VUV Photolysis of CO Ices with a Tunable Light Source

Experimental results on the VUV photolysis of pure CO ices at 18 K have been obtained by employing a narrow bandwidth synchrotron radiation light source at the National Synchrotron Radiation Research Center, Hsinchu, Taiwan. In the present study we specifically select three photon wavelengths at 121.6, 139.9, and 153.0 nm with a spectral bandwidth (fwhm) of 0.2 nm. The destruction and desorption yields of CO and the production yields of CO2 have been measured. Furthermore, we have investigated the dependence of these yields on the thickness (ranging from 80 to 280 monolayers) of CO ices. The magnitude of the initial destruction and desorption yields of CO is of the order of 10-3, and that of the initial production yields of CO2 is of the order of 10-4 for photolysis at 121.6 and 139.9 nm. Comparison with results obtained from photolysis of thick ices available in the literature will also be given. The goal of our work is to provide accurate data to improve our understanding of ice photochemistry, which may be relevant to surface evolution of cosmic icy objects. This research is based on work supported by the NSF Planetary Astronomy Program under Grant AST-1108898 (Wu) and by NSC99-2112-M-008-001-MY3 and The Aim for the Top University (Yih).