RADIATION-INDUCED ADDITION OF HBr TO C2H4 IN THE GASEOUS STATE

Abstract

The gas phase addition of hydrogen bromide to ethylene in a pyrex irradiation cell was induced by the action of Co60 γ-rays. Dose rates were calculated by means of the Bragg–Gray cavity principle from saturation ionization currents measured in air in a similar cell. The only product detected was ethyl bromide and the ion pair yield was of the order of 105. The rate of addition was followed with an electrically adjusted "spoon gauge" and was studied (a) with HBr in great excess, (b) with HBr and C2H4 in equal concentration, (c) with C2H4 in great excess. For condition (a) the rate showed a first-order dependence on [C2H4], an approximate second-order dependence on [HBr], a negative temperature coefficient, and a dose rate exponent of unity. It was concluded that the reaction rate was determined by the same step as for the photobromination reaction and that wall termination predominated. For conditions (b) and (c) the dose rate exponent was found to be approximately 0.5 indicating a predominance of mutual termination. Definite conclusions with regard to the termination reaction were not possible but the data suggested that certain ion–molecule reactions may precede ion combinations.