Abstract
A mechanism is suggested for the radiolysis of hydrocarbons. Both ions and excited molecules are produced in the initial excitation. Ion–electron recombination leads to the formation of excited molecules which have similar properties to those formed initially; all subsequent decomposition proceeds through these excited molecules. In mixtures of hydrocarbons, ions and molecules may undergo positive charge exchange and additives reduce the hydrogen yield by capturing electrons or reacting with the positive ion. The mechanism provides a rationalization for a variety of observations.