R-matrix Floquet theory of molecular multiphoton processes: II. Multiphoton ionization of H-2

Multiphoton ionization rates for Ha immersed in an intense linearly polariz ed 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-n uclei approximation, in which the motion of the target electrons is calcula ted 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 cal culate one-, two- and four-photon ionization rates for H-2 at several inter nuclear separations over a range of frequencies and intensities. Analysis o f 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 excit ed state. These resonances give rise to resonant enhanced multiphoton ioniz ation peaks in many of the ionization rates studied in this paper, and thei r possible role in controlling the vibrational population of the final H-2( +) ion is discussed.