Quantum dynamics study of torsional excitation of glycine in collision with hydrogen atom on ab initio potential energy surface

Quantum mechanical study has been carried out to investigate C-C torsional excitation in glycine via collisional energy transfer with hydrogen atom. In this study, ab initio calculation is carried out to generate potential energies on a two-dimensional grid (torsional angle and radial coordinate) for given fixed orientational angle (θ, Φ). These discrete energies are fitted with a local linear least-squares method to generate potential energies at any given point in two-dimensional space for dynamics calculation. Time-dependent quantum wave packet calculation is employed to study energy transfer to the C-C torsional mode of glycine, and state-to-state transition probabilities are obtained for different initial angles of collision. Strong angle-dependent energy transfer is observed from the calculation. Although the total energy transferred to the torsional mode is small, collision from certain angles can result in relatively large conformational change in torsion by as much as 30° degrees.