High resolution pulsed field ionization-photoelectron bands for CS2+((A)over-tilde2πu):: An experimental and theoretical study

The vacuum ultraviolet pulsed field ionization-photoelectron (PFI-PE) spectra for CS2 were measured in the full energy range of 12.6-13.5 eV, revealing complex vibronic band structures for the CS2+((A) over tilde (2)Pi (u)) state. Three-dimensional potential energy functions (PEFs) for CS2+((A) over tilde (2)Pi (u)) were also generated theoretically using the complete active space self-consistent field and internally contracted multireference configuration interaction methods. Using these PEFs, the harmonic frequencies, anharmonic constants, and Renner-Teller rovibronic energy levels for CS2+((A) over tilde (2)Pi (u)) were calculated variationally. Many Fermi polyads have been identified in the rovibronic states of CS2+((A) over tilde (2)Pi (u)). Using present theoretical and available optical data, we assigned most of the PFI-PE rovibronic bands due to excitation of the v(1)(+) (symmetric stretching), v(2)(+) (bending), and v(3)(+) (asymmetric stretching) modes for CS2+((A) over tilde (2)Pi (u)). The simulation of rotational contours resolved in the high-resolution PFI-PE bands for CS2+((A) over tilde (2)Pi (u)); v(2)(+) = 0-3, v(2)(+) = 0,2, v(3)(+) = 0) provided accurate ionization energies for the formation of these states from CS2((X) over tilde (1)Sigma (+)(g)).