The Mercury-Photosensitized Decomposition of Methane

The mercury-photosensitized decomposition of methane has been studied at temperatures ranging from about 25 to 400 °C, and pressures from about 100 to 1000 mm. Very low conversions and light intensities were employed, and it was shown that at temperatures of 120 °C and above, the hydrogen produced was a direct measure of the primary yield of hydrogen atoms. The low, temperature-dependent quantum yield found in earlier studies persisted even under these conditions, and it seems necessary to postulate an inefficiency in the primary quenching process, involving essentially the quenching of 3 P 1 mercury atoms by methane without decomposition of the methane.Experiments with added ethylene showed that practically all the hydrogen produced in the decomposition of methane was scavengeable by ethylene, indicating that only atomic hydrogen was produced in the primary process. The rate of addition of hydrogen atoms to ethylene was estimated to be about 4 × 10 5 times faster than the rate of abstraction from methane at 120 °C.