Fluorescence lifetimes of the single vibrational levels of H 2CS 1, D 2CS, and Cl 2CS in the Ā 1A 2 state

Abstract

Fluorescence lifetimes of the single vibronic levels of the first excited singlet states of H 2CS, D 2CS and Cl 2CS have been measured under effusive flow conditions. The single exponential lifetimes of H 2CS (D 2CS) decrease from 140 μs (182 μs) to 72 μs (95 μs) with increasing vibrational levels of Ā 1A 2 state. At the same excitation energy, the lifetime of H 2CS (Ā 1A 2) is shorter than that of D 2CS (Ā 1A 2). The difference is attributed to a tunnelling effect in a non-radiative process. The decay of Cl 2CS( \\ ̄ A 1A 2) is not single exponential. Assuming a bi-exponential decay, the shorter fluorescence lifetime decreases with the vibrational levels, while the longer one increases. The difference between H 2CS and Cl 2CS is discussed in terms of non-radiative processes including dissociation and intersystem crossing.