LABORATORY INVESTIGATION OF X-RAY PHOTOLYSIS OF METHANOL ICE AND ITS IMPLICATION ON ASTROPHYSICAL ENVIRONMENTS

Methanol (CH3OH) is one of the most abundant organic molecules in astrophysical environments. It has been found in cold regions such as surfaces of comets, ices near young stellar objects and protoplanetary disks, as well as in the gas phase in different regions in space. In this work, we experimentally simulate the methanol ice and its behavior when irradiated by broadband soft X-rays. The experiments were performed at the Brazilian Synchrotron Facility LNLS/CNPEM, employing a broadband photon beam (6 to 2000 eV). The frozen sample was analyzed in situ by infrared spectroscopy (IR) in simulated astrophysical at different radiation fluences. The results show the formation of several new species such as CO2, CO, H2O and CH4 during the photolysis CH3OH ice by soft X-rays. We determined effective destruction and formation cross-section, as well as the chemical equilibrium fluence (FE) and desorption yields. The timescale to reach chemical equilibrium in some astrophysical environments with soft X-rays were estimated. The result helps us to understand the photolysis induced by X-rays in organic-rich ices in space environments.

甲醇（Methanol，CH₃OH）是天体物理环境中丰度最高的有机分子之一，已在彗星表面、年轻恒星天体附近的冰体与原行星盘等寒冷区域，以及宇宙不同区域的气相中被探测到。本研究通过实验模拟了甲醇冰及其在宽带软X射线辐照下的行为。实验在巴西同步辐射装置LNLS/CNPEM中开展，采用能量范围为6至2000 eV的宽带光子束。实验过程中，我们借助红外光谱（infrared spectroscopy, IR）对冷冻样品进行原位分析，且在不同辐射注量的模拟天体物理环境下完成检测。结果表明，在软X射线辐照甲醇冰引发的光解过程中，会生成二氧化碳（CO₂）、一氧化碳（CO）、水（H₂O）及甲烷（CH₄）等多种新物质。我们测定了有效破坏截面与生成截面，同时确定了化学平衡注量（chemical equilibrium fluence, FE）与解吸产率。此外，我们还估算了部分存在软X射线的天体物理环境达到化学平衡所需的时间尺度。本研究结果有助于理解宇宙环境中富含有机物的冰体受X射线诱导发生的光解过程。