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.