Close-coupling calculations ofCa−formation by charge transfer from Rydberg atoms

Abstract

We formulate the semiclassical close-coupling method for a theoretical description of ion-pair formation in Rydberg-atom--ground-state-atom collisions at thermal energies and apply it to the process $\mathrm{Ca}{(4s}^{2})+{\mathrm{Ne}}^{*}(n)\ensuremath{\rightarrow}{\mathrm{Ca}}^{\ensuremath{-}}{(4s}^{2}4p)+{\mathrm{Ne}}^{+}.$ Our results for the formation of an isolated negative-ion state are very close to those obtained previously using the decay model, although the results for S states are somewhat higher, since the decay model underestimates the survival probability for the ion pair. After the inclusion in our close-coupling calculations of the two fine-structure components of ${\mathrm{Ca}}^{\ensuremath{-}},$ we find that the cross section increases substantially (by about a factor of 2) because of correlation between probabilities for population of two fine-structure sublevels.