Studies of differential and total photoionization cross sections of molecular nitrogen

TLDR: In this paper, the effects of initial-state correlation were studied by comparing cross sections obtained using a configuration-interaction-type initial state wave function with those obtained by a Hartree-Fock initial-State wave function, and they found that earlier single-center cross sections were not well converged with respect to their expansion parameters.

Abstract: The photoionization of molecular nitrogen has been studied using a frozen-core Hartree-Fock final-state wave function with a correlated intitial-state wave function. The final-state wave function was obtained using the iterative Schwinger variational method. The effects of initial-state correlation were studied by comparing cross sections obtained using a configuration-interaction-type initial-state wave function with those obtained using a Hartree-Fock initial-state wave function. In this paper we compare our accurate single-center expansion results with other theoretical results. We find that earlier single-center cross sections were not well converged with respect to their expansion parameters. The results of the continuum multiple-scattering method and the Stieltjes-Tchebycheff moment-theory approach are found to be in qualitative but not quantitative agreement with the present results. We also compare our computed total cross sections as well as integrated target angular distributions with experimental results for photoionization leading to the $X^{2}\ensuremath{\Sigma}_{g}^{+}$, $A^{2}\ensuremath{\Pi}_{u}$, and $B^{2}\ensuremath{\Sigma}_{u}^{+}$ states of ${\mathrm{N}}_{2}^{+}$. We find generally good agreement, which is improved by the inclusion of initial-state correlation effects, especially in the resonant photoionization channel leading to the $X^{2}\ensuremath{\Sigma}_{g}^{+}$ state of ${\mathrm{N}}_{2}^{+}$. We also report integrated detector angular distributions for these three channels.