Vacuum ultraviolet photolysis of CH4:O2 ice mixtures and the formation of CO and CO2

Abstract Vacuum ultraviolet (VUV) photolysis of CH4:O2 ice mixtures at 10 K using 121.6, 157, and 170-nm wavelengths was performed to examine photochemical reactions for the oxidation of hydrocarbon species. Ice samples with three component ratios were prepared: CH4-dominated (CH4:O2 = 100:1), mixed (CH4:O2 = 1:1), and O2-dominated (CH4:O2 = 1:100) ice samples. Photochemical behavior with dependence on the photolysis wavelength and component ratio was observed. In addition, the column densities of CO and CO2 formed by the VUV photolysis of the three ice samples and the abundance ratios of CO and CO2 as a function of the photon dosage and photolysis wavelength were examined. The results may imply a correlation between the unknown depletion of interstellar oxygen and the formation of CO and CO2.