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 progres sion is assigned corresponding to the transition between the linear gr ound state and a bent excited state ...6b(2)9a(1)(1)B(2) correlating w ith the ...5 sigma(u)3 pi(u)(1) Pi(g) state of the linear molecule. Th e same progression is observed in the (3 + 1) resonance enhanced ioniz ation (REMPI) spectrum of Baker and Couris [J. Chem. Phys. 103, 4847 ( 1995); 104, 6130 (1996); 105, 62 (1996)]. Another observed bending pro gression in the [(1+1')+1 REMPI spectrum for the same region is here a ssigned to the other, less bent state ...6b(2)3b(1)(1)A(2) issuing fro m 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 essen tially of 2(1)(0), 2(0)(1), and 2(0)(3) bands associated with excitati on 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 transitio ns related to the same configurations, are assigned to bands observed in the [(1+1')+1] REMPI spectra. The rotational band profile associate d with two-photon one-color excitation of the 3d, 5s supercomplex of C S2, is calculated using a program based on Hund's case (e) representat ion. The band positions and relative intensities in the simulated cont our are in excellent agreement with those assigned to origin transitio ns 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 quantu m defect values used in the final band contour calculation are consist ent 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 sever al authors as possible assignments in this spectral region but are ind eed at much higher energy. The 4p(3) Sigma(u)(-), and 5p(1) Sigma(u)<- -(X) over tilde(1) Sigma(g)(+) transition bands near, respectively, th e lower and higher limits of the interval studied here, are also assig ned. (C) 1997 American Institute of Physics.