Reaction between hydrogen atoms and methane

Abstract

The reaction between hydrogen atoms and methane has been studied in a flow-discharge system over the temperature range 640–818 K at argon pressures between 5.2 and 14.8 Torr. The pressures of hydrogen atoms and of methane were, respectively, in the ranges 8.5–90 and 17–346 mTorr. Reaction times ranged from 16.9 to 22.4 ms. Ethane was the only measurable product.

The detailed mechanism has been established and computer calculations have been used to derive the set of best-fit rate parameters which reproduce the experimental results. The results of this work yield the result log (k₁/cm³ mol^–1s^–1)= 14.26 ± 0.26–55.1 ± 3.5 kJ mol^–1/(2.3 RT); H + CH₄→ H₂+ CH₃. (1)

A survey of published data, some of which have been revised by us to take account of more recent information shows that, over the range 400–1800 K, the best published data can be represented by the Arrhenius expression, log (k₁/cm³ mol^–1 s^–1)= 13.88 ± 0.06–49.9 ± 0.8 kJ mol^–1/(2.3 RT).

Values of the pressure-dependent rate constants for CH₃+ H → CH₄(2), 2CH₃→ C₂H₆(3), are given, typical values for 7.4 and for ∼14 Torr argon pressure being log (k₂/cm³ mol^–1 s^–1)= 12.20 and 12.45 and log (k₃/cm³ mol^–1 s^–1)= 12.60 and 12.70, respectively.