Proton radiolysis of carbon monoxide

Abstract

The radiation chemistry of CO has been studied, using principally low-energy protons from a Van de Graaff accelerator, as a function of dose rate, temperature and small amounts of additives (CO₂ and O₂). At dose rates higher than those used in previous work a true dose-rate inhibition effect has been found which is interpreted on the basis of competition between second-order and first-order processes. The effect of CO₂ on yields is negligible at concentrations up to 0.5% by volume but initial yields are extremely sensitive to traces of O₂, particularly at low dose rates.

Increased temperature reduces yields of solid and increases yields of CO₂, but this effect is controlled mainly by subsequent thermal decomposition of the solid. The empirical composition of the solid is unaffected by changes in dose rate, and varies from (C₃O₂)_n at room temperature to essentially pure carbon at temperatures >450°C. Nucleation of the solid occurs predominantly in the gas phase. The relative importance of ionic and excitation processes is discussed.