On the unimolecular elimination of gas-phase iodine monobromide following excitation in the visible wavelength region

摘要

Dissociation dynamics of iodine monobromide has been theoretically investigated at numerous excitation wavelengths in the visible wavelength region (450–540 nm) by an accurate time-dependent dynamical simulation technique. The interatomic potential energy curves are derived from ab initio methods which are then employed in a Landau–Zener treatment to calculate the spin-orbit branching ratios in the two halogen products. The extinction coefficients, in arbitrary units, for the discrete electron transition are obtained through a numerical algorithm. Based on these elastic scattering calculations, the results of Br*: Br branching ratios are determined at several simulation wavelengths. Also the electronic properties are evaluated to elucidate the mechanism of chemical dynamics of the system. It is found that the branching dynamics can be clarified via the Landau–Zener model, which treats an avoided crossing between two states of a given nature and evaluates a nonadiabatic effect relevant to the dissociation of IBr molecule.