Optical–optical double resonance study of the and &([a-z]+);(3A2) states of thiophosgene

Abstract

The &([a-z]+);(3A2) and [Formula: see text] states of jet-cooled thiophosgene (Cl2CS) have been studied by optical–optical double resonance (OODR) spectroscopy. Two OODR schemes have been used to probe the [Formula: see text] state. One scheme uses selected vibronic levels of the &([a-z]+);(1A2) state as the intermediate state, while the other uses the vibrationless and 2131 levels of the &([a-z]+);(3A2) state. All of the vibronic levels in the 33 980−35 600 cm−1 region can be rationalized with the following origin band and fundamentals: 0° = 34 277 cm−1, v1 = 505 cm−1, v2 = 470 cm−1, v3 = 213 cm−1, v6 = 249 cm−1, 42 = 341 cm−1, 44 = 627 cm−1. The discrepancies among the various studies of the [Formula: see text] state will be discussed and reconciled. It is conjectured that the [Formula: see text] state potential along the C—S coordinate exhibits an asymmetric double-minimum potential resulting from the interaction of the 1A1 states arising from the [Formula: see text] configurations. The minimum corresponding to the [Formula: see text] configuration lies higher in energy and the principal decay mechanism for molecules pumped to its first few vibronic levels is fluorescence. On the other hand, molecules pumped to the minimum corresponding to the nominal [Formula: see text] configuration decay nonradiatively. The barrier height to inversion and the out-of-plane bending angle along the out-of-plane bending coordinate, v4, have been determined to be 945 cm−1 and 25°, respectively, by fitting quartic-quadratic and quadratic-Gaussian double-minimum potentials to the observed energy levels. The &([a-z]+);(3A2) state has been studied by a novel OODR scheme which uses the fluorescent vibrationless level of the [Formula: see text] state to monitor [Formula: see text]transitions. A vibronic analysis has been carried out and the following origin band and fundamentals derived for the &([a-z]+);(3A2) state: 0° = 17 499 cm−1, v1 = 923 cm−1, v2 = 474 cm−1, v3 = 247 cm−1, 42 = 297 cm−1, 44 = 560 cm−1, 46 = 741 cm−1. With the exception of a few corrections and additions, the results confirm the findings of previous studies, notably regarding the bent geometry and barrier height to inversion. An overall comparison of the data suggests that the wavenumber of v6 in theÃ(1A2) state is 279 cm−1 instead of 189 cm−1.