Low-energy elastic and inelastic scattering of electrons fromSO2using theR-matrix method

Abstract

$R$-matrix method is used to calculate elastic differential, integral, and momentum transfer cross sections for electron-$\mathrm{S}{\mathrm{O}}_{2}$ collision. The electron-impact excitation cross sections for first seven low-lying electronic excited states of $\mathrm{S}{\mathrm{O}}_{2}$ molecule from the ground state of $\mathrm{S}{\mathrm{O}}_{2}$ molecule have been calculated for the first time. Sixteen low-lying electronic states of $\mathrm{S}{\mathrm{O}}_{2}$ molecule are included in the close coupling expansion of the wave function of the entire scattering system, which have vertical excitation energies up to $10.51\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Configuration-interaction (CI) wave functions are used to calculate these excitation energies. In our CI model, we keep the core 14 electrons frozen in doubly occupied molecular orbitals $1{a}_{1}$, $2{a}_{1}$, $3{a}_{1}$, $4{a}_{1}$, $1{b}_{1}$, $1{b}_{2}$, $2{b}_{2}$ and the remaining 18 electrons span the relevant active space: $5{a}_{1}$, $6{a}_{1}$, $7{a}_{1}$, $8{a}_{1}$, $9{a}_{1}$, $2{b}_{1}$, $3{b}_{1}$, $3{b}_{2}$, $4{b}_{2}$, $5{b}_{2}$, $6{b}_{2}$, and $1{a}_{2}$. Our calculated dipole moment of the ground state of $\mathrm{S}{\mathrm{O}}_{2}$ at its equilibrium geometry is $0.79\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$, which is in reasonable agreement with the corresponding experimental value $0.64\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ Our calculations detect one bound $\mathrm{S}\mathrm{O}_{2}{}^{\ensuremath{-}}$ state $(^{2}\mathrm{B}_{1})$ at the equilibrium geometry of $\mathrm{S}{\mathrm{O}}_{2}$ molecule. Both shape as well as core-excited shape resonances have been identified in the present work and are correlated with the experimental results on dissociative electron attachment study. A detailed analysis of resonances is provided. Cross sections are reported for the electron impact energy range $0--15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. All cross section calculations are performed in the fixed-nuclei approximation at the experimental equilibrium geometry of the ground state of $\mathrm{S}{\mathrm{O}}_{2}$ molecule. We have also investigated dependence of resonances on the geometry of $\mathrm{S}{\mathrm{O}}_{2}$ molecule to probe the possible pathways for dissociation of resulting negative ion upon electron attachment. We have excellent agreement of differential, elastic integral, and momentum transfer cross sections calculated in the 16-state $R$-matrix approximation with the available experimental results for electron-impact energy range $0--15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Our resonant peaks correlate well with the peaks observed in the study of dissociative electron attachment (DEA) of electron with $\mathrm{S}{\mathrm{O}}_{2}$ molecule.