Mechanism of isotope exchange reaction between methane and deuterium

The rate of CH4 disappearance in a shock‐heated CH4:D2:Ar = 9.70:9.86:80.44 mixture was monitored by coincidence absorption of the 2948 cm−1 He‐Ne laser line over the shockfront temperature range of 1900–2300K. Comparison with CH4 pyrolysis results by means of computer simulations suggested that atom and free radical chains are responsible for the homogeneous D/H exchange reaction on CH4. Additional simulations for the experimental conditions of previous single‐pulse shock tube experiments led to the recognition of a high sensitivity of the exchange rate to trace amounts of hydrocarbon impurity and to the dissociation rate of CH4.