Spectroscopy and relaxation of CS₂⁺ in solid Ne

Absorption and laser induced fluorescence spectra of CS₂ ⁺ in solid Ne are re-examined. Isotopic studies with ¹³CS₂ confirm that most of the strong vibronic bands of the X̃²Π_g→òΠ_u transition are due to an almost perfect mixture of ν₁ and ν₂ modes. Extension of the spectrum into the UV leads to identification of the overtone of the third vibrational mode, 2ν′₃=3288 cm_-1, whose frequency increases considerably in the upper state. The origin of the X ²Πg→B̃²Σ_u⁺ transition is also observed. B̃²Σ_u⁺ state excitation results in efficient nonradiative transition into the òΠ_u state. Study of spectral line shapes associated with the X̃ ²Π_g→à ²Π_u transition suggests inefficient energy transfer between ν₃ and the lower frequency modes.