Electron-impact excitation of lithium

Abstract

The results of R-matrix with pseudostates (RMPS) and time-dependent close-coupling (TDCC) calculations of electron-impact excitation in Li are presented. We included 55 terms in the RMPS close-coupling expansion, of which nine are spectroscopic and 46 are pseudostates. The two-electron radial wave functions generated from earlier TDCC calculations for ionization from the ground state of Li by Colgan et al. [Phys. Rev. A 63, 062709 (2001)] are employed to determine the TDCC excitation cross sections. The RMPS and TDCC cross sections for transitions from ${1s}^{2}2s$ to ${1s}^{2}2p,$ ${1s}^{2}3l,$ and ${1s}^{2}4l$ are compared to each other and to cross sections determined from our R-matrix calculation without pseudostates, the convergent close-coupling calculations presented by Schweinzer et al. [At. Data Nucl. Data Tables 72, 239 (1999)], the coupled-channel optical calculations of Bray et al. [Phys. Rev. A 47, 1101 (1993)], and experimental measurements. These results indicate that coupling to the target continuum has a significant effect on electron-impact excitation in this atom; this increases with the principal quantum number of the excited term, and is large for transitions to ${1s}^{2}4l.$