Chemi-ionization reactions of metastable Ar(3P0,2) atoms

Using a discharge-flow system and the saturation ion-current technique, branching fractions for chemi-ionization of a wide range of reagents by electronically-excited Ar(3P0,2) atoms have been measured. In contrast to excited He and Ne atoms, ionization by excited Ar atoms is in no case the dominant channel, most branching fractions lying in the range 0.1 to 0.4. Significantly lower branching fractions are shown by the three reagents Cl2, Br2, and NO2 with the largest electron affinities. The results are discussed in terms of the charge transfer model for electronic quenching.