Vibrationally resolved photoionization of the 1σ_g and 1σ_u shells of N₂ molecule

Theoretical and experimental study of vibrationally resolved partial photoionization cross sections and angular asymmetry parameter β for the 1σ_g and 1σ_u shells of N₂ molecule in the region of the σ* shape resonance is reported. The measurements were made at the synchrotron radiation facility SPring-8 in Japan. The calculations in the random phase approximation have been performed using the relaxed core Hartree-Fock wavefunctions with the fractional charge of the ion core equal to 0.7. With its help, the role of interchannel coupling between the closely spaced 1σ_g and 1σ_u shells was studied. The experiment demonstrates the existence of a correlational maximum in the 1σ_u shell photoionization cross section induced by the σ* shape resonance in the 1σ_g shell. This maximum reveals itself even more clearly in the angular asymmetry parameter β for the v′ ≤ 0 and v′ ≤ 1 vibrational states of the ion. The calculation in the random phase approximation gives a consistent interpretation of the experimental data.