A vacuum ultraviolet photolysis of methyl bromide at 121.6nm(253.1kal/mol) by using the hydrogen resonance lamp was studied over the pressure range of 1-50 Torr at room temperature. The result demonstrate the two decomposition mode, i.e., the molecular elimination of HBr to frommethylene, and the C-Br bond cleavage to form methyl radical. The major products of the reaction were found to be $CH_4$, $C_2H_4$, and $C_2H_6$. The branching ratios between the molecular elimination and the methyl radical formation were 0.05:0.95.
The scavenger effect was studued by adding HBr as a radical capture to obtain information about primary process. The pressure was also observed by adding inert gases, i.e., $N_2$ and He.