One-photon mass-analyzed threshold ionization spectroscopy of CH_2Brl:Extensive bending progression,reduced steric effect,and spin-orbit effect in the cation

摘要

One-photon mass-analyzed threshold ionization (MATI) spectrum of CH_2BrI was obtained using coherent vacuum-ultraviolet radiation generated by four-wave difference-frequency mixing in Kr.Unlike CH_2C1I investigated previously,a very extensive bending (Br-C-I) progression was observed.Vibrational frequencies of CH_2BrI~+ were measured from the spectra and the vibrational assignments were made by utilizing frequencies calculated by the density-functional-theory (DFT) method using relativistic effective core potentials with and without the spin-orbit terms.A noticeable spin-orbit effect on the vibrational frequencies was observed from the DFT calculations,even though its influence was not so dramatic as in CH_2C1I~+.A simple explanation based on the bonding characteristics of the molecular orbitals involved in the ionization is presented to account for the above differences between the MATI spectra of CH_2BrI and CH_2C1I.The 0-0 band of the CH_2BrI spectrum could be identified through the use of combined data from calculations and experiments.The adiabatic ionization energy determined from the position of this band was 9.5944 +-0.0006 eV,which was significantly smaller than the vertical ionization energy reported previously.