LASER-INDUCED FLUORESCENCE STUDIES OF JET-COOLED S2O - AXIS-SWITCHING AND PREDISSOCIATION EFFECTS

Abstract

Laser‐induced fluorescence spectroscopy has been used to probe the intense C̃ 1A′–X̃ 1A′ (π*←π) electronic system of S2O (315–340 nm) under supersonic free‐jet conditions that yield effective rotational temperatures of roughly 1 K. Least‐squares analysis of high‐resolution scans performed on the 2v0(v=0–5) progression, where ν2 corresponds to the S–S stretching mode, not only furnish refined band origins and rotational constants, but also provide evidence for an axis‐switching effect in this asymmetric triatomic species. Based on the limited set of vibronic bands examined in the present study, the harmonic frequency and anharmonicity for S–S stretching motion in the C̃ state are determined to be ω2=415.2(4) cm−1 and x22=−2.10(6) cm−1, respectively. Predissociation of the C̃ 1A′ potential energy surface is found to become more pronounced with increasing excitation of the ν2 mode. Collision‐free lifetime data, obtained either directly from time‐resolved fluorescence decay profiles or indirectly from measurements of broadened spectral linewidths, permit formulation of a simple, one‐dimensional tunneling model which predicts the excited state predissociation barrier to be located in the vicinity of the 26 vibrational level. These results, as well as possible candidates for the electronic manifold responsible for the predissociation process, are discussed in light of preliminary ab initio calculations.