Two-photon ionization and dissociation of ethyl iodide

Both spin–orbit states of C2H5I+, the X̃1 2E1/2 and the X̃2 2E1/2 electronic states, are studied by one-color two-photon ionization of ethyl iodide, utilizing the zero kinetic energy pulsed field ionization (ZEKE-PFI) photoelectron technique. Compared with conventional photoelectron data the two-photon spectra exhibit a more extensive vibrational structure mainly involving the C–I stretching and the C–C–I bending modes. This additional vibrational excitation in the two-photon spectra is discussed in terms of mode selective resonance enhancement by the dissociative Ã-state continuum. Accurate values for the vibrational frequencies and the ionization energies are obtained. The appearance of nontotally symmetric modes in the two-color ZEKE spectra is reported.