Photolysis of bromoethylene at 163.3nm

Abstract

A vacuum ultraviolet photolysis of bromoethylene was studied in the pressure range of 1-70 Torr at 163.3nm using bromine atom resonance lamp. The result demonstrates the two decomposition mode, i.e., one for molecular elimination of HBr to form acetylene, and the other for C-Br bond cleavage to form vinyl radical. The principal products were found to be $C_2H_2,\;C_2H_4,\;C_2H_4Br_2$, and small amount of $C_4H_7Br$. The HBr was added as radical capture to obtain information about the primary process. The pressure effect by adding inert gases, i.e., $CF_4$ and He, was also observed in the presence and absence of HBr. The ratio of quantum yield, $\Phi(C_2H_2)/\Phi(C_2H_2)$, was decreased as the pressure increased in absence of HBr. But with the presence of HBr the ratio remains constant as the pressure increased. This observation may be attributed by the fact that "hot" vinyl radical, produced from C-Br bond cleavage, decomposes to acetylene and hydrogen atom. This process has been quenched by adition of HBr, radical capture.