10.6084/m9.figshare.1012113.v1 Daniele Toffoli Daniele Toffoli Piero Decleva Piero Decleva Two-photon differential cross section of the C 1s ionization of CH<sub>4</sub> for an incident photon energy of 260 eV IOP Publishing 2013 C 1 light polarizations carbon monoxide ionization radiation beam core valence excitations order perturbation theory section incident photon energy CH 4 multicentric basis nuclei approximation asymmetry parameters Atomic Physics Molecular Physics 2013-06-13 00:00:00 Figure https://iop.figshare.com/articles/figure/_Two_photon_differential_cross_section_of_the_C_1s_ionization_of_CH_sub_4_sub_for_an_incident_photon/1012113 <p><strong>Figure 2.</strong> Two-photon differential cross section of the C 1s ionization of CH<sub>4</sub> for an incident photon energy of 260 eV.</p> <p><strong>Abstract</strong></p> <p>The two-photon core ionization dynamics of gas-phase methane, carbon monoxide and nitrogen have been studied with a recent implementation of the lowest order perturbation theory in the framework of density functional theory and a multicentric basis set expansion of bound and scattering states. Ionization cross sections and angular asymmetry parameters have been calculated for the case of a single radiation beam and for both linear and circular light polarizations in the fixed nuclei approximation. Expected resonances due to core valence excitations enhance the cross section by several orders of magnitude.</p>