Cross sections for ionization of metastable rare-gas atoms (Ne*, Ar*, Kr*, Xe*) and of metastable N2*,CO* molecules by electron impact

Cross sections for the collisional ionization of the metastable atoms Ne*, Ar*, Kr*, and Xe* by electrons with impact energy E in the range 6 < E < 250 eV are determined in the Born and binary-encounter approximations. For low energies epsilon of ejection, the s-d and s-f bound-free transitions dominate the associated form factor, while transitions to continuum states with progressively higher angular momentum gain importance with increasing epsilon. While up to nine partial waves are normally sufficient for convergence of the bound-free form factor at a given energy epsilon and momentum change K of the ejected electron, as many as 30 are required for those K in the vicinity of the Bethe ridge at large epsilon. These properties are the origin of the overall closeness obtained between the Born and binary-encounter cross sections. Also inner-shell ionization, as described by the binary-encounter treatment, becomes increasingly important as the target atom becomes more complex. Cross sections for ionization of metastable N2* and CO* are also determined. Good agreement with available measurements (for Ne* and Ar*) is obtained