VUV photolysis of pure CO ices: A study of spectral bandwidth dependence

An intense and tunable synchrotron radiation light source and a microwave-discharged H2 flow lamp have been used in the photolysis study of pure CO ice systems. We have measured the production yields of photon-induced chemical products and the depletion yield of the parent CO molecules using Fourier transform infrared spectroscopy. The initial production yields and initial destruction yields are determined. Comparison of the present results with others available in the literature is given. From the reported data, we find that the magnitude of the initial depletion yields of CO is of the order of 10-1, that of the initial production yields of CO₂ and C₃O₂ is of the order of 10-2, and CO3 of 10-3. We show that the initial production yield of CO2 depends on the spectral output of different light sources, as expected. It is suggested that the data required for an accurate modeling of cosmic ice photochemistry should be those obtained using monochromatic measurements in order to construct the appropriate spectral content of the incident radiation on cosmic ices.