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 (³P_0,2) 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.