Associative ionization in collisions of metastable helium with H and D

Abstract

The exothermic reactions He*+H→HeH⁺+e and He*+D→HeD⁺+e have been studied by merging‐beams techniques over a range of interaction energy W from 0.05–10 eV. The He* represents a composite of He(2 ¹S) and He(2 ³S). Data were obtained by observing currents due to the product ions. For each process the relative effective cross section Q_R (i.e., for the composite He*) as a function of W is the same within experimental error and monotonically decreases with increasing W. The Q_R are in excellent agreement with theoretical predictions by Miller, Slocomb, and Schaefer for the reaction He(2 ³S)+H→HeH⁺+e. Absolute cross sections have also been extracted from the merging‐beams data. These are in fair agreement with calculated values but lower than some recent crossed‐beam results.