Experimental study of the formation and destruction of carbonates in circumstellar and interstellar environments and their impact on the oxygen depletion in the interstellar medium

碳酸盐存在于各种天体物理环境中，包括演化恒星、原行星盘、太阳系和太阳系外行星以及彗星周围的星际包围层。它们在天体物理环境中的形成和破坏是不同的耐火和非耐火固体、气体成分以及高能光子辐射之间的复杂相互作用。碳酸盐可以由硅酸盐和含碳物质形成。相当数量的碳，特别是氧可以被隔离在这种无机和有机碳酸盐中，这为星际介质中的氧气耗尽问题提供了一个可能的解决方案。在项目过程中，我们将在实验室中模拟在各种天体物理环境中普遍存在的条件下碳酸盐的形成和破坏。无机和有机碳酸盐将从我们实验室生产的碳质和硅酸盐粉尘类似物中生产出来。硅酸盐的碳化将通过在含有CO2/H2O的气氛中的气相冷凝、CO、CO2和H2O分子与宇宙硅酸盐类似物之间的气面反应、冷硅酸盐或硅酸盐/碳混合物与由CO、CO2和H2O组成的分子冰的反应来实现。此外，还将研究同时紫外线照射对硅酸盐在气相或颗粒/冰界面生成碳酸盐的影响。碳颗粒暴露在氧原子的轰击和CO和CO2分子的流动中将被用来合成有机碳酸盐。它们的形成预计将分两个反应步骤进行，包括形成环氧化物官能团和它们反应成环状碳酸酯。红外光谱将用于现场监测无机和有机碳酸盐的形成。形成速度将被确定为温度的函数，范围在10K到~400K之间。红外光谱、电子显微镜和有机分析将用于解释硅酸盐和碳粒的化学和结构修饰。除了碳酸盐的形成速度外，真空紫外光照射对碳酸盐的光子破坏也起着重要的作用，必须进行分析。我们的研究结果将为我们提供关于宇宙碳酸盐光谱性质的重要信息，以及它们在天体化学和天体物理过程中的潜在作用，例如星际介质中氧气的耗尽和复杂有机分子的形成，以及行星的形成。

Carbonates are found in various astrophysical environments including circumstellar envelopes around evolved stars, protoplanetary disks, solar and extrasolar planets, and comets. Their formation and destruction in astrophysical environments is a complex interplay between different refractory and nonrefractory solids, gaseous components, and irradiation with energetic photons. Carbonates can be formed from silicates and carbonaceous material. A considerable amount of carbon and in particular of oxygen can be sequestered in such inorganic and organic carbonates, which provides a possible solution to the oxygen depletion problem in the interstellar medium. In the course of the project, we are going to simulate the formation and destruction of carbonates in the laboratory at conditions prevailing in various astrophysical environments. Inorganic and organic carbonates will be produced from carbonaceous and silicate dust analogues produced in our laboratory. The carbonation of silicates will be realized by gas phase condensation in CO2/H2O-containing atmospheres, gas-surface reactions between CO, CO2, and H2O molecules and cosmic silicate analogues, reactions of cold silicates or silicate/carbon mixtures with molecular ice composed of CO, CO2, and H2O. In addition, the effect of simultaneous ultraviolet irradiation on the carbonate formation produced from silicates either in the gas phase or at the interface grains/ice will be investigated. The exposure of carbon grains to a bombardment of oxygen atoms and a flow of CO and CO2 molecules will be used to synthesize organic carbonates. Their formation is expected to occur in two reaction steps including the formation of epoxide functional groups and their reaction into cyclic carbonates. IR spectroscopy will be used to monitor the formation of inorganic and organic carbonates in situ. The formation rates will be determined as a function of temperature covering a range between 10 K and ~400 K. IR spectroscopy, electron microscopy, and organic analyses will be used to explain the chemical and structural modifications of the silicate and carbon grains. Besides the formation rate of carbonates, their photon-induced destruction by VUV irradiation plays an important role and has to be analyzed. The results of our studies will provide us significant information on the spectral properties of cosmic carbonates and their potential role in astrochemical and astrophysical processes such as the depletion of oxygen and the formation of complex organic molecules in the interstellar medium, as well as the formation of planets.