HIGH-RESOLUTION VACUUM-ULTRAVIOLET PULSED-FIELD IONIZATION PHOTOELECTRON BAND FOR OCS-2-PI) - AN EXPERIMENTAL AND THEORETICAL-STUDY((X)

The vacuum ultraviolet pulsed field ionization photoelectron (PFI-PE) band for OCS+(X (2) Pi) in the energy region of 11.09-11.87 eV has bee n measured using high resolution monochromatized synchrotron radiation , The ionization energies (IEs) for the formation of the (0,0,0) X (2) Pi(3/2) and (0,0,0) (2) Pi(1/2) states of OCS+ are determined to be 1 1.1831+/-0.0005 and 11.2286+/-0.0005 eV, respectively, yielding a valu e of 367+/-1.2 cm(-1) for the spin-orbit splitting. Using the internal ly contracted multireference configuration interaction approach, three -dimensional potential energy functions (PEFs) for the OCS+(X (2) Pi) state have been generated and used in the variational Renner-Teller ca lculations of the vibronic states. The energies of all vibronic states (J=P) for J=1/2, 3/2, 5/2, and 7/2 have been computed in the energy r ange of approximate to 4000 cm(-1) above the IE[OCS+(X (2) Pi(3/2))] f or the assignment of the experimental spectrum. By a minor modificatio n of the nb initio PEFs, good correlations are found between the exper imental and theoretical Renner-Teller structures. Similar to the PFI-P E bands for CO2+(X (2) Pi(g)) and CS2+(X (2) Pi(g)), weak transitions have been detected in the PFI-PE band for OCS+(X (2) Pi), which are fo rbidden in the Franck-Condon approximation. The nonvanishing single-ph oton ionization cross sections involving the excitation of the bending vibrational modes of OCS+, CO2+, and CS2+, in their ground electronic states are attributed to the symmetries of the geometry-dependent ele ctronic transition dipole operator components. (C) 1998 American Insti tute of Physics. [S0021-9606(98)00415-2].