A study of the reactions of fluorine with hydrogen and methane in the initiation phase using a miniature tubular reactor

A small tubular reactor having an inner diameter of 1–2 mm andused as the source in a molecular beam apparatus is described in detail. This arrangement allows the study of fast reactions with reaction times smaller than 1 msec. The preexplosive reaction phase between F 2 and H 2 and CH 4 , respectively, is investigated to find out the initiation reactions. In the F 2 /H 2 reaction, initiation is brought about by heterogeneous generation of F atoms or some other surface reaction. Evidence is also obtained for chain branching reactions. In the F 2 /CH 4 case the dominant initiation reaction is the homogeneous reaction CH 4 + F 2 → CH 3 + HF + F. The rate constant for the reaction between 300 and 400 K is 10 12.3±0.3 exp[−47 ± 8 kJ/mol/ RT ] cm 3 /mol sec. The analysis of the experimental data also yields the rate constant for the propagation reaction CH 3 + F 2 → CH 3 F + F, which is 10 12.3±0.3 exp[−4.6 ±2.1 kJ/mol/ RT ] cm 3 /mol sec.