One-, two- and three-photon ionization of the calcium atom from its ground state has been analysed in the perturbative regime by studying its electronic structure employing B-spline basis functions in a configuration interaction procedure based on a frozen-core Hartree–Fock approach combined with model potentials. We investigate the photoionization spectrum in the region located between the 4s 2Se and 3d 2De thresholds and focus our attention on the features originating from the excitation of autoionizing states. Good quantitative agreement is obtained with available theoretical and experimental data for one-photon and two-photon ionization. The three-photon excitation of the 1Po and 1Fo series of autoionizing states is also reported.

The anisotropic scattering spectrum of the symmetric stretching n 1 band by CO 2 was recorded up to the far Stokes wing, and its theoretical analysis was attempted through the non-Markovian energy-corrected sudden approximation -a useful approach which has thus far been successfully applied to the anisotropic scattering spectrum by N 2 , up to the far wing. Despite the excellent agreement observed in N 2 here, a substantial inconsistency between theory and experiment was found in the wing of the spectrum. Although the influence of other missing processes or neighboring bands cannot be totally excluded, our findings rather suggest that highly anisotropic perturbers, such as CO 2 , are improperly described when they are handled as point-like molecules, a cornerstone hypothesis in the approach employed.

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