Factors Affecting the Branching Ratio of Photodissociation: Thiophenol Studied through Quantum Wavepacket Dynamics

Abstract

The photodissociation dynamics of thiophenol (PhSH) excited to the 1 (1) pi pi* state was investigated by time-dependent quantum wavepacket propagation within two-dimensional (2D) space consisting of the S- H bond and - SH torsion. We systematically studied the dependence of the branching ratio ((A) over tilde/(X) over tilde) between the two electronic states of the phenylthiyl radical (PhSC) on several factors of the 2D potential energy surfaces (PESs). The effect of a reduced initial barrier to the first pi pi*/pi sigma* conical intersection (CI) was found to be marginal, whereas the effects of a reduced torsional barrier of - SH on the excited pi pi* state and the mitigated slope of the pi sigma* PES between the first (pi pi*/pi sigma*) and the second (pi sigma*/S-0) CIs were noticeable. The effect of the slope on the branching ratio has never been previously noticed. It was shown that the branching ratio can be sufficiently above unity without pre-excitation of the torsion mode of -SH, which has been assumed so far.