Energy dependence study on photodissociation reaction of ethyl bromide

Abstract

The vacuum ultraviolet photolyses of ethyl bromide were investigated in the wavelength range of 100-200nm by using various energy sources, i.e., 104.8-106.7, 123.6, 147, 163.3, 174.3-174.5 and 193.1 nm. The pressure effect by adding inert gases, He, $N_2$ and $CF_4$, was also observed. The order of collisional efficiencies were found to be $CF_4>N_2>He$. A scavenger effect of the reaction was performed by using NO as a radical scavenger. The establishment in this work may be summarized as follows: (i) the major products are $C_2H_4$ and $C_2H_6$ regardless the energy sources; (ii) $C_2H_4$ is derived, primarily, from non-radical precursors by molecular elimination of HBr while $C_2H_6$ is originated from radical sources; (iii) the competitions between these two modes of reactions are found to be strong energy dependent to the irradiation wavelength. The fraction of molecular elimination has shown to increase as the wavelength shift to shorter side while that of radical reactions has shown the opposite trend. Secondary reaction mechanisms are also found to be energy dependent. A derived products $C_2H_2$, for example, was formed from $C_2H_4$ by molecular elimination at very short wavelengths such as 104.8-106.7 and 123.6 nm. Whereas these phenomena were not found at longer wavelength. Only exception was observed at 147 nm where small quantity of $C_2H_2$ was derived from the radical source.