Analysis of a ¹Δ_u–¹Σ_g⁺ Transition of CS₂ in the Near Ultraviolet

Abstract

The strongest features of the gas-phase absorption spectrum of CS 2 in the region 2900–3300 Å (Kleman's V system) are shown to belong to a 1 B 2 – 1 Σ g + transition, where the 1 B 2 state correlates with the upper Renner–Teller component of the π → π* 1 Δ u 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, 1 A 2 ( 1 Δ u ), 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 K 2 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.