Electron-Induced Desorption-Relevant Depth in CO:H:₂O Ice Mixture

Chun-Yi Lee^1*, Jr-Yao Lee¹, Chao-Hui Huang¹, Ni-En Sie¹, Yu-Jung Chen¹

¹Department of Physics, National Center University, Taoyuan, Taiwan

* Presenter:Chun-Yi Lee, email:kenads305@gmail.com

CO and H₂O are the two most abundant molecules in interstellar grain mantle. In this study, CO:H₂O (1:4) ice mixture is irradiated by 1keV electrons to investigate the desorption-relevant depth. To find out whether the deeper molecules near ice surface contributing to Electron-Stimulated Desorption (ESD), the ice sample is designed as a two-layer structural ice with isotope substitution to identify the signal from the different layers. During preparing of layered ice mixture, some of the bottom layer ¹³CO molecules are sputtered out when the top layer ice are deposited via normal deposition method. That caused by introduced molecules directly hit on the condensed molecules, therefore another method, background deposition, are used for producing the top layer ice. In this study, the results show that the ESD of m/z = 29 (¹³CO) decayed significantly, while the top layer thickness increased. That means the particles in a certain depth can involve in desorption from the ice. And the different results between background deposition and normal deposition verify that the sputter phenomenon can pollute the top layer ice and form a fuzzier interface, reducing the resolution of depth-dimension. More experiments should be done to confirm the desorption involved depth in different electron energy and realize whether stopping power or the total energy within the desorption-relevant depth dominating the ESD yield.

Keywords: ISM astrophysics, desorption-relevant depth, QMS