Exchange effects in elastic collisions of spin-polarized electrons with open-shell molecules withΣ3g−symmetry

Abstract

The spin-exchange effect in spin-polarized electron collisions with unpolarized open-shell molecules ${\text{O}}_{2}$, ${\text{B}}_{2}$, ${\text{S}}_{2}$, and ${\text{Si}}_{2}$, has been studied by the $R$-matrix method with the fixed-bond approximation. All of these molecules have ${^{3}\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}$ symmetry in their ground states. Usual integrated cross sections with unpolarized electrons have also been studied. We used the complete active space self-consistent field orbitals and put more than ten target electronic states in the $R$-matrix models. In electron ${\text{O}}_{2}$ elastic collisions, calculated polarization fractions agree well with the experimental results, especially around the ${^{4}\ensuremath{\Sigma}}_{u}^{\ensuremath{-}}$ resonance. In $e{\text{-B}}_{2}$, ${\text{S}}_{2}$, and ${\text{Si}}_{2}$ elastic collisions, larger spin-exchange effect is observed compared to the $e{\text{-O}}_{2}$ elastic collisions. In all four cases, spin-exchange effect becomes prominent near resonances. This association of resonance and magnitude of the spin-exchange effect was studied by explicitly removing the resonance configurations from the $R$-matrix calculations. In general, spin-exchange effect is larger in $e{\text{-B}}_{2}$ collisions than in $e{\text{-S}}_{2}$ and ${\text{Si}}_{2}$ collisions, and is smallest in $e{\text{-O}}_{2}$ collisions.