Photolysis of methyl bromide at 163.3nm

Abstract

A vacuum ultraviolet photolysis of methyl bromide at 163.3 nm (735 kj/mol) by using the bromine atom resonance lamp was studied over the pressure range of 1-70 Torr at room temperature. The scavenger effect was studied by adding HBr as a radical capture to obtain information about primary process. The pressure effect was also studied at the presence of inert gases, i.e., Ar, $N_2$, $SF_6$. The result demonstrates the two decomposition mode, i.e., the molecular elimination of HBr to form methylene, and the C-Br bond cleavage to form methyl radical. The branching ratios between the molecular elimination and the methyl radical formation were 0.06 : 0.94. The products produced from primary process had enough excess energy to proceed further reaction. The major products by the secondary reaction were found to be $CH_4$, $C_2H_4$, and $C_2H_6$. Contrary that of the methyl bromide photolyses at 184.9 and 253.7 nm, molecular process was observed and ethane was the major product in this experiment.