Rate constants and quenching mechanisms for the metastable states of argon, krypton, and xenon

Abstract

Rate constants have been measured by the flowing afterglow technique at 300 °K for the quenching of Ar(³P₂), Ar(³P₀), Kr(³P₂), and Xe(³P₂) by a large number of small molecules. For the same reagent, the magnitudes of the cross‐sections usually increase in the series Ar(³P₂), Ar(³P₀), Kr(³P₂), and Xe(³P₂). The Ar(³P₂) and Ar(³P₀) data are compared to results in the literature for these states and to data for Ar(³P₁) and Ar(¹P₁). The set of thermal quenching cross sections are used to test the correlations between the magnitudes of the cross sections and properties of the reagents as predicted by the orbiting, absorbing‐sphere, golden rule, and curve‐crossing mechanisms for quenching. The best correlation is between the cross sections and the C₆ coefficient. The analysis supports the proposition that the orbiting‐controlled, curve‐crossing model is the general mechanism governing the magnitude of the thermal cross sections for quenching of the metastable states. This model explains the very large quenching cross sections of F₂ and OF₂ (relative to other molecules composed of first row elements) because covalent–ionic curve crossing occurs outside the conventional orbiting radius. The validity of the simple van der Waals dispersion forces as being the dominant entrance channel interaction between the excited state rare gas atoms and the reagents is discussed.