CHEMICAL EVOLUTION OF A CO ICE INDUCED BY SOFT X-RAYS

Abstract

We irradiated a pure carbon monoxide ice with soft X-rays of energies up to 1.2 keV. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan, exploiting both monochromatic (at 0.3 and 0.55 keV) and broader energy (0.25–1.2 keV) fluxes. The infrared spectra of the irradiated ices showed the formation of a number of products such as polycarbon mono- and dioxides C n O m , and chains containing up to 10 carbon atoms. While a gentle increase in the energy absorbed by the ice sample is reflected by an increase in the column densities of newly born species, such correlation breaks down at very high fluxes. In this regime the production yield falls down sharply by about a factor of 100. The refractory residue obtained in the broad energy irradiation is a “compromise” between those obtained with proton irradiation of C 3 O 2 and CO ices in previous experiments. Finally, we discuss the possible implications for space chemistry