Two channel competitive photodecomposition reaction of ethyl bromide at 193.1 nm

Abstract

A vacuum ultraviolet photolysis of ethyl bromide at 193.1 nm was studied over the pressure range of 1.1-303.2 Torr at room temperature using a carbon atom lamp. The pressure effect with and without additives, i.e., He and $N_2$, was investigated. A scavenger effect of the reaction was also observed by adding NO as a radical scavenger. The principal reaction products were $C_2H_6$, $C_2H_4,\;C_2H_4Br_2$, and $C_4H_{10}$. Increasing pressure without additives the product quantum yields of $C_2H_4$ remain almost constant, while those of $C_2H_6$ was found to be weak positive pressure dependence. When the pressure of He or $N_2$ was varied at a constant pressure of $C_2H_5Br$, however, the quantum yields of $C_2H_3$ and $C_2H_6$ were found to be pressure independence. Addition of NO completely suppressed the formation of $C_2H_6,\;C_2H_4Br_2$, and $C_4H_{10}$, and partially reduced that of $C_2H_4$. These results were interpreted in terms of two channel competition between the molecular eliminations and the formation of radicals. Two different decomposition modes were 82\% radical reactions and 18\% molecular elimination, respectively. From the aforementioned results, it is suggested that there exist two electronically excited states and that reactant molecule which absorbs a photon proceeds to any one of two different electronically excited states through of two pathways.