MANY-BODY CALCULATION OF TOTAL AND PARTIAL PHOTOIONIZATION CROSS-SECTIONS IN ATOMIC NITROGEN

Polarizabilities and photoionization cross sections are computed for t he S-4(o) ground state of atomic nitrogen. The present method is based on the use of basis sets and on an integral equation (dispersion rela tion) that relates the real polarizability on the imaginary frequency axis to the photoionization cross section. Many-body perturbation theo ry is used to compute the polarization and the perturbation expansion is complete to second order in the Coulomb interaction. Hence, there i s a comprehensive inclusion of correlation effects in our calculations . Comparison with other theory and experiment is made.