Title

Multielectron effects of diatomic molecules in strong laser fields

Date of Completion

January 1999

Keywords

Physics, Molecular|Physics, Atomic

Degree

Ph.D.

Abstract

The interaction of diatomic molecules and laser fields is investigated with a 30 fs, 1 kHz repetition rate Ti:sapphire laser system in a highly nonperturbative strong field regime. A considerable amount of new phenomena and physics on the ionization behavior and multielectron effects of diatomic molecules has been explored in the studies for this dissertation. ^ Single and double ionization of diatomic molecules, N2 and O 2, have been studied and compared to the rare gas atoms, Ar and Xe, which have corresponding single and double ionization potentials. The study reveals both atomic-like and non-atomic-like behavior of diatomic molecules and demonstrates the complexity of molecular ionization in strong laser fields. The study of nonsequential ionization is also extended from atoms to the doubly ionized diatomic molecules including the metastable, charge symmetric and charge asymmetric dissociating channels. The detailed electronic structure is found to be a critical factor influencing both single and double ionization of diatomic molecules in strong laser fields. ^ Charge asymmetric dissociation (CAD) is observed, for the first time with 30 fs near-infrared laser radiation, in doubly ionized small molecules, N2 and O2. The charge asymmetric dipole coupling to the external field is demonstrated to be insufficient to populate the charge transfer states leading to CAD. Rather, the diverse pathways to access the CAD states, non-sequentially in N2 and sequentially in O2 , shows that CAD is in fact a natural result of strong field excitation and ionization. These results in the tunneling regime are also compared with previous experiments performed with UV radiation in the multiphoton regime. ^ In addition to the experimental investigation, a theoretical ab initio calculation is performed on two-electron strong field induced ionization. The results of the calculation, for the first time, reveal the influence of the spatial symmetry of the electron wavefunction on the dynamics of strong field ionization and provide a deeper understanding of the behavior and multielectron effects of atoms and molecules in strong fields. ^