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Two-photon ionization of xenon was investigated theoretically for exciting-photon energies from 6.7 to 11.5 eV, which results in the ionization of Xe between $5{p}_{1/2}$ (13.43 eV) and $5s$ (23.40 eV) thresholds. We describe the extension of a previously developed computational technique for the inclusion of relativistic effects to calculate energies of intermediate resonance state and cross sections for two-photon ionization. Reasonable consistency of cross sections calculated in length and velocity form was obtained only after considering many-electron correlations. Agreement between calculated and measured resonance energies is found when core polarization was additionally included in the calculations. The presently computed two-photon photoionization cross sections of Xe are compared with Ar cross sections in our previous work. Photoelectron angular distribution parameters calculated here indicate that intermediated resonances strongly influence photoelectron angular distribution of Xe.

Cross sections and angular distribution parameters of electrons ejected via two-photon ionization of the hydrogen molecule by linearly and circularly polarized light are computed in the exciting-photon energy range of 8--14 eV, which covers the first four optical resonant states of the molecule. Photoelectron partial waves in the continuous spectrum are obtained within the single center method in precise numerical potential of the molecular ion field. The correlation function technique is used to calculate the two-photon transition matrix element. The presently computed angular-resolved spectra are in good agreement with the theoretical results available for the photon energy of 8.854 eV and can be considered as reliable predictions in the respective energy range.

We have measured the photoabsorption spectra of the Kr-like ions Rb{sup +} and Sr{sup 2+} at photon energies corresponding to the excitation of 4s-np resonances using, the dual laser plasma photoabsorption technique. Dramatic changes in the line profiles, with increasing ionization and also proceeding along the Rydberg series of each ion, are observed and explained by the trends in 4s-transition amplitudes computed within a framework of configuration-interaction Pauli-Fock calculations. Total photoionization cross sections show very good agreement with relative absorption data extracted from the measured spectra.