Exchange effects in elastic collisions of spin-polarized electrons with open-shell molecules with $^3\Sigma_g^-$ symmetry

TL;DR

This study investigates spin-exchange effects in elastic collisions of spin-polarized electrons with open-shell molecules using the R-matrix method, revealing resonance-related enhancements and molecule-specific differences in the exchange effect.

Contribution

It provides detailed computational analysis of spin-exchange effects in electron collisions with open-shell molecules, highlighting the role of resonances and molecule symmetry in these interactions.

Findings

Spin-exchange effects are prominent near resonances.

Larger spin-exchange effects observed in B₂, S₂, Si₂ compared to O₂.

Polarization fractions in O₂ agree with experimental data.

Abstract

The spin-exchange effect in spin-polarized electron collisions with unpolarized open-shell molecules, O$_2$, B$_2$, S$_2$ and Si$_2$, has been studied by the R-matrix method with the fixed-bond approximation. All of these molecules have ${}^3 \Sigma_{g}^{-}$ symmetry in their ground states. Usual integrated cross sections with unpolarized electrons has also been studied. We used the complete active space self consistent field orbitals and put more than 10 target electronic states in the R-matrix models. In electron O$_2$ elastic collisions, calculated polarization fractions agree well with the experimental results, especially around the ${}^4 \Sigma_u^-$ resonance. In e-B$_2$, S$_2$ and Si$_2$ elastic collisions, larger spin-exchange effect is observed compared to the e-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-B$_2$ collisions than in e-S$_2$ and Si$_2$ collisions, and is smallest in e-O$_2$ collisions.