Theoretical studies of strong-field photoionization of CH3I

Abstract

The CH3I molecule serves as an important model system in photochemistry. The photoionization usually includes the laser-molecule interaction and ionization process. Theoretical simulations of the laser-induced ionization process are, however, difficult due to multi-electrons involved. In this work, the ionization process of CH3I is studied based on the Frank-Condon principle. Three two-dimensional potential energy surfaces along the CI bond length and the HCI umbrella angle are constructed for the ground electronic state of CH3I and the ground and first excited states of CH3I+, with internally contracted multireference configuration interaction method and the aug-cc-pVTZ basis set used for the atoms C and H and the aug-cc-pvtz-pp basis set for the atom I. The vibrational frequencies of the CI stretching mode and the umbrella mode of CH3 are calculated for both CH3I and CH3I+, and are consistent with the experimental measurements. Furthermore, based on the Ammosov-Delone-Krainov ionization model, dynamics calculations are carried out to simulate ionization process induced by R-selective depletion mechanism and the vibrational wave packet motion on CH3I+ PESs.