Electron-impact study of the B2molecule using theR-matrix method

Abstract

The results of ab initio scattering calculations for low-energy electron collisions with the B${}_{2}$ molecule using the $R$-matrix method have been presented. The differential and momentum-transfer cross sections along with effective collision frequency over a wide electron temperature range (300--30 000 K) are computed at the one-state close-coupling level. In this work, 61-state close-coupling calculations are performed to compute the integral cross sections (elastic and excitations). We investigated five resonances: two in the excitation cross sections of $A{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}$, two in the excitation cross sections of $a{\phantom{\rule{0.16em}{0ex}}}^{5}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{u}^{\ensuremath{-}}$ and one in both $b{\phantom{\rule{0.16em}{0ex}}}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Delta}}_{g}$ and $c{\phantom{\rule{0.16em}{0ex}}}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{g}^{+}$ excited states. The Born correction for the dipole-allowed transition ($X{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}$ to $A{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}$) has been carried out to account for the contribution of partial waves higher than the $g$ wave ($l=4$) up to which the $R$-matrix scattering calculations are carried. We have detected a stable anionic bound state ${}^{2}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}$ of B${}_{2}^{\ensuremath{-}}$ having the configuration $1{\ensuremath{\sigma}}_{g}^{2}$ $2{\ensuremath{\sigma}}_{g}^{2}$ $1{\ensuremath{\sigma}}_{u}^{2}$ $2{\ensuremath{\sigma}}_{u}^{2}$ $1{\ensuremath{\pi}}_{u}^{3}$. The ionization cross sections are calculated in the binary-encounter Bethe model in which Hartree-Fock molecular orbitals at a self-consistent level are used to calculate kinetic and binding energies of the occupied molecular orbitals. We have also evaluated scattering length for electron-B${}_{2}$ collisions at the one-state close-coupling level (6.8${a}_{0}$) and at the static exchange plus polarization level (6.2${a}_{0}$).