Pei-Yu Zhang

Nonadiabatic ab initio molecular dynamics of photoisomerization in bridged azobenzene.

The photoisomerization mechanisms of bridged azobenzene are investigated by means of surface hopping dynamics simulations based on the Zhu-Nakamura theory. In the geometry optimizations and potential energy surface calculations, four minimum-energy conical intersections between the ground state and the lowest excited state are found to play important roles in the trans-cis and cis-trans isomerization processes. The trans-cis photoisomerization proceeds through two minimum-energy conical intersections. Ultrafast pedal motion of the N atoms and twisting of phenyl rings around their N-C bonds allows the molecule to move to a minimum-energy conical intersection, after which surface hopping from S(1) to S(0) occurs. In the S(0) state, further rotation occurs around the N=N bond and two N-C bonds until the azo moiety and phenyl rings complete their isomerization. Finally, the cis form is achieved by subsequent adjustment of the ethylene bridge. In the cis-trans photodynamics, there is one rotational pathway, in the middle of which two CIs are responsible for the surface hopping to the S(0) state. After the nonadiabatic transition, the molecule reaches the trans form through a barrierless pathway and the two phenyl rings and the additional bridge complete their reorientation almost at the same time.

Dissociation and ionization competing processes for H2+ in intense laser field: Which one is larger?

Competition between dissociation and ionization of H(2)(+) in intense laser field has been investigated by using an accurate three-dimensional time-dependent wavepacket approach. The disagreement between the experiment and the former one-dimensional theory has been resolved. In a comparison of the calculated results with the available experimental data, a good agreement is reached, not only for the relative probabilities between dissociation and ionization but also for the two-peak structures and the peak energy locations for these two processes.

Coriolis Coupling Effects in O+(S-4) + H-2(X-1 Sigma(+)(g)) -> OH+(X-3 Sigma(-)) + H(S-2) Reaction and Its Isotopic Variants: Exact Time-Dependent Quantum Scattering Study

The time-dependent wave packet quantum method taking into account the Coriolis coupling (CC) has been employed to investigate the dynamics of O(+) + H(2)/D(2)/HD (v(i) = 0, j(i) = 0) reactions based on an accurate potential energy surface [ Martínez et al. J. Chem. Phys. 2004 , 120 , 4705 ]. Through the comparison between the results with and without CC, the pronounced CC effects have been revealed in the title reactions. Moreover, the calculated results with the CC method can well reproduce the data of close-coupling hyperspherical (CCH) exact quantum method. The calculations demonstrate that the CC effects play an important role in the O(+) + H(2) system.

Accurate high level ab initio-based global potential energy surface and dynamics calculations for ground state of CH2+

A global many-body expansion potential energy surface is reported for the electronic ground state of CH2 (+) by fitting high level ab initio energies calculated at the multireference configuration interaction level with the aug-cc-pV6Z basis set. The topographical features of the new global potential energy surface are examined in detail and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. In turn, in order to validate the potential energy surface, a test theoretical study of the reaction CH(+)(X(1)Σ(+))+H((2)S)→C(+)((2)P)+H2(X(1)Σg (+)) has been carried out with the method of time dependent wavepacket on the title potential energy surface. The total integral cross sections and the rate coefficients have been calculated; the results determined that the new potential energy surface can both be recommended for dynamics studies of any type and as building blocks for constructing the potential energy surfaces of larger C(+)/H containing systems.

Quantum dynamical study of the electronic nonadiabaticity in the D + DBr → Br(Br*) + D2 reaction on new diabatic potential energy surfaces

A set of diabatic potential energy surfaces, that describe the D + DBr → Br(P(1/2,3/2)) + D(2) reaction, is constructed based on MRCI/aug-cc-pV5Z calculations at 29,526 grid points. Time-dependent wave packet calculations are performed for ground-state DBr initially with collision energies up to 2.0 eV to investigate possible electronic nonadiabaticity in this reaction. Reaction probabilities and integral cross sections are calculated. The results show negligible nonadiabatic effects for the title reaction in the energy range considered here, confirming experimental work of Zare and co-workers. In addition, the calculated thermal rate constants are in good agreement with experimental ones.

Time-dependent Wave Packet Quantum Scattering Study of Reaction S(3P)+H2→HS+H on a New ab initio Potential Energy Surface 3A′

A new potential energy surface is presented for the triplet state 3A′ of the chemical reaction S(3P)+H2 from a set of accurate ab initio data. The single point energies are computed using highly correlated complete active space self-consistent-field and multi-reference configuration interaction wave functions with a basis set of aug-cc-pV5Z. We have fitted the full set of energy values using many-body expansion method with an Aguado-Paniagua function. Based on the new potential energy surface, we carry out the time-dependent wave packet scattering calculations over the collision energy range of 0.8-2.2 eV. Both the centrifugal-sudden approximation and Coriolis Coupling cross sections are obtained. In addition, the total reaction probabilities are calculated for the reactant H2 initially in the vibrational states v=0–3 (j=0). It is found that initial vibrational excitation enhances the title reaction.

Quantum Dynamics Study on D+OD+ Reaction: Competition between Exchange and Abstraction Channels

Quantum dynamics for the D+OD+ reaction at the collision energy range of 0.0–1.0 eV was studied on an accurate ab initio potential energy surface. Both of the endothermic abstraction (D+OD+→O++D2) and thermoneutral exchange (D+OD+→D+OD+) channels were investigated from the same set of time‐dependent quantum wave packets method under centrifugal sudden approximation. The reaction probability dependence with collision energy, the integral cross sections, and the thermal rate constant of the both channels are calculated. It is found that there is a convex structure in the reaction path of the exchange reaction. The calculated time evolution of the wave packet distribution at J=0 clearly indicates that the convex structure significantly influences the dynamics of the exchange and abstraction channels of title reaction.