Kinetic Studies of Diatomic Free Radicals using Mass Spectrometry: Part 1.—System Description and Applications to F Atoms and FO Radicals

Abstract

A system for sampling of free radicals from a discharge-flow system to a mass spectrometer is described. The molecular radicals FO, ClO, BrO, IO, OH, SF, NF2, and SF2, and the atoms N, O, Br, Cl and F have been detected mass spectrometrically. Methods for the calibration of ion current in terms of absolute concentrations of atoms, and of the radicals FO, ClO and BrO have been developed. The lower concentration limits of detection (signal-to-noise of unity) were: FO, 1 × 1011 cm–3; ClO, 1 × 109 cm–3; BrO, 1.5 × 109 cm–3. The applications of the technique are exemplified by kinetic studies of F 2P atoms and FO X2II radicals, and the following rate constants are reported (298 K): FO + FO [graphic omitted] 2F + O2; ΔU°298=– 68 kj mol–1(1), k1=(8.5 ± 2.8)× 10–12 cm3 molecule–1 s–1. F + NF2+ M [graphic omitted] NF3+ M; ΔU°298=– 253 kj mol–1k2=(8.9 ± 3.3)× 10–3 1 cm6 molecule–2 s–1.