| dc.description.abstract | In molecular clouds, the icy mantles are anticipated to form a bi-layered structure,
CO:CH3OH/H2O:NH3:CH4 (Ciaravella et al. 2020 [1]). Cosmic rays, which are ubiquitous, stimulate various chemical reactions and molecular desorption. In the cold interstellar environment, radiation-induced diffusion is crucial for bringing molecules closer
together and facilitating chemical reactions, rather than relying on thermal diffusion. In
this study, we irradiated the bi-layered ice mixtures with 1 keV and 2 keV electrons. The
13CH4 in the bottom layer was used as a tracer to produce 13CO. As the irradiation time
increased, the products in the bottom layer diffused deeper into the cap layer, resulting in
a gradual increase in the fraction of 13CO. The desorption signals of 13CO were linearly
fitted to calculate the diffusion time and length. Our results revealed that the diffusion
coefficient in the 2 keV experiments was nearly 50% higher than in the 1 keV experiments,
indicating that higher energy electrons result in higher diffusion coefficients. However, the
diffusion coefficient in 2 keV electron irradiation was still approximately three orders of
magnitude lower than in X-ray sources (250-1250 eV) due to the higher penetrative power
and secondary electron generation by X-rays inside the bottom layer. These experiments
unveiled the electron-induced diffusion in bi-layered ice mixtures. Further investigations
are needed to delve deeper into the mechanisms underlying this diffusion process, including the role of chemical reaction in bottom and a simpler, more controlled environment
in the cap layer. | en_US |