Soft X-ray Irradiation of Ice Analogues: A Realistic Ice Mantle

Abstract

Interstellar ice is a remarkable material: it enables a dramatic chemical transformation to take place in the interstellar medium. This transformation converts relatively simple chemical species (such as CO, H$_\textbf{2}$O, and NH$_\textbf{3}$) into some that are relatively complex. In the environments of solar-type stars, the intense soft X-ray irradiation impacts significantly on disc evolution, and must affect the physical and chemical structure of circumstellar ices. The effects of soft X-rays have been studied in dedicated experiments, which have largely demonstrated that X-rays can contribute to efficient organic chemistry. We discuss soft X-rays processing of layered ices composed of a H$_\textbf{2}$O:CH$_\textbf{4}$:NH$_\textbf{3}$ mixture, covered by a mixture of CH$_\textbf{3}$OH and CO. Irradiation of layered ice with isotopologues of methane $^{13}$CH$_\textbf{4}$ and ammonia $^{15}$NH$_\textbf{3}$ have been used to interpret the contribution from both layers to the detected volatiles species during irradiation. Bulk diffusion occurs in the ice under irradiation.