High resolution absorption spectrum of jet-cooled CS2 between 65 000 and 71 000 cm−1: Assignment of bent …5σu3πu and linear …2πg3 3d and 5s gerade states

Abstract

The absorption spectrum of jet-cooled CS2 was photographed between 65 000 and 71 000 cm−1 at a resolution limit of 0.0008 nm. In the first half of the energy interval considered, a bending vibrational progression is assigned corresponding to the transition between the linear ground state and a bent excited state …6b29a11B2 correlating with the …5σu3πu1Πg state of the linear molecule. The same progression is observed in the (3+1) resonance enhanced ionization (REMPI) spectrum of Baker and Couris [J. Chem. Phys. 103, 4847 (1995); 104, 6130 (1996); 105, 62 (1996)]. Another observed bending progression in the [(1+1)+1] REMPI spectrum for the same region is here assigned to the other, less bent state …6b23b11A2 issuing from the …5σu3πu1Πg linear state. In both progressions, Δv1=1 transitions are also observed. In the upper half of the energy range considered, the absorption spectrum consists essentially of 210, 201, and 203 bands associated with excitation of …2πg3 3d and 5s Πg1 states. The corresponding origin bands, as well as those of all the other two-photon allowed transitions related to the same configurations, are assigned to bands observed in the [(1+1)+1] REMPI spectra. The rotational band profile associated with two-photon one-color excitation of the 3d, 5s supercomplex of CS2, is calculated using a program based on Hund’s case (e) representation. The band positions and relative intensities in the simulated contour are in excellent agreement with those assigned to origin transitions in the two-color parallel polarized REMPI spectrum. All other bands of the experimental two-photon spectrum can be assigned as the 101 bands associated with the observed 3d electronic origins. The quantum defect values used in the final band contour calculation are consistent with those obtained in an ab initio calculation. A calculation of the same type is performed for the excitation energy from 2πu and 5σu orbitals to 7σg (4sσg) and from 6σg to the valence 3πu orbital. These transitions were suggested by several authors as possible assignments in this spectral region but are indeed at much higher energy. The 4p 3Σu− and 5p 1Σu+←X̃ 1Σg+ transition bands near, respectively, the lower and higher limits of the interval studied here, are also assigned.