Quenching rate constants for metastable argon, krypton, and xenon atoms by fluorine containing molecules and branching ratios for XeF* and KrF* formation

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Abstract
The flowing afterglow technique was used to study the reactions of Xe(3P2), Kr(3P2), and Ar(3P2) metastable atoms with small fluorine containing molecules. Fluorides from Groups III through VIII (XeF2) were examined. Although all the fluorides have large quenching rate constants, only F2, XeF2, some interhalogen fluorides, and small molecules with the OF or NF bond have high branching ratios for XeF* or KrF* excimer formation. The branching ratio measurements were made via comparison to the XeCl* and KrCl* emission intensities from reaction of Xe(3P2) and Kr(3P2) with Cl2, which were adopted as reference reactions. Within experimental error, the branching ratios are unity for Kr(3P2) and Xe(3P2) with Cl2, F2, and OF2. Increasing the argon pressure from 1–40 torr gives extensive vibrational relaxation but no electronic quenching of the lowest energy excimer state of XeF*, XeCl*, KrCl*, or KrF*. Increasing pressure also reduces the intensity of the secondary emission system of KrCl* and XeCl* which implies collisional transfer from the (2Π3/2) to the 2Σ+ excimer state. The occurrence of vibrational relaxation suggests a spontaneous radiative lifetime of ∼50 nsec. A higher energy excimer state (2Π1/2) was identified for XeF*, XeCl*, XeBr*, XeI*, KrF*, and KrCl*. Discussion is presented regarding the chemical dynamics and chemiluminescence of these reaction systems.