New vibrational analysis of the 1B2(1Δu) state of CS2

Sub-Doppler excitation spectra of CS2 in the spectral range of 29 600 - 32 800 cm(-1) (V-system) are measured with a frequency doubled continuous wave (cw) single-mode dye laser. The ultraviolet (UV) radiation is generated in an external enhancement cavity. The average output power is about 5 mW, which is sufficient to resolve weak rotational lines in the excitation spectra of hot bands from the (0,2(2),0) level of the ground state. This increased the number of measured transitions with K >0 considerably. The low temperature achieved by adiabatic cooling of CS2 seeded in a supersonic argon beam simplifies the spectrum and allows an exact assignment of the rotational lines. Based on new ab initio calculations, a revised electronic state and vibrational assignment of the bands were necessary and will be presented. From this vibrational analysis the geometry, the position of the barrier to Linearity, and the rotational constants of the CS2 molecule in the V B-1(2)((1)Delta(u)) state have been determined, revising former results. A statistical analysis of the positions of all measured bands shows a pure Poissonian nearest level distribution indicating no correlation between neighboring vibrational levels nor long-range interactions. (C) 1998 American Institute of Physics.