2-PHOTON IONIZATION AND DISSOCIATION OF ETHYL IODIDE

Both spin-orbit states of C2H5I+, the (X) over tilde, (2)E(1/2) and th e (X) over tilde(2) (2)E,/ electronic states, are studied by one color two-photon ionization of ethyl iodide, utilizing the zero kinetic ene rgy pulsed field ionization (ZEKE-PFI) photoelectron technique. Compar ed with conventional photoelectron data the two-photon spectra exhibit a more extensive vibrational structure mainly involving the C-I stret ching and the C-C-I bending modes. This additional vibrational excitat ion in the two-photon spectra is discussed in terms of mode selective resonance enhancement by the dissociative A-state continuum. Accurate values for the vibrational frequencies and the ionization energies are obtained. The appearance of nontotally symmetric modes in the two-col or ZEKE spectra is reported. (C) 1995 American Institute of Physics.