Analysis of a 1Δu–1Σg+ Transition of CS2 in the Near Ultraviolet

Abstract

The strongest features of the gas-phase absorption spectrum of CS2 in the region 2900–3300 Å (Kleman's V system) are shown to belong to a 1B2–1Σg+ transition, where the 1B2 state correlates with the upper Renner–Teller component of the π → π* 1Δu state of the linear molecule. The barrier to linearity is about 1300 cm−1, and the structure of the molecule in the zero-point level is r(C–S) = 1.544 ± 0.006 Å, [Formula: see text]. Transitions to the lower Renner–Teller component, 1A2(1Δu), have been identified in the region 3340–3500 Å: these consist of a progression of vibronic Δ–Δ bands and a weaker progression of Π–Π bands. This is a new type of electronic transition, which does not appear in cold absorption, but whose 'hot' bands derive an amount of intensity proportional to K2 through Renner–Teller mixing (in this case from the V system). The bands of both systems are very severely perturbed: possible causes of the perturbations are discussed.