Quenching cross sections for electronic energy transfer reactions between metastable argon atoms and noble gases and small molecules

Abstract

Reaction rate constants for the quenching of electronic energy in metastable argon (3P0,2) by Kr, Xe, and a number of simple molecules have been measured. A hollow, cold-cathode discharge excites the metastables in a flow apparatus. The concentration of metastables was followed by absorption spectroscopy as a function of time and of quenching molecule concentration. Quenching of Ar*(3P2) by Kr, CO, N2, CF4, and H2(D2) proceeds at rates between 0.6 and 7 × 10−11 cm3 molecule −1 · sec−1. Except for Kr, Xe, N2, CO, and CH4, the 3P0 metastable level is quenched slightly more rapidly than the 3P2 level. With the aid of data in the literature, the contribution from the product channels (Penning and associative ionization) are considered for quenching by NO and C2H2. These channels appear not to be of major importance for quenching since the ionization efficiency of these two reactions is low: ∼ 0.2 for NO and ∼ 0.1 for C2H2. The quenching mechanism is discussed in terms of both a curve crossing and a ``golden rule'' rate law; the latter appears to be favored.