Knowledge Bank

Laser-induced fluorescence spectroscopy has been used to probe the intense $C~A\prime -X~1A\prime (\pi \ast \leftarrow \pi )$ electronic system of $S2O$ (315-340nm) under supersonic free-jet conditions that yield effective rotational temperatures of roughly 1 K. Least squares analysis of high-resolution scans performed on the $2\nu 0(\nu =0-5)$ progression, where $\nu 2$ 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 $C~$ state are determined to be $\omega 2=415.2(4)cm-1$ and $x22=-2.10(6)cm-1$, respectively, where values in parentheses correspond to one standard deviation uncertainties. Predissociation of the $C~1A\prime$ potential energy surface is found to become more pronounced with increasing excitations of the $\nu 2$ mode. Collision-free lifetime data, obtained either directly from time-resolved fluorescence decay profiles or indirectly from measurements of broadened spectral linewidths, permits formulation of a simple, onedimensional 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 reposible for the predissociation process, will be discussed in light of preliminary ab initi calculations.