Control of optically dark n<i>σ*</i> state mediated photodissociation of thioanisole

Abstract

The methyl photodissociation of thioanisole molecule has been investigated within the mathematical framework of optimal control theory (OCT) considering a reduced dimensional model of three electronic states (ππ, ππ*, and nσ*) and two vibrational modes (S–CH3 stretching and S–CH3 torsional angle). The model includes two bound states (ground state and the ππ* state) and one repulsive state (nσ* state). The effect of the initial vibrational excitation on the branching ratio of the two dissociation channels is examined. In the presence of optimal pulse, methyl photodissociation predominantly occurs via two successive conical intersections. For further justification of the findings of OCT calculations, the field-free quantum dynamics calculations, where the initial wave packet is vertically excited to the ππ* state, are also examined under different initial conditions. A comparative study of these two types of calculations reveals that in the field-free case, photodissociation occurs via the adiabatic path, whereas it follows the nonadiabatic path in the presence of optimal pulse. Therefore, the branching ratio also changes accordingly with the initial conditions for these two types of dynamical events.