Velocity dependence of the absolute cross sections for the chemi-ionization of Ar, Kr, and Xe on impact of 21S and 23S helium atoms

Abstract

Measurements of the velocity dependence of the absolute cross sections for the chemi-ionization of Ar, Kr, and Xe on impact of thermal energy metastable helium atoms in the relative velocity range 1–3 km sec−1 have been made using a single velocity-selected beam, collision-chamber method. Separate measurements for both 23S and 21S helium atoms are obtained through the use of a He discharge lamp to quench the singlets from the beam. The metastable atom electron ejection efficiencies are separately measured in the same apparatus. The results are compared with the relative measurements of other workers. The constants are evaluated in a two-parameter exponential function representing the coupling width for decay of the discrete electronic state of the incoming channel into the continuum electronic state of the outgoing channel, which give the best fit to the experimental data for the He* (23S) –Ar and He* (23S) –Kr systems.