VUV Photon-induced desorption of CO₂ Ice: Temperature Dependent Study
陳俞融1*, 吳尚叡1, Guillermo. M. Munoz Caro2
1物理, 國立中央大學, 桃園市, Taiwan
2Center of Astrobiology, CSIC-INTA, Mardrid, Spain
* presenting author:Yu-Jung Chen,
Photodesorption of ices is thought to be a source of gas phase molecules in cold interstellar clouds. In this talk, we present CO₂ ice deposited and VUV irradiated at several different temperatures, in order to understand the thermal effect on VUV photodesorption yield and the mechanism of VUV photodesorption of CO₂ ice.

A quartz crystal microbalance (QCM) and a Fourier transform infrared spectroscopy (FTIR) are used to measure photodesorption yield in two separated systems, both systems equipped with a quadrupole mass spectrometer (QMS) to measure the species of desorbed molecules during the whole experimental process.

The results of QCM show that the photodesorption yield of CO₂ ice, which was deposited and irradiated at 50 K and 70 K, increases almost an order of magnitude higher than that was at 14 K, due to the photodesorption occurred only on the top few monolayers of CO₂ ice at 14 K, but CO and O₂ can desorbed from deeper monolayers of CO₂ ice at temperature above 50 K. On the other hand, mass spectra show that desorbed molecules mostly originated from CO₂ decomposed to CO, but also with smaller amount of C, O, CO₂ and O₂. However, the desorbed amount of O₂ increases rapidly while the deposition temperature of CO₂ ice is above 50 K. While the CO₂ ice was deposited and irradiated above 50 K, CO molecule was kept desorbing from CO₂ ice after stop VUV irradiation, and the migration distance of CO and O₂ molecule in CO₂ ice was estimated at 50 K and 70 K.

Keywords: Photodesorption, cold molecular cloud, interstellar ice, electronic transition