Effect of Electrical Fields in the Gamma Radiolysis of Propane

Abstract

The γ-ray radiolysis of C3H8–C3D8 mixtures and of CD3CH2CD3 has been investigated as a function of applied electrical field up to voltages necessary to cause secondary ionization. In the saturation current region, those products which in previous studies were ascribed to ethyl and vinyl ions remain constant with a change in field strength, while products which were originally attributed to the decomposition of neutral excited propane molecules are seen to increase about fivefold before the onset of secondary ionization. The inferred yields of C2H5+ and C2H3+ per ion pair at a propane pressure of 3 cm are 0.40 and 0.08, respectively. These values compare favorably with those deduced from the fragmentation of propane within 10—10 sec as calculated by Vestal, Wahrhaftig, and Johnston on the basis of the quasiequilibrium theory of mass spectra. The modes of decomposition of the neutral excited propane molecules formed by electron impact are the same as those observed in the vacuum-ultraviolet photolysis at 1470 and 1237 Å. From the isotopic analysis of the products formed in the radiolysis of CD3CH2CD3 at high field strengths, it can be concluded that the average energy imparted to the neutral propane molecule by electron impact is larger than 10 eV, indicating that superexcited states of propane may be produced in the radiolysis. A value of 0.3±0.1 can be ascribed to the ratio of the number of neutral excited molecule decompositions to the number of ion pairs produced in the direct radiolysis of propane in the absence of an electrical field.