Methane formation during the interaction of energetic protons and deuterons with carbon

Methane production has been investigated as a function of temperature during ion bombardment and during post-irradiation thermal release of implanted hydrogen in pyrocarbon. The reaction is shown to be directly correlated with the release of trapped hydrogen rather than an ion/surface interaction. During bombardment, methane production is not observed below target temperatures of 450 K. The methane yield reaches a maximum of 9% of the hydrogen release rate at 850 K after which it falls to <0.2% at 1200 K. No residual gas effects on hydrocarbon production have been observed even at pressures up to 10^?5 torr. Following bombardment, methane is formed during heating of the carbon at temperatures in excess of 800 K. A peak in methane production is observed at 1000 K, whilst the peak in hydrogen release occurs at 1200 K. An analytical model for the temperature dependence of methane production during bombardment is presented and this agrees well with the experimental results.