γ-Radiolysis of benzene at high temperatures and pressures

Abstract

Benzene was irradiated at 260–390°C, and yields of hydrogen, methane, acetylene, ethylene, ethane, biphenyl and conversion to polymer were measured as functions of dose, density and temperature. No special phenomena were observed at or near the critical temperature. In general, all yields decreased smoothly with increasing density, and increased with increasing temperature. The most marked increase with temperature was in G(H₂) which increased approximately thirty-fold (from ∼0.1 to ∼3) from 260 to 390°C. The only dimer found was biphenyl whose yield was also strongly temperature dependent. The effect of density was attributed to the competition between deactivation and decomposition of excited molecules, and the effect of temperature to the competition between different reactions of hydrogen atoms, or cyclohexadienyl radicals. The competing hydrogen atom reactions considered were: H·+ C₆H₆→ C₆H₇·, H ·+ C₆H₆→ H₂+ C₆H₅· but competing modes of decomposition of the cyclohexadienyl radical C₆H₇·→ C₆H₆+ H·; C₆H₇·→ C₆H₅·+ H₂ were adjudged a more probable cause of the variation of G(H₂) with temperature. Methane, ethylene, and ethane, appeared to be secondary products, and in the long irradiations necessary to measure G(→polymer) thermal reactions, such as the polymerization of acetylene, and the hydrogenation of acetylene and ethylene affected the observed yields. The effects of density and temperature on radiolytic yields were considered in relation to models which have been proposed to explain product formation in the radiolysis of aromatic liquids.