Time-dependent Wave Packet Approach Research Articles

On the (E⊗e)-Jahn-Teller conical intersections in the 3p(E′) and 3d(E″) Rydberg electronic states of triatomic hydrogen

The static and dynamic aspects of the Jahn-Teller (JT) interactions in the 3p(E') and 3d(E") Rydberg electronic states of H3 are analyzed theoretically. The static aspects are discussed based on recent ab initio quantum chemistry results, and the dynamic aspects are examined in terms of the vibronic spectra and nonradiative decay behavior of these states. The adiabatic potential-energy surfaces of these degenerate electronic states are derived from extensive ab initio calculations. The calculated adiabatic potential-energy surfaces are diabatized following our earlier study on this system in its 2p(E') ground electronic state. The nuclear dynamics on the resulting conically intersecting manifold of electronic states is studied by a time-dependent wave-packet approach. Calculations are performed both for the uncoupled and coupled state situations in order to understand the importance of nonadiabatic interactions due to the JT conical intersections in these excited Rydberg electronic states.

Quantum Wave Packet Study of the H+ + D2 Reaction on Diabatic Potential Energy Surfaces

The exact three-dimensional nonadiabatic quantum dynamics calculations were carried out for the title reaction by a time-dependent wave packet approach based on a newly constructed diabatic potential energy surface (Kamisaka et al. J. Chem. Phys. 2002, 116, 654). Three processes including those of reactive charge transfer, nonreactive charge transfer, and reactive noncharge transfer were investigated to determine the initial state-resolved probabilities and reactive cross sections. The results show that a large number of resonances can be observed in the calculated probabilities due to the deep well on adiabatic ground surface and the dominant process is the reactive noncharge-transfer process. Some interesting dynamical features such as v-dependent and j-dependent behaviors of the probabilities are also revealed. In addition, a good agreement has been achieved in the comparison between the calculated quantum cross sections from the ground rovibrational initial state and the experimental measurement data.

Time-dependent wavepacket approach to the influence of intense fields on the population of molecular excited states

The influence of laser-field parameters, such as intensity and pulse width, on the population of molecular excited state is investigated by using the time-dependent wavepacket method. For a two-state system in intense laser fields, the populations in the upper and lower states are given by the wavefunctions obtained by solving the Schrödinger equation through split-operator scheme. The calculation shows that both the laser intensity and the pulse width have a strong effect on the population in molecular excited state, and that as the common feature of light–matter interaction (LMI), the periodic changing of the population with the evolution time in each state can be interpreted by Rabi oscillation and area-theorem. The results illustrate that by controlling these two parameters, the needed population in excited state of interest can be obtained, which provides the foundation of light manipulation of molecular processes.

A Quantum Wave Packet Dynamical Study of the Electronic and Spin−Orbit Coupling Effects on the Resonances in Cl(2P) + H2 Scattering

Dynamical resonances in Cl(2P) + H2 scattering are investigated with the aid of a time-dependent wave packet approach using the Capecchi-Werner coupled ab initio potential energy surfaces [Phys. Chem. Chem. Phys. 2004, 6, 4975]. The resonances arising from the prereactive van der Waals well (approximately 0.5 kcal/mol) and the transition-state (TS) region of the 2Sigma(1/2) ground spin-orbit (SO) state of the Cl(2P) + H2 system are calculated and assigned by computing their eigenfunctions and lifetimes. The excitation of even quanta along the bending coordinate of the resonances is observed. The resonances exhibit an extended van der Waals progression, which can be attributed to the dissociative states of ClH2. Excitation of H2 vibration is also identified in the high-energy resonances. The effect of the excited 2P(1/2) SO state of Cl on these resonances is examined by considering the electronic and SO coupling in the dynamical simulations. While the electronic coupling has only a minor impact on the resonance structures, the SO coupling has significant effect on them. The nonadiabatic effect due to the SO coupling is stronger, and as a result, the spectrum becomes broad and diffuse particularly at high energies. We also report the photodetachment spectrum of ClD2- and compare the theoretical findings with the available experimental results.

Quantum wave-packet dynamics of H+HLi scattering: reaction cross section and thermal rate constant.

The channel specific and initial state-selected reaction cross section and temperature-dependent rate constant for the title system is calculated with the aid of a time-dependent wave-packet approach and using the ab initio potential energy surface of Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)]. All partial-wave contributions up to the total angular momentum J=74 are explicitly calculated within the coupled states (CS) approximation. Companion calculations are also carried out employing the standard as well as the uniform J-shifting (JS) approximation. The overall variation of reaction cross sections corresponds well to the behavior of a barrierless reaction. The hydrogen exchange channel yielding HLi+H products is seen to be more favored over the HLi depletion channel yielding Li+H(2) products at low and moderate collision energies. Sharp resonance features are observed in the cross-section results for the HLi depletion channel at low energies. Resonance features in the reaction cross sections average out with various partial-wave contributions, when compared to the same observed in the individual reaction probability curve. Except near the onset of the reaction, the vibrational and rotational excitation of the reagent HLi, in general, does not dramatically influence the reactivity of either channel. The thermal rate constants calculated up to 4000 K show nearly Arrhenius type behavior. The rate constant decreases with vibrational excitation of the reagent HLi, indicating that the cold HLi molecules are efficiently depleted in the reactive encounter with H at relatively low temperatures. The results obtained from the JS approximation are found to agree well qualitatively with the CS results.

A time-dependent wave packet study of the vibronic and spin-orbit interactions in the dynamics of Cl((2)P)+H(2)-->HCl(X (1)Sigma(g) (+))+H((2)S) reaction.

We investigate the vibronic and spin-orbit (SO) coupling effects in the state-selected dynamics of the title reaction with the aid of a time-dependent wave packet approach. The ab initio potential energy surfaces of Capecchi and Werner [Science 296, 715 (2002)] have been employed for this purpose. Collinear approach of the Cl((2)P) atom to the H(2) molecule splits the degeneracy of the (2)P state and gives rise to (2)Sigma and (2)Pi electronic states. These two surfaces form a conical intersection at this geometry. These states transform as 1 (2)A('), 1 (2)A("), and 2 (2)A('), respectively, at the nonlinear configurations of the nuclei. In addition, the SO interaction due to Cl atom further splits these states into (2)Sigma(1/2), (2)Pi(3/2), and (2)Pi(1/2) components at the linear geometry. The ground-state reagent Cl((2)P(3/2))+H(2) correlates with (2)Sigma(1/2) and (2)Pi(3/2), where as the SO excited reagent Cl(*)((2)P(1/2))+H(2) correlates with (2)Pi(1/2) at the linear geometry. In order to elucidate the impact of the vibronic and SO coupling effects on the initial state-selected reactivity of these electronic states we carry out quantum scattering calculations based on a flux operator formalism and a time-dependent wave packet approach. In this work, total reaction probabilities and the time dependence of electronic population of the system by initiating the reaction on each of the above electronic states are presented. The role of conical intersection alone on the reaction dynamics is investigated with a coupled two-state model and for the total angular momentum J=0 (neglecting the electronic orbital angular momentum) both in a diabatic as well as in the adiabatic electronic representation. The SO interaction is then included and the dynamics is studied with a coupled three-state model comprising six diabatic surfaces for the total angular momentum J=0.5 neglecting the Coriolis Coupling terms of the Hamiltonian. Companion calculations are carried out for the uncoupled adiabatic and diabatic surfaces in order to explicitly reveal the impact of two different surface coupling mechanisms in the dynamics of this prototypical reaction.

Theoretical study of the photodetachment spectroscopy of [formula omitted

The photodetachment spectrum of ClH 2 - , probing the van der Waals well region of the coupled multi-sheeted reactive Cl + H 2 potential energy surfaces, is theoretically calculated with the aid of a time-dependent wave packet approach. The theoretical findings are compared with the available experimental results [J. Chem. Phys. 117 (2002) 8181]. The calculated photodetachment spectrum reveals resolved structures that can be attributed to the low-frequency van der Waals progression. The spectral envelopes are ∼0.1 eV apart in energy (nearly equal to the spin–orbit splitting of ∼0.109 eV of atomic Cl) in accord with the experiment. The congestion of the spectral lines in the coupled states results mainly arises from the non-adiabatic effects due to spin–orbit coupling.

The semirigid vibrating rotor target model for atom-polyatom reaction: Application to F+CH2D2 -> CH2D/CHD2+DF/HF

The semirigid vibrating rotor target (svrt) model is applied for the reaction f + ch2d2-->ch2d/chd2 + df/hf. the time-dependent wave packet approach is also used in the calculation. reaction probabilities, cross-sections, and rate constants are calculated for the title reaction from the ground state of the reagent on the modified j1 ( mj1) potential energy surface (pes) for both channels. numerical calculation shows the oscillatory structures in the energy dependence of the calculated reaction probability. those structures are generally associated with broad dynamical resonances. they are smooth in the energy dependence of integral cross-sections due to summation over partial waves. the calculated rate constants are in good agreement with the experimental measurement.

Time-Dependent Quantum Dynamics of Dissociation for CH4on an Ni(100) Surface

The semirigid vibrating rotor target (SVRT) modelproposed by Zhang [J. Chem. Phys. 111 (1999) 3929] isapplied to study the dynamics of dissociative adsorption for CH4on a flat and static Ni(100) surface. The molecule CH4 is treatedas a semirigid vibrating rotor CH3-H, and theLondon–Eyring–Polanyi–Sato potential energy surface is utilized. Thenumerical calculation for the reaction system is carried out by usingthe time-dependent wave packet approach, and the propagation of wavepackets is obtained by the split-operator method. The resultsdemonstrate many important properties of the CH4 moleculedissociation process on the metal Ni. The dissociation probability is astrongly increasing function of the incident kinetic energy, and isenhanced significantly when the molecule CH4 is excited, whichdenotes the clear vibration-excitation effect, as observed in themolecular beam studies of Holmblad et al. [J. Chem. Phys.102 (1995) 8255] The isotopic effect is also studied formolecules CH4 and CD4 at the ground rovibrational states.

Quantum dynamics scattering study of AB+CDE reactions: A seven-dimensional treatment for the H2+C2H reaction

A time-dependent wave packet approach is presented for the quantum dynamics study of the AB+CDE reaction system for zero total angular momentum. A seven-degree-of-freedom calculation is employed to study the chemical reaction of H2+C2H→H+C2H2 by treating C2H as a linear molecule. Initial state selected reaction probabilities are presented for various initial rovibrational states. This study shows that the vibrational excitation of H2 enhances the reaction probability, whereas the excitation of C2H has only a small effect on the reactivity. An integral cross section is also reported for the initial ground states of H2 and C2H. The theoretical and experimental results agree with each other very well when the calculated seven-dimensional results are adjusted to account for the lower transition state barrier heights found in recent ab initio calculations.

Time-dependent wave-packet approach for fusion reactions of halo nuclei

The fusion reaction of a halo nucleus 11Be on 208Pb is described by a three-body direct reaction model. A time-dependent wave packet approach is applied to a three-body reaction problem. The wave packet approach enables us to obtain scattering solutions without considering the three-body scattering boundary conditions. The time evolution of the wave packet also helps us to obtain intuitive understanding of the reaction dynamics. The calculations indicate a decrease of the fusion probability by the presence of the halo neutron.

Bound and Quasibound States of He2H+ and He2D+

Bound and quasibound states of He 2 H + and He 2 D + in three dimensions have been computed by use of a time-dependent quantum-mechanical wave packet approach for total angular momentum J=0. Seven bound states were found for He 2 H + and 14 for He 2 D + , as compared to five for both systems by Lee and Secrest (J. Chem. Phys. 1986, 85, 6565). The potential energy surface needed for the dynamical calculation has been computed by carrying out an ab initio calculation with coupled cluster single and double excitations with perturbative triple excitations [CCSD(T)] employing d-aug-cc-PVTZ basis set. A many-body expansion function proposed by Aguado et al. (Comput. Phys. Commun. 1998, 108, 259) was fitted to the ab initio potential energy values and the resulting fit has a root-mean-square deviation of 10.8 meV (0.25 kcal/mol).

Close-Coupling Time-Dependent Quantum Dynamics Study of the H + HCl Reaction

The paper presents a theoretical study of the dynamics of the H + HCl system on the potential energy surface (PES) of Bian and Werner (Bian, W.; Werner, H. -J., J. Chem. Phys. 2000, 112, 220). A time-dependent wave packet approach was employed to calculate state-to-state reaction probabilities for the exchanged and abstraction channels. The most recent PES for the system has been used in the calculations. Reaction probabilities have also been calculated for several values of the total angular momentum J > 0. Those have then been used to estimate cross sections and rate constants for both channels. The calculated cross sections can be compared with the results of previous quasiclassical trajectory calculations and reaction dynamics experimental on the abstraction channel. In addition, the calculated rate constants are in the reasonably good agreement with experimental measurement.

Multistate vibronic interactions and nonadiabatic wave packet dynamics in the second photoelectron band of chlorine dioxide

Abstract We report theoretical investigations on the second photoelectron band of chlorine dioxide molecule by ab initio quantum dynamical methods. This band exhibits a highly complex structure and represents a composite portrait of five excited energetically close-lying electronic states of ClO2+. Much of this complexity is likely to be arising due to strong vibronic interactions among these electronic states – which we address and examine herein. The near equilibrium MRCI potential energy surfaces (PESs) of these five cationic states reported by Peterson and Werner [J. Chem. Phys. 99 (1993) 302] for the C2v configuration, are extended for the Cs geometry assuming a harmonic vibration along the asymmetric stretching mode. The strength of the vibronic coupling parameters of the Hamiltonian are calculated by ab initio CASSCF-MRCI method and conical intersections of the PESs are established. The diabatic Hamiltonian matrix is constructed within a linear vibronic coupling scheme and the resulting PESs are employed in the nuclear dynamical simulations, carried out with the aid of a time-dependent wave packet approach. Companion calculations are performed for transitions to the uncoupled electronic states in order to reveal explicitly the impact of the nonadiabatic coupling on the photoelectron dynamics. The theoretical findings are in good accord with the experimental observations. The femtosecond nonradiative decay dynamics of ClO2+ excited electronic states mediated by conical intersections is also examined and discussed.

Resonance Raman study of the solvent dynamics for ultrafast charge transfer transition in 4-nitro-4′-dimethylamino-azobenzene

Contribution of solvent reorganization energy is known to be significant for ultrafast charge transfer processes, when the solvent relaxation times are slower than the rate of charge transfer. In this paper, we show that from resonance Raman intensities of a charge transfer transition in combination with Heller’s time-dependent wave packet approach and Brownian oscillator model, one can have a reasonable estimate for the different types of solvent (inertial as well as diffusive) and vibrational reorganization energies. Resonance Raman spectra have been recorded for 4-nitro-4′-dimethylamino-azobenzene (DA) that undergoes photoinduced charge transfer transition, in acetonitrile and benzonitrile. In the two solvents, the total solvent reorganization energy is partitioned into its inertial and diffusive components from the available information on their relaxation time scales. Thus, partitioning of the solvent reorganization energy reveals the importance of the extent of contribution of the two components to the charge transfer rates. The short time dynamics of DA in the two solvents is then examined from a priori knowledge of the ground state normal modes in order to convert the wave packet motion in dimensionless displacements to internal coordinates. The dynamics in DA infers that within 20 fs after photoexcitation from the ground to the charge transfer state, the excited state evolution occurs along N–O, N=N, C–N, and C–C stretching vibrations.

Time-dependent wave packet dynamics of the H+HLi reactive scattering

We report the initial-state-selected and energy-resolved total reaction probabilities for the H+HLi system calculated with the aid of a time-dependent wave packet approach. The ab initio potential energy surface (PES) of Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)] is employed for the purpose. The reaction probabilities are reported for both the collinear and the three-dimensional arrangements of the reacting system. In the collinear arrangement the exothermic reaction path H+HLi→H2+Li is investigated only, whereas in the three-dimensional arrangement both competing reaction paths are investigated and the channel specific reaction probabilities are reported. The hydrogen exchange channel, in general, is found to be more favored over the LiH depletion channel. Both the collinear and the three-dimensional reaction probabilities reveal that the scattering occurs via resonance formation at low energies and the dynamics follows a more direct path at high energies. The overall dynamical characteristics of the system are consistent with the absence of any barrier in the underlying PES. The effect of the rotationally and vibrationally excited reactant LiH molecule on the dynamics is discussed. The importance of the noncollinear configuration of the reacting system on the LiH depletion dynamics is also delineated.

Full-dimensional quantum study of the vibrational predissociation of the I2⋯Ne2 cluster

The dynamics of the vibrational predissociation of the I2Ne2(B,ν=21) cluster is studied using a full-dimensional time-dependent wave packet approach. The 6-D propagation is performed with the multiconfiguration time-dependent Hartree (MCTDH) method. The time dependence of the I2 vibrational state populations is monitored during the dissociation process. The final vibrational populations are compared to experimental findings of Levy et al.

A time-dependent wave packet approach for reaction and dissociation in H 2+H 2

A time-dependent wave packet method to study four center (4C) reactions in competition with collision-induced dissociation is presented and applied to the H 2+H 2 system, using the potential of Aguado et al. [J. Chem. Phys. 101 (1994) 4004] and a reduced dimensionality model. The calculated probabilities are better converged than previous time-independent quantum calculations and, in addition, compare quite satisfactorily with quasiclassical trajectory calculations. Tunneling effects near reaction thresholds are, however, important. For the 4C reaction in H 2( v 1=10)+H 2( v 2=0), it is estimated that such effects are dominant for temperatures below 1200 K, with decreasing values for more excited initial states or for the dissociation process.

Time-dependent wave-packet treatment of theSi4++Hecollision

The collisional system ${\mathrm{Si}}^{4+}+\mathrm{He}$ has been studied over a range of mean relative ion kinetic energy going from ${10}^{\ensuremath{-}2}$ to ${10}^{2}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u}.$ In the low-energy range, a time-dependent wave-packet approach is used both in the diabatic and the adiabatic representation using two different propagator techniques. The agreement between the two sets of results assess the accuracy of the present numerical approach. Above 2.5 eV/amu., a semiclassical eikonal calculation is performed, which includes the Coriolis couplings. Finally, the rate constant is calculated and compared with the other theoretical data as well as with the experimental value of [Fang and Kwong, Phys. Rev. A 59, 342 (1999)]. The present results confirm the order of magnitude of previous theoretical values.

Reactive Scattering Dynamics on Conically Intersecting Potential Energy Surfaces: The H + H2 Exchange Reaction

We investigate the dynamics of a bimolecular reaction on conically intersecting potential energy surfaces. The flux operator method of calculating the state-specific total reaction probability is extended to a coupled-surface problem, both in the diabatic and adiabatic electronic representations. The reaction probabilities are calculated from their expectation values with the aid of a time-dependent wave packet (WP) approach. The initial WP is prepared in an adiabatic electronic state, and it is propagated in a suitable diabatic electronic representation. The initial state-specific and energy-resolved reaction probability is given in analytical forms in both the adiabatic and diabatic picture. The diagonal correction (Born−Huang term) to the uncoupled adiabatic (Born−Oppenheimer) Hamiltonian is discussed. The above formalism is applied to the H + H2 exchange reaction on its conically intersecting double many-body expansion (DMBE) potential energy surfaces. We report the initial state-selected reaction pro...