R-matrix Floquet theory of molecular multiphoton processes: II. Multiphoton ionization of H2

Multiphoton ionization rates for H 2 immersed in an intense linearly polarized laser field are calculated using the recently developed R -matrix Floquet theory of molecular multiphoton processes. We assume that the H 2 molecule is aligned along the laser polarization direction and we adopt the fixed-nuclei approximation, in which the motion of the target electrons is calculated in the laser field and in the field of the nuclei, which are assumed to be fixed in space. An accurate multi-state wavefunction is employed to calculate one-, two- and four-photon ionization rates for H 2 at several internuclear separations over a range of frequencies and intensities. Analysis of the ionization rates reveals the important role played both by resonances corresponding to Rydberg bound states converging to the H 2 + ion ground state and by doubly excited states converging to the H 2 + ion first excited state. These resonances give rise to resonant enhanced multiphoton ionization peaks in many of the ionization rates studied in this paper, and their possible role in controlling the vibrational population of the final H 2 + ion is discussed.