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arXiv · 2001.01590

On The Photodesorption of CO$_2$ Ice Analogues: The Formation of Atomic C in The Ice and the Effect of The VUV Emission Spectrume

N. -E. Sie·G. M. Muñoz Caro·Z. -H. Huang·R. Martín-Doménech·A. Fuente·Y. -J. Chen
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Abstract

CO$_2$ ice has a phase transition at 35 K when its structure changes from amorphous to crystalline. Using Reflection absorption Infrared Spectroscopy (RAIRS), \"Oberg et al. observed that the photodesorption yield of CO$_2$ ice deposited at 60 K and irradiated at 18 K is 40% lower than that of CO$_2$ ice deposited and irradiated at 18 K. In this work, CO$_2$ ices were deposited at 16-60 K and UV-irradiated at 16 K to rule out the temperature effect and figure out the relationship between photodesorption yield and ice structure. IR spectroscopy is a common method used for measurement of the photodesorption yield in ices. We found that undetectable C atoms produced in irradiated CO$_2$ ice can account for 33% of the amount of depleted CO$_2$ molecules in the ice. A quantitative calibration of QMS was therefore performed to convert the measured ion current into photodesorption yield. During various irradiation periods, the dominant photodesorbing species were CO, O$_2$, and CO$_2$, and their photodesorption yields in CO$_2$ ices deposited at different temperature configurations were almost the same, indicating that ice morphology has no effect on the photodesorption yield of CO$_2$ ice. In addition, we found that the lower desorption yield reported by Mart\'in-Dom\'enech et al. is due to a linear relationship between the photodesorption yield and the combination of energy distribution of Microwave-Discharge Hydrogen-flow Lamp (MDHL) and UV absorption cross section of ices.

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N. -E. Sie, G. M. Muñoz Caro, Z. -H. Huang, R. Martín-Doménech, A. Fuente, Y. -J. Chen. 2020-01-06. On The Photodesorption of CO$_2$ Ice Analogues: The Formation of Atomic C in The Ice and the Effect of The VUV Emission Spectrume. https://doi.org/10.3847/1538-4357/ab06be

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