Correlation of Energy Levels of Linear and Bent Triatomic Molecules, and the Ultraviolet CS2Absorption Spectrum

Abstract

A set of vibronic levels for a $^{1}\ensuremath{\Sigma}^{+}_{g}$ and a $^{1}\ensuremath{\Pi}_{g}$ electronic state of linear A${\mathrm{B}}_{2}$ is shown in a diagram, together with gyrovibronic levels of the corresponding electronic states (a $^{1}A_{1}$ and a $^{1}B_{2}$ and a $^{1}A_{2}$) of bent A${\mathrm{B}}_{2}$; and a correlation is set up between the sets of gyrovibronic levels of the two cases. This diagram is then used in a discussion of the near-ultraviolet absorption bands of carbon disulfide, where the molecule is linear in the $^{1}\ensuremath{\Sigma}^{+}_{g}$ ground state. The band types and structures for such a transition are discussed; the structures should be practically identical in character whether the upper state is linear or bent. Vibrational intensities, and their relation to a strong allowed electronic transition at shorter wave-lengths, are also discussed. It is concluded that the near-ultraviolet system is an electronic-allowed transition to a $^{1}\mathrm{B}_{2}$ bent molecule upper state related to a $^{1}\ensuremath{\Pi}_{g}$ linear molecule state.