Penning and associative ionization in the metastable helium–atomic deuterium system

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Abstract
Measurements of Penning and associative ionization cross sections (QPI and QAI) and branching ratios (R) for the He*–D system have been repeated in this laboratory. The studies were made using a merging‐beams technique for a relative kinetic energy W of the reactants from nominally 0.01 to 10 eV. This is a wider energy range than covered previously. The He* represents a composite of about 15% He(2 1S) and 85% He(2 3S). The new results are more acurate than the old due to improvements in the apparatus. From the new studies, a well depth of approximately 2.1 eV was obtained for the He(2 3S) –D potential and between 0.25 and 0.4 eV for the He(2 1S) –D potential. These well depths agree with values obtained by others. Laboratory‐energy distributions of Penning ions indicate differences in the kinetics of reaction for He(2 1S) and He(2 3S). The new QAI, QPI, and R agree with those of several other experimenters although there are discrepancies in QPI and R with the calculations of Hickman and Morgner.