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Abstract

The strongest features in the absorption spectrum of CS₂ in the region 2900Å to 3500Å are identified, from temperature studies, as a π → π* ¹Δu - ¹Σ⁺g transition, where the Renner-Teller effect has split the ¹Δu state into ¹B₂ and ¹A₂ component states of a bent molecule. Analysis of some of the least severely perturbed bands of the ¹B₂ - ¹Σ⁺g transitions (3300 - 2900Å) shows that they form a parallel-polarized progression in the bending vibration, to an upper state with r(C - S) = 1.54₄Å, < SĈS = 163°, and a barrier to linearity of ~ 1400 cm⁻¹. Two hitherto unrecognized progressions of 'hot' bands, a weak vibronic ∏ - ∏ and a stronger vibronic Δ - Δ progression in the region 3300Å to 3500Å, are assigned to the ¹A₂ - ¹Σ⁺g transiton. This is a new type of transition, which does not appear in cold absorption, but whose 'hot' bands can obtain an amount of intensity (proportional to K²) through Renner-Teller mixing.