Time-dependent Quantum Wave Packet Dynamics Research Articles

Photodissociation dynamics of the pyridinyl radical: Time-dependent quantum wave-packet calculations.

The H-atom photodissociationreaction from the pyridinyl radical (C5H5NH) via the low-lying πσ* excited electronic state is investigated by nonadiabatic time-dependent quantum wave-packet dynamics calculations. A model comprising three electronic states and three nuclear coordinates has been constructed using ab initio multi-configurational self-consistent-field and multi-reference perturbation theory methods. Two conical intersections among the three lowest electronic states have been characterized in the framework of the linear vibronic-coupling model. Time-dependent wave-packet simulations have been performed using the multi-configuration time-dependent Hartree method. The population dynamics of the diabatic and adiabatic electronic states and the time-dependent dissociation behavior are analyzed for various vibrational initial conditions. The results provide detailed mechanistic insight into the photoinduced H-atom dissociation process from a hypervalent aromatic radical and show that an efficient dissociationreaction through two conical intersections is possible.

Time-dependent quantum wave packet dynamics to study charge transfer in heavy particle collisions.

The method of time-dependent quantum wave packet dynamics has been successfully extended to study the charge transfer/exchange process in low energy two-body heavy particle collisions. The collision process is described by coupled-channel equations with diabatic potentials and (radial and rotational) couplings. The time-dependent coupled equations are propagated with the multiconfiguration time-dependent Hartree method and the modulo squares of S-matrix is extracted from the wave packet by the flux operator with complex absorbing potential (FCAP) method. The calculations of the charge transfer process 12Σ+ H-(1s2)+Li(1s22s)→22Σ+/32Σ+/12Π H(1s)+Li-(1s22s2l)(l=s,p) at the incident energy of about [0.3, 1.3] eV are illustrated as an example. It shows that the calculated reaction probabilities by the present FCAP reproduce that of quantum-mechanical molecular-orbital close-coupling very well, including the peak structures contributed by the resonances. Since time-dependent external interactions can be directly included in the present FCAP calculations, the successful implementation of FCAP provides us a powerful potential tool to study the quantum control of heavy particle collisions by lasers in the near future.

State-to-State Quantum Dynamics of Reactions O((3)P) + HD (v = 0-1, j = 0) → OH+D and OD+H: Reaction Mechanism and Vibrational Excitation.

Time-dependent quantum wave packet dynamics calculations have been performed in order to characterize the dynamics and mechanism of O((3)P) + HD (v = 0-1, j = 0) → OH+D and OD+H reactive collisions using the adiabatic potential energy surface by Rogers et al. [J. Phys. Chem. A 2000, 104, 2308] Special attention has been paid to the calculations and discussion of the state resolved integral and differential cross sections and the product state distributions. In addition, the intramolecular isotopic branching ratio has been determined. The results revealed that the OD + H is the favored product channel and the product OH has the same quantum number v as the reactant HD. For low collision energy, the product angular distributions concentrate in the backward region being consistent with a rebounding mechanism. In the case of higher collision energy, the stripping collisions with larger impact parameters tend to produce sideways and forward scatterings, especially for the HD vibrationally excited state. The cross section and intramolecular isotopic branching ratio are in agreement with the previous theoretical results. A cartoon depiction collision model is built and works well for our calculation results.

Time-dependent quantum wave packet dynamics of S + OH reaction on its electronic ground state.

Initial state-selected dynamics of the S((3)P) + OH (X(2)Π) → SO (X(3)Σ(-)) + H ((2)S) reaction on its electronic ground potential energy surface (X̃(2)A") is investigated here by a time-dependent wave packet propagation (TDWP) approach. Total reaction probabilities for the three-body rotational angular momentum up to J = 138 are calculated to obtain converged integral reaction cross sections and state-specific rate constants employing the centrifugal sudden (CS) approximation. The convergence of the latter quantities is checked by varying all parameters used in the numerical calculations. The cross section and rate constant results are compared with those available in the literature, calculated with the aid of the quasi-classical trajectory method on the same potential energy surface. Reaction probabilities obtained with the TDWP approach exhibit dense oscillatory structures, implying formation of a metastable quasi-bound complex during the collision process. The effect of rotational and vibrational excitations of reagent OH on the dynamical attributes is also examined. While the rotational excitation of reagent OH decreases the reactivity, its vibrational excitation enhances the same.

Time-dependent quantum wave packet dynamics of the C + OH reaction on the excited electronic state

Quantum state-selected dynamics of C((3)P) + OH (X(2)Π) → CO(a(3)Π) + H ((2)S) reaction on its first excited electronic potential energy surface (1(2)A(")) is examined here using a time-dependent wave packet propagation approach. All partial wave contributions for the total angular momentum, J = 0-95, are included to obtain the converged cross sections and initial state-selected rate constants in the temperature range of 10-500 K. The reaction probability, as a function of collision energy, exhibits dense oscillatory structures owing to the formation of resonances during collision. These resonance structures also persist in reaction cross sections. The effect of reagent rotational and vibrational excitation on the dynamical attributes is examined and discussed. Reagent rotational excitation decreases the reactivity whereas, vibrational excitation of the reagent has minor effects on the reactivity. The results presented here are in good accord with those obtained using the time-independent quantum mechanical and quasi-classical trajectory methods.

Quantum dynamics of H + LiH reaction and its isotopic variants

Time-dependent quantum wave packet dynamics study is carried out to investigate the initial state selected channel specific reactivity of H + LiH collisional system on a new and more accurate ab initio potential energy surface developed by Wernli et al. [J. Phys. Chem. A 113, 1121 (2009)]. The H + LiH reaction proceeds through LiH depletion and H-exchange paths. While the former path is highly exoergic (by ∼2.258 eV), the latter path is thermoneutral. State selected and energy resolved integral reaction cross sections and thermal rate constants are reported and compared with the literature data. The reactivity of the LiH depletion channel is found to be greater than the H-exchange channel. Rotational excitation of the reagent LiH molecule causes a decrease of reactivity of both the channels. On the other hand, the vibrational excitation of the reagent LiH decreases the reactivity of the LiH depletion channel and increases the reactivity of the H-exchange channel. The effect of isotopic substitution (H by D) on the reaction dynamics is also examined.

Time-dependent quantum wave-packet description of H and D atom tunneling in N–H and N–D photodissociation of methylamine and methylamine-d2

The degree to which tunneling through a barrier in the N-H and N-D photodissociation channels of methylamine (CH3NH2) and its deuterated variant (CH3ND2), respectively, plays a role was investigated by time-dependent quantum wave-packet dynamics calculations. Two dimensional potential energy surfaces (PESs) of methylamine, presenting the N-H stretch and the HNC bend, were constructed employing multireference ab initio electronic-structure methods, allowing full description of the H motion on the HC-NH2 plane. The time-dependent Schrödinger equation was solved employing the Fourier method for calculating the Hamiltonian operation together with the Chebychev polynomial expansion of the evolution operator. The results show that tunneling and decay to vibrational resonant states on the first excited electronic PES are faster for the H atom than for the D. The decay into two of the resonant states found on the first PES strongly depends on the initially excited vibrational state on the ground electronic PES.

Photoionization of NaK molecule with a double-well potential in femtosecond pump–probe pulse laser fields

The method of time-dependent quantum wave packet dynamics is used to calculate the femtosecond pump–probe photoelectron spectra and study the wave packet dynamic processes of the double-minimum potential state 61Σ+ of NaK in intense laser fields. The evolutions of the wave packet and the photoelectron energy spectra with time and internuclear distance are described in detail. The wave packet dynamic information of the 61Σ+ state can be extracted from the photoelectron energy spectra.

Selective excitation of the OClO molecule with femtosecond laser pulse

The three-dimensional time-dependent quantum wave packet dynamics $(J=0)$ using a Hamiltonian for a triatomic molecule in Radau coordinates is employed to study laser pulse excitation of the OClO molecule. The fast Fourier transform (FFT) and the split operator methods are applied to propagate the wave packet. The vibronic excitations $A\phantom{\rule{0.2em}{0ex}}^{2}A_{2}({\ensuremath{\nu}}_{1},{\ensuremath{\nu}}_{2},{\ensuremath{\nu}}_{3})\ensuremath{\leftarrow}X\phantom{\rule{0.2em}{0ex}}^{2}B_{1}(0,0,0)$ of the triatomic molecule OClO using femtosecond laser pulses of varying intensities are investigated. With an ultrashort laser pulse of certain FWHM (full width at half maximum), the vibrational level can be selectively excited. The changes in the vibrational population distributions caused by simple variation of the pulse are remarkable.

Time-dependent quantum wave-packet description of the 1pi sigma* photochemistry of pyrrole.

The photoinduced hydrogen elimination reaction in pyrrole via the conical intersection of the 1B1 (1pi sigma*) excited state with the electronic ground state has been investigated by time-dependent quantum wave-packet dynamics. A two-dimensional model potential-energy surface has been constructed as a function of the NH stretching and the hydrogen out-of-plane bending mode, employing multi-reference ab initio electronic-structure methods. The branching ratio of the reactive flux at the conical intersection has been investigated in dependence on the initial vibrational state of the molecule. The results suggest that laser control of the photodissociation of pyrrole via mode-specific vibrational excitation should be possible.