale, followed by a slow ground state recovery of the hot ground state within 18 ps.

Direct determination of resonance energy transfer in photolyase: structural alignment for the functional state.

PubMed

Tan, Chuang; Guo, Lijun; Ai, Yuejie; Li, Jiang; Wang, Lijuan; Sancar, Aziz; Luo, Yi; Zhong, Dongping

2014-11-13

Photoantenna is essential to energy transduction in photoinduced biological machinery. A photoenzyme, photolyase, has a light-harvesting pigment of methenyltetrahydrofolate (MTHF) that transfers its excitation energy to the catalytic flavin cofactor FADH¯ to enhance DNA-repair efficiency. Here we report our systematic characterization and direct determination of the ultrafast dynamics of resonance energy transfer from excited MTHF to three flavin redox states in E. coli photolyase by capturing the intermediates formed through the energy transfer and thus excluding the electron-transfer quenching pathway. We observed 170 ps for excitation energy transferring to the fully reduced hydroquinone FADH¯, 20 ps to the fully oxidized FAD, and 18 ps to the neutral semiquinone FADH(•), and the corresponding orientation factors (κ(2)) were determined to be 2.84, 1.53 and 1.26, respectively, perfectly matching with our calculated theoretical values. Thus, under physiological conditions and over the course of evolution, photolyase has adopted the optimized orientation of its photopigment to efficiently convert solar energy for repair of damaged DNA.

Nuclear Structure Studies in the 132Sn Region: Safe Coulex with Carbon Targets

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

Allmond, James M; Stuchbery, Andrew E; Galindo-Uribarri, Alfredo

2015-01-01

The collective and single-particle structure of nuclei in the 132Sn region was recently studied by Coulomb excitation and heavy-ion induced transfer reactions using carbon, beryllium, and titanium targets. In particular, Coulomb excitation was used determine a complete set of electromagnetic moments for the first 2 + states and one-neutron transfer was used to probe the purity and evolution of single-neutron states. These recent experiments were conducted at the Holifield Radioactive Ion Beam Facility at ORNL using a CsI-HPGe detector array (BareBall- CLARION) to detect scattered particles and emitted gamma rays from the in-beam reactions. A Bragg-curve detector was used tomore » measure the energy loss of the various beams through the targets and to measure the radioactive beam compositions. A sample of the Coulomb excitation results is presented here with an emphasis placed on 116Sn. In particular, the safe Coulex criterion for carbon targets will be analyzed and discussed.« less

Evolution of CO lines in time-dependent models of protostellar disk formation

NASA Astrophysics Data System (ADS)

Harsono, D.; Visser, R.; Bruderer, S.; van Dishoeck, E. F.; Kristensen, L. E.

2013-07-01

Context. Star and planet formation theories predict an evolution in the density, temperature, and velocity structure as the envelope collapses and forms an accretion disk. While continuum emission can trace the dust evolution, spectrally resolved molecular lines are needed to determine the physical structure and collapse dynamics. Aims: The aim of this work is to model the evolution of the molecular excitation, line profiles, and related observables during low-mass star formation. Specifically, the signatures of disks during the deeply embedded stage (Menv > M⋆) are investigated. Methods: The semi-analytic 2D axisymmetric model of Visser and collaborators has been used to describe the evolution of the density, stellar mass, and luminosity from the pre-stellar to the T-Tauri phase. A full radiative transfer calculation is carried out to accurately determine the time-dependent dust temperatures. The time-dependent CO abundance is obtained from the adsorption and thermal desorption chemistry. Non-LTE near-IR (NIR), far-IR (FIR), and submm lines of CO have been simulated at a number of time steps. Results: In single dish (10-20'' beams), the dynamics during the collapse are best probed through highly excited 13CO and C18O lines, which are significantly broadened by the infall process. In contrast to the dust temperature, the CO excitation temperature derived from submm/FIR data does not vary during the protostellar evolution, consistent with C18O observations obtained with Herschel and from ground-based telescopes. The NIR spectra provide complementary information to the submm lines by probing not only the cold outer envelope but also the warm inner region. The NIR high-J (≥8) absorption lines are particularly sensitive to the physical structure of the inner few AU, which does show evolution. The models indicate that observations of 13CO and C18O low-J submm lines within a ≤1″ (at 140 pc) beam are well suited to probe embedded disks in Stage I (Menv < M⋆) sources, consistent with recent interferometric observations. High signal-to-noise ratio subarcsec resolution data with ALMA are needed to detect the presence of small rotationally supported disks during the Stage 0 phase and various diagnostics are discussed. The combination of spatially and spectrally resolved lines with ALMA and at NIR is a powerful method to probe the inner envelope and disk formation process during the embedded phase. Appendices are available in electronic form at http://www.aanda.org

Rate and State Friction Relation for Nanoscale Contacts: Thermally Activated Prandtl-Tomlinson Model with Chemical Aging

NASA Astrophysics Data System (ADS)

Tian, Kaiwen; Goldsby, David L.; Carpick, Robert W.

2018-05-01

Rate and state friction (RSF) laws are widely used empirical relationships that describe macroscale to microscale frictional behavior. They entail a linear combination of the direct effect (the increase of friction with sliding velocity due to the reduced influence of thermal excitations) and the evolution effect (the change in friction with changes in contact "state," such as the real contact area or the degree of interfacial chemical bonds). Recent atomic force microscope (AFM) experiments and simulations found that nanoscale single-asperity amorphous silica-silica contacts exhibit logarithmic aging (increasing friction with time) over several decades of contact time, due to the formation of interfacial chemical bonds. Here we establish a physically based RSF relation for such contacts by combining the thermally activated Prandtl-Tomlinson (PTT) model with an evolution effect based on the physics of chemical aging. This thermally activated Prandtl-Tomlinson model with chemical aging (PTTCA), like the PTT model, uses the loading point velocity for describing the direct effect, not the tip velocity (as in conventional RSF laws). Also, in the PTTCA model, the combination of the evolution and direct effects may be nonlinear. We present AFM data consistent with the PTTCA model whereby in aging tests, for a given hold time, static friction increases with the logarithm of the loading point velocity. Kinetic friction also increases with the logarithm of the loading point velocity at sufficiently high velocities, but at a different increasing rate. The discrepancy between the rates of increase of static and kinetic friction with velocity arises from the fact that appreciable aging during static contact changes the energy landscape. Our approach extends the PTT model, originally used for crystalline substrates, to amorphous materials. It also establishes how conventional RSF laws can be modified for nanoscale single-asperity contacts to provide a physically based friction relation for nanoscale contacts that exhibit chemical bond-induced aging, as well as other aging mechanisms with similar physical characteristics.

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

Zhu, Yi; Cai, Zhonghou; Chen, Pice

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO 2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation ismore » initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO 2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO 2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.« less

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

PubMed

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

2016-08-17

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

Photoinduced electron-transfer in perylenediimide triphenylamine-based dendrimers: single photon timing and femtosecond transient absorption spectroscopy.

PubMed

Fron, Eduard; Pilot, Roberto; Schweitzer, Gerd; Qu, Jianqiang; Herrmann, Andreas; Müllen, Klaus; Hofkens, Johan; Van der Auweraer, Mark; De Schryver, Frans C

2008-05-01

The excited state dynamics of two generations perylenediimide chromophores substituted in the bay area with dendritic branches bearing triphenylamine units as well as those of the respective reference compounds are investigated. Using single photon timing and multi-pulse femtosecond transient absorption experiments a direct proof of a reversible charge transfer occurring from the peripheral triphenylamine to the electron acceptor perylenediimide core is revealed. Femtosecond pump-dump-probe experiments provide evidence for the ground state dynamics by populating excited vibronic levels. It is found by the means of both techniques that the rotational isomerization of the dendritic branches occurs on a time scale that ranges up to 1 ns. This time scale of the isomerization depends on the size of the dendritic arms and is similar both in the ground and excited state.

Measurement of filling factor 5/2 quasiparticle interference with observation of charge e/4 and e/2 period oscillations.

PubMed

Willett, R L; Pfeiffer, L N; West, K W

2009-06-02

A standing problem in low-dimensional electron systems is the nature of the 5/2 fractional quantum Hall (FQH) state: Its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices may be used to manipulate and measure quantum Hall edge excitations. Here we use a small-area edge state interferometer designed to observe quasiparticle interference effects. Oscillations consistent in detail with the Aharonov-Bohm effect are observed for integer quantum Hall and FQH states (filling factors nu = 2, 5/3, and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these factors as charge calibrations, periodic transmission through the device consistent with quasiparticle charge e/4 is observed at nu = 5/2 and at lowest temperatures. The principal finding of this work is that, in addition to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at 5/2 nu and at lowest temperatures. Properties of the e/4 and e/2 oscillations are examined with the device sensitivity sufficient to observe temperature evolution of the 5/2 quasiparticle interference. In the model of quasiparticle interference, this presence of an effective e/2 period may empirically reflect an e/2 quasiparticle charge or may reflect multiple passes of the e/4 quasiparticle around the interferometer. These results are discussed within a picture of e/4 quasiparticle excitations potentially possessing non-Abelian statistics. These studies demonstrate the capacity to perform interferometry on 5/2 excitations and reveal properties important for understanding this state and its excitations.

Measurement of filling factor 5/2 quasiparticle interference with observation of charge e/4 and e/2 period oscillations

PubMed Central

Willett, R. L.; Pfeiffer, L. N.; West, K. W.

2009-01-01

A standing problem in low-dimensional electron systems is the nature of the 5/2 fractional quantum Hall (FQH) state: Its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices may be used to manipulate and measure quantum Hall edge excitations. Here we use a small-area edge state interferometer designed to observe quasiparticle interference effects. Oscillations consistent in detail with the Aharonov–Bohm effect are observed for integer quantum Hall and FQH states (filling factors ν = 2, 5/3, and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these factors as charge calibrations, periodic transmission through the device consistent with quasiparticle charge e/4 is observed at ν = 5/2 and at lowest temperatures. The principal finding of this work is that, in addition to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at 5/2 ν and at lowest temperatures. Properties of the e/4 and e/2 oscillations are examined with the device sensitivity sufficient to observe temperature evolution of the 5/2 quasiparticle interference. In the model of quasiparticle interference, this presence of an effective e/2 period may empirically reflect an e/2 quasiparticle charge or may reflect multiple passes of the e/4 quasiparticle around the interferometer. These results are discussed within a picture of e/4 quasiparticle excitations potentially possessing non-Abelian statistics. These studies demonstrate the capacity to perform interferometry on 5/2 excitations and reveal properties important for understanding this state and its excitations. PMID:19433804

Visible-Light-Mediated Excited State Relaxation in Semi-Synthetic Genetic Alphabet: d5SICS and dNaM.

PubMed

Bhattacharyya, Kalishankar; Datta, Ayan

2017-08-25

The excited state dynamics of an unnatural base pair (UBP) d5SICS/dNaM were investigated by accurate ab-initio calculations. Time-dependent density functional and high-level multireference calculations (MS-CASPT2) were performed to elucidate the excitation of this UBP and its excited state relaxation mechanism. After excitation to the bright state S 2 (ππ*), it decays to the S 1 state and then undergoes efficient intersystem crossing to the triplet manifold. The presence of sulfur atom in d5SICS leads to strong spin-orbit coupling (SOC) and a small energy gap that facilitates intersystem crossing from S 1 (n s π*) to T 2 (ππ*) followed by internal conversion to T 1 state. Similarly in dNaM, the deactivation pathway follows analogous trends. CASPT2 calculations suggest that the S 1 (ππ*) state is a dark state below the accessible S 2 (ππ*) bright state. During the ultrafast deactivation, it exhibits bond length inversion. From S 1 state, significant SOC leads the population transfer to T 3 due to a smaller energy gap. Henceforth, fast internal conversion occurs from T 3 to T 2 followed by T 1 . From time-dependent trajectory surface hopping dynamics, it is found that excited state relaxation occurs on a sub-picosecond timescale in d5SICS and dNaM. Our findings strongly suggest that there is enough energy available in triplet state of UBP to generate reactive oxygen species and induce phototoxicity with respect to cellular DNA. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kinetics of propagation of the lattice excitation in a swift heavy ion track

NASA Astrophysics Data System (ADS)

Lipp, V. P.; Volkov, A. E.; Sorokin, M. V.; Rethfeld, B.

2011-05-01

In this research we verify the applicability of the temperature and heat diffusion conceptions for the description of subpicosecond lattice excitations in nanometric tracks of swift heavy ions (SHI) decelerated in solids in the electronic stopping regime. The method is based on the molecular dynamics (MD) analysis of temporal evolutions of the local kinetic and configurational temperatures of a lattice. We used solid argon as the model system. MD simulations demonstrated that in a SHI track (a) thermalization of lattice excitations takes time of several picoseconds, and (b) application of the parabolic heat diffusion equations for the description of spatial and temporal propagation of lattice excitations is questionable at least up to 10 ps after the ion passage.

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.

Study of high-j neutron excitations outside 136Xe

NASA Astrophysics Data System (ADS)

Talwar, R.; Kay, B. P.; Mitchell, A. J.; Adachi, S.; Entwisle, J. P.; Fujita, Y.; Gey, G.; Noji, S.; Ong, H. J.; Schiffer, J. P.; Tamii, A.

2017-09-01

The character of single-neutron excitations outside of N = 82 has been studied using nucleon transfer reactions in terms of the energy centroid of their strength as well as the fragmentation of this strength among the actual states of the nucleus. However, extending the systematic study of the N = 83 isotones to 137Xe has been challenging due to xenon being a gas at room temperature. Though several attempts have been made, a quantitative determination of the spectroscopic factors for the neutron 9/2- and 13/2+ excitations in 137Xe is still lacking. In the present work, we report on a study of the 136Xe(α,3He)137Xe reaction carried out at 100 MeV to probe the l = 5 , 9/2- and l = 6 , 13/2+ single-neutron excitations. The experimental technique and results will be presented discussing them in context of the evolution of these single-neutron excitations and the influence of the tensor interaction on the neutron single-particle states as the proton orbits are filling. This work has been supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357, the Australian Research Council Discovery Project 120104176, and the UK Science and Technology Facilities.

Evidence of Photo-induced Dynamic Competition of Metallic and Insulating Phase in a Layered Manganite.

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

Li, Yuelin; Walko, Donald A.; Li, Qing'an

2015-12-16

We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time- dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the lasermore » excitation modulates the local competition between the metallic and the insulating phases.« less

Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite

DOE PAGES

Li, Yuelin; Walko, Daonld A.; Li, Qing'an; ...

2015-11-17

We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr 2Mn 2O 7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario wherebymore » the laser excitation modulates the local competition between the metallic and the insulating phases.« less

Excited-state dynamics of mononucleotides and DNA strands in a deep eutectic solvent.

PubMed

Zhang, Yuyuan; de La Harpe, Kimberly; Hariharan, Mahesh; Kohler, Bern

2018-04-17

The photophysics of several mono- and oligonucleotides were investigated in a deep eutectic solvent for the first time. The solvent glyceline, prepared as a 1 : 2 mole ratio mixture of choline chloride and glycerol, was used to study excited-state deactivation in a non-aqueous solvent by the use of steady-state and time-resolved spectroscopy. DNA strands in glyceline retain the secondary structures that are present in aqueous solution to some degree, thus enabling a study of the effects of solvent properties on the excited states of stacked bases and stacked base pairs. The excited-state lifetime of the mononucleotide 5'-AMP in glyceline is 630 fs, or twice as long as in aqueous solution. Even slower relaxation is seen for 5'-TMP in glyceline, and a possible triplet state with a lifetime greater than 3 ns is observed. Circular dichroism spectra show that the single strand (dA)18 and the duplex d(AT)9·d(AT)9 adopt similar structures in glyceline and in aqueous solution. Despite having similar conformations in both solvents, femtosecond transient absorption experiments reveal striking changes in the dynamics. Excited-state decay and vibrational cooling generally take place more slowly in glyceline than in water. Additionally, the fraction of long-lived excited states in both oligonucleotide systems is lower in glyceline than in aqueous solution. For a DNA duplex, water is suggested to favor decay pathways involving intrastrand charge separation, while the deep eutectic solvent favors interstrand deactivation channels involving neutral species. Slower solvation dynamics in the viscous deep eutectic solvent may also play a role. These results demonstrate that the dynamics of excitations in stacked bases and stacked base pairs depend not only on conformation, but are also highly sensitive to the solvent.

Quadrupole collectivity beyond N = 50 in neutron- rich Se and Kr isotopes

NASA Astrophysics Data System (ADS)

Elman, Brandon; Gade, A.; Barofsky, D.; Bender, P. C.; Bowry, M.; Hjorth-Jensen, M.; Kemper, K. W.; Lipschutz, S.; Lunderberg, E.; Sachmpazidi, N.; Terpstra, N.; Walters, W. B.; Weisshaar, D.; Westerberg, A.; Williams, S. J.; Wimmer, K.

2017-09-01

We will present results on measuring the B (E 2 ;01+ ->2n+) strength for the neutron-rich 88,90Kr and 86Se isotopes from intermediate-energy Coulomb excitation. The electric quadrupole transition strengths to the first 2+ state complete, with considerably improved uncertainties, the evolution of quadrupole collectivity in the Kr and Se isotopes approaching N = 60 , for which 90Kr and 86Se had previously been the most uncertain. We also report significant excitation strength to several higher lying 2+ states in the krypton isotopes. The results confirm shell model calculations in the π (fpg) - ν (sdg) shell with only a minimally tuned shell model setup that is based on a nucleon-nucleon interaction derived from effective field theory with effective charges adjusted to 86Kr.

Steady state quantum discord for circularly accelerated atoms

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

Hu, Jiawei, E-mail: hujiawei@nbu.edu.cn; Yu, Hongwei, E-mail: hwyu@hunnu.edu.cn; Synergetic Innovation Center for Quantum Effects and Applications, Hunan Normal University, Changsha, Hunan 410081

2015-12-15

We study, in the framework of open quantum systems, the dynamics of quantum entanglement and quantum discord of two mutually independent circularly accelerated two-level atoms in interaction with a bath of fluctuating massless scalar fields in the Minkowski vacuum. We assume that the two atoms rotate synchronically with their separation perpendicular to the rotating plane. The time evolution of the quantum entanglement and quantum discord of the two-atom system is investigated. For a maximally entangled initial state, the entanglement measured by concurrence diminishes to zero within a finite time, while the quantum discord can either decrease monotonically to an asymptoticmore » value or diminish to zero at first and then followed by a revival depending on whether the initial state is antisymmetric or symmetric. When both of the two atoms are initially excited, the generation of quantum entanglement shows a delayed feature, while quantum discord is created immediately. Remarkably, the quantum discord for such a circularly accelerated two-atom system takes a nonvanishing value in the steady state, and this is distinct from what happens in both the linear acceleration case and the case of static atoms immersed in a thermal bath.« less

TIME EVOLUTION OF KELVIN–HELMHOLTZ VORTICES ASSOCIATED WITH COLLISIONLESS SHOCKS IN LASER-PRODUCED PLASMAS

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

Kuramitsu, Y.; Moritaka, T.; Mizuta, A.

2016-09-10

We report experimental results on Kelvin–Helmholtz (KH) instability and resultant vortices in laser-produced plasmas. By irradiating a double plane target with a laser beam, asymmetric counterstreaming plasmas are created. The interaction of the plasmas with different velocities and densities results in the formation of asymmetric shocks, where the shear flow exists along the contact surface and the KH instability is excited. We observe the spatial and temporal evolution of plasmas and shocks with time-resolved diagnostics over several shots. Our results clearly show the evolution of transverse fluctuations, wavelike structures, and circular features, which are interpreted as the KH instability andmore » resultant vortices. The relevant numerical simulations demonstrate the time evolution of KH vortices and show qualitative agreement with experimental results. Shocks, and thus the contact surfaces, are ubiquitous in the universe; our experimental results show general consequences where two plasmas interact.« less

Early events associated with the excited state proton transfer in 2-(2{sup '}-pyridyl)benzimidazole

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

Burai, Tarak Nath; Mukherjee, Tushar Kanti; Lahiri, Priyanka

2009-07-21

2-(2{sup '}-pyridyl)benzimidazole (2PBI) undergoes excited state proton transfer (ESPT) in acidic solutions, leading to a tautomer emission at 460 nm. This photoprocess has been studied using ultrafast fluorescence spectroscopic techniques in acidic neat aqueous solutions, in viscous mixtures of glycerol with water, as well as in sucrose solutions. The tautomer is found to be stabilized in the more viscous medium, leading to a greater relative quantum yield as well as lifetime. The long rise time in tautomer emission is not affected by viscosity though. Rather, it appears to have the same value as the long component of the decay ofmore » the cationic excited state (C*). In addition to the subnanosecond lifetime reported earlier, C* is found to exhibit a decay time of 2 ps. This is assigned to its protonation to form the nonfluorescent dication in its excited state (D*) considering the ground and excited state pK{sub a} values reported earlier. An additional rising component of 100 ps is observed in the region of C* emission. This is likely to arise from a structural change or charge redistribution in C* immediately after its creation and before the phototautomerization.« less

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

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

Egorova, Dassia

2014-01-21

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

Unraveling the electronic relaxation dynamics in photoexcited 2,4-difluoroaniline via femtosecond time-resolved photoelectron imaging

NASA Astrophysics Data System (ADS)

Ling, Fengzi; Li, Shuai; Wei, Jie; Liu, Kai; Wang, Yanmei; Zhang, Bing

2018-04-01

Time-resolved photoelectron imaging is employed to investigate the relaxation dynamics of the lowest two excited electronic states S1(ππ*) and S2(π3s/πσ*) in 2,4-difluoroaniline (24DFA). As the S1(ππ*) state is populated directly following 289 nm excitation, the population undergoes ultrafast intramolecular vibrational redistribution on a 540 fs time scale, followed by efficient intersystem crossing from S1(ππ*) to the triplet state within 379 ps, and the subsequent slower deactivation process of the triplet state. For excitation to the S2(π3s/πσ*) state at 238 nm, the population probably bifurcates into two decay channels. The dominant channel with 84 fs involves ultrafast internal conversion to the S1(ππ*) state, from which it relaxes to the electronic ground state on a 116 ps time scale. The other appears to involve motion along the S2(π3s/πσ*) potential energy surface. Our data also determine experimentally the electronic energies of S2(π3s/πσ*), S3(ππ*), and several Rydberg states in 24DFA.

The boomerang effect in electron-hydrogen molecule scattering as determined by time-dependent calculations

NASA Astrophysics Data System (ADS)

Ben-Asher, Anael; Moiseyev, Nimrod

2017-05-01

The appearance of oscillations in the energy-dependent cross sections of the vibrational excitation ν =0 →ν ≥3 of the hydrogen molecule in its electronic ground state as predicted by Mündel, Berman, and Domcke [Phys. Rev. A 32, 181 (1985)] was confirmed in the electron scattering experiments by Allan [J. Phys. B: At. Mol. Phys. 18, L451 (1985)]. These unusual structures were obtained in spite of the extremely short lifetime of H2- in its ro-vibrational states. Based on the standard (Hermitian) time-independent scattering calculations, Horáček et al. [Phys. Rev. A 73, 022701 (2006)] associated these oscillations with the boomerang effect. Here, we show the boomerang effect as developed in time, based on our time-dependent nuclear wavepacket (WP) calculations. The nuclear WP dynamics of H2- is determined using the non-Hermitian quantum mechanics (NH-QM) which enables the use of the Born-Oppenheimer approximation with complex potential energy surfaces. This NH-QM approach, which enables us the association of the nuclear WP dynamics as obtained from the complex potential energy curve of H2- with the evolution of cross section in time, can enlighten the dynamics in other scattering experiments.

The boomerang effect in electron-hydrogen molecule scattering as determined by time-dependent calculations.

PubMed

Ben-Asher, Anael; Moiseyev, Nimrod

2017-05-28

The appearance of oscillations in the energy-dependent cross sections of the vibrational excitation ν=0→ν≥3 of the hydrogen molecule in its electronic ground state as predicted by Mündel, Berman, and Domcke [Phys. Rev. A 32, 181 (1985)] was confirmed in the electron scattering experiments by Allan [J. Phys. B: At. Mol. Phys. 18, L451 (1985)]. These unusual structures were obtained in spite of the extremely short lifetime of H 2 - in its ro-vibrational states. Based on the standard (Hermitian) time-independent scattering calculations, Horáček et al. [Phys. Rev. A 73, 022701 (2006)] associated these oscillations with the boomerang effect. Here, we show the boomerang effect as developed in time, based on our time-dependent nuclear wavepacket (WP) calculations. The nuclear WP dynamics of H 2 - is determined using the non-Hermitian quantum mechanics (NH-QM) which enables the use of the Born-Oppenheimer approximation with complex potential energy surfaces. This NH-QM approach, which enables us the association of the nuclear WP dynamics as obtained from the complex potential energy curve of H 2 - with the evolution of cross section in time, can enlighten the dynamics in other scattering experiments.

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.

Tight-binding approximations to time-dependent density functional theory — A fast approach for the calculation of electronically excited states

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

Rüger, Robert, E-mail: rueger@scm.com; Department of Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam; Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Linnéstr. 2, 04103 Leipzig

2016-05-14

We propose a new method of calculating electronically excited states that combines a density functional theory based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed time-dependent density functional theory TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive TD-DFT calculations. Errors in vertical excitation energies are reduced by a factor of twomore » compared to TD-DFTB.« less

Excited-state lifetime measurement of silicon vacancy centers in diamond by single-photon frequency upconversion

NASA Astrophysics Data System (ADS)

Rong, Youying; Ma, Jianhui; Chen, Lingxiao; Liu, Yan; Siyushev, Petr; Wu, Botao; Pan, Haifeng; Jelezko, Fedor; Wu, E.; Zeng, Heping

2018-05-01

We report a method with high time resolution to measure the excited-state lifetime of silicon vacancy centers in bulk diamond avoiding timing jitter from the single-photon detectors. Frequency upconversion of the fluorescence emitted from silicon vacancy centers was achieved from 738 nm to 436 nm via sum frequency generation with a short pump pulse. The excited-state lifetime can be obtained by measuring the intensity of upconverted light while the pump delay changes. As a probe, a pump laser with pulse duration of 11 ps provided a high temporal resolution of the measurement. The lifetime extracted from the pump–probe curve was 0.755 ns, which was comparable to the timing jitter of the single-photon detectors.

Angle-resolved photoemission spectroscopy studies of the Mott insulator to superconductor evolution in calcium-sodium-copper-chloride

NASA Astrophysics Data System (ADS)

Shen, Kyle Michael

The parent compounds of the high-temperature cuprate superconductors are antiferromagnetic Mott insulators. To explain the microscopic mechanism behind high-temperature superconductivity, it is first necessary to understand how the electronic states evolve from the parent Mott insulator into the superconducting compounds. This dissertation presents angle-resolved photoemission spectroscopy (ARPES) studies of one particular family of the cuprate superconductors, Ca 2-xNaxCuO 2Cl2, to investigate how the single-electron excitations develop throughout momentum space as the system is hole doped from the Mott insulator into a superconductor with a transition temperature of 22 K. These measurements indicate that, due to very strong electron-boson interactions, the quasiparticle residue, Z, approaches zero in the parent Mott insulator due to the formation of small lattice polarons. As a result, many fundamental quantities such as the chemical potential, quasiparticle excitations, and the Fermi surface evolve in manners wholly unexpected from conventional weakly-interacting theories. In addition, highly anisotropic interactions have been observed in momentum space where quasiparticle-like excitations persist to low doping levels along the nodal direction of the d-wave super-conducting gap, in contrast to the unusual excitations near the d-wave antinode. This anisotropy may reflect the propensity of the lightly doped cuprates towards forming a competing, charge-ordered state. These results provide a novel and logically consistent explanation of the hole doping evolution of the lineshape, spectral weight, chemical potential, quasiparticle dispersion, and Fermi surface as Ca2- xNaxCuO2Cl2 evolves from the parent Mott insulator into a high-temperature superconductor.

The simulation of electromagnetically driven strong Langmuir turbulence effect on the backscatter radiation from ionosphere

NASA Astrophysics Data System (ADS)

Kochetov, Andrey

2016-07-01

Numerical simulations of the dynamics of electromagnetic fields in a smoothly inhomogeneous nonlinear plasma layer in frameworks of the nonlinear Schrödinger equation with boundary conditions responsible for the pumping of the field in the layer by an incident wave and the inverse radiation losses supplemented the volume field dissipation due to the electromagnetic excitation of Langmuir turbulence are carried out. The effects of the threshold of non-linearity and it's evolution, of the threshold and saturation levels of dissipation in the vicinity of the wave reflection point on the features of the dynamics of reflection and absorption indexes are investigated. We consider the hard drive damping depending on the local field amplitude and hysteresis losses with different in several times "on" and "off" absorption thresholds as well. The dependence of the thresholds of the steady-state, periodic and chaotic regimes of plasma-wave interaction on the scenario of turbulence evolution is demonstrated. The results are compared with the experimental observations of Langmuir stage ionospheric modification.

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.

Testing time-dependent density functional theory with depopulated molecular orbitals for predicting electronic excitation energies of valence, Rydberg, and charge-transfer states and potential energies near a conical intersection

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

Li, Shaohong L.; Truhlar, Donald G., E-mail: truhlar@umn.edu

2014-09-14

Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH{sub 3}-F{sub 2} and on the potentialmore » energy curves of NH{sub 3} near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces.« less

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

PubMed

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

2018-04-05

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

Optically dark excitonic states mediated exciton and biexciton valley dynamics in monolayer WSe₂.

PubMed

Zhang, Minghua; Fu, Jiyong; Dias, A C; Qu, Fanyao

2018-05-18

We present a theory to address the photoluminescence (PL) intensity and valley polarization (VP) dynamics in monolayer WSe$_2$, under the impact of excitonic dark states of both excitons and biexcitons. We find that the PL intensity of all excitonic channels including intravalley exciton (X$_{\\rm b}$), intravalley biexciton (XX$_{\\rm k,k}$) and intervalley biexciton (XX$_{\\rm k,k^\\prime}$) in particular for the {XX$_{\\rm k,k}$} PL is enhanced by laser excitation fluence. In addition, our results indicate the anomalous temperature dependence of PL, i.e., increasing with temperature, as a result of favored phonon assisted dark-to-bright scatterings at high temperatures. Moreover, we observe that the PL is almost immune to intervalley scatterings, which trigger the exchange of excitonic states between the two valleys. As far as the valley polarization is concerned, we find that the VP of X$_{\\rm b}$ shrinks as temperature increases, exhibiting opposite temperature response to PL, while the intravalley XX$_{\\rm k,k}$ VP is found almost independent of temperature. In contrast to both X$_{\\rm b}$ and XX$_{\\rm k,k}$, the intervalley XX$_{\\rm k,k^\\prime}$ VP identically vanishes, because of equal populations of excitons in the $K$ and $K^\\prime$ valleys bounded to form intervalley biexcitons. Notably, it is found that the X$_{\\rm b}$ VP much more strongly depends on bright-dark scattering than that of {XX$_{\\rm k,k}$}, making dark state act as a robust reservoir for valley polarization against intervalley scatterings for X$_{\\rm b}$ at strong bright-dark scatterings, but not for XX$_{\\rm k,k}$. Dark excitonic states enabled enhancement of VP benefits quantum technology for information processing based on the valley degree of freedom in valleytronic devices. Furthermore, the VP has strong dependence on intervalley scattering but maintains essentially constant with excitation fluence. Finally, the time evolution of PL and VP, depending on temperature and excitation fluence, is discussed. © 2018 IOP Publishing Ltd.

Transient and stationary spectroscopy of cytochrome c: ultrafast internal conversion controls photoreduction.

PubMed

Löwenich, Dennis; Kleinermanns, Karl; Karunakaran, Venugopal; Kovalenko, Sergey Alexander

2008-01-01

Photoreduction of cytochrome c (Cyt c) has been reinvestigated using femtosecond-to-nanosecond transient absorption and stationary spectroscopy. Femtosecond spectra of oxidized Cyt c, recorded in the probe range 270-1000 nm, demonstrate similar evolution upon 266 or 403 nm excitation: an ultrafast 0.3 ps internal conversion followed by a 4 ps vibrational cooling. Late transient spectra after 20 ps, from the cold ground-state chromophore, reveal a small but measurable signal from reduced Cyt c. The yield phi for Fe3+-->Fe2+ photoreduction is measured to be phi(403) = 0.016 and phi(266) = 0.08 for 403 and 266 nm excitation. These yields lead to a guess of the barrier E(f)(A) = 55 kJ mol(-1) for thermal ground-state electron transfer (ET). Nanosecond spectra initially show the typical absorption from reduced Cyt c and then exhibit temperature-dependent sub-microsecond decays (0.5 micros at 297 K), corresponding to a barrier E(A)(b) = 33 kJ mol(-1) for the back ET reaction and a reaction energy DeltaE = 22 kJ mol(-1). The nanosecond transients do not decay to zero on a second time scale, demonstrating the stability of some of the reduced Cyt c. The yields calculated from this stable reduced form agree with quasistationary reduction yields. Modest heating of Cyt c leads to its efficient thermal reduction as demonstrated by differential stationary absorption spectroscopy. In summary, our results point to ultrafast internal conversion of oxidized Cyt c upon UV or visible excitation, followed by Fe-porphyrin reduction due to thermal ground-state ET as the prevailing mechanism.

Quasiparticle spectra from molecules to bulk

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

Vlček, Vojtěch; Rabani, Eran; Neuhauser, Daniel

We present a stochastic cumulant GW method, allowing us to map the evolution of photoemission spectra, quasiparticle energies, lifetimes, and emergence of collective excitations from molecules to bulklike systems with up to thousands of valence electrons, including Si nanocrystals and nanoplatelets. The quasiparticle energies rise due to their coupling with collective shake-up (plasmon) excitations, and this coupling leads to significant spectral weight loss (up to 50% for the low-energy states), shortening the lifetimes and shifting the spectral features to lower energies by as much as 0.6 eV. Such features are common to all the systems studied irrespective of their sizesmore » and shapes. For small and low-dimensional systems the surface plasmon resonances affect the frequency of the collective excitation and position of the satellites.« less

Quasiparticle spectra from molecules to bulk

DOE PAGES

Vlček, Vojtěch; Rabani, Eran; Neuhauser, Daniel

2018-03-16

We present a stochastic cumulant GW method, allowing us to map the evolution of photoemission spectra, quasiparticle energies, lifetimes, and emergence of collective excitations from molecules to bulklike systems with up to thousands of valence electrons, including Si nanocrystals and nanoplatelets. The quasiparticle energies rise due to their coupling with collective shake-up (plasmon) excitations, and this coupling leads to significant spectral weight loss (up to 50% for the low-energy states), shortening the lifetimes and shifting the spectral features to lower energies by as much as 0.6 eV. Such features are common to all the systems studied irrespective of their sizesmore » and shapes. For small and low-dimensional systems the surface plasmon resonances affect the frequency of the collective excitation and position of the satellites.« less

Dynamic evolution of double Λ five-level atom interacting with one-mode electromagnetic cavity field

NASA Astrophysics Data System (ADS)

Abdel-Wahab, N. H.; Salah, Ahmed

2017-12-01

In this paper, the model describing a double Λ five-level atom interacting with a single mode electromagnetic cavity field in the (off) non-resonate case is studied. We obtained the constants of motion for the considered model. Also, the state vector of the wave function is given by using the Schrödinger equation when the atom is initially prepared in its excited state. The dynamical evolutions for the collapse revivals, the antibunching of photons and the field squeezing phenomena are investigated when the field is considered in a coherent state. The influence of detuning parameters on these phenomena is investigated. We noticed that the atom-field properties are influenced by changing the detuning parameters. The investigation of these aspects by numerical simulations is carried out using the Quantum Toolbox in Python (QuTip).

Role of excited N2 in the production of nitric oxide

NASA Astrophysics Data System (ADS)

Campbell, L.; Cartwright, D. C.; Brunger, M. J.

2007-08-01

Excited N2 plays a role in a number of atmospheric processes, including auroral and dayglow emissions, chemical reactions, recombination of free electrons, and the production of nitric oxide. Electron impact excitation of N2 is followed by radiative decay through a series of excited states, contributing to auroral and dayglow emissions. These processes are intertwined with various chemical reactions and collisional quenching involving the excited and ground state vibrational levels. Statistical equilibrium and time step atmospheric models are used to predict N2 excited state densities and emissions (as a test against previous models and measurements) and to investigate the role of excited nitrogen in the production of nitric oxide. These calculations predict that inclusion of the reaction N2[A3Σu +] + O, to generate NO, produces an increase by a factor of up to three in the calculated NO density at some altitudes.

Excitation energies of molecules within time-independent density functional theory

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

Hemanadhan, M., E-mail: hemanadh@iitk.ac.in; Harbola, Manoj K., E-mail: hemanadh@iitk.ac.in

2014-04-24

Recently proposed exchange energy functional for excited-states is tested for obtaining excitation energies of diatomic molecules. The functional is the ground-state counterpart of the local-density approximation, the modified local spin density (MLSD). The MLSD functional is tested for the N{sub 2} and CO diatomic molecules. The excitation energy obtained with the MLSD functional for the N{sub 2} molecule is in close vicinity to that obtained from the exact exchange orbital functional, Krieger, Li and Iafrate (KLI). For the CO molecule, the departure in excitation energy is observed and is due to the overcorrection of self-interaction.

Excitation energies of molecules within time-independent density functional theory

NASA Astrophysics Data System (ADS)

Hemanadhan, M.; Harbola, Manoj K.

2014-04-01

Recently proposed exchange energy functional for excited-states is tested for obtaining excitation energies of diatomic molecules. The functional is the ground-state counterpart of the local-density approximation, the modified local spin density (MLSD). The MLSD functional is tested for the N2 and CO diatomic molecules. The excitation energy obtained with the MLSD functional for the N2 molecule is in close vicinity to that obtained from the exact exchange orbital functional, Krieger, Li and Iafrate (KLI). For the CO molecule, the departure in excitation energy is observed and is due to the overcorrection of self-interaction.

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.

Real-time decay of a highly excited charge carrier in the one-dimensional Holstein model

NASA Astrophysics Data System (ADS)

Dorfner, F.; Vidmar, L.; Brockt, C.; Jeckelmann, E.; Heidrich-Meisner, F.

2015-03-01

We study the real-time dynamics of a highly excited charge carrier coupled to quantum phonons via a Holstein-type electron-phonon coupling. This is a prototypical example for the nonequilibrium dynamics in an interacting many-body system where excess energy is transferred from electronic to phononic degrees of freedom. We use diagonalization in a limited functional space (LFS) to study the nonequilibrium dynamics on a finite one-dimensional chain. This method agrees with exact diagonalization and the time-evolving block-decimation method, in both the relaxation regime and the long-time stationary state, and among these three methods it is the most efficient and versatile one for this problem. We perform a comprehensive analysis of the time evolution by calculating the electron, phonon and electron-phonon coupling energies, and the electronic momentum distribution function. The numerical results are compared to analytical solutions for short times, for a small hopping amplitude and for a weak electron-phonon coupling. In the latter case, the relaxation dynamics obtained from the Boltzmann equation agrees very well with the LFS data. We also study the time dependence of the eigenstates of the single-site reduced density matrix, which defines the so-called optimal phonon modes. We discuss their structure in nonequilibrium and the distribution of their weights. Our analysis shows that the structure of optimal phonon modes contains very useful information for the interpretation of the numerical data.

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.

Clusters in intense x-ray pulses

NASA Astrophysics Data System (ADS)

Bostedt, Christoph

2012-06-01

Free-electron lasers can deliver extremely intense, coherent x-ray flashes with femtosecond pulse length, opening the door for imaging single nanoscale objects in a single shot. All matter irradiated by these intense x-ray pulses, however, will be transformed into a highly-excited non-equilibrium plasma within femtoseconds. During the x-ray pulse complex electron dynamics and the onset of atomic disorder will be induced, leading to a time-varying sample. We have performed first experiments about x-ray laser pulse -- cluster interaction with a combined spectroscopy and imaging approach at both, the FLASH free electron laser in Hamburg (Germany) and the LCLS x-ray free-electron laser in Stanford (California). Atomic clusters are ideal for investigating the light - matter interaction because their size can be tuned from the molecular to the bulk regime, thus allowing to distinguish between intra and inter atomic processes. Imaging experiments with xenon clusters show power-density dependent changes in the scattering patterns. Modeling the scattering data indicates that the optical constants of the clusters change during the femtosecond pulse due to the transient creation of high charge states. The results show that ultra fast scattering is a promising approach to study transient states of matter on a femtosecond time scale. Coincident recording of time-of-flight spectra and scattering patterns allows the deconvolution of focal volume and particle size distribution effects. Single-shot single-particle experiments with keV x-rays reveal that for the highest power densities an highly excited and hot cluster plasma is formed for which recombination is suppressed. Time resolved infrared pump -- x-ray probe experiments have started. Here, the clusters are pumped into a nanoplasma state and their time evolution is probed with femtosecond x-ray scattering. The data show strong variations in the scattering patterns stemming from electronic reconfigurations in the cluster plasma. The results will be compared to theoretical predictions and discussed in light of current developments at free-electron laser sources.

Description of ground and excited electronic states by ensemble density functional method with extended active space

DOE PAGES

Filatov, Michael; Martínez, Todd J.; Kim, Kwang S.

2017-08-14

An extended variant of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, the REKS(4,4) method, designed to describe the ground electronic states of strongly multireference systems is modified to enable calculation of excited states within the time-independent variational formalism. The new method, the state-interaction state-averaged REKS(4,4), i.e., SI-SA-REKS(4,4), is capable of describing several excited states of a molecule involving double bond cleavage, polyradical character, or multiple chromophoric units.We demonstrate that the newmethod correctly describes the ground and the lowest singlet excited states of a molecule (ethylene) undergoing double bond cleavage. The applicability of the new method for excitonic states is illustrated withmore » π stacked ethylene and tetracene dimers. We conclude that the new method can describe a wide range of multireference phenomena.« less

Description of ground and excited electronic states by ensemble density functional method with extended active space

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

Filatov, Michael; Martínez, Todd J.; Kim, Kwang S.

An extended variant of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, the REKS(4,4) method, designed to describe the ground electronic states of strongly multireference systems is modified to enable calculation of excited states within the time-independent variational formalism. The new method, the state-interaction state-averaged REKS(4,4), i.e., SI-SA-REKS(4,4), is capable of describing several excited states of a molecule involving double bond cleavage, polyradical character, or multiple chromophoric units.We demonstrate that the newmethod correctly describes the ground and the lowest singlet excited states of a molecule (ethylene) undergoing double bond cleavage. The applicability of the new method for excitonic states is illustrated withmore » π stacked ethylene and tetracene dimers. We conclude that the new method can describe a wide range of multireference phenomena.« less

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

GRID and Multiphonon States

PubMed Central

Robinson, S. J.

2000-01-01

The development of the GRID technique for determining nuclear level lifetimes of excited low-spin states populated in thermal neutron capture reactions has resulted in the ability to perform detailed studies of proposed multiphonon excitations for the first time. This paper discusses the experimental evidence for multiphonon excitations determined using the GRID technique. In deformed nuclei several good examples of γγKπ = 4+ excitations have been established, whereas the experimental evidence gathered on Kπ= 0+ bands is contradictory, and any interpretations will likely involve the mixing of several different configurations. In vibrational nuclei the GRID technique has helped to establish the existence of multiple quadrupole phonon excitations in 114Cd, and an almost complete set of quadrupole-octupole coupled states in 144Nd. PMID:27551594

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

Cavity QED implementation of non-adiabatic holonomies for universal quantum gates in decoherence-free subspaces with nitrogen-vacancy centers.

PubMed

Zhou, Jian; Yu, Wei-Can; Gao, Yu-Mei; Xue, Zheng-Yuan

2015-06-01

A cavity QED implementation of the non-adiabatic holonomic quantum computation in decoherence-free subspaces is proposed with nitrogen-vacancy centers coupled commonly to the whispering-gallery mode of a microsphere cavity, where a universal set of quantum gates can be realized on the qubits. In our implementation, with the assistant of the appropriate driving fields, the quantum evolution is insensitive to the cavity field state, which is only virtually excited. The implemented non-adiabatic holonomies, utilizing optical transitions in the Λ type of three-level configuration of the nitrogen-vacancy centers, can be used to construct a universal set of quantum gates on the encoded logical qubits. Therefore, our scheme opens up the possibility of realizing universal holonomic quantum computation with cavity assisted interaction on solid-state spins characterized by long coherence times.

Stochastic response and bifurcation of periodically driven nonlinear oscillators by the generalized cell mapping method

NASA Astrophysics Data System (ADS)

Han, Qun; Xu, Wei; Sun, Jian-Qiao

2016-09-01

The stochastic response of nonlinear oscillators under periodic and Gaussian white noise excitations is studied with the generalized cell mapping based on short-time Gaussian approximation (GCM/STGA) method. The solutions of the transition probability density functions over a small fraction of the period are constructed by the STGA scheme in order to construct the GCM over one complete period. Both the transient and steady-state probability density functions (PDFs) of a smooth and discontinuous (SD) oscillator are computed to illustrate the application of the method. The accuracy of the results is verified by direct Monte Carlo simulations. The transient responses show the evolution of the PDFs from being Gaussian to non-Gaussian. The effect of a chaotic saddle on the stochastic response is also studied. The stochastic P-bifurcation in terms of the steady-state PDFs occurs with the decrease of the smoothness parameter, which corresponds to the deterministic pitchfork bifurcation.

Real-time ab initio simulations of excited-state dynamics in nanostructures

NASA Astrophysics Data System (ADS)

Tomanek, David

2007-03-01

Combining time-dependent ab initio density functional calculations for electrons with molecular dynamics simulations for ions, we investigate the effect of excited-state dynamics in nanostructures. In carbon nanotubes, we find electronic excitations to last for a large fraction of a picosecond. The de-excitation process is dominated by coupling to other electronic degrees of freedom during the first few hundred femtoseconds. Later, the de-excitation process becomes dominated by coupling to ionic motion. The onset point and damping rate in that regime change with initial ion velocities, a manifestation of temperature dependent electron-phonon coupling. Considering the fact that the force field in the electronically excited state differs significantly from the ground state, as reflected in the Franck-Condon effect, atomic bonds can easily be broken or restored during the relatively long lifetime of electronic excitations. This effect can be utilized in a ``photo-surgery" of nanotubes, causing structural self-healing at vacancy sites or selective de-oxidation processes induced by photo-absorption. Also, electronic excitations are a key ingredient for the understanding of sputtering processes in nanostructures, induced by energetic collisions with ions. Yoshiyuki Miyamoto, Angel Rubio, and David Tomanek, Phys. Rev. Lett. 97, 126104 (2006). Yoshiyuki Miyamoto, Savas Berber, Mina Yoon, Angel Rubio, and David Tomanek, Chem. Phys. Lett. 392, 209 (2004). Yoshiyuki Miyamoto, Noboru Jinbo, Hisashi Nakamura, Angel Rubio, and David Tomanek, Phys. Rev. B 70, 233408 (2004). Yoshiyuki Miyamoto, Arkady Krasheninnikov, and David Tomanek (in preparation).

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.

Mechanism for Broadband White-Light Emission from Two-Dimensional (110) Hybrid Perovskites.

PubMed

Hu, Te; Smith, Matthew D; Dohner, Emma R; Sher, Meng-Ju; Wu, Xiaoxi; Trinh, M Tuan; Fisher, Alan; Corbett, Jeff; Zhu, X-Y; Karunadasa, Hemamala I; Lindenberg, Aaron M

2016-06-16

The recently discovered phenomenon of broadband white-light emission at room temperature in the (110) two-dimensional organic-inorganic perovskite (N-MEDA)[PbBr4] (N-MEDA = N(1)-methylethane-1,2-diammonium) is promising for applications in solid-state lighting. However, the spectral broadening mechanism and, in particular, the processes and dynamics associated with the emissive species are still unclear. Herein, we apply a suite of ultrafast spectroscopic probes to measure the primary events directly following photoexcitation, which allows us to resolve the evolution of light-induced emissive states associated with white-light emission at femtosecond resolution. Terahertz spectra show fast free carrier trapping and transient absorption spectra show the formation of self-trapped excitons on femtosecond time-scales. Emission-wavelength-dependent dynamics of the self-trapped exciton luminescence are observed, indicative of an energy distribution of photogenerated emissive states in the perovskite. Our results are consistent with photogenerated carriers self-trapped in a deformable lattice due to strong electron-phonon coupling, where permanent lattice defects and correlated self-trapped states lend further inhomogeneity to the excited-state potential energy surface.

Electron-driven excitation of O 2 under night-time auroral conditions: Excited state densities and band emissions

NASA Astrophysics Data System (ADS)

Jones, D. B.; Campbell, L.; Bottema, M. J.; Teubner, P. J. O.; Cartwright, D. C.; Newell, W. R.; Brunger, M. J.

2006-01-01

Electron impact excitation of vibrational levels in the ground electronic state and seven excited electronic states in O 2 have been simulated for an International Brightness Coefficient-Category 2+ (IBC II+) night-time aurora, in order to predict O 2 excited state number densities and volume emission rates (VERs). These number densities and VERs are determined as a function of altitude (in the range 80-350 km) in the present study. Recent electron impact excitation cross-sections for O 2 were combined with appropriate altitude dependent IBC II+ auroral secondary electron distributions and the vibrational populations of the eight O 2 electronic states were determined under conditions of statistical equilibrium. Pre-dissociation, atmospheric chemistry involving atomic and molecular oxygen, radiative decay and quenching of excited states were included in this study. This model predicts relatively high number densities for the X3Σg-(v'⩽4),a1Δandb1Σg+ metastable electronic states and could represent a significant source of stored energy in O 2* for subsequent thermospheric chemical reactions. Particular attention is directed towards the emission intensities of the infrared (IR) atmospheric (1.27 μm), Atmospheric (0.76 μm) and the atomic oxygen 1S→ 1D transition (5577 Å) lines and the role of electron-driven processes in their origin. Aircraft, rocket and satellite observations have shown both the IR atmospheric and Atmospheric lines are dramatically enhanced under auroral conditions and, where possible, we compare our results to these measurements. Our calculated 5577 Å intensity is found to be in good agreement with values independently measured for a medium strength IBC II+ aurora.

The electronically excited states of LH2 complexes from Rhodopseudomonas acidophila strain 10050 studied by time-resolved spectroscopy and dynamic Monte Carlo simulations. II. Homo-arrays of LH2 complexes reconstituted into phospholipid model membranes.

PubMed

Pflock, Tobias J; Oellerich, Silke; Krapf, Lisa; Southall, June; Cogdell, Richard J; Ullmann, G Matthias; Köhler, Jürgen

2011-07-21

We performed time-resolved spectroscopy on homoarrays of LH2 complexes from the photosynthetic purple bacterium Rhodopseudomonas acidophila. Variations of the fluorescence transients were monitored as a function of the excitation fluence and the repetition rate of the excitation. These parameters are directly related to the excitation density within the array and to the number of LH2 complexes that still carry a triplet state prior to the next excitation. Comparison of the experimental observations with results from dynamic Monte Carlo simulations for a model cluster of LH2 complexes yields qualitative agreement without the need for any free parameter and reveals the mutual relationship between energy transfer and annihilation processes.

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.

Excited state intramolecular proton transfer reaction of 4'-N,N-diethylamino-3-hydroxyflavone and solvation dynamics in room temperature ionic liquids studied by optical Kerr gate fluorescence measurement.

PubMed

Kimura, Yoshifumi; Fukuda, Masanori; Suda, Kayo; Terazima, Masahide

2010-09-16

Fluorescence dynamics of 4'-N,N-diethylamino-3-hydroxyflavone (DEAHF) and its methoxy derivative (DEAMF) in various room temperature ionic liquids (RTILs) have been studied mainly by an optical Kerr gate method. DEAMF showed a single band fluorescence whose peak shifted with time by the solvation dynamics. The averaged solvation time determined by the fluorescence peak shift was proportional to the viscosity of the solvent except for tetradecyltrihexylphosphonium bis(trifluoromethanesulfonyl)amide. The solvation times were consistent with reported values determined with different probe molecules. DEAHF showed dual fluorescence due to the normal and tautomer forms produced by the excited state intramolecular proton transfer (ESIPT), and the relative intensities were dependent on the time and the solvent cation or anion species. By using the information of the fluorescence spectrum of DEAMF, the fluorescence spectrum of DEAHF at each delay time after the photoexcitation was decomposed into the normal and the tautomer fluorescence components, respectively. The normal component showed a very fast decay simulated by a biexponential function (2-3 and 20-30 ps) with an additional slower decay component. The tautomer component showed a rise with the time constants corresponding to the faster decay of the normal form with an additional instantaneous rise. The faster dynamics of the normal and tautomer population changes were assigned to the ESIPT process, while the slower decay of the fluorescence was attributed to the population decay from the excited state through the radiative and nonradiative processes. The average ESIPT time was much faster than the averaged solvation time of RTILs. Basically, the ESIPT kinetics in RTILs is similar to those in conventional liquid solvents like acetonitrile (Chou et al. J. Phys. Chem. A 2005, 109, 3777). The faster ESIPT is interpreted in terms of the activation barrierless process from the Franck-Condon state before the solvation of the normal state in the electronic excited state. With the advance of the solvation in the excited state, the normal form becomes relatively more stable than the tautomer form, which makes the ESIPT become an activation process.

Mapping GFP structure evolution during proton transfer with femtosecond Raman spectroscopy.

PubMed

Fang, Chong; Frontiera, Renee R; Tran, Rosalie; Mathies, Richard A

2009-11-12

Tracing the transient atomic motions that lie at the heart of chemical reactions requires high-resolution multidimensional structural information on the timescale of molecular vibrations, which commonly range from 10 fs to 1 ps. For simple chemical systems, it has been possible to map out in considerable detail the reactive potential-energy surfaces describing atomic motions and resultant reaction dynamics, but such studies remain challenging for complex chemical and biological transformations. A case in point is the green fluorescent protein (GFP) from the jellyfish Aequorea victoria, which is a widely used gene expression marker owing to its efficient bioluminescence. This feature is known to arise from excited-state proton transfer (ESPT), yet the atomistic details of the process are still not fully understood. Here we show that femtosecond stimulated Raman spectroscopy provides sufficiently detailed and time-resolved vibrational spectra of the electronically excited chromophore of GFP to reveal skeletal motions involved in the proton transfer that produces the fluorescent form of the protein. In particular, we observe that the frequencies and intensities of two marker bands, the C-O and C = N stretching modes at opposite ends of the conjugated chromophore, oscillate out of phase with a period of 280 fs; we attribute these oscillations to impulsively excited low-frequency phenoxyl-ring motions, which optimize the geometry of the chromophore for ESPT. Our findings illustrate that femtosecond simulated Raman spectroscopy is a powerful approach to revealing the real-time nuclear dynamics that make up a multidimensional polyatomic reaction coordinate.

Small signal analysis of four-wave mixing in InAs/GaAs quantum-dot semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Ma, Shaozhen; Chen, Zhe; Dutta, Niloy K.

2009-02-01

A model to study four-wave mixing (FWM) wavelength conversion in InAs-GaAs quantum-dot semiconductor optical amplifier is proposed. Rate equations involving two QD states are solved to simulate the carrier density modulation in the system, results show that the existence of QD excited state contributes to the ultra fast recover time for single pulse response by serving as a carrier reservoir for the QD ground state, its speed limitations are also studied. Nondegenerate four-wave mixing process with small intensity modulation probe signal injected is simulated using this model, a set of coupled wave equations describing the evolution of all frequency components in the active region of QD-SOA are derived and solved numerically. Results show that better FWM conversion efficiency can be obtained compared with the regular bulk SOA, and the four-wave mixing bandwidth can exceed 1.5 THz when the detuning between pump and probe lights is 0.5 nm.

Lifetimes and energetics of the first electronically excited states of NaH2O from time-resolved photoelectron imaging

NASA Astrophysics Data System (ADS)

Gartmann, Thomas E.; Yoder, Bruce L.; Chasovskikh, Egor; Signorell, Ruth

2017-09-01

The energetics and lifetimes of the first electronically excited states (;3p-states;) of NaH2O and NaD2O have been measured by pump-probe (740/780 and 400 nm) photoelectron imaging. The photoelectron spectra of NaH2O show two bands at an electron kinetic energy of 0.14 and 0.38 eV, respectively. We assign the former to excitation via the two energetically close lying ;pπ-states; with flat potential curves in the intermolecular degrees of freedom, and the latter to the excitation via the ;pσ-state; characterized by significantly steeper potential curves. The relaxation of all ;p-states; follows a double exponential decay with a lifetime around 110 ps for the dominant fast component.

Rate kernel theory for pseudo-first-order kinetics of diffusion-influenced reactions and application to fluorescence quenching kinetics.

PubMed

Yang, Mino

2007-06-07

Theoretical foundation of rate kernel equation approaches for diffusion-influenced chemical reactions is presented and applied to explain the kinetics of fluorescence quenching reactions. A many-body master equation is constructed by introducing stochastic terms, which characterize the rates of chemical reactions, into the many-body Smoluchowski equation. A Langevin-type of memory equation for the density fields of reactants evolving under the influence of time-independent perturbation is derived. This equation should be useful in predicting the time evolution of reactant concentrations approaching the steady state attained by the perturbation as well as the steady-state concentrations. The dynamics of fluctuation occurring in equilibrium state can be predicted by the memory equation by turning the perturbation off and consequently may be useful in obtaining the linear response to a time-dependent perturbation. It is found that unimolecular decay processes including the time-independent perturbation can be incorporated into bimolecular reaction kinetics as a Laplace transform variable. As a result, a theory for bimolecular reactions along with the unimolecular process turned off is sufficient to predict overall reaction kinetics including the effects of unimolecular reactions and perturbation. As the present formulation is applied to steady-state kinetics of fluorescence quenching reactions, the exact relation between fluorophore concentrations and the intensity of excitation light is derived.

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.

Application of spectroscopy and super-resolution microscopy: Excited state

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

Bhattacharjee, Ujjal

Photophysics of inorganic materials and organic molecules in complex systems have been extensively studied with absorption and emission spectroscopy.1-4 Steady-state and time-resolved fluorescence studies are commonly carried out to characterize excited-state properties of fluorophores. Although steady-state fluorescence measurements are widely used for analytical applications, time-resolved fluorescence measurements provide more detailed information about excited-state properties and the environment in the vicinity of the fluorophore. Many photophysical processes, such as photoinduced electron transfer (PET), rotational reorientation, solvent relaxation, and energy transfer, occur on a nanosecond (10 -9 s) timescale, thus affecting the lifetime of the fluorophores. Moreover, time-resolved microscopy methods, such asmore » lifetimeimaging, combine the benefits of the microscopic measurement and information-rich, timeresolved data. Thus, time-resolved fluorescence spectroscopy combined with microscopy can be used to quantify these processes and to obtain a deeper understanding of the chemical surroundings of the fluorophore in a small area under investigation. This thesis discusses various photophysical and super-resolution microscopic studies of organic and inorganic materials, which have been outlined below.« less

Diagnostics of Laser Produced Plume Under Carbon Nanotube Growth Conditions

NASA Technical Reports Server (NTRS)

Arepalli, Sivaram; Nikolaev, Pavel; Holmes, William; Scott, Carl D.

1999-01-01

This paper presents diagnostic data obtained from the plume of a graphite composite target during carbon nanotube production by the double-pulse laser oven method. The insitu emission spectrum (300 to 650 nm) is recorded at different locations upstream of the target and at different delay times from the lasers (IR and green). Spectral features are identified as emissions from C2 (Swan System: a (sup 3)pi(sub g) - delta (sup 3)pi(sub u) and C3 (Comet Head System: A (sup 1)pi(sub u) - chi (sup 1)sigma(sub u) (sup +). Experimental spectra are compared with computed spectra to estimate vibrational temperatures of excited state C2 in the range of 2500 to 4000 kappa The temporal evolution of the 510 nm band of C2 is monitored for two target positions in various locations which shows confinement of the plume in the inner tube and increase in plume velocity with temperature. The excitation spectra of C2 are obtained by using a dye laser to pump the (0,1) transition of the Swan System and collecting the Laser Induced Fluorescence signal from C2 These are used to obtain "ground-state" rotational and vibrational temperatures which are close to the oven temperature. Images of the plume are also collected and are compared with the spectral measurements.

Study of thermal annealing effect on Bragg gratings photo-inscribed in step-index polymer optical fibers

NASA Astrophysics Data System (ADS)

Hu, X.; Kinet, D.; Mégret, P.; Caucheteur, C.

2016-04-01

In this paper, both non-annealed and annealed trans-4-stilbenemethanol-doped step-index polymer optical fibers were photo-inscribed using a 325 nm HeCd laser with two different beam power densities reaching the fiber core. In the high density regime where 637 mW/mm2 are used, the grating reflectivity is stable over time after the photo-writing process but the reflected spectrum is of limited quality, as the grating physical length is limited to 1.2 mm. To produce longer gratings exhibiting more interesting spectral features, the beam is enlarged to 6 mm, decreasing the power density to 127 mW/mm2. In this second regime, the grating reflectivity is not stable after the inscription process but tends to decay for both kinds of fibers. A fortunate property in this case results from the possibility to fully recover the initial reflectivity using a post-inscription thermal annealing, where the gratings are annealed at 80 °C during 2 days. The observed evolutions for both regimes are attributed to the behavior of the excited intermediate states between the excited singlet and the ground singlet state of trans- and cis-isomers as well as the temperature-dependent glassy polymer matrix.

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.

Direct numerical simulation of two-dimensional wall-bounded turbulent flows from receptivity stage.

PubMed

Sengupta, T K; Bhaumik, S; Bhumkar, Y G

2012-02-01

Deterministic route to turbulence creation in 2D wall boundary layer is shown here by solving full Navier-Stokes equation by dispersion relation preserving (DRP) numerical methods for flow over a flat plate excited by wall and free stream excitations. Present results show the transition caused by wall excitation is predominantly due to nonlinear growth of the spatiotemporal wave front, even in the presence of Tollmien-Schlichting (TS) waves. The existence and linear mechanism of creating the spatiotemporal wave front was established in Sengupta, Rao and Venkatasubbaiah [Phys. Rev. Lett. 96, 224504 (2006)] via the solution of Orr-Sommerfeld equation. Effects of spatiotemporal front(s) in the nonlinear phase of disturbance evolution have been documented by Sengupta and Bhaumik [Phys. Rev. Lett. 107, 154501 (2011)], where a flow is taken from the receptivity stage to the fully developed 2D turbulent state exhibiting a k(-3) energy spectrum by solving the Navier-Stokes equation without any artifice. The details of this mechanism are presented here for the first time, along with another problem of forced excitation of the boundary layer by convecting free stream vortices. Thus, the excitations considered here are for a zero pressure gradient (ZPG) boundary layer by (i) monochromatic time-harmonic wall excitation and (ii) free stream excitation by convecting train of vortices at a constant height. The latter case demonstrates neither monochromatic TS wave, nor the spatiotemporal wave front, yet both the cases eventually show the presence of k(-3) energy spectrum, which has been shown experimentally for atmospheric dynamics in Nastrom, Gage and Jasperson [Nature 310, 36 (1984)]. Transition by a nonlinear mechanism of the Navier-Stokes equation leading to k(-3) energy spectrum in the inertial subrange is the typical characteristic feature of all 2D turbulent flows. Reproduction of the spectrum noted in atmospheric data (showing dominance of the k(-3) spectrum over the k(-5/3) spectrum in Nastrom et al.) in laboratory scale indicates universality of this spectrum for all 2D turbulent flows. Creation of universal features of 2D turbulence by a deterministic route has been established here for the first time by solving the Navier-Stokes equation without any modeling, as has been reported earlier in the literature by other researchers.

Late-time particle emission from laser-produced graphite plasma

NASA Astrophysics Data System (ADS)

Harilal, S. S.; Hassanein, A.; Polek, M.

2011-09-01

We report a late-time "fireworks-like" particle emission from laser-produced graphite plasma during its evolution. Plasmas were produced using graphite targets excited with 1064 nm Nd: yttrium aluminum garnet (YAG) laser in vacuum. The time evolution of graphite plasma was investigated using fast gated imaging and visible emission spectroscopy. The emission dynamics of plasma is rapidly changing with time and the delayed firework-like emission from the graphite target followed a black-body curve. Our studies indicated that such firework-like emission is strongly depended on target material properties and explained due to material spallation caused by overheating the trapped gases through thermal diffusion along the layer structures of graphite.

3D Modeling of Antenna Driven Slow Waves Excited by Antennas Near the Plasma Edge

NASA Astrophysics Data System (ADS)

Smithe, David; Jenkins, Thomas

2016-10-01

Prior work with the 3D finite-difference time-domain (FDTD) plasma and sheath model used to model ICRF antennas in fusion plasmas has highlighted the possibility of slow wave excitation at the very low end of the SOL density range, and thus the prudent need for a slow-time evolution model to treat SOL density modifications due to the RF itself. At higher frequency, the DIII-D helicon antenna has much easier access to a parasitic slow wave excitation, and in this case the Faraday screen provides the dominant means of controlling the content of the launched mode, with antenna end-effects remaining a concern. In both cases, the danger is the same, with the slow-wave propagating into a lower-hybrid resonance layer a short distance ( cm) away from the antenna, which would parasitically absorb power, transferring energy to the SOL edge plasma, primarily through electron-neutral collisions. We will present 3D modeling of antennas at both ICRF and helicon frequencies. We've added a slow-time evolution capability for the SOL plasma density to include ponderomotive force driven rarefaction from the strong fields in the vicinity of the antenna, and show initial application to NSTX antenna geometry and plasma configurations. The model is based on a Scalar Ponderomotive Potential method, using self-consistently computed local field amplitudes from the 3D simulation.

Relaxed structure of typical nitro explosives in the excited state: Observation, implication and application

NASA Astrophysics Data System (ADS)

Chu, Genbai; Yang, Zuhua; Xi, Tao; Xin, Jianting; Zhao, Yongqiang; He, Weihua; Shui, Min; Gu, Yuqiu; Xiong, Ying; Xu, Tao

2018-04-01

Understanding the structural, geometrical, and chemical changes that occur after an electronic excitation is essential to elucidate the inherent mechanism of nitro explosives. Herein, relaxed structures of typical nitro explosives in the lowest singlet excited state are investigated using time-dependent density functional theory. During the excitation process, the nitro group is activated and relaxes via geometrical change. The five explosives RDX, HMX, CL-20, PETN, and LLM-105 exhibit similar relaxed structures, and the impact sensitivity is related to their excitation energy. High-sensitivity δ-HMX has a lower excitation energy for relaxed structure than β-HMX. This study offers novel insight into energetic materials.

Quantitative conditions for time evolution in terms of the von Neumann equation

NASA Astrophysics Data System (ADS)

Wang, WenHua; Cao, HuaiXin; Chen, ZhengLi; Wang, Lie

2018-07-01

The adiabatic theorem describes the time evolution of the pure state and gives an adiabatic approximate solution to the Schödinger equation by choosing a single eigenstate of the Hamiltonian as the initial state. In quantum systems, states are divided into pure states (unite vectors) and mixed states (density matrices, i.e., positive operators with trace one). Accordingly, mixed states have their own corresponding time evolution, which is described by the von Neumann equation. In this paper, we discuss the quantitative conditions for the time evolution of mixed states in terms of the von Neumann equation. First, we introduce the definitions for uniformly slowly evolving and δ-uniformly slowly evolving with respect to mixed states, then we present a necessary and sufficient condition for the Hamiltonian of the system to be uniformly slowly evolving and we obtain some upper bounds for the adiabatic approximate error. Lastly, we illustrate our results in an example.

Heterogeneous to homogeneous melting transition visualized with ultrafast electron diffraction

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

None

The ultrafast laser excitation of matters leads to non-equilibrium states with complex solid-liquid phase transition dynamics. We used electron diffraction at mega-electronvolt energies to visualize the ultrafast melting of gold on the atomic scale length. For energy densities approaching the irreversible melting regime, we first observed heterogeneous melting on time scales of 100 ps to 1000 ps, transitioning to homogeneous melting that occurs catastrophically within 10-20 ps at higher energy densities. We showed evidence for the heterogeneous coexistence of solid and liquid. We determined the ion and electron temperature evolution and found superheated conditions. Our results constrain the electron-ion couplingmore » rate, determine the Debye temperature and reveal the melting sensitivity to nucleation seeds.« less

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

Le, Hai P.; Cambier, Jean -Luc

Here, we present a numerical model and a set of conservative algorithms for Non-Maxwellian plasma kinetics with inelastic collisions. These algorithms self-consistently solve for the time evolution of an isotropic electron energy distribution function interacting with an atomic state distribution function of an arbitrary number of levels through collisional excitation, deexcitation, as well as ionization and recombination. Electron-electron collisions, responsible for thermalization of the electron distribution, are also included in the model. The proposed algorithms guarantee mass/charge and energy conservation in a single step, and is applied to the case of non-uniform gridding of the energy axis in the phasemore » space of the electron distribution function. Numerical test cases are shown to demonstrate the accuracy of the method and its conservation properties.« less

Laser-induced breakup of helium 3S 1s2s with intermediate doubly excited states

NASA Astrophysics Data System (ADS)

Simonsen, A. S.; Bachau, H.; Førre, M.

2014-02-01

Solving the time-dependent Schrödinger equation in full dimensionality for two electrons, it is found that in the XUV regime the two-photon double ionization dynamics of He(1s2s) is predominantly dictated by the process of resonance enhanced multiphoton ionization via doubly excited states (DESs). We have studied a pump-probe scenario where the full laser-driven breakup of the 3S 1s2s metastable state is dominated by intermediate quasiresonant excitation to doubly excited (autoionizing) states in the 3Po series. Clear evidence of multipath interference effects is revealed in the resulting angular distributions of the ejected electrons in cases where more than one intermediate DES is populated in the process.

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.

Spectroscopic Studies of Carotenoid-to-Bacteriochlorophyll Energy Transfer in LHRC Photosynthetic Complex from Roseiflexus castenholzii

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

Niedzwiedzki, Dariusz; Collins, Aaron M.; LaFountain, Amy M.

Carotenoids present in the photosynthetic light-harvesting reaction center (LHRC) complex from chlorosome lacking filamentous anoxygenic phototroph, Roseiflexus castenholzii were purified and characterized for their photochemical properties. The LHRC from anaerobically grown cells contains five different carotenoids, methoxy-keto-myxocoxanthin, γ-carotene, and its three derivatives, whereas the LHRC from aerobically grown cells contains only three carotenoid pigments with methoxy-keto-myxocoxanthin being the dominant one. The spectroscopic properties and dynamics of excited singlet states of the carotenoids were studied by steady-state absorption, fluorescence and ultrafast time-resolved optical spectroscopy in organic solvent and in the intact LHRC complex. Time-resolved transient absorption spectroscopy performed in the near-infraredmore » (NIR) on purified carotenoids combined with steady-state absorption spectroscopy led to the precise determination of values of the energies of the S 1(2 1A g -) excited state. Global and single wavelength fitting of the ultrafast spectral and temporal data sets of the carotenoids in solvents and in the LHRC revealed the pathways of de-excitation of the carotenoid excited states.« less

Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion

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

Winghart, Marc-Oliver, E-mail: marc-oliver.winghart@kit.edu; Unterreiner, Andreas-Neil; Yang, Ji-Ping

2016-02-07

Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt{sub 2}(μ-P{sub 2}O{sub 5}H{sub 2}){sub 4} + 2H]{sup 2−} after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet {sup 1}A{sub 2u} state and concomitant rise in population of the triplet {sup 3}A{sub 2u} state, via sub-picosecond intersystem crossing (ISC). Wemore » find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet {sup 1}A{sub 2u} state takes only a few picoseconds, ESETD from the triplet {sup 3}A{sub 2u} state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt{sub 2}(μ-P{sub 2}O{sub 5}H{sub 2}){sub 4} + 2H]{sup 2−} is the first example of a photoexcited multianion for which ESETD has been observed following ISC.« less

The Evolution of Modulated Wavetrains Into Turbulent Spots

NASA Technical Reports Server (NTRS)

Gaster, M.

2007-01-01

Experiment are being carried out to study the process by which th almost periodic disturbance waves generated naturally by the freestream evolve into turbulence. The boundary layer on a flat plate has been used for this study. The novelty of the approach is in the form of artificial excitation that is used. In this work the flow is excited artificially by deterministic white noise. The weak T-S wave created develops down stream, becomes nonlinear and blows up locally onto a highly distorted flow. These large local distortions of the mean flow allow very high frequency disturbances to grow and form into small turbulent spots. The spots arise from the excitation, and if the same noise sequence is repeated a spot will form at the same position and time instant relative to the excitation.

Ultrafast Excited-state Deactivation of Flavins Bound to Dodecin*

PubMed Central

Staudt, Heike; Oesterhelt, Dieter; Grininger, Martin; Wachtveitl, Josef

2012-01-01

Dodecins, a group of flavin-binding proteins with a dodecameric quaternary structure, are able to incorporate two flavins within each of their six identical binding pockets building an aromatic tetrade with two tryptophan residues. Dodecin from the archaeal Halobacterium salinarum is a riboflavin storage device. We demonstrate that unwanted side reactions induced by reactive riboflavin species and degradation of riboflavin are avoided by ultrafast depopulation of the reactive excited state of riboflavin. Intriguingly, in this process, the staggered riboflavin dimers do not interact in ground and photoexcited states. Rather, within the tetrade assembly, each riboflavin is kept under the control of the respective adjacent tryptophan, which suggests that the stacked arrangement is a matter of optimizing the flavin load. We further identify an electron transfer in combination with a proton transfer as a central element of the effective excited state depopulation mechanism. Structural and functional comparisons of the archaeal dodecin with bacterial homologs reveal diverging evolution. Bacterial dodecins bind the flavin FMN instead of riboflavin and exhibit a clearly different binding pocket design with inverse incorporations of flavin dimers. The different adoption of flavin changes photochemical properties, making bacterial dodecin a comparably less efficient quencher of flavins. This supports a functional role different for bacterial and archaeal dodecins. PMID:22451648

Kinetics and dynamics of near-resonant vibrational energy transfer in gas ensembles of atmospheric interest

NASA Astrophysics Data System (ADS)

McCaffery, Anthony J.

2018-03-01

This study of near-resonant, vibration-vibration (V-V) gas-phase energy transfer in diatomic molecules uses the theoretical/computational method, of Marsh & McCaffery (Marsh & McCaffery 2002 J. Chem. Phys. 117, 503 (doi:10.1063/1.1489998)) The method uses the angular momentum (AM) theoretical formalism to compute quantum-state populations within the component molecules of large, non-equilibrium, gas mixtures as the component species proceed to equilibration. Computed quantum-state populations are displayed in a number of formats that reveal the detailed mechanism of the near-resonant V-V process. Further, the evolution of quantum-state populations, for each species present, may be followed as the number of collision cycles increases, displaying the kinetics of evolution for each quantum state of the ensemble's molecules. These features are illustrated for ensembles containing vibrationally excited N2 in H2, O2 and N2 initially in their ground states. This article is part of the theme issue `Modern theoretical chemistry'.

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.

  Ultrasonic monitoring of fish thawing process optimal time of thawing and effect of freezing/thawing.

PubMed

El Kadi, Youssef Ait; Moudden, Ali; Faiz, Bouazza; Maze, Gerard; Decultot, Dominique

2013-01-01

Fish quality is traditionally controlled by chemical and microbiological analysis. The non-destructive control presents an enormous professional interest thanks to the technical contribution and precision of the analysis to which it leads. This paper presents the results obtained from a characterisation of fish thaw-ing process by the ultrasonic technique, with monitoring thermal processing from frozen to defrosted states. The study was carried out on fish type red drum and salmon cut into fillets of 15 mm thickness. After being frozen at -20°C, the sample is enclosed in a plexiglas vessel with parallel walls at the ambient temperature 30°C and excited in perpendicular incidence at 0.5 MHz by an ultrasonic pulser-receiver Sofranel 5052PR. the technique of measurement consists to study the signals reflected by fish during its thawing, the specific techniques of signal processing are implemented to deduce informations characterizing the state of fish and its thawing process by examining the evolution of the position echoes reflected by the sample and the viscoelastic parameters of fish during its thawing. The obtained results show a relationship between the thermal state of fish and its acoustic properties, which allowed to deduce the optimal time of the first thawing in order to restrict the growth of microbial flora. For salmon, the results show a decrease of 36% of the time of the second thawing and an increase of 10.88% of the phase velocity, with a decrease of 65.5% of the peak-to-peak voltage of the signal reflected, thus a decrease of the acoustic impedance. This study shows an optimal time and an evolution rate of thawing specific to each type offish and a correlation between the acoustic behavior of fish and its thermal state which approves that this technique of ultrasonic monitoring can substitute the control using the destructive chemical analysis in order to monitor the thawing process and to know whether a fish has suffered an accidental thawing.

Laser pulses for coherent xuv Raman excitation

NASA Astrophysics Data System (ADS)

Greenman, Loren; Koch, Christiane P.; Whaley, K. Birgitta

2015-07-01

We combine multichannel electronic structure theory with quantum optimal control to derive femtosecond-time-scale Raman pulse sequences that coherently populate a valence excited state. For a neon atom, Raman target populations of up to 13% are obtained. Superpositions of the ground and valence Raman states with a controllable relative phase are found to be reachable with up to 4.5% population and arbitrary phase control facilitated by the pump pulse carrier-envelope phase. Analysis of the optimized pulse structure reveals a sequential mechanism in which the valence excitation is reached via a fast (femtosecond) population transfer through an intermediate resonance state in the continuum rather than avoiding intermediate-state population with simultaneous or counterintuitive (stimulated Raman adiabatic passage) pulse sequences. Our results open a route to coupling valence excitations and core-hole excitations in molecules and aggregates that locally address specific atoms and represent an initial step towards realization of multidimensional spectroscopy in the xuv and x-ray regimes.

Kinetics model for the wavelength-dependence of excited-state dynamics of hetero-FRET sensors

NASA Astrophysics Data System (ADS)

Schwarz, Jacob; Leighton, Ryan; Leopold, Hannah J.; Currie, Megan; Boersma, Arnold J.; Sheets, Erin D.; Heikal, Ahmed A.

2017-08-01

Foerster (or fluorescence) resonance energy transfer (FRET) is a powerful tool for investigating protein-protein interactions, in both living cells and in controlled environments. A typical hetero-FRET pair consists of a donor and acceptor tethered together with a linker. The corresponding energy transfer efficiency of a hetero-FRET pair probe depends upon the donor-acceptor distance, relative dipole orientation, and spectral overlap. Because of the sensitivity of the energy transfer efficiency on the donor-acceptor distance, FRET is often referred to as a "molecular ruler". Time-resolved fluorescence approach for measuring the excited-state lifetime of the donor and acceptor emissions is one of the most reliable approaches for quantitative assessment of the energy transfer efficiency in hetero-FRET pairs. In this contribution, we provide an analytical kinetics model that describes the excited-state depopulation of a FRET probe as a means to predicts the time-resolved fluorescence profile as a function of excitation and detection wavelengths. In addition, we used this developed kinetics model to simulate the time-dependence of the excited-state population of both the donor and acceptor. These results should serve as a guide for our ongoing studies of newly developed hetero-FRET sensors (mCerulean3-linker-mCitrine) that are designed specifically for in vivo studies of macromolecular crowding. The same model is applicable to other FRET pairs with the careful consideration of their steady-state spectroscopy and the experimental design for wavelength- dependence of the fluorescence lifetime measurements.

Systematics of hot giant electric dipole resonance widths

NASA Astrophysics Data System (ADS)

Schiller, A.; Thoennessen, M.; McAlpine, K. M.

2007-05-01

Giant Electric Dipole Resonance (GDR) parameters for γ decay to excited states with finite spin and temperature have been compiled by two of the authors ( nucl-ex/0605004). Over 100 original works have been reviewed and from some 70 of them, more than 300 sets of hot GDR parameters for different isotopes, excitation energies, and spin regions have been extracted. All parameter sets have been brought onto a common footing by calculating the equivalent Lorentzian parameters. Together with a complementary compilation by Samuel S. Dietrich and Barry L. Berman [At. Data Nucl. Data Tables 38, 199-338, (1988)] on ground-state photo-neutron and photo-absorption cross sections and their Lorentzian parameters, it is now possible by means of a comparison of the two data sets to shed light on the evolution of GDR parameters with temperature and spin.

High temperature electronic excitation and ionization rates in gases

NASA Technical Reports Server (NTRS)

Hansen, Frederick

1991-01-01

The relaxation times for electronic excitation due to electron bombardment of atoms was found to be quite short, so that electron kinetic temperature (T sub e) and the electron excitation temperature (T asterisk) should equilibrate quickly whenever electrons are present. However, once equilibrium has been achieved, further energy to the excited electronic states and to the kinetic energy of free electrons must be fed in by collisions with heavy particles that cause vibrational and electronic state transitions. The rate coefficients for excitation of electronic states produced by heavy particle collision have not been well known. However, a relatively simple semi-classical theory has been developed here which is analytic up to the final integration over a Boltzmann distribution of collision energies; this integral can then be evaluated numerically by quadrature. Once the rate coefficients have been determined, the relaxation of electronic excitation energy can be evaluated and compared with the relaxation rates of vibrational excitation. Then the relative importance of these two factors, electronic excitation and vibrational excitation by heavy particle collision, on the transfer of energy to free electron motion, can be assessed.

Coulomb excitation with radioactive nuclear beam of 64Cu

NASA Astrophysics Data System (ADS)

Guo, Gang; Xu, Jincheng; Chen, Quan; He, Ming; Qin, Jiuchang; Shen, Dongjun; Wu, Shaoyong; Jiang, Yongliang; Cheng, Yehao

2003-09-01

The radioactive nuclear beam of 64Cu was obtained utilizing a two-stage method at the HI-13 tandem accelerator of China Institute of Atomic Energy. The B(E2) value of the first excitation state of 64Cu has been directly measured for the first time by Coulomb excitation method, using the radioactive nuclear beam of 64Cu. An upper limit of the B(E2;2 1+→1 gs+) value from the first excitation state to the ground state of 64Cu is determined to be 49 W.u., which is significantly smaller than 250±170 W.u., the value adopted by Nuclear Data Sheets. The reliability of the experimental method was verified by simultaneously performing the Coulomb excitation experiment of 181Ta.

Time Evolution of Radiation-Induced Luminescence in Terbium-Doped Silicate Glass

NASA Technical Reports Server (NTRS)

West, Michael S.; Winfree, William P.

1996-01-01

A study was made on two commercially available terbium-doped silicate glasses. There is an increased interest in silicate glasses doped with rare-earth ions for use in high-energy particle detection and radiographic applications. These glasses are of interest due to the fact that they can be formed into small fiber sensors; a property that can be used to increase the spatial resolution of a detection system. Following absorption of radiation, the terbium ions become excited and then emit photons via 4f-4f electronic transitions as they relax back to the ground state. The lifetime of these transitions is on the order of milliseconds. A longer decay component lasting on the order of minutes has also been observed. While radiative transitions in the 4f shell of rare-earth ions are generally well understood by the Judd-Olfelt theory, the pr'esence of a longer luminescence decay component is not. Experimental evidence that the long decay component is due, in part, to the thermal release of trapped charge carriers will be presented. In addition, a theoretical model describing the time evolution of the radiation-induced luminescence will be presented.

Two-color two-photon excited fluorescence of indole: Determination of wavelength-dependent molecular parameters

NASA Astrophysics Data System (ADS)

Herbrich, Sebastian; Al-Hadhuri, Tawfik; Gericke, Karl-Heinz; Shternin, Peter S.; Smolin, Andrey G.; Vasyutinskii, Oleg S.

2015-01-01

We present a detailed study of two-color two-photon excited fluorescence in indole dissolved in propylene glycol. Femtosecond excitation pulses at effective wavelengths from 268 to 293.33 nm were used to populate the two lowest indole excited states 1La and 1Lb and polarized fluorescence was then detected. All seven molecular parameters and the two-photon polarization ratio Ω containing information on two-photon absorption dynamics, molecular lifetime τf, and rotation correlation time τrot have been determined from experiment and analyzed as a function of the excitation wavelength. The analysis of the experimental data has shown that 1Lb-1La inversion occurred under the conditions of our experiment. The two-photon absorption predominantly populated the 1La state at all excitation wavelengths but in the 287-289 nm area which contained an absorption hump of the 1Lb state 0-0 origin. The components of the two-photon excitation tensor S were analyzed giving important information on the principal tensor axes and absorption symmetry. The results obtained are in a good agreement with the results reported by other groups. The lifetime τf and the rotation correlation time τrot showed no explicit dependence on the effective excitation wavelength. Their calculated weighted average values were found to be τf = 3.83 ± 0.14 ns and τrot = 0.74 ± 0.06 ns.

Multiresolution quantum chemistry in multiwavelet bases: excited states from time-dependent Hartree–Fock and density functional theory via linear response

DOE PAGES

Yanai, Takeshi; Fann, George I.; Beylkin, Gregory; ...

2015-02-25

Using the fully numerical method for time-dependent Hartree–Fock and density functional theory (TD-HF/DFT) with the Tamm–Dancoff (TD) approximation we use a multiresolution analysis (MRA) approach to present our findings. From a reformulation with effective use of the density matrix operator, we obtain a general form of the HF/DFT linear response equation in the first quantization formalism. It can be readily rewritten as an integral equation with the bound-state Helmholtz (BSH) kernel for the Green's function. The MRA implementation of the resultant equation permits excited state calculations without virtual orbitals. Moreover, the integral equation is efficiently and adaptively solved using amore » numerical multiresolution solver with multiwavelet bases. Our implementation of the TD-HF/DFT methods is applied for calculating the excitation energies of H 2, Be, N 2, H 2O, and C 2H 4 molecules. The numerical errors of the calculated excitation energies converge in proportion to the residuals of the equation in the molecular orbitals and response functions. The energies of the excited states at a variety of length scales ranging from short-range valence excitations to long-range Rydberg-type ones are consistently accurate. It is shown that the multiresolution calculations yield the correct exponential asymptotic tails for the response functions, whereas those computed with Gaussian basis functions are too diffuse or decay too rapidly. Finally, we introduce a simple asymptotic correction to the local spin-density approximation (LSDA) so that in the TDDFT calculations, the excited states are correctly bound.« less

Short-time dynamics of 2-thiouracil in the light absorbing S{sub 2}(ππ{sup ∗}) state

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

Jiang, Jie; Zhang, Teng-shuo; Xue, Jia-dan

2015-11-07

Ultrahigh quantum yields of intersystem crossing to the lowest triplet state T{sub 1} are observed for 2-thiouracils (2TU), which is in contrast to the natural uracils that predominantly exhibit ultrafast internal conversion to the ground state upon excitation to the singlet excited state. The intersystem crossing mechanism of 2TU has recently been investigated using second-order perturbation methods with a high-level complete-active space self-consistent field. Three competitive nonadiabatic pathways to the lowest triplet state T{sub 1} from the initially populated singlet excited state S{sub 2} were proposed. We investigate the initial decay dynamics of 2TU from the light absorbing excited statesmore » using resonance Raman spectroscopy, time-dependent wave-packet theory in the simple model, and complete-active space self-consistent field (CASSCF) and time dependent-Becke’s three-parameter exchange and correlation functional with the Lee-Yang-Parr correlation functional (TD-B3LYP) calculations. The obtained short-time structural dynamics in easy-to-visualize internal coordinates were compared with the CASSCF(16,11) predicted key nonadiabatic decay routes. Our results indicate that the predominant decay pathway initiated at the Franck-Condon region is toward the S{sub 2}/S{sub 1} conical intersection point and S{sub 2}T{sub 3} intersystem crossing point, but not toward the S{sub 2}T{sub 2} intersystem crossing point.« less

Computational studies on the excited state properties of citrinin and application in fluorescence analysis

USDA-ARS?s Scientific Manuscript database

Citrinin is a mycotoxin of increasing concern that is produced by fungi associated with maize, red yeast rice, and other agricultural commodities. A comprehensive time-dependent density functional study on the excited state properties of citrinin was conducted to identify parameters for reliable det...

The Protolysis of Singlet Excited B-Naphtol.

ERIC Educational Resources Information Center

van Stam, Jan; Lofroth, Jan-Erik

1986-01-01

Presents a two-day experiment to estimate the pK for the protolysis of beta-naphtol in its ground state and the first singlet excited state. Results are compared to results obtained from the integrated rate equations in which values of the rate constants were taken from a time-resolved study. (JN)

Improving Rydberg Excitations within Time-Dependent Density Functional Theory with Generalized Gradient Approximations: The Exchange-Enhancement-for-Large-Gradient Scheme.

PubMed

Li, Shaohong L; Truhlar, Donald G

2015-07-14

Time-dependent density functional theory (TDDFT) with conventional local and hybrid functionals such as the local and hybrid generalized gradient approximations (GGA) seriously underestimates the excitation energies of Rydberg states, which limits its usefulness for applications such as spectroscopy and photochemistry. We present here a scheme that modifies the exchange-enhancement factor to improve GGA functionals for Rydberg excitations within the TDDFT framework while retaining their accuracy for valence excitations and for the thermochemical energetics calculated by ground-state density functional theory. The scheme is applied to a popular hybrid GGA functional and tested on data sets of valence and Rydberg excitations and atomization energies, and the results are encouraging. The scheme is simple and flexible. It can be used to correct existing functionals, and it can also be used as a strategy for the development of new functionals.

Improving Rydberg Excitations within Time-Dependent Density Functional Theory with Generalized Gradient Approximations: The Exchange-Enhancement-for-Large-Gradient Scheme

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

Li, Shaohong L.; Truhlar, Donald G.

Time-dependent density functional theory (TDDFT) with conventional local and hybrid functionals such as the local and hybrid generalized gradient approximations (GGA) seriously underestimates the excitation energies of Rydberg states, which limits its usefulness for applications such as spectroscopy and photochemistry. We present here a scheme that modifies the exchange-enhancement factor to improve GGA functionals for Rydberg excitations within the TDDFT framework while retaining their accuracy for valence excitations and for the thermochemical energetics calculated by ground-state density functional theory. The scheme is applied to a popular hybrid GGA functional and tested on data sets of valence and Rydberg excitations andmore » atomization energies, and the results are encouraging. The scheme is simple and flexible. It can be used to correct existing functionals, and it can also be used as a strategy for the development of new functionals.« less

Improving Rydberg Excitations within Time-Dependent Density Functional Theory with Generalized Gradient Approximations: The Exchange-Enhancement-for-Large-Gradient Scheme

DOE PAGES

Li, Shaohong L.; Truhlar, Donald G.

2015-05-22

Time-dependent density functional theory (TDDFT) with conventional local and hybrid functionals such as the local and hybrid generalized gradient approximations (GGA) seriously underestimates the excitation energies of Rydberg states, which limits its usefulness for applications such as spectroscopy and photochemistry. We present here a scheme that modifies the exchange-enhancement factor to improve GGA functionals for Rydberg excitations within the TDDFT framework while retaining their accuracy for valence excitations and for the thermochemical energetics calculated by ground-state density functional theory. The scheme is applied to a popular hybrid GGA functional and tested on data sets of valence and Rydberg excitations andmore » atomization energies, and the results are encouraging. The scheme is simple and flexible. It can be used to correct existing functionals, and it can also be used as a strategy for the development of new functionals.« less

Excited states of aniline by photoabsorption spectroscopy in the 30,000-90,000 cm(-1) region using synchrotron radiation.

PubMed

Rajasekhar, B N; Veeraiah, A; Sunanda, K; Jagatap, B N

2013-08-14

The photoabsorption spectrum of aniline (C6H5NH2) in gas phase in the 30,000-90,000 cm(-1) (3.7-11.2 eV) region is recorded at resolution limit of 0.008 eV using synchrotron radiation source for the first time to comprehend the nature of the excited valence and Rydberg states. The first half of the energy interval constitutes the richly structured valence transitions from the ground to excited states up to the first ionization potential (IP) at 8.02 eV. The spectrum in the second half consists of vibrational features up to second IP (9.12 eV) and structureless broad continuum up to the third IP (10.78 eV). The electronic states are assigned mainly to the singlets belonging to π → π* transitions. A few weak initial members of Rydberg states arising from π → 4s, np or nd transitions are also identified. Observed vibrational features are assigned to transitions from the ground state A' to the excited states 1A", 3A', 5A", 6A', and 10A" in C(s) symmetry. Time dependent density functional theory (TDDFT) calculations at B3LYP level of theory are employed to obtain the vertical excitation energies and the symmetries of the excited states in equilibrium configuration. The computed values of the transition energies agree fairly well with the experimental data. Further the calculated oscillator strengths are used to substantiate the assignments of the bands. The work provides a comprehensive picture of the vacuum ultraviolet photoabsorption spectrum of aniline up to its third ionization limit.

Time-resolved radiation chemistry: Dynamics of electron attachment to uracil following UV excitation of iodide-uracil complexes

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

King, Sarah B.; Yandell, Margaret A.; Stephansen, Anne B.

Electron attachment to uracil was investigated by applying time-resolved photoelectron imaging to iodide-uracil (I{sup –}U) complexes. In these studies, an ultraviolet pump pulse initiated charge transfer from the iodide to the uracil, and the resulting dynamics of the uracil temporary negative ion were probed. Five different excitation energies were used, 4.00 eV, 4.07 eV, 4.14 eV, 4.21 eV, and 4.66 eV. At the four lowest excitation energies, which lie near the vertical detachment energy of the I{sup –}U complex (4.11 eV), signatures of both the dipole bound (DB) as well as the valence bound (VB) anion of uracil were observed.more » In contrast, only the VB anion was observed at 4.66 eV, in agreement with previous experiments in this higher energy range. The early-time dynamics of both states were highly excitation energy dependent. The rise time of the DB anion signal was ∼250 fs at 4.00 eV and 4.07 eV, ∼120 fs at 4.14 eV and cross-correlation limited at 4.21 eV. The VB anion rise time also changed with excitation energy, ranging from 200 to 300 fs for excitation energies 4.00–4.21 eV, to a cross-correlation limited time at 4.66 eV. The results suggest that the DB state acts as a “doorway” state to the VB anion at 4.00–4.21 eV, while direct attachment to the VB anion occurs at 4.66 eV.« less

Unveiling the excited state energy transfer pathways in peridinin-chlorophyll a-protein by ultrafast multi-pulse transient absorption spectroscopy.

PubMed

Redeckas, Kipras; Voiciuk, Vladislava; Zigmantas, Donatas; Hiller, Roger G; Vengris, Mikas

2017-04-01

Time-resolved multi-pulse methods were applied to investigate the excited state dynamics, the interstate couplings, and the excited state energy transfer pathways between the light-harvesting pigments in peridinin-chlorophyll a-protein (PCP). The utilized pump-dump-probe techniques are based on perturbation of the regular PCP energy transfer pathway. The PCP complexes were initially excited with an ultrashort pulse, resonant to the S 0 →S 2 transition of the carotenoid peridinin. A portion of the peridinin-based emissive intramolecular charge transfer (ICT) state was then depopulated by applying an ultrashort NIR pulse that perturbed the interaction between S 1 and ICT states and the energy flow from the carotenoids to the chlorophylls. The presented data indicate that the peridinin S 1 and ICT states are spectrally distinct and coexist in an excited state equilibrium in the PCP complex. Moreover, numeric analysis of the experimental data asserts ICT→Chl-a as the main energy transfer pathway in the photoexcited PCP systems. Copyright © 2017 Elsevier B.V. All rights reserved.

Interstate vibronic coupling constants between electronic excited states for complex molecules

NASA Astrophysics Data System (ADS)

Fumanal, Maria; Plasser, Felix; Mai, Sebastian; Daniel, Chantal; Gindensperger, Etienne

2018-03-01

In the construction of diabatic vibronic Hamiltonians for quantum dynamics in the excited-state manifold of molecules, the coupling constants are often extracted solely from information on the excited-state energies. Here, a new protocol is applied to get access to the interstate vibronic coupling constants at the time-dependent density functional theory level through the overlap integrals between excited-state adiabatic auxiliary wavefunctions. We discuss the advantages of such method and its potential for future applications to address complex systems, in particular, those where multiple electronic states are energetically closely lying and interact. We apply the protocol to the study of prototype rhenium carbonyl complexes [Re(CO)3(N,N)(L)]n+ for which non-adiabatic quantum dynamics within the linear vibronic coupling model and including spin-orbit coupling have been reported recently.

Investigating the intersystem crossing rate and triplet quantum yield of Protoporphyrin IX by means of pulse train fluorescence technique

NASA Astrophysics Data System (ADS)

Gotardo, Fernando; Cocca, Leandro H. Z.; Acunha, Thiago V.; Longoni, Ana; Toldo, Josene; Gonçalves, Paulo F. B.; Iglesias, Bernardo A.; De Boni, Leonardo

2017-04-01

Photophysical investigations of PPIX were described in order to determine the triplet conversion efficiency. Time resolved fluorescence and pulse train fluorescence were employed to characterize the main mechanism responsible for deactivation of the first singlet excited state (excited singlet and triplet states). Single pulse and Z-Scan analysis were employed to measure the singlet excited state absorption cross-sections. Theoretical calculations were performed in order to get some properties of PPIX in ground state, first singlet and triplet excited state. A TD-DFT result shows a great possibility of ISC associated to out-of-plane distortions in porphyrinic ring. Furthermore, the B and Q bands in the calculated spectrum are assigned to the four frontier molecular orbitals as proposed by Gouterman for free-based porphyrins.

Controlling the excited-state dynamics of low band gap, near-infrared absorbers via proquinoidal unit electronic structural modulation

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

Bai, Yusong; Rawson, Jeff; Roget, Sean A.

While the influence of proquinoidal character upon the linear absorption spectrum of low optical bandgap π-conjugated polymers and molecules is well understood, its impact upon excited-state relaxation pathways and dynamics remains obscure. We report the syntheses, electronic structural properties, and excited-state dynamics of a series of model highly conjugated near-infrared (NIR)-absorbing chromophores based on a (porphinato)metal(II)-proquinoidal spacer-(porphinato)metal(II) (PM-Sp-PM) structural motif. A combination of excited-state dynamical studies and time-dependent density functional theory calculations: (i) points to the cardinal role that excited-state configuration interaction (CI) plays in determining the magnitudes of S 1 → S 0 radiative (k r), S 1 → T 1 intersystem crossing (k ISC), and S 1 → S 0 internal conversion (k IC) rate constants in these PM-Sp-PM chromophores, and (ii) suggests that a primary determinant of CI magnitude derives from the energetic alignment of the PM and Sp fragment LUMOs (ΔE L). These insights not only enable steering of excited-state relaxation dynamics of high oscillator strength NIR absorbers to realize either substantial fluorescence or long-lived triplets (τmore » $$_ {T_1}$$ > μs) generated at unit quantum yield (Φ ISC = 100%), but also crafting of those having counter-intuitive properties: for example, while (porphinato)platinum compounds are well known to generate non-emissive triplet states (Φ ISC = 100%) upon optical excitation at ambient temperature, diminishing the extent of excited-state CI in these systems realizes long-wavelength absorbing heavy-metal fluorophores. In conclusion, this work highlights approaches to: (i) modulate low-lying singlet excited-state lifetime over the picosecond-to-nanosecond time domain, (ii) achieve NIR fluorescence with quantum yields up to 25%, (iii) tune the magnitude of S 1–T 1 ISC rate constant from 10 9 to 10 12 s -1 and (iv) realize T 1-state lifetimes that range from ~0.1 to several μs, for these model PM-Sp-PM chromophores, and renders new insights to evolve bespoke photophysical properties for low optical bandgap π-conjugated polymers and molecules based on proquinoidal conjugation motifs.« less

Controlling the excited-state dynamics of low band gap, near-infrared absorbers via proquinoidal unit electronic structural modulation

DOE PAGES

Bai, Yusong; Rawson, Jeff; Roget, Sean A.; ...

2017-06-07

While the influence of proquinoidal character upon the linear absorption spectrum of low optical bandgap π-conjugated polymers and molecules is well understood, its impact upon excited-state relaxation pathways and dynamics remains obscure. We report the syntheses, electronic structural properties, and excited-state dynamics of a series of model highly conjugated near-infrared (NIR)-absorbing chromophores based on a (porphinato)metal(II)-proquinoidal spacer-(porphinato)metal(II) (PM-Sp-PM) structural motif. A combination of excited-state dynamical studies and time-dependent density functional theory calculations: (i) points to the cardinal role that excited-state configuration interaction (CI) plays in determining the magnitudes of S 1 → S 0 radiative (k r), S 1 → T 1 intersystem crossing (k ISC), and S 1 → S 0 internal conversion (k IC) rate constants in these PM-Sp-PM chromophores, and (ii) suggests that a primary determinant of CI magnitude derives from the energetic alignment of the PM and Sp fragment LUMOs (ΔE L). These insights not only enable steering of excited-state relaxation dynamics of high oscillator strength NIR absorbers to realize either substantial fluorescence or long-lived triplets (τmore » $$_ {T_1}$$ > μs) generated at unit quantum yield (Φ ISC = 100%), but also crafting of those having counter-intuitive properties: for example, while (porphinato)platinum compounds are well known to generate non-emissive triplet states (Φ ISC = 100%) upon optical excitation at ambient temperature, diminishing the extent of excited-state CI in these systems realizes long-wavelength absorbing heavy-metal fluorophores. In conclusion, this work highlights approaches to: (i) modulate low-lying singlet excited-state lifetime over the picosecond-to-nanosecond time domain, (ii) achieve NIR fluorescence with quantum yields up to 25%, (iii) tune the magnitude of S 1–T 1 ISC rate constant from 10 9 to 10 12 s -1 and (iv) realize T 1-state lifetimes that range from ~0.1 to several μs, for these model PM-Sp-PM chromophores, and renders new insights to evolve bespoke photophysical properties for low optical bandgap π-conjugated polymers and molecules based on proquinoidal conjugation motifs.« less

Sounds of Failure: Passive Acoustic Measurements of Excited Vibrational Modes

NASA Astrophysics Data System (ADS)

Brzinski, Theodore A.; Daniels, Karen E.

2018-05-01

Granular materials can fail through spontaneous events like earthquakes or brittle fracture. However, measurements and analytic models which forecast failure in this class of materials, while of both fundamental and practical interest, remain elusive. Materials including numerical packings of spheres, colloidal glasses, and granular materials have been known to develop an excess of low-frequency vibrational modes as the confining pressure is reduced. Here, we report experiments on sheared granular materials in which we monitor the evolving density of excited modes via passive monitoring of acoustic emissions. We observe a broadening of the distribution of excited modes coincident with both bulk and local plasticity, and evolution in the shape of the distribution before and after bulk failure. These results provide a new interpretation of the changing state of the material on its approach to stick-slip failure.

Sounds of Failure: Passive Acoustic Measurements of Excited Vibrational Modes.

PubMed

Brzinski, Theodore A; Daniels, Karen E

2018-05-25

Granular materials can fail through spontaneous events like earthquakes or brittle fracture. However, measurements and analytic models which forecast failure in this class of materials, while of both fundamental and practical interest, remain elusive. Materials including numerical packings of spheres, colloidal glasses, and granular materials have been known to develop an excess of low-frequency vibrational modes as the confining pressure is reduced. Here, we report experiments on sheared granular materials in which we monitor the evolving density of excited modes via passive monitoring of acoustic emissions. We observe a broadening of the distribution of excited modes coincident with both bulk and local plasticity, and evolution in the shape of the distribution before and after bulk failure. These results provide a new interpretation of the changing state of the material on its approach to stick-slip failure.

Giant Spin Gap and Magnon Localization in the Disordered Heisenberg Antiferromagnet Sr2Ir1-xRuxO4

NASA Astrophysics Data System (ADS)

Cao, Yue; Liu, Xuerong; Xu, Wenhu; Yin, Weiguo; Meyers, Derek; Kim, Jungho; Casa, Diego; Upton, Mary; Gog, Thomas; Berlijn, Tom; Alvarez, Gonzalo; Yuan, Shujuan; Terzic, Jasminka; Tranquada, J. M.; Hill, John; Cao, Gang; Konik, Robert; Dean, M. P. M.

We study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr_2Ir_1-xRu_xO_4. A gigantic magnetic gap greater than 40 meV opens at x = 0.27 and increases with Ru concentration, from 40 meV to >150 meV, rendering the dispersive magnetic excitations in Sr2IrO4 almost momentum independent. Up to a Ru concentration of x = 0.77, both experiments and first-principles calculations show the Ir J_eff = 1/2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest neighbor ferromagnetic coupling.

Photodissociation dynamics of allyl chloride at 200 and 266 nm studied by time-resolved mass spectrometry and photoelectron imaging.

PubMed

Shen, Huan; Chen, Jianjun; Hua, Linqiang; Zhang, Bing

2014-06-26

The photodissociation dynamics of allyl chloride at 200 and 266 nm has been studied by femtosecond time-resolved mass spectrometry coupled with photoelectron imaging. The molecule was prepared to different excited states by selectively pumping with 400 or 266 nm pulse. The dissociated products were then probed by multiphoton ionization with 800 nm pulse. After absorbing two photons at 400 nm, several dissociation channels were directly observed from the mass spectrum. The two important channels, C-Cl fission and HCl elimination, were found to decay with multiexponential functions. For C-Cl fission, two time constants, 48 ± 1 fs and 85 ± 40 ps, were observed. The first one was due to the fast predissociation process on the repulsive nσ*/πσ* state. The second one could be ascribed to dissociation on the vibrationally excited ground state which is generated after internal conversion from the initially prepared ππ* state. HCl elimination, which is a typical example of a molecular elimination reaction, was found to proceed with two time constants, 600 ± 135 fs and 14 ± 2 ps. We assigned the first one to dissociation on the excited state and the second one to the internal conversion from the ππ* state to the ground state and then dissociation on the ground state. As we excited the molecule with 266 nm light, the transient signals decayed exponentially with a time constant of ∼48 fs, which is coincident with the time scale of C-halogen direct dissociation. Photoelectron images, which provided translational and angular distributions of the generated electron, were also recorded. Detailed analysis of the kinetic energy distribution strongly suggested that C3H4(+) and C3H5(+) were generated from ionization of the neutral radical. The present study reveals the dissociation dynamics of allyl chloride in a time-resolved way.

Sediment erosion by Görtler vortices: the scour-hole problem

NASA Astrophysics Data System (ADS)

Hopfinger, E. J.; Kurniawan, A.; Graf, W. H.; Lemmin, U.

2004-12-01

Experimental results on sediment erosion (scour) by a plane turbulent wall jet, issuing from a sluice gate, are presented which show clearly it seems for the first time that the turbulent wall layer is destabilized by the concave curvature of the water/sediment interface. The streamwise Görtler vortices which emerge create sediment streaks or longitudinal sediment ridges. The analysis of the results in terms of Görtler instability of the wall layer indicates that the strength of these curvature-excited streamwise vortices is such that the sediment transport is primarily due to turbulence created by these vortices. Their contribution to the wall shear stress is taken to be of the same form as the normal turbulent wall shear stress. For this reason, the model developed by Hogg et al. (J. Fluid Mech. Vol. 338, 1997, p. 317) remains valid; only the numerical coefficients are affected. The logarithmic dependency of the time evolution of the scour-hole depth predicted by this model is shown to be in good agreement with experiments. New scaling laws for the quasi-steady state depth and the associated time, inspired by the Hogg et al. (1997) model are proposed. Furthermore, it is emphasized that at least two scouring regimes must be distinguished: a short-time regime after which a quasi-steady state is reached, followed by a long-time regime, leading to an asymptotic state of virtually no sediment transport.

Blending ecology and evolution using emerging technologies to determine species distributions with a non-native pathogen in a changing climate

Treesearch

K. Waring; S. Cushman; A. Eckert; L. Flores-Renteria; H. Lintz; R. Sniezko; C. Still; C. Wehenkel; A. Whipple; M. Wing

2017-01-01

A collaborative team of researchers from the United States and Mexico has begun an exciting new research project funded by The National Science Foundation’s Macrosystems Biology program. The project will study ecological and evolutionary processes affecting the distribution of southwestern white pine (Pinus strobiformis), an important tree species of mixed conifer...

The mutable nature of particle-core excitations with spin in the one-valence-proton nucleus 133Sb

NASA Astrophysics Data System (ADS)

Bocchi, G.; Leoni, S.; Fornal, B.; Colò, G.; Bortignon, P. F.; Bottoni, S.; Bracco, A.; Michelagnoli, C.; Bazzacco, D.; Blanc, A.; de France, G.; Jentschel, M.; Köster, U.; Mutti, P.; Régis, J.-M.; Simpson, G.; Soldner, T.; Ur, C. A.; Urban, W.; Fraile, L. M.; Lozeva, R.; Belvito, B.; Benzoni, G.; Bruce, A.; Carroll, R.; Cieplicka-Oryǹczak, N.; Crespi, F. C. L.; Didierjean, F.; Jolie, J.; Korten, W.; Kröll, T.; Lalkovski, S.; Mach, H.; Mărginean, N.; Melon, B.; Mengoni, D.; Million, B.; Nannini, A.; Napoli, D.; Olaizola, B.; Paziy, V.; Podolyák, Zs.; Regan, P. H.; Saed-Samii, N.; Szpak, B.; Vedia, V.

2016-09-01

The γ-ray decay of excited states of the one-valence-proton nucleus 133Sb has been studied using cold-neutron induced fission of 235U and 241Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between γ-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 μs isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr3(Ce) scintillators, revealed a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus 132Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin.

Linking photochemistry in the gas and solution phase: S-H bond fission in p-methylthiophenol following UV photoexcitation.

PubMed

Oliver, Thomas A A; Zhang, Yuyuan; Ashfold, Michael N R; Bradforth, Stephen E

2011-01-01

Gas-phase H (Rydberg) atom photofragment translational spectroscopy and solution-phase femtosecond-pump dispersed-probe transient absorption techniques are applied to explore the excited state dynamics of p-methylthiophenol connecting the short time reactive dynamics in the two phases. The molecule is excited at a range of UV wavelengths from 286 to 193 nm. The experiments clearly demonstrate that photoexcitation results in S-H bond fission--both in the gas phase and in ethanol solution-and that the resulting p-methythiophenoxyl radical fragments are formed with significant vibrational excitation. In the gas phase, the recoil anisotropy of the H atom and the vibrational energy disposal in the p-MePhS radical products formed at the longer excitation wavelengths reveal the operation of two excited state dissociation mechanisms. The prompt excited state dissociation motif appears to map into the condensed phase also. In both phases, radicals are produced in both their ground and first excited electronic states; characteristic signatures for both sets of radical products are already apparent in the condensed phase studies after 50 fs. No evidence is seen for either solute ionisation or proton coupled electron transfer--two alternate mechanisms that have been proposed for similar heteroaromatics in solution. Therefore, at least for prompt S-H bond fissions, the direct observation of the dissociation process in solution confirms that the gas phase photofragmentation studies indeed provide important insights into the early time dynamics that transfer to the condensed phase.

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.

Energy Dispersive XAFS: Characterization of Electronically Excited States of Copper(I) Complexes

PubMed Central

2013-01-01

Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of [Cu(dmp)2]+ (dmp =2,9-dimethyl-1,10-phenanthroline) and [Cu(dbtmp)2]+ (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns. DFT calculations of the longer lived MLCT excited state of [Cu(dbp)2]+ (dbp =2,9-di-n-butyl-1,10-phenanthroline) with the bulkier diimine ligands, indicated that the excited state behaves as a Jahn–Teller distorted Cu(II) site, with the interligand dihedral angle changing from 83 to 60° as the tetrahedral coordination geometry flattens and a reduction in the Cu–N distance of 0.03 Å. PMID:23718738

Absolute Measurements of Field Enhanced Dielectronic Recombination and Electron Impact Excitation

NASA Astrophysics Data System (ADS)

Savin, Daniel Wolf

Absolute measurements have been made of the dielectronic recombination (DR) rate coefficient for C^ {3+}, via the 2s-2p core -excitation, in an external electric field of 11.4 +/- 0.9(1sigma) V cm ^{-1}; and of the electron impact excitation (EIE) rate coefficient for C ^{3+}(2s-2p) at energies near threshold. The ion-rest-frame FWHM of the electron energy spread was 1.74 +/- 0.22(1sigma) eV. The measured DR rate, at a mean electron energy of 8.26 +/- 0.07(1sigma ) eV, was (2.76+/- 0.75)times 10^{-10} cm^{3 } s^{-1}. The uncertainty quoted for the DR rate is the total experimental uncertainty at a 1sigma<=vel. The present DR result appears to agree with an intermediate coupling calculation which uses the isolated-resonance, single-configuration approximation. In comparing with theory, a semi-classical formula was used to determine which recombined ions were field-ionized by the 4.65 kV cm^{-1} fields in the final-charge-state analyzer and not detected. A more precise treatment of field-ionization, which includes the lifetime of the high Rydberg C^{2+} ions in the external field and the time evolution and rotation of the fields experienced by the recombined ions, is needed before a definitive comparison between experiment and theory can be made. For the EIE results, at an ion-rest-frame energy of 10.10 eV, the measured rate coefficient was (7.79+/- 2.10)times 10^{ -8} cm^3 s^ {-1}. The measured cross section was (4.15+/- 1.12)times 10^{ -16} cm^2. The uncertainties quoted here represent the total experimental uncertainty at a 90 percent confidence level. Good agreement is found with other measurements. Agreement is not good with Coulomb -Born with exchange and two-state close-coupling calculations which fall outside the 90-percent-confidence uncertainty limits. Agreement is better with a nine-state close-coupling calculation which lies at the extreme of the uncertainty limits. Taking into account previous measurements in C ^{3+} and also a measurement of EIE in Be^+ which lies 19 percent below close-coupling calculations, there is a suggestion that the C^{3+}(2s-2p) EIE rate coefficient may fall slightly below presently accepted values.

Ultrafast photodissociation dynamics of 1,4-diiodobenzene

NASA Astrophysics Data System (ADS)

Stankus, Brian; Zotev, Nikola; Rogers, David M.; Gao, Yan; Odate, Asami; Kirrander, Adam; Weber, Peter M.

2018-05-01

The photodissociation dynamics of 1,4-diiodobenzene is investigated using ultrafast time-resolved photoelectron spectroscopy. Following excitation by laser pulses at 271 nm, the excited-state dynamics is probed by resonance-enhanced multiphoton ionization with 405 nm probe pulses. A progression of Rydberg states, which come into resonance sequentially, provide a fingerprint of the dissociation dynamics of the molecule. The initial excitation decays with a lifetime of 33 ± 4 fs, in good agreement with a previous study. The spectrum is interpreted by reference to ab initio calculations at the CASPT2(18,14) level, including spin-orbit coupling. We propose that both the 5B1 and 6B1 states are excited initially, and based on the calculations, we identify diabatic spin-orbit coupled states corresponding to the main dissociation pathways.

Understanding Hawking radiation in the framework of open quantum systems

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

Yu Hongwei; Zhang Jialin

2008-01-15

We study the Hawking radiation in the framework of open quantum systems by examining the time evolution of a detector (modeled by a two-level atom) interacting with vacuum massless scalar fields. The dynamics of the detector is governed by a master equation obtained by tracing over the field degrees of freedom from the complete system. The nonunitary effects are studied by analyzing the time behavior of a particular observable of the detector, i.e., its admissible state, in the Unruh, Hartle-Hawking, as well as Boulware vacua outside a Schwarzschild black hole. We find that the detector in both the Unruh andmore » Hartle-Hawking vacua would spontaneously excite with a nonvanishing probability the same as what one would obtain if there is thermal radiation at the Hawking temperature from the black hole, thus reproducing the basic results concerning the Hawking effect in the framework of open quantum systems.« less

Spontaneous light emission by atomic hydrogen: Fermi's golden rule without cheating

NASA Astrophysics Data System (ADS)

Debierre, V.; Durt, T.; Nicolet, A.; Zolla, F.

2015-10-01

Focusing on the 2 p- 1 s transition in atomic hydrogen, we investigate through first order perturbation theory the time evolution of the survival probability of an electron initially taken to be in the excited (2 p) state. We examine both the results yielded by the standard dipole approximation for the coupling between the atom and the electromagnetic field - for which we propose a cutoff-independent regularisation - and those yielded by the exact coupling function. In both cases, Fermi's golden rule is shown to be an excellent approximation for the system at hand: we found its maximal deviation from the exact behaviour of the system to be of order 10-8 /10-7. Our treatment also yields a rigorous prescription for the choice of the optimal cutoff frequency in the dipole approximation. With our cutoff, the predictions of the dipole approximation are almost indistinguishable at all times from the exact dynamics of the system.

Butterfly deformation modes in a photoexcited pyrazolate-bridged Pt complex measured by time-resolved x-ray scattering in solution

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

Haldrup, Kristoffer; Dohn, Asmus O.; Shelby, Megan L.

2016-08-27

Pyrazolate-bridged di-nuclear Pt complexes represent a series of molecules with tunable absorption and emission properties that can be directly modulated by structural factors, such as the Pt-Pt distance. However, direct experimental information regarding the structure of the emissive triplet excited state has remained scarce. Using time-resolved wide angle X-ray scattering (WAXS), the molecular structure of the triplet excited state for one of the complexes [Pt(ppy)(μ-tBu 2pz)] 2 was obtained in a dilute (0.5 mM) toluene solution utilizing the monochromatic X-ray beamline 11IDD of the Advanced Photon Source. The excited state structural analysis was carried out based on the results frommore » both transient WAXS measurements and DFT calculations to shed light on the primary structural changes, in particular the Pt-Pt distance and ligand rotation taking place following the photo-excitation of [Pt(ppy)(μ-tBu 2pz)] 2 in toluene solution. We find that in the triplet excited state a pronounced contraction along the Pt-Pt axis has taken place accompanied by rotational motions of ppy ligands toward one another. Our results suggest that the contraction is larger than what has previously been reported, but are in good agreement with recent theoretical efforts and suggest the ppy moieties as targets for rational synthesis aimed at tuning the excited-state structure and properties« less

Polaronic effects at finite temperatures in the B850 ring of the LH2 complex.

PubMed

Chorošajev, Vladimir; Rancova, Olga; Abramavicius, Darius

2016-03-21

Energy transfer and relaxation dynamics in the B850 ring of LH2 molecular aggregates are described, taking into account the polaronic effects, by a stochastic time-dependent variational approach. We explicitly include the finite temperature effects in the model by sampling the initial conditions of the vibrational states randomly. This is in contrast to previous applications of the variational approach, which consider only the zero-temperature case. The method allows us to obtain both the microscopic dynamics at the single-wavefunction level and the thermally averaged picture of excitation relaxation over a wide range of temperatures. Spectroscopic observables such as temperature dependent absorption and time-resolved fluorescence spectra are calculated. Microscopic wavefunction evolution is quantified by introducing the exciton participation (localization) length and the exciton coherence length. Their asymptotic temperature dependence demonstrates that the environmental polaronic effects range from exciton self-trapping and excitonic polaron formation at low temperatures to thermally induced state delocalization and decoherence at high temperatures. While the transition towards the polaronic state can be observed on the wavefunction level, it does not produce a discernible effect on the calculated spectroscopic observables.

Rare isotopes and the sound of dilute nuclear matter

NASA Astrophysics Data System (ADS)

Papakonstantinou, P.

2018-04-01

Dilute baryonic matter, at densities below the normal saturation density of symmetric matter, is found on the crust of neutron stars and in collapsing supernova matter, its properties determining the evolution of those stellar objects. It is also readily found on the surface of ordinary and exotic atomic nuclei and lives fleetingly in the form of space-extended resonances of excited nucleons. Liminal states of nuclear matter, between saturation and full evaporation or clusterization, are manifest in the structure of symmetric nuclei through clustering and of very asymmetric rare species in haloes and the neutron skin; they stand literally at the threshold of a nucleus's response to hadronic probes, including processes which hinder or enable fusion. In this contribution I focus on excited states, and in particular exotic or not-so-exotic dipole excitation modes of N = Z nuclei and neutron-rich species, including new theoretical results on threshold strength. Modes of special interest are vibrations of and within diffuse surface layers and alpha-cluster oscillations. The modeling of such processes is relevant, directly or indirectly, for the description of reactions at astrophysical energies.

Three-dimensional spectroscopy of vibrational energy in liquids: nitromethane and acetonitrile.

PubMed

Sun, Yuxiao; Pein, Brandt C; Dlott, Dana D

2013-12-12

We introduce a novel type of three-dimensional (3D) spectroscopy to study vibrational energy transfer, where an IR pulse tunable through the CH-stretching and CD-stretching regions was used to create parent vibrational excitations in liquids and a visible probe pulse was used to generate both Stokes and anti-Stokes Raman spectra as a function of delay time. The Raman spectra determine how much vibrational excitation was present in each probed state. The three dimensions are the wavenumber of the pumped state, the wavenumber of the probed state, and the time interval. The technique was used to study nitromethane (NM) and acetonitrile (ACN) and their deuterated analogues at ambient temperature. The 3D spectra were quite complicated. Three types of artifacts due to nonlinear light scattering were observed. Along the diagonal were two fundamental CH-stretch (or CD-stretch) transitions and several weaker combination bands or overtone transitions. Because Raman spectroscopy allows us to simultaneously probe a wide wavenumber region, for every diagonal peak, there were ∼10 off-diagonal peaks. The cross-peaks at shorter delay times reveal the nature of the initial excitation by showing which lower-wavenumber excitations were produced along with the pumped CH-stretch or CD-stretch. The longer-time spectra characterized vibrational energy relaxation processes, and showed how daughter vibrations were generated by different parent excitations.

A search for evidence of below threshold dielectronic recombination in low temperature plasmas

NASA Astrophysics Data System (ADS)

Nemer, Ahmad; Loch, Stuart; Sterling, Nicholas C.; Raymond, John C.

2018-06-01

There are two main types of photoionized gaseous nebulae that exist in the universe, H II regions and Planetary Nebulae (PNe), that mark the endpoints of stellar evolution, and understanding their composition will lead to better understanding of stellar evolution processes, and galactic chemical nucleosynthesis. Determination of heavy elements’ abundances is essential in the analysis of these nebulae. In addition, lines emitted from these heavy elements are typically used for nebular condition deduction. There has been a long-standing problem regarding discrepancy of temperatures and abundances resolved from optical recombination lines and collisionally excited lines. One of the reasons suggested to explain the discrepancy is Dielectronic Recombination (DR). DR is thought to necessarily occur through continuum states overlapping with autoionizing states that are above the ionization threshold. Robicheaux et al. (2010) proposed that DR to below threshold states is possible through ‘negative’ energy electrons recombining to below threshold doubly excited states. The spectral lines emitted from this process could provide an efficient mechanism to cool off plasma in addition to having satellite lines blended with collisionally excited lines related to plasma diagnostics. Furthermore, this phenomenon would occur significantly in low temperature plasmas which makes it challenging to prepare an experiment for testing it in a lab. In this research we present a spectroscopic study into this process through observed optical spectra from seven PNe that suffer from abundance discrepancy problem. A code was developed that produces a synthetic spectrum for 2 cases; namely, C IV recombining to C III and C III to C II. There is faint emission in the optical for these cases. Other possible mechismas to activiate these lines were included in the model and found insignificant. The Auger rates were calculated using the atomic physics code AUTOSTRUCTURE, and the lines were synthesized using a collisional-radiative model.

X-ray induced dimerization of cinnamic acid: Time-resolved inelastic X-ray scattering study

NASA Astrophysics Data System (ADS)

Inkinen, Juho; Niskanen, Johannes; Talka, Tuomas; Sahle, Christoph J.; Müller, Harald; Khriachtchev, Leonid; Hashemi, Javad; Akbari, Ali; Hakala, Mikko; Huotari, Simo

2015-11-01

A classic example of solid-state topochemical reactions is the ultraviolet-light induced photodimerization of α-trans-cinnamic acid (CA). Here, we report the first observation of an X-ray-induced dimerization of CA and monitor it in situ using nonresonant inelastic X-ray scattering spectroscopy (NRIXS). The time-evolution of the carbon core-electron excitation spectra shows the effects of two X-ray induced reactions: dimerization on a short time-scale and disintegration on a long time-scale. We used spectrum simulations of CA and its dimerization product, α-truxillic acid (TA), to gain insight into the dimerization effects. From the time-resolved spectra, we extracted component spectra and time-dependent weights corresponding to CA and TA. The results suggest that the X-ray induced dimerization proceeds homogeneously in contrast to the dimerization induced by ultraviolet light. We also utilized the ability of NRIXS for direct tomography with chemical-bond contrast to image the spatial progress of the reactions in the sample crystal. Our work paves the way for other time-resolved studies on chemical reactions using inelastic X-ray scattering.

X-ray induced dimerization of cinnamic acid: Time-resolved inelastic X-ray scattering study

PubMed Central

Inkinen, Juho; Niskanen, Johannes; Talka, Tuomas; Sahle, Christoph J.; Müller, Harald; Khriachtchev, Leonid; Hashemi, Javad; Akbari, Ali; Hakala, Mikko; Huotari, Simo

2015-01-01

A classic example of solid-state topochemical reactions is the ultraviolet-light induced photodimerization of α-trans-cinnamic acid (CA). Here, we report the first observation of an X-ray-induced dimerization of CA and monitor it in situ using nonresonant inelastic X-ray scattering spectroscopy (NRIXS). The time-evolution of the carbon core-electron excitation spectra shows the effects of two X-ray induced reactions: dimerization on a short time-scale and disintegration on a long time-scale. We used spectrum simulations of CA and its dimerization product, α-truxillic acid (TA), to gain insight into the dimerization effects. From the time-resolved spectra, we extracted component spectra and time-dependent weights corresponding to CA and TA. The results suggest that the X-ray induced dimerization proceeds homogeneously in contrast to the dimerization induced by ultraviolet light. We also utilized the ability of NRIXS for direct tomography with chemical-bond contrast to image the spatial progress of the reactions in the sample crystal. Our work paves the way for other time-resolved studies on chemical reactions using inelastic X-ray scattering. PMID:26568420

Ultrafast excited-state dynamics of 2,5-dimethylpyrrole.

PubMed

Yang, Dongyuan; Min, Yanjun; Chen, Zhichao; He, Zhigang; Yuan, Kaijun; Dai, Dongxu; Yang, Xueming; Wu, Guorong

2018-04-17

The ultrafast excited-state dynamics of 2,5-dimethylpyrrole following excitation at wavelengths in the range of 265.7-216.7 nm is studied using the time-resolved photoelectron imaging method. It is found that excitation at longer wavelengths (265.7-250.2 nm) results in the population of the S1(1πσ*) state, which decays out of the photoionization window in about 90 fs. At shorter pump wavelengths (242.1-216.7 nm), the assignments are less clear-cut. We tentatively assign the initially photoexcited state(s) to the 1π3p Rydberg state(s) which has lifetimes of 159 ± 20, 125 ± 15, 102 ± 10 and 88 ± 10 fs for the pump wavelengths of 242.1, 238.1, 232.6 and 216.7 nm, respectively. Internal conversion to the S1(1πσ*) state represents at most a minor decay channel. The methyl substitution effects on the decay dynamics of the excited states of pyrrole are also discussed. Methyl substitution on the pyrrole ring seems to enhance the direct internal conversion from the 1π3p Rydberg state to the ground state, while methyl substitution on the N atom has less influence and the internal conversion to the S1(πσ*) state represents a main channel.

A switched systems approach to image-based estimation

NASA Astrophysics Data System (ADS)

Parikh, Anup

With the advent of technological improvements in imaging systems and computational resources, as well as the development of image-based reconstruction techniques, it is necessary to understand algorithm performance when subject to real world conditions. Specifically, this dissertation focuses on the stability and performance of a class of image-based observers in the presence of intermittent measurements, caused by e.g., occlusions, limited FOV, feature tracking losses, communication losses, or finite frame rates. Observers or filters that are exponentially stable under persistent observability may have unbounded error growth during intermittent sensing, even while providing seemingly accurate state estimates. In Chapter 3, dwell time conditions are developed to guarantee state estimation error convergence to an ultimate bound for a class of observers while undergoing measurement loss. Bounds are developed on the unstable growth of the estimation errors during the periods when the object being tracked is not visible. A Lyapunov-based analysis for the switched system is performed to develop an inequality in terms of the duration of time the observer can view the moving object and the duration of time the object is out of the field of view. In Chapter 4, a motion model is used to predict the evolution of the states of the system while the object is not visible. This reduces the growth rate of the bounding function to an exponential and enables the use of traditional switched systems Lyapunov analysis techniques. The stability analysis results in an average dwell time condition to guarantee state error convergence with a known decay rate. In comparison with the results in Chapter 3, the estimation errors converge to zero rather than a ball, with relaxed switching conditions, at the cost of requiring additional information about the motion of the feature. In some applications, a motion model of the object may not be available. Numerous adaptive techniques have been developed to compensate for unknown parameters or functions in system dynamics; however, persistent excitation (PE) conditions are typically required to ensure parameter convergence, i.e., learning. Since the motion model is needed in the predictor, model learning is desired; however, PE is difficult to insure a priori and infeasible to check online for nonlinear systems. Concurrent learning (CL) techniques have been developed to use recorded data and a relaxed excitation condition to ensure convergence. In CL, excitation is only required for a finite period of time, and the recorded data can be checked to determine if it is sufficiently rich. However, traditional CL requires knowledge of state derivatives, which are typically not measured and require extensive filter design and tuning to develop satisfactory estimates. In Chapter 5 of this dissertation, a novel formulation of CL is developed in terms of an integral (ICL), removing the need to estimate state derivatives while preserving parameter convergence properties. Using ICL, an estimator is developed in Chapter 6 for simultaneously estimating the pose of an object as well as learning a model of its motion for use in a predictor when the object is not visible. A switched systems analysis is provided to demonstrate the stability of the estimation and prediction with learning scheme. Dwell time conditions as well as excitation conditions are developed to ensure estimation errors converge to an arbitrarily small bound. Experimental results are provided to illustrate the performance of each of the developed estimation schemes. The dissertation concludes with a discussion of the contributions and limitations of the developed techniques, as well as avenues for future extensions.

Evolution of synchrotron-radiation-based Mössbauer absorption spectroscopy for various isotopes

NASA Astrophysics Data System (ADS)

Seto, Makoto; Masuda, Ryo; Kobayashi, Yasuhiro; Kitao, Shinji; Kurokuzu, Masayuki; Saito, Makina; Hosokawa, Shuuich; Ishibashi, Hiroki; Mitsui, Takaya; Yoda, Yoshitaka; Mibu, Ko

2017-11-01

Synchrotron-radiation-based Mössbauer spectroscopy that yields absorption type Mössbauer spectra has been applied to various isotopes. This method enables the advanced measurement by using the excellent features of synchrotron radiation, such as Mössbauer spectroscopic measurement under high-pressures. Furthermore, energy selectivity of synchrotron radiation allows us to measure 40K Mössbauer spectra, of which observation is impossible by using ordinary radioactive sources because the first excited state of 40K is not populated by any radioactive parent nuclides. Moreover, this method has flexibility of the experimental setup that the measured sample can be used as a transmitter or a scatterer, depending on the sample conditions. To enhance the measurement efficiency of the spectroscopy, we developed a detection system in which a windowless avalanche photodiode (APD) detector is combined with a vacuum cryostat to detect internal conversion electrons adding to X-rays accompanied by nuclear de-excitation. In particular, by selecting the emission from the scatterer sample, depth selective synchrotron-radiation-based Mössbauer spectroscopy is possible. Furthermore, limitation of the time window in the delayed components enables us to obtain narrow linewidth in Mössbauer spectra. Measurement system that records velocity dependent time spectra and energy information simultaneously realizes the depth selective and narrow linewidth measurement.

Vibrational spectroscopy of the electronically excited state. 4. Nanosecond and picosecond time-resolved resonance Raman spectroscopy of carotenoid excited states

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

Dallinger, R.F.; Farquharson, S.; Woodruff, W.H.

Resonance Raman and electronic absorption spectra are reported for the S/sub 0/ and T/sub 1/ states of the carotenoids ..beta..-carotene, zeaxanthin, echinenone, canthaxanthin, dihydroxylycopene, astaxanthin, decapreno(C/sub 50/)-..beta..-carotene, ..beta..-apo-8'-carotenal, and ethyl ..beta..-apo-8'-carotenoate. The results reveal qualitatively similar ground-state spectra and similar frequency shifts in all observed resonance Raman modes between S/sub 0/ and T/sub 1/, regardless of carotenoid structure. Examinations of the relationship of the putative C--C and C==C frequencies in S/sub 0/ and T/sub 1/ reveals anomalous shifts to lower frequency in the ''single-bond'' mode upon electronic excitation. These shifts may be due to molecular distortions in the excited statemore » which force changes in molecular motions comprising the observed modes. However, another possibility requiring no distortion is that the interaction (off-diagonal) force constants connecting the C--C and C==C modes change sign upon electronic excitation. This latter phenomenon may provide a unitary explanation for the ''anomalous'' frequency shifts in the C--C and C==C modes, both in the T/sub 1/ states of carotenoids and in the S/sub 1/ states of simpler polyenes, without postulating large, unpredicted structural changes upon excitation or general errors in existing vibrational or theoretical analyses. Resonance Raman and absorbance studies with 35-ps time resolution suggest that S/sub 1/ lifetime (of the /sup 1/B/sub u/ and/or the /sup 1/A/sub g/* states) of ..beta..-carotene in benzene is less than 1 ps.« less

Determination of the formation of dark state via depleted spontaneous emission in a complex solvated molecule.

PubMed

Guo, Xunmin; Wang, Sufan; Xia, Andong; Su, Hongmei

2007-07-05

We present a general two-color two-pulse femtosecond pump-dump approach to study the specific population transfer along the reaction coordinate through the higher vibrational energy levels of excited states of a complex solvated molecule via the depleted spontaneous emission. The time-dependent fluorescence depletion provides the correlated dynamical information between the monitored fluorescence state and the SEP "dumped" dark states, and therefore allow us to obtain the dynamics of the formation of the dark states corresponding to the ultrafast photoisomerization processes. The excited-state dynamics of LDS 751 have been investigated as a function of solvent viscosity and solvent polarity, where a cooperative two-step isomerization process is clearly identified within LDS 751 upon excitation.

Spatial evolution of quantum mechanical states

NASA Astrophysics Data System (ADS)

Christensen, N. D.; Unger, J. E.; Pinto, S.; Su, Q.; Grobe, R.

2018-02-01

The time-dependent Schrödinger equation is solved traditionally as an initial-time value problem, where its solution is obtained by the action of the unitary time-evolution propagator on the quantum state that is known at all spatial locations but only at t = 0. We generalize this approach by examining the spatial evolution from a state that is, by contrast, known at all times t, but only at one specific location. The corresponding spatial-evolution propagator turns out to be pseudo-unitary. In contrast to the real energies that govern the usual (unitary) time evolution, the spatial evolution can therefore require complex phases associated with dynamically relevant solutions that grow exponentially. By introducing a generalized scalar product, for which the spatial generator is Hermitian, one can show that the temporal integral over the probability current density is spatially conserved, in full analogy to the usual norm of the state, which is temporally conserved. As an application of the spatial propagation formalism, we introduce a spatial backtracking technique that permits us to reconstruct any quantum information about an atom from the ionization data measured at a detector outside the interaction region.

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.

Ultrafast photocarrier dynamics related to defect states of Si1-xGex nanowires measured by optical pump-THz probe spectroscopy.

PubMed

Bae, Jung Min; Lee, Woo-Jung; Jung, Seonghoon; Ma, Jin Won; Jeong, Kwang-Sik; Oh, Seung Hoon; Kim, Seongsin M; Suh, Dongchan; Song, Woobin; Kim, Sunjung; Park, Jaehun; Cho, Mann-Ho

2017-06-14

Slightly tapered Si 1-x Ge x nanowires (NWs) (x = 0.29-0.84) were synthesized via a vapor-liquid-solid procedure using Au as a catalyst. We measured the optically excited carrier dynamics of Si 1-x Ge x NWs as a function of Ge content using optical pump-THz probe spectroscopy. The measured -ΔT/T 0 signals of Si 1-x Ge x NWs were converted into conductivity in the THz region. We developed a fitting formula to apply to indirect semiconductors such as Si 1-x Ge x , which explains the temporal population of photo-excited carriers in the band structure and the relationship between the trapping time and the defect states on an ultrafast time scale. From the fitting results, we extracted intra- and inter-valley transition times and trapping times of electrons and holes of Si 1-x Ge x NWs as a function of Ge content. On the basis of theoretical reports, we suggest a physical model to interpret the trapping times related to the species of interface defect states located at the oxide/NW: substoichiometric oxide states of Si(Ge) 0+,1+,2+ , but not Si(Ge) 3+ , could function as defect states capturing photo-excited electrons or holes and could determine the different trapping times of electrons and holes depending on negatively or neutrally charged states.

Chemistry, photophysics, and ultrafast kinetics of two structurally related Schiff bases containing the naphthalene or quinoline ring

NASA Astrophysics Data System (ADS)

Fita, P.; Luzina, E.; Dziembowska, T.; Radzewicz, Cz.; Grabowska, A.

2006-11-01

The two structurally related Schiff bases, 2-hydroxynaphthylidene-(8-aminoquinoline) (HNAQ) and 2-hydroxynaphthylidene-1'-naphthylamine (HNAN), were studied by means of steady-state and time resolved optical spectroscopies as well as time-dependent density functional theory (TDDFT) calculations. The first one, HNAQ, is stable as a keto tautomer in the ground state and in the excited state in solutions, therefore it was used as a model of a keto tautomer of HNAN which exists mainly in its enol form in the ground state at room temperature. Excited state intramolecular proton transfer in the HNAN molecule leads to a very weak (quantum yield of the order of 10-4) strongly Stokes-shifted fluorescence. The characteristic time of the proton transfer (about 30fs) was estimated from femtosecond transient absorption data supported by global analysis and deconvolution techniques. Approximately 35% of excited molecules create a photochromic form whose lifetime was beyond the time window of the experiment (2ns). The remaining ones reach the relaxed S1 state (of a lifetime of approximately 4ps), whose emission is present in the decay associated difference spectra. Some evidence for the back proton transfer from the ground state of the keto form with the characteristic time of approximately 13ps was also found. The energies and orbital characteristics of main electronic transitions in both molecules calculated by TDDFT method are also discussed.

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.

Real-time electron dynamics for massively parallel excited-state simulations

NASA Astrophysics Data System (ADS)

Andrade, Xavier

The simulation of the real-time dynamics of electrons, based on time dependent density functional theory (TDDFT), is a powerful approach to study electronic excited states in molecular and crystalline systems. What makes the method attractive is its flexibility to simulate different kinds of phenomena beyond the linear-response regime, including strongly-perturbed electronic systems and non-adiabatic electron-ion dynamics. Electron-dynamics simulations are also attractive from a computational point of view. They can run efficiently on massively parallel architectures due to the low communication requirements. Our implementations of electron dynamics, based on the codes Octopus (real-space) and Qball (plane-waves), allow us to simulate systems composed of thousands of atoms and to obtain good parallel scaling up to 1.6 million processor cores. Due to the versatility of real-time electron dynamics and its parallel performance, we expect it to become the method of choice to apply the capabilities of exascale supercomputers for the simulation of electronic excited states.

Bottom-up excited state dynamics of two cinnamate-based sunscreen filter molecules.

PubMed

Peperstraete, Yoann; Staniforth, Michael; Baker, Lewis A; Rodrigues, Natércia D N; Cole-Filipiak, Neil C; Quan, Wen-Dong; Stavros, Vasilios G

2016-10-12

Methyl-E-4-methoxycinnamate (E-MMC) is a model chromophore of the commonly used commercial sunscreen agent, 2-ethylhexyl-E-4-methoxycinnamate (E-EHMC). In an effort to garner a molecular-level understanding of the photoprotection mechanisms in operation with E-EHMC, we have used time-resolved pump-probe spectroscopy to explore E-MMC's and E-EHMC's excited state dynamics upon UV-B photoexcitation to the S 1 (1 1 ππ*) state in both the gas- and solution-phase. In the gas-phase, our studies suggest that the excited state dynamics are driven by non-radiative decay from the 1 1 ππ* to the S 3 (1 1 nπ*) state, followed by de-excitation from the 1 1 nπ* to the ground electronic state (S 0 ). Using both a non-polar-aprotic solvent, cyclohexane, and a polar-protic solvent, methanol, we investigated E-MMC and E-EHMC's photochemistry in a more realistic, 'closer-to-shelf' environment. A stark change to the excited state dynamics in the gas-phase is observed in the solution-phase suggesting that the dynamics are now driven by efficient E/Z isomerisation from the initially photoexcited 1 1 ππ* state to S 0 .

Energy landscape-driven non-equilibrium evolution of inherent structure in disordered material

DOE PAGES

Fan, Yue; Iwashita, Takuya; Egami, Takeshi

2017-05-19

Complex states in glasses can be neatly expressed by the potential energy landscape (PEL). But, because PEL is highly multi-dimensional it is difficult to describe how the system moves around in PEL. We demonstrate that it is possible to predict the evolution of macroscopic state in a metallic glass, such as ageing and rejuvenation, through a set of simple equations describing excitations in the PEL. The key to this simplification is the realization that the step of activation from the initial state to the saddle point in PEL and the following step of relaxation to the final state are essentiallymore » decoupled. Furthermore, the model shows that the interplay between activation and relaxation in PEL is the key driving force that simultaneously explains both the equilibrium of supercooled liquid and the thermal hysteresis observed in experiments. It further predicts anomalous peaks in truncated thermal scanning, validated by independent molecular dynamics simulation.« less

Local Complex Potential Based Time Dependent Wave Packet Approach to Calculation of Vibrational Excitation Cross-sections in e-N2, e-H2 and e-CO Scattering

NASA Astrophysics Data System (ADS)

Sarma, Manabendra; Singh, Raman K.; Mishra, Manoj K.

2007-12-01

Vibrational excitation cross-sections σn←m(E) in resonant e-N2, e-CO and e-H2 scattering are calculated from transition matrix elements Tn←m(E) obtained using Fourier transform of the cross correlation function <φn(R)|ψm(R,t)> where ψm(R,t); e-iHA-(R)t/ℏφm(R). Time evolution under the influence of the resonance anionic Hamiltonian HA-(A- = N2-/CO/H2-) is effected using Lanczos and fast Fourier transforms and the target (A) vibrational eigenfunctions φm(R) and φn(R) are calculated using Fourier grid Hamiltonian method applied to PE curve of the neutral target. The resulting vibrational excitation cross-section profiles provide reasonable agreement with experimental results and the cross correlation functions offer an unequivocal differentiation between the boomerang and impulse models.

Early time evolution of a localized nonlinear excitation in the β-FPUT chain

NASA Astrophysics Data System (ADS)

Kashyap, Rahul; Westley, Alexandra; Datta, Amitava; Sen, Surajit

2017-04-01

We present the detailed dynamics of the particles in the β-Fermi-Pasta-Ulam-Tsingou (FPUT) chain after the initiation of a localized nonlinear excitation (LNE) by squeezing a central bond in the monodispersed chain at time t = 0 while all other particles remain in their original relaxed positions. In the absence of phonons in the system, the LNE appears to initiate its relaxation process by symmetrically emitting two very weak solitary waves. The next stage involves the spreading of the LNE and the formation of nonsolitary wave-like objects to broaden the excitation region until a stage is reached when many weak solitary wave-like objects can be emitted as the system begins its journey to quasi-equilibrium and then to equilibrium. In addition to being of fundamental interest, these systems may be realized using cantilever systems and could well hold the key to constructing the next generation of broadband energy harvesting systems.

Large-k exciton dynamics in GaN epilayers: Nonthermal and thermal regimes

NASA Astrophysics Data System (ADS)

Vinattieri, Anna; Bogani, Franco; Cavigli, Lucia; Manzi, Donatella; Gurioli, Massimo; Feltin, Eric; Carlin, Jean-François; Martin, Denis; Butté, Raphaël; Grandjean, Nicolas

2013-02-01

We present a detailed investigation performed at low temperature (T<50 K) concerning the exciton dynamics in GaN epilayers grown on c-plane sapphire substrates, focusing on the exciton formation and the transition from the nonthermal to the thermal regime. The time-resolved kinetics of longitudinal-optical-phonon replicas is used to address the energy relaxation in the excitonic band. From picosecond time-resolved spectra, we bring evidence for a long lasting nonthermal excitonic distribution, which accounts for the first 50 ps. Such a behavior is confirmed in different experimental conditions when both nonresonant and resonant excitations are used. At low excitation power density, the exciton formation and their subsequent thermalization are dominated by impurity scattering rather than by acoustic phonon scattering. The estimate of the average energy of the excitons as a function of delay after the excitation pulse provides information on the relaxation time, which describes the evolution of the exciton population to the thermal regime.

Nonradiative relaxation in tunable solid state laser crystals

NASA Technical Reports Server (NTRS)

Gayen, S. K.; Wang, W. B.; Petricevic, V.; Alfano, R. R.

1986-01-01

The characteristics of nonradiative transitions between the 4T2 and 2E excited states of trivalent-chromium-ion-activated ruby (containing 0.04 percent Cr2O3 by weight) and alexandrite (containing 0.4 at. percent chromium ion) laser crystals were studied using the technique described by Gayen et al. (1985). In this technique, a 527-nm pulse excites the 4T2 band of the Cr(3+), and the subsequent population kinetics among excited states is monitored by an IR picosecond probe pulse as a function of pump-probe delay. In ruby, a resolution-limited sharp rise in the excited state population was followed by a long-lifetime decay, leading to an upper limit of 7 ps for the 4T2-state nonradiative lifetime. In alexandrite, a longer rise time was followed by a multicomponent decay. A theoretical model is proposed for explaining the induced absorption and the transition dynamics observed in these crystals.

Vibrational energy flow in photoactive yellow protein revealed by infrared pump-visible probe spectroscopy.

PubMed

Nakamura, Ryosuke; Hamada, Norio

2015-05-14

Vibrational energy flow in the electronic ground state of photoactive yellow protein (PYP) is studied by ultrafast infrared (IR) pump-visible probe spectroscopy. Vibrational modes of the chromophore and the surrounding protein are excited with a femtosecond IR pump pulse, and the subsequent vibrational dynamics in the chromophore are selectively probed with a visible probe pulse through changes in the absorption spectrum of the chromophore. We thus obtain the vibrational energy flow with four characteristic time constants. The vibrational excitation with an IR pulse at 1340, 1420, 1500, or 1670 cm(-1) results in ultrafast intramolecular vibrational redistribution (IVR) with a time constant of 0.2 ps. The vibrational modes excited through the IVR process relax to the initial ground state with a time constant of 6-8 ps in parallel with vibrational cooling with a time constant of 14 ps. In addition, upon excitation with an IR pulse at 1670 cm(-1), we observe the energy flow from the protein backbone to the chromophore that occurs with a time constant of 4.2 ps.

New results on thermalization of electrons in GaAs

NASA Astrophysics Data System (ADS)

Hannak, Reinhard M.; Ruehle, Wolfgang W.

1994-05-01

The transition from a nonthermal into a thermal distribution of electrons at low densities (< 1014 cm-3) is traced on a picosecond time-scale by the time evolution of a band-to-acceptor transition in GaAs:Be. Two narrow, nonthermal electron distributions are detected during the first picoseconds originating from the heavy- and light-hole valence band, respectively. Measurements with circular polarization of excitation and luminescence confirm this assignment. The variation of their energetic peak-positions with excitation energy allows the experimental determination of the valence band dispersions for very small wave vectors near k equals 0, where only parabolic energy terms contribute to the dispersions. The results are consistent with the commonly used effective hole masses.

Vibrational and rotational excitation of CO in comets. Part 1: Non-equilibrium calculations. Part 2: Results of the calculation for standard bright comet, comet Iras-Araki-Alcock and comet Halley

NASA Technical Reports Server (NTRS)

Chin, G.; Weaver, H. A.

1984-01-01

The vibrational and rotational excitation of the CO molecule in cometary comae were investigated using a model which includes IR vibrational pumping by the solar flux, vibrational and rotational radiative decay, and collisional coupling among rotational states. Steady state was not assumed in solving the rate equations. The evolution of a shell of CO gas was monitored as it expanded from the nucleus into the outer coma. Collisional effects were treated using a kinetic temperature profile derived from theoretical work on the coma energy balance. The kinetic temperature was assumed to be extremely cold in the inner coma; this has significant consequences for the CO excitation. If optical depth effects are ignored, only low J transitions will be significantly excited in comets observed at high spatial resolution. Ground-based observations of CO co-vibrational and rotational transitions will be extremely difficult due to lack of sensitivity and/or terrestrial absorption. However, CO should be detectable from a large comet with favorable observing geometry if the CO is a parent molecule present at the 10% level (or greater) relative to H2O. Observations using cooled, spaceborne instruments should be capable of detecting CO emission from even moderately bright comets.

Vibrational and rotational excitation of CO in comets. Part 1: Non-equilibrium calculations. Part 2: Results of the calculation for standard bright comet, comet Iras-Araki-Alcock and comet Halley

NASA Astrophysics Data System (ADS)

Chin, G.; Weaver, H. A.

1984-05-01

The vibrational and rotational excitation of the CO molecule in cometary comae were investigated using a model which includes IR vibrational pumping by the solar flux, vibrational and rotational radiative decay, and collisional coupling among rotational states. Steady state was not assumed in solving the rate equations. The evolution of a shell of CO gas was monitored as it expanded from the nucleus into the outer coma. Collisional effects were treated using a kinetic temperature profile derived from theoretical work on the coma energy balance. The kinetic temperature was assumed to be extremely cold in the inner coma; this has significant consequences for the CO excitation. If optical depth effects are ignored, only low J transitions will be significantly excited in comets observed at high spatial resolution. Ground-based observations of CO co-vibrational and rotational transitions will be extremely difficult due to lack of sensitivity and/or terrestrial absorption. However, CO should be detectable from a large comet with favorable observing geometry if the CO is a parent molecule present at the 10% level (or greater) relative to H2O. Observations using cooled, spaceborne instruments should be capable of detecting CO emission from even moderately bright comets.

Unifying time evolution and optimization with matrix product states

NASA Astrophysics Data System (ADS)

Haegeman, Jutho; Lubich, Christian; Oseledets, Ivan; Vandereycken, Bart; Verstraete, Frank

2016-10-01

We show that the time-dependent variational principle provides a unifying framework for time-evolution methods and optimization methods in the context of matrix product states. In particular, we introduce a new integration scheme for studying time evolution, which can cope with arbitrary Hamiltonians, including those with long-range interactions. Rather than a Suzuki-Trotter splitting of the Hamiltonian, which is the idea behind the adaptive time-dependent density matrix renormalization group method or time-evolving block decimation, our method is based on splitting the projector onto the matrix product state tangent space as it appears in the Dirac-Frenkel time-dependent variational principle. We discuss how the resulting algorithm resembles the density matrix renormalization group (DMRG) algorithm for finding ground states so closely that it can be implemented by changing just a few lines of code and it inherits the same stability and efficiency. In particular, our method is compatible with any Hamiltonian for which ground-state DMRG can be implemented efficiently. In fact, DMRG is obtained as a special case of our scheme for imaginary time evolution with infinite time step.

Ultrafast Photodissociation Dynamics of Nitromethane.

PubMed

Nelson, Tammie; Bjorgaard, Josiah; Greenfield, Margo; Bolme, Cindy; Brown, Katie; McGrane, Shawn; Scharff, R Jason; Tretiak, Sergei

2016-02-04

Nitromethane (NM), a high explosive (HE) with low sensitivity, is known to undergo photolysis upon ultraviolet (UV) irradiation. The optical transparency, homogeneity, and extensive study of NM make it an ideal system for studying photodissociation mechanisms in conventional HE materials. The photochemical processes involved in the decomposition of NM could be applied to the future design of controllable photoactive HE materials. In this study, the photodecomposition of NM from the nπ* state excited at 266 nm is being investigated on the femtosecond time scale. UV femtosecond transient absorption (TA) spectroscopy and excited state femtosecond stimulated Raman spectroscopy (FSRS) are combined with nonadiabatic excited state molecular dynamics (NA-ESMD) simulations to provide a unified picture of NM photodecomposition. The FSRS spectrum of the photoproduct exhibits peaks in the NO2 region and slightly shifted C-N vibrational peaks pointing to methyl nitrite formation as the dominant photoproduct. A total photolysis quantum yield of 0.27 and an nπ* state lifetime of ∼20 fs were predicted from NA-ESMD simulations. Predicted time scales revealed that NO2 dissociation occurs in 81 ± 4 fs and methyl nitrite formation is much slower having a time scale of 452 ± 9 fs corresponding to the excited state absorption feature with a decay of 480 ± 17 fs observed in the TA spectrum. Although simulations predict C-N bond cleavage as the primary photochemical process, the relative time scales are consistent with isomerization occurring via NO2 dissociation and subsequent rebinding of the methyl radical and nitrogen dioxide.

A search for excited fermions in electron-proton collisions at HERA

NASA Astrophysics Data System (ADS)

Derrick, M.; Krakauer, D.; Magill, S.; Musgrave, B.; Repond, J.; Schlereth, J.; Stanek, R.; Talaga, R. L.; Thron, J.; Arzarello, F.; Ayad, R.; Bari, G.; Basile, M.; Bellagamba, L.; Boscherini, D.; Bruni, A.; Bruni, G.; Bruni, P.; Romeo, G. Cara; Castellini, G.; Chiarini, M.; Cifarelli, L.; Cindolo, F.; Ciralli, F.; Contin, A.; D'Auria, S.; Frasconi, F.; Gialas, I.; Giusti, P.; Iacobucci, G.; Laurenti, G.; Levi, G.; Margotti, A.; Massam, T.; Nania, R.; Nemoz, C.; Palmonari, F.; Polini, A.; Sartorelli, G.; Timellini, R.; Garcia, Y. Zamora; Zichichi, A.; Bargende, A.; Crittenden, J.; Desch, K.; Diekmann, B.; Doeker, T.; Eckart, M.; Feld, L.; Frey, A.; Geerts, M.; Geitz, G.; Grothe, M.; Hartmann, H.; Haun, D.; Heinloth, K.; Hilger, E.; Jakob, H.-P.; Katz, U. F.; Mari, S. M.; Mass, A.; Mengel, S.; Mollen, J.; Paul, E.; Rembser, Ch.; Schattevoy, R.; Schneider, J.-L.; Schramm, D.; Stamm, J.; Wedemeyer, R.; Campbell-Robson, S.; Cassidy, A.; Dyce, N.; Foster, B.; George, S.; Gilmore, R.; Heath, G. P.; Heath, H. F.; Llewellyn, T. J.; Morgado, C. J. S.; Norman, D. J. P.; O'Mara, J. A.; Tapper, R. J.; Wilson, S. S.; Yoshida, R.; Rau, R. R.; Arneodo, M.; Iannotti, L.; Schioppa, M.; Susinno, G.; Bernstein, A.; Caldwell, A.; Parsons, J. A.; Ritz, S.; Sciulli, F.; Straub, P. B.; Wai, L.; Yang, S.; Borzemski, P.; Chwastowski, J.; Eskreys, A.; Piotrzkowski, K.; Zachara, M.; Zawiejski, L.; Adamczyk, L.; Bednarek, B.; Eskreys, K.; Jeleń, K.; Kisielewska, D.; Kowalski, T.; Rulikowska-Zarebska, E.; Suszycki, L.; Zajac, J.; Kedzierski, T.; Kotański, A.; Przybycień, M.; Bauerdick, L. A. T.; Behrens, U.; Bienlein, J. K.; Böttcher, S.; Coldewey, C.; Drews, G.; Flasiński, M.; Gilkinson, D. J.; Göttlicher, P.; Gutjahr, B.; Haas, T.; Hain, W.; Hasell, D.; Heßling, H.; Hultschig, H.; Iga, Y.; Joos, P.; Kasemann, M.; Klanner, R.; Koch, W.; Köpke, L.; Kötz, U.; Kowalski, H.; Kroger, W.; Krüger, J.; Labs, J.; Ladage, A.; Löhr, B.; Löwe, M.; Lüke, D.; Mańczak, O.; Ng, J. S. T.; Nickel, S.; Notz, D.; Ohrenberg, K.; Roco, M.; Rohde, M.; Roldán, J.; Schneekloth, U.; Schulz, W.; Selonke, F.; Stiliaris, E.; Voß, T.; Westphal, D.; Wolf, G.; Youngman, C.; Grabosch, H. J.; Leich, A.; Meyer, A.; Rethfeldt, C.; Schlenstedt, S.; Barbagli, G.; Pelfer, P.; Anzivino, G.; Maccarrone, G.; de Pasquale, S.; Qian, S.; Votano, L.; Bamberger, A.; Freidhof, A.; Poser, T.; Söldner-Rembold, S.; Schroeder, J.; Theisen, G.; Trefzger, T.; Brook, N. H.; Bussey, P. J.; Doyle, A. T.; Fleck, I.; Jamieson, V. A.; Saxon, D. H.; Utley, M. L.; Wilson, A. S.; Dannemann, A.; Holm, U.; Horstmann, D.; Kammerlocher, H.; Krebs, B.; Neumann, T.; Sinkus, R.; Wick, K.; Badura, E.; Burow, B. D.; Fürtjes, A.; Hagge, L.; Lohrmann, E.; Mainusch, J.; Milewski, J.; Nakahata, M.; Pavel, N.; Poelz, G.; Schott, W.; Terron, J.; Zetsche, F.; Bacon, T. C.; Beuselinck, R.; Butterworth, I.; Gallo, E.; Harris, V. L.; Hung, B. H.; Long, K. R.; Miller, D. B.; Morawitz, P. P. O.; Prinias, A.; Sedgbeer, J. K.; Whitfield, A. F.; Mallik, U.; McCliment, E.; Wang, M. Z.; Wang, S. M.; Wu, J. T.; Zhang, Y.; Cloth, P.; Filges, D.; An, S. H.; Hong, S. M.; Nam, S. W.; Park, S. K.; Suh, M. H.; Yon, S. H.; Imlay, R.; Kartik, S.; Kim, H.-J.; McNeil, R. R.; Metcalf, W.; Nadendla, V. K.; Barreiro, F.; Cases, G.; Graciani, R.; Hernández, J. M.; Hervás, L.; Labarga, L.; Del Peso, J.; Puga, J.; de Trocóniz, J. F.; Ikraiam, F.; Mayer, J. K.; Smith, G. R.; Corriveau, F.; Hanna, D. S.; Hartmann, J.; Hung, L. W.; Lim, J. N.; Matthews, C. G.; Patel, P. M.; Sinclair, L. E.; Stairs, D. G.; St. Laurent, M.; Ullmann, R.; Zacek, G.; Bashkirov, V.; Dolgoshein, B. A.; Stifutkin, A.; Bashindzhagyan, G. L.; Ermolov, P. F.; Gladilin, L. K.; Golubkov, Y. A.; Kobrin, V. D.; Kuzmin, V. A.; Proskuryakov, A. S.; Savin, A. A.; Shcheglova, L. M.; Solomin, A. N.; Zotov, N. P.; Bentvelsen, S.; Botje, M.; Chlebana, F.; Dake, A.; Engelen, J.; de Jong, P.; de Kamps, M.; Kooijman, P.; Kruse, A.; O'Dell, V.; Tenner, A.; Tiecke, H.; Verkerke, W.; Vreeswijk, M.; Wiggers, L.; de Wolf, E.; van Woudenberg, R.; Acosta, D.; Bylsma, B.; Durkin, L. S.; Honscheid, K.; Li, C.; Ling, T. Y.; McLean, K. W.; Murray, W. N.; Park, I. H.; Romanowski, T. A.; Seidlein, R.; Bailey, D. S.; Blair, G. A.; Byrne, A.; Cashmore, R. J.; Cooper-Sarkar, A. M.; Daniels, D.; Devenish, R. C. E.; Harnew, N.; Lancaster, M.; Luffman, P. E.; Lindemann, L.; McFall, J.; Nath, C.; Quadt, A.; Uijterwaal, H.; Walczak, R.; Wilson, F. F.; Yip, T.; Abbiendi, G.; Bertolin, A.; Brugnera, R.; Carlin, R.; Dal Corso, F.; de Giorgi, M.; Dosselli, U.; Limentani, S.; Morandin, M.; Posocco, M.; Stanco, L.; Stroili, R.; Voci, C.; Bulmahn, J.; Butterworth, J. M.; Feild, R. G.; Oh, B. Y.; Whitmore, J. J.; D'Agostini, G.; Iori, M.; Marini, G.; Mattioli, M.; Nigro, A.; Tassi, E.; Hart, J. C.; McCubbin, N. A.; Prytz, K.; Shah, T. P.; Short, T. L.; Barberis, E.; Cartiglia, N.; Dubbs, T.; Heusch, C.; van Hook, M.; Hubbard, B.; Lockman, W.; Rahn, J. T.; Sadrozinski, H. F.-W.; Seiden, A.; Biltzinger, J.; Seifert, R. J.; Walenta, A. H.; Zech, G.; Abramowicz, H.; Briskin, G.; Dagan, S.; Levy, A.; Hasegawa, T.; Hazumi, M.; Ishii, T.; Kuze, M.; Mine, S.; Nagasawa, Y.; Nagira, T.; Nakao, M.; Suzuki, I.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Chiba, M.; Hamatsu, R.; Hirose, T.; Homma, K.; Kitamura, S.; Nagayama, S.; Nakamitsu, Y.; Cirio, R.; Costa, M.; Ferrero, M. I.; Lamberti, L.; Maselli, S.; Peroni, C.; Sacchi, R.; Solano, A.; Staiano, A.; Dardo, M.; Bailey, D. C.; Bandyopadhyay, D.; Benard, F.; Brkic, M.; Crombie, M. B.; Gingrich, D. M.; Hartner, G. F.; Joo, K. K.; Levman, G. M.; Martin, J. F.; Orr, R. S.; Sampson, C. R.; Teuscher, R. J.; Catterall, C. D.; Jones, T. W.; Kaziewicz, P. B.; Lane, J. B.; Saunders, R. L.; Shulman, J.; Blankenship, K.; Kochocki, J.; Lu, B.; Mo, L. W.; Bogusz, W.; Charchula, K.; Ciborowski, J.; Gajewski, J.; Grzelak, G.; Kasprazak, M.; Krzyżanowski, M.; Muchorowski, K.; Nowak, R. J.; Pawlak, J. M.; Tymieniecka, T.; Wróblewski, A. K.; Zakrzewski, J. A.; Żarnecki, A. F.; Adamus, M.; Eisenberg, Y.; Glasman, C.; Karshon, U.; Revel, D.; Shapira, A.; Ali, I.; Behrens, B.; Dasu, S.; Fordham, C.; Foudas, C.; Goussiou, A.; Loveless, R. J.; Reeder, D. D.; Silverstein, S.; Smith, W. H.; Tsurugai, T.; Bhadra, S.; Frisken, W. R.; Furutani, K. M.

1995-12-01

A search for excited states of the standard model fermions was performed using the ZEUS detector at the HERA electron-proton collider, operating at a centre of mass energy of 296 GeV. In a sample corresponding to an integrated luminosity of 0.55 pb-1, no evidence was found for any resonant state decaying into final states composed of a fermion and a gauge boson. Limits on the coupling strength times branching ratio of excited fermions are presented for masses between 50 GeV and 250 GeV, extending previous search regions significantly.

Ultrafast electronic and vibrational dynamics of stabilized A state mutants of the green fluorescent protein (GFP): Snipping the proton wire

NASA Astrophysics Data System (ADS)

Stoner-Ma, Deborah; Jaye, Andrew A.; Ronayne, Kate L.; Nappa, Jérôme; Tonge, Peter J.; Meech, Stephen R.

2008-06-01

Two blue absorbing and emitting mutants (S65G/T203V/E222Q and S65T at pH 5.5) of the green fluorescent protein (GFP) have been investigated through ultrafast time resolved infra-red (TRIR) and fluorescence spectroscopy. In these mutants, in which the excited state proton transfer reaction observed in wild-type GFP has been blocked, the photophysics are dominated by the neutral A state. It was found that the A∗ excited state lifetime is short, indicating that it is relatively less stabilised in the protein matrix than the anionic form. However, the lifetime of the A state can be increased through modifications to the protein structure. The TRIR spectra show that a large shifts in protein vibrational modes on excitation of the A state occurs in both these GFP mutants. This is ascribed to a change in H-bonding interactions between the protein matrix and the excited state.

Improved efficiency of selective photoionization of palladium isotopes via autoionizing Rydberg states

NASA Astrophysics Data System (ADS)

Locke, Clayton R.; Kobayashi, Tohru; Midorikawa, Katsumi

2017-01-01

Odd-mass-selective ionization of palladium for purposes of resource recycling and management of long-lived fission products can be achieved by exploiting transition selection rules in a well-established three-step excitation process. In this conventional scheme, circularly polarized lasers of the same handedness excite isotopes via two intermediate 2D5/2 core states, and a third laser is then used for ionization via autoionizing Rydberg states. We propose an alternative excitation scheme via intermediate 2D3/2 core states before the autoionizing Rydberg state, improving ionization efficiency by over 130 times. We confirm high selectivity and measure odd-mass isotopes of >99.7(3)% of the total ionized product. We have identified and measured the relative ionization efficiency of the series of Rydberg states that converge to upper ionization limit of the 4 d 9(2D3/2) level, and identify the most efficient excitation is via the Rydberg state at 67668.18(10) cm-1.

Species-to-species rate coefficients for the H3+ + H2 reacting system

NASA Astrophysics Data System (ADS)

Sipilä, O.; Harju, J.; Caselli, P.

2017-10-01

Aims: We study whether or not rotational excitation can make a large difference to chemical models of the abundances of the H3+ isotopologs, including spin states, in physical conditions corresponding to starless cores and protostellar envelopes. Methods: We developed a new rate coefficient set for the chemistry of the H3+ isotopologs, allowing for rotational excitation, using previously published state-to-state rate coefficients. These new so-called species-to-species rate coefficients are compared with previously-used ground-state-to-species rate coefficients by calculating chemical evolution in variable physical conditions using a pseudo-time-dependent chemical code. Results: We find that the new species-to-species model produces different results to the ground state-to-species model at high density and toward increasing temperatures (T> 10 K). The most prominent difference is that the species-to-species model predicts a lower H3+ deuteration degree at high density owing to an increase of the rate coefficients of endothermic reactions that tend to decrease deuteration. For example at 20 K, the ground-state-to-species model overestimates the abundance of H2D+ by a factor of about two, while the abundance of D3+ can differ by up to an order of magnitude between the models. The spin-state abundance ratios of the various H3+ isotopologs are also affected, and the new model better reproduces recent observations of the abundances of ortho and para H2D+ and D2H+. The main caveat is that the applicability regime of the new rate coefficients depends on the critical densities of the various rotational transitions which vary with the abundances of the species and the temperature in dense clouds. Conclusions: The difference in the abundances of the H3+ isotopologs predicted by the species-to-species and ground state-to-species models is negligible at 10 K corresponding to physical conditions in starless cores, but inclusion of the excited states is very important in studies of deuteration at higher temperatures, for example in protostellar envelopes. The species-to-species rate coefficients provide a more realistic approach to the chemistry of the H3+ isotopologs than the ground-state-to-species rate coefficients do, and so the former should be adopted in chemical models describing the chemistry of the H3+ + H2 reacting system.

Electronic Excitations in Solution: The Interplay between State Specific Approaches and a Time-Dependent Density Functional Theory Description.

PubMed

Guido, Ciro A; Jacquemin, Denis; Adamo, Carlo; Mennucci, Benedetta

2015-12-08

We critically analyze the performances of continuum solvation models when coupled to time-dependent density functional theory (TD-DFT) to predict solvent effects on both absorption and emission energies of chromophores in solution. Different polarization schemes of the polarizable continuum model (PCM), such as linear response (LR) and three different state specific (SS) approaches, are considered and compared. We show the necessity of introducing a SS model in cases where large electron density rearrangements are involved in the excitations, such as charge-transfer transitions in both twisted and quadrupolar compounds, and underline the very delicate interplay between the selected polarization method and the chosen exchange-correlation functional. This interplay originates in the different descriptions of the transition and ground/excited state multipolar moments by the different functionals. As a result, the choice of both the DFT functional and the solvent polarization scheme has to be consistent with the nature of the studied electronic excitation.

Time-resolved x-ray absorption spectroscopy: Watching atoms dance

NASA Astrophysics Data System (ADS)

Milne, Chris J.; Pham, Van-Thai; Gawelda, Wojciech; van der Veen, Renske M.; El Nahhas, Amal; Johnson, Steven L.; Beaud, Paul; Ingold, Gerhard; Lima, Frederico; Vithanage, Dimali A.; Benfatto, Maurizio; Grolimund, Daniel; Borca, Camelia; Kaiser, Maik; Hauser, Andreas; Abela, Rafael; Bressler, Christian; Chergui, Majed

2009-11-01

The introduction of pump-probe techniques to the field of x-ray absorption spectroscopy (XAS) has allowed the monitoring of both structural and electronic dynamics of disordered systems in the condensed phase with unprecedented accuracy, both in time and in space. We present results on the electronically excited high-spin state structure of an Fe(II) molecular species, [FeII(bpy)3]2+, in aqueous solution, resolving the Fe-N bond distance elongation as 0.2 Å. In addition an analysis technique using the reduced χ2 goodness of fit between FEFF EXAFS simulations and the experimental transient absorption signal in energy space has been successfully tested as a function of excited state population and chemical shift, demonstrating its applicability in situations where the fractional excited state population cannot be determined through other measurements. Finally by using a novel ultrafast hard x-ray 'slicing' source the question of how the molecule relaxes after optical excitation has been successfully resolved using femtosecond XANES.

Singlet versus Triplet Excited State Mediated Photoinduced Dehalogenation Reactions of Itraconazole in Acetonitrile and Aqueous Solutions.

PubMed

Zhu, Ruixue; Li, Ming-de; Du, Lili; Phillips, David Lee

2017-04-06

Photoinduced dehalogenation of the antifungal drug itraconazole (ITR) in acetonitrile (ACN) and ACN/water mixed solutions was investigated using femtosecond and nanosecond time-resolved transient absorption (fs-TA and ns-TA, respectively) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR 3 ) experiments. An excited resonance energy transfer is found to take place from the 4-phenyl-4,5-dihydro-3H-1,2,4-triazol-3-one part of the molecule to the 1,3-dichlorobenzene part of the molecule when ITR is excited by ultraviolet light. This photoexcitation is followed by a fast carbon-halogen bond cleavage that leads to the generation of radical intermediates via either triplet and/or singlet excited states. It is found that the singlet excited state-mediated carbon-halogen cleavage is the predominant dehalogenation process in ACN solvent, whereas a triplet state-mediated carbon-halogen cleavage prefers to occur in the ACN/water mixed solutions. The singlet-to-triplet energy gap is decreased in the ACN/water mixed solvents and this helps facilitate an intersystem crossing process, and thus, the carbon-halogen bond cleavage happens mostly through an excited triplet state in the aqueous solutions examined. The ns-TA and ns-TR 3 results also provide some evidence that radical intermediates are generated through a homolytic carbon-halogen bond cleavage via predominantly the singlet excited state pathway in ACN but via mainly the triplet state pathway in the aqueous solutions. In strong acidic solutions, protonation at the oxygen and/or nitrogen atoms of the 1,2,4-triazole-3-one group appears to hinder the dehalogenation reactions. This may offer the possibility that the phototoxicity of ITR due to the generation of aryl or halogen radicals can be reduced by protonation of certain moieties in suitably designed ITR halogen-containing derivatives.

Dynamics of edge currents in a linearly quenched Haldane model

NASA Astrophysics Data System (ADS)

Mardanya, Sougata; Bhattacharya, Utso; Agarwal, Amit; Dutta, Amit

2018-03-01

In a finite-time quantum quench of the Haldane model, the Chern number determining the topology of the bulk remains invariant, as long as the dynamics is unitary. Nonetheless, the corresponding boundary attribute, the edge current, displays interesting dynamics. For the case of sudden and adiabatic quenches the postquench edge current is solely determined by the initial and the final Hamiltonians, respectively. However for a finite-time (τ ) linear quench in a Haldane nanoribbon, we show that the evolution of the edge current from the sudden to the adiabatic limit is not monotonic in τ and has a turning point at a characteristic time scale τ =τ0 . For small τ , the excited states lead to a huge unidirectional surge in the edge current of both edges. On the other hand, in the limit of large τ , the edge current saturates to its expected equilibrium ground-state value. This competition between the two limits lead to the observed nonmonotonic behavior. Interestingly, τ0 seems to depend only on the Semenoff mass and the Haldane flux. A similar dynamics for the edge current is also expected in other systems with topological phases.