K selection in one-photon mass-analyzed threshold ionization of CH3I and CD3I to the (X)over-tilde2E3/2 state cations

One-photon mass-analyzed threshold ionization (MATI) spectra for the X E-2(3/2) states of CH3I+ and CD3I+ were measured using vacuum ultraviolet radiation generated by four-wave mixing in Kr. Spin-orbit density functional theory calculations at the B3LYP/aug-cc-pVTZ level and spin-orbit/Jahn-Teller calculations were made to aid vibrational assignment. Each vibrational band consisted of several peaks due to different Delta K transitions, which could be assigned by using molecular parameters determined in the previous high resolution photodissociation spectroscopic study. Possibility of generating mass-selected, vibronically selected and K-selected ion beam with decent intensity by one-photon MATI was demonstrated. The ionization energies to the X E-2(3/2) states of CH3I+ and CD3I+ corrected for the rotational contribution were 9.5386 +/- 0.0006 and 9.5415 +/- 0.0006 eV, respectively.