Experimental studies on the low-temperature condensation of cosmic dust in the interstellar medium

在ISM中，在约10至20 K的温度下需要有效的粉尘形成过程，以保持粉尘破坏和形成过程之间的平衡。这一过程被认为发生在分子云中，其中气态难熔物质在幸存的尘埃颗粒上聚集，并最终在这些颗粒上形成固体层。在第一个项目阶段，硅质和碳质固体的冷冷凝没有额外的能量已被实验证明。凝聚层的结构和成分类似于在演化恒星的拱壳中形成的尘埃物质。在第二个项目阶段，我们的活动集中在冷表面上碳质和硅质物种的同时吸积，以及原子和分子前体固体材料的最终形成。由于星际尘埃的观测清楚地证实了分离的硅酸盐和碳质颗粒的形成，即使硅质和碳质气态物质可能反应形成碳化物或硅有机化合物，我们将研究可能阻止碳化物或具有C-Si键的化合物形成的可能情况。真空紫外光子的作用，可能会引发特定分子物种的解吸过程或化学反应，挑起选择性冷凝过程中的实验研究。这些冷凝物的光谱特性，碳和硅酸盐形成的效率为不同比例的碳质和硅质物种的表面上的颗粒，并在界面上的化学键的光谱特性方面进行研究，以完全了解冷冷凝过程的星际尘埃。

An efficient dust formation process in the ISM at temperatures of about 10 to 20 K is required to keep the balance between dust destruction and formation processes. This process is supposed to occur in molecular clouds where gaseous refractory species accrete on surviving dust grains and finally form a solid layer on those grains. In the first project phase, the cold condensation of siliceous and carbonaceous solids without additional energy has been experimentally proven. The structure and composition of the condensed layers is similar to dust materials that are formed in circumstellar shells of evolved stars. In the second project phase, we focus our activities on the simultaneous accretion of carbonaceous and siliceous species on cold surfaces and the final formation of solid materials from atomic and molecular precursors. Since observations of interstellar dust clearly verify the formation of separated silicates and carbonaceous grains even though siliceous and carbonaceous gaseous species may react to form carbides or silicon organic compounds, we will study possible scenarios that may prevent the formation of carbides or compounds having C-Si bonds. The role of VUV photons that may trigger desorption processes of specific molecular species or chemical reactions provoking selective condensation processes has to be studied experimentally. The spectral properties of such condensates, efficiencies of carbon and silicate formation for different ratios of carbonaceous and siliceous species that accrete on the surfaces of grains, and the chemical bonds at interfaces with regard to the spectral properties will be studied to completely understand the cold condensation process of interstellar dust.