An adiabatic model for the photodissociation of CH3SH in the first ultraviolet absorption band

The photodissociation of CH3SH in the first absorption band is studied via ab initio computation of the relevant potential energy surfaces and exact quantum scattering calculations. The effective valence shell Hamiltonian (H! ab initio many-body perturbation technique is used to calculate the global ground X A8 and 1 A9 surfaces as functions of the C–S and S–H internuclear distances. The finite range scattering wave function ~FRSW! time-independent quantum scattering method is used to compute the adiabatic dynamics of S–H and C–S bond fission on the 1 A9 surface following excitation. Two calculations are performed, one in which the ground state is represented by a cubic spline function fitted to the ab initio data and another in which it is represented as the sum of two uncoupled Morse oscillators. Absorption spectra as well as the branching ratios and photofragment translational energy distributions corresponding to various excitation energies are presented and compared to recent experimental results. A final calculation examines how the branching ratio and product vibrational state distribution changes for the photodissociation of a CH3SH molecule with one quantum of vibrational excitation in the C–S stretch. © 1995 American Institute of Physics.