S-matrix theory of inelastic vibronic ionization of molecules in intense laser fields

Inelastic vibronic ionization (IVI) in the presence of an intense laser field refers to the process of ionization of a target molecule accompanied by vibrational excitation of the residual molecular ion. The recently proposed intense-field many-body S-matrix theory of IVI is presented and applied to investigate the distributions of the vibrational states of the residual H₂⁺ ion from ionization of H₂ molecule, and the results are compared with the experimental data. The characteristic features of the calculated distributions are found to agree well with those observed. The shift of the IVI distributions toward the lower vibrational states compared to the Frank-Condon distributions, the positions of the maxima of the distributions, as well as the reversal of the maximum from a lower vibrational state to a higher vibrational state (peak-reversal) are analyzed. The results of the “adiabatic nuclei” theory and the “frozen nuclei” approximation are compared to assess the latter. Influences of the choice of the vibrational wave functions on the calculated distributions, the dependence of the distributions on the alignments of the molecular axis with respect to the linear polarization direction of the laser, and the effect of circular polarization of the laser on the IVI distribution are discussed. Possible origins of the remaining discrepancy in the individual heights of the calculated vs. measured yields are pointed out. Finally, an isotopic shift of the IVI distributions toward the higher vibrational states, for the heavier isotopes, is predicted and the corresponding distributions for the two isotopes HD and D₂ are given.