Potential energies for Ca2+: Cross sections for collisions of Ca+ and Rydberg Ca** with Ca

Ab initio self-consistent-field (SCF) and configuration interaction (CI) calculations have yielded potential energy curves for the lowest u+2 and g+2 states of Ca2+. The best CI calculation yields the following parameters for the u+2 state: De=1.04 eV, Re=7.55a0, ωe=119 cm-1, and Be=0.0526 cm-1. The long-range regions of the u+2 and g+2 potential curves are both characterized by a Ca dipole polarizability of 170.4a03, in good agreement with the experimental value of (169±17)a03. The charge-transfer total cross sections have been calculated over the energy range Ecm=10-10 000 eV and are well reproduced by the functional form Q12=15.67-3.276log10Ecm (eV). The elastic differential-scattering rainbow angle is predicted to be located at EθR90 eV deg. Collisional-ionization cross sections and rates were also estimated for Rydberg-atom Ca** + ground-state Ca collisions. The reaction rates are predicted to be on the order of 10-10 cm3/sec and depend linearly on the principal quantum number n of the Rydberg atom. © 1978 The American Physical Society.