High resolution vacuum ultraviolet pulsed field ionization photoelectron band for OCS+(X-2 Pi): An experimental and theoretical study

摘要

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 been 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 11.1831+/-0.0005 and 11.2286+/-0.0005 eV, respectively, yielding a value of 367+/-1.2 cm(-1) for the spin-orbit splitting. Using the internally 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 calculations 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 range of approximate to 4000 cm(-1) above the IE[OCS+(X (2) Pi(3/2))] for the assignment of the experimental spectrum. By a minor modification of the nb initio PEFs, good correlations are found between the experimental and theoretical Renner-Teller structures. Similar to the PFI-PE 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 forbidden in the Franck-Condon approximation. The nonvanishing single-photon 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 electronic transition dipole operator components. (C) 1998 American Institute of Physics. [S0021-9606(98)00415-2]. [References: 46]