Chemi-ionization reactions of state-selected electronically excited Ar(3P0) and Ar(3P2) atoms

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Abstract
Using a chemical method to separate the spin‐orbit Ar(3P0) and Ar(3P2) metastable states in a discharge‐flow system, branching fractions, f0 and f2, for ionization of several molecular reagents by these species have been measured. Experiments have been performed at room temperature and at 220 K. The large differences between f0 and f2 observed for CCl4, CF3Br, HBr, and DBr are ascribed to energy effects and it is concluded that the yield of chemi‐ionization increases sharply as the electronic energy of the excited atom rises above the ionization potential of the molecule. This contrasts with the much smaller effect of reagent kinetic energy on the chemi‐ionization yield. Branching fractions for some reaction channels leading to emission of light are also reported.