A study of the kinetics of the reaction between H 2 and F 2 by EPR methods

Abstract

Attesting to its interest for laser-related studies, the reaction between hydrogen and fluorine has recently been studied by a variety of experimental approaches in laboratories throughout the world. An EPR superheterodyne X-band spectrometer was used in the present work in conjunction with a fast flow gas mixing system to obtain both hydrogen and fluorine atom concentrations. The reactant hydrogen atoms were produced by the dissociation of molecular hydrogen in a 2450 MHz microwave discharge unit; the product fluorine atoms were produced by the reaction of hydrogen atoms with molecular fluorine. The changes in both atom concentrations were followed as fluorine was added incrementally to the helium-diluted reactants, H + H 2. Values of the specific rate constants for the H + F 2 and F + H 2 reactions at 300°K have been found to be 2.5 ± 0.2 × 10 12 cm 3 mole −1 sec −1 and 4 ± 1 × 10 12 cm 3 mole −1 sec 1, respectively. Under the conditions of our experiments, i.e., at pressures of ca. 2 Torr and with quartz flow tube walls coated with boric acid, the contribution of a branched-chain step to the reaction mechanism appears to be minimal.