Fluorescence excitation spectra, lifetimes, and quenching of S2(<i>B</i> 3Σ<i>u</i>−) in the wavelength region 280–315 nm

Abstract

Fluorescence lifetimes have been determined for S2 vapor excited to the B 3Σu− state at wavelengths in the range 280–315 nm, with a spectral resolution of ∼0.5 cm−1. For states with v′⩽8, excitation in the bandhead region leads to fluorescence lifetimes of ∼30–45 ns. In addition, low-intensity peaks with much longer lifetimes are observed throughout the absorption spectrum. The decreased intensity and increased lifetime are attributed to perturbations by the B′ 3πu state. For the v′ = 9 state, lifetimes generally decrease as the excitation wavelength moves away from the bandhead and at some wavelengths a double exponential decay was observed. Although the v′ = 10 state is known to predissociate, weak fluorescence peaks with very short lifetimes (&amp;lt;3 ns) were observed. The addition of Ar as a quenching gas leads to complex fluorescence decay curves with two or three components for both v′ = 3 and v′ = 9 states. Lifetimes and quenching rate constants obtained in this work agree with those measured previously in this laboratory using a broad-band excitation source.