Research Interest
Quantum wavepacket calculations in chemical reaction dynamics
Quantum wavepacket calculations provide results that can be compared in detail about the dynamics of a chemical reaction with those obtained in the experiments, and serve as one of the most rigorous tests of the accuracy of potential energy surfaces (PESs) for chemical reactions. We have developed initial state selected wavepacket (ISSWP) simulations to study dynamics in multiple channels for elementary chemical reactions, e.g., H_{2} (v_{1}, j_{1}) +H_{2}/D_{2} (v_{2}, j_{2}) in collision induced dissociation (CID), four-center (4C), and single exchange (SE) channels. Also, we have extended wavepacket calculations to high dimensional space in poly-atomic systems, e.g., the abstraction reaction of H+CH_{4}/CD_{4}, as well as simultaneously constructing accurate potential energy surfaces for the reaction.
FIG. (a)–(c) The six-dimensional reaction flux distribution for the H2 (v1 = 10, j1 = 0) + D2 (v2 = 0, j2 = 0) reaction at a translational energy of 0.5 eV on the planes S[r^{F}1 ], S[r^{F}2 ], and S[R^{F} ]; (d) |ψ+i (E)|^{2} as a function of r_{min} and r^{CP}_{min}.
“CO2 family” van der Waals clusters
The “CO_{2} family” molecules include CO_{2}, N_{2}O, OCS, and CS_{2}. Their dimers and trimers, have been the focus of experiment over the past few years. Recently some new structures have been experimentally observed for these complexes, including the polar isomers of N_{2}O dimer and OCS dimer, planar cyclic isomer of CO_{2} trimer and two distinct structures of OCS-CO_{2} complex. Some interesting questions arose, such as the relative stability of the isomers and the interconversion mechanism between these isomers.
We have studied the NO_{2} dimer theoretically through the construction of very high accuracy inter-molecular potential energy surface and the calculation of bound states on the PES. Three co-planar local minima are found on this PES. They correspond to a nonpolar isomer with slipped-antiparallel planar structure and two equivalent polar isomers with slipped-parallel planar structures. The nonpolar isomer is energetically more stable by 162 cm^{-1} than the polar ones. The calculated vibrational frequencies are in good agreement with the available experimental data. Quantum tunneling effect between the two equivalent polar structures has been found in the higher vibrational excited states. Microwave spectra of the polar structure are also calculated. The accuracy of the PES has been validated by the good agreement between theoretical and experimental results of transition frequencies and spectroscopic parameters. More work will be performed to study other dimers and trimers.
FIG. The θ_{1}-θ_{2} contour plots of the wave functions and the schematic diagrams of corresponding vibrational modes. (a) Disrotation mode of the nonpolar isomer; (b) Conrotation mode of the nonpolar isomer; (c) Disrotation mode of the polar isomer; (d) Conrotation mode of the polar isomer.
Ab initio calculations in chemistry
We have been working on ab initio calculations to understand organocatalysis reaction mechanism, e.g., aminoxylation catalyzed by chiral Bronsted acid, in collaboration with experimental group in CBC. We have also performed electronic structure calculations to understand tungsten-phosphinidene complex.