Σu+3bound and continuum states ine−-He2+scattering

Ab initio calculations are performed on the ${\mathit{e}}^{\mathrm{-}\mathrm{-}}$ ${\mathrm{He}}_2^{+}$ complex using the R-matrix technique. A two-state approximation is utilized in which the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ and the A ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ electronic states of ${\mathrm{He}}_2^{+}$, in the close-coupling expansion, are represented by truncated configuration-interaction (CI) wave functions obtained from multiconfiguration-self-consistent-field–complete-active-space-SCF (MCSCF-CASSCF) calculations. A (4s,2p,2d) Slater basis is used to perform bound-state calculations at SCF, full CI, and MCSCF-CASSCF levels, to gauge the quality of wave functions at various bond separations. Elastic cross sections are presented for selected bond lengths in the range 1.5–4.0${\mathit{a}}_0$, for the ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$ total symmetry. ${\mathrm{He}}_2^{\mathrm{*}}$(1${\mathrm{\sigma }}_{\mathit{g}}$1${\mathrm{\sigma }}_{\mathit{u}}^2$npσ and nfσ ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$) resonances are detected at each separation and fitted to Breit-Wigner formulas in order to determine their energies and autoionization widths. In addition, low-lying ${\mathrm{He}}_2^{\mathrm{*}}$(1${\mathrm{\sigma }}_{\mathit{g}}^2$1${\mathrm{\sigma }}_{\mathit{u}}$ns,nd, and ${\mathit{ng}}^3$ ${\mathrm{\Sigma }}_{\mathit{u}}^{+}$) bound states are also calculated at several geometries.