Journal of Chemical Physics, Vol.107, No.5, 1308-1316, 1997
High-Resolution Absorption-Spectrum of Jet-Cooled Cs2 Between 65000 and 71000 cm(-1) - Assignment of Bent ...5-Sigma(U)3-Pi(U) and Linear ...2-Pi(3)(G)3D and 5S Gerade States
The absorption spectrum of jet-cooled CS2 was photographed between 65 000 and 71 900 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 ...6b(2)9a(1)(1)B(2) correlating with the ...5 sigma(u)3 pi(u)(1) Pi(g) 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 ...6b(2)3b(1)(1)A(2) issuing from the ...5 sigma(u)3 pi(u)(1) Pi(g) linear state. In both progressions, Delta upsilon(1)=1 transitions are also observed. In the upper half of the energy range considered, the absorption spectrum consists essentially of 2(1)(0), 2(0)(1), and 2(0)(3) bands associated with excitation of ...2 pi(g)(3)3d and 5s(1) Pi(g) 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 1(0)(1) 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 2 pi(u) and 5 sigma(u) orbitals to 7 sigma(g) (4s sigma g) and from 6 sigma(g) to the valence 3 pi(u) orbital. These transitions were suggested by several authors as possible assignments in this spectral region but are indeed at much higher energy. The 4p(3) Sigma(u)(-), and 5p(1) Sigma(u)<--(X) over tilde(1) Sigma(g)(+) transition bands near, respectively, the lower and higher limits of the interval studied here, are also assigned.