Pulsed field ionization-photoelectron bands for CS[sub 2][sup +] in the energy range of 13.2–17.6 eV: An experimental and theoretical study.

Vacuum ultraviolet pulsed field ionization-photoelectron (PFI-PE) spectra for CS[SUB2] have been obtained in the energy range of 13.2-17.6 eV, revealing complex vibronic structures for the CS[SUB2,SUP+](&Btilde;[SUP2]∑[SUBu,SUP+] and &Ctilde;[SUP2]∑[SUBg,SUP+]) states. The PFI-PE spectra for CS[SUB2,SUP+](&Btilde;[SUP2]∑[SUBu,SUP+] and &Ctilde;[SUP2]∑[SUBg,SUP+]) are dominated by v[SUB1,SUP+] (symmetric stretching) mode. However, PFI-PE bands due to the v[SUB2,SUP+] (bending) and v[SUB3,SUP+] (antisymmetric stretching) modes with both even and odd quanta are clearly resolved. The simulation of rotational contours resolved in the origin PFI-PE bands yields accurate ionization energies of 14.4742±0.0005 eV (116742±4 cm[SUP-1]) and 16.1883±0.0005 eV (130567±4 cm[SUP-1]) for the formation of CS[SUB2,SUP+](&Btilde;[SUP2]∑[SUBu,SUP+] and &Ctilde;[SUP2]∑[SUBg,SUP+]) states from CS[SUB2](&Xtilde;[SUP1]∑[SUBg,SUP+]), respectively. The PFI-PE bands for [SUP2]∑[SUBu,SUP+](3[SUB0,SUP3]) and [SUP2]∑[SUBg,SUP+](3[SUB0,SUP3]) at 14.805 and 14.965 eV, which are in near energy resonance with the 0 K dissociation thresholds for the formation of S[SUP+]([SUP4]S)+CS(&Xtilde;[SUP1]∑[SUP+]; v"=0 and 1) from CS[SUB2], respectively, are found to be enhanced. These enhancements are rationalized by the prompt dissociation of excited CS[SUB2] in high-n (n⩾100) Rydberg states prior to PFI. Three-dimensional potential energy functions (PEFs) for CS[SUB2,SUP+](2[SUP2]II[SUBu], &Btilde;[SUP2]∑[SUBu,SUP+], and &Ctilde;[SUP2]∑[SUBg,SUP+]) states have been generated theoretically using the complete active space self-consistent field and internally contracted multireference configuration interaction methods. On the basis of these PEFs, the harmonic frequencies for CS[SUB2,SUP+](2[SUP2]II[SUBu], (&Btilde;[SUP2]∑[SUBu,SUP+] and &Ctilde;[SUP2]∑[SUBg,SUP+]) and vibronic energy levels for CS[SUB2,SUP+](&Btilde... [ABSTRACT FROM AUTHOR]