Material evolution simulator

为了模拟星际颗粒上有机难熔膜的形成和演化过程，提出了一套研究低温下光子和离子照射下固体有机物演化的室内实验。有机残余物是浓云中冰膜在紫外光作用下的产物，由2-3个碳原子组成。通过室内实验，给出了有机残留物形成效率与紫外线辐射剂量的函数关系。有机残留物的产量如此之高，可能是星际介质中固体碳质物质的主要来源。用10e VUV光子照射和3ke V He^+离子轰击模拟了更复杂的碳质物质的加工过程。后者具有类似于宇宙射线1mev质子的停止能力。剩余物随后的演化表现为两个过程：H、O的损失。和N（碳化）和在聚合固体中形成多芳簇（聚合）。这两个过程都可以发生，但值得注意的是，宇宙射线离子聚合的效率比每单位吸收能量的紫外线光子聚合的效率高10^3倍。然而，紫外光子将主导聚合和碳化，因为在漫射介质中，紫外光子在有机可折射颗粒地幔中沉积的能量是宇宙射线的10^5倍。在扩散介质中经过典型寿命后，加工后的有机难熔颗粒地幔成为具有较大光学间隙（约0.6-1）的氢化非晶碳。le V，含有少量的氢、氧和氮，以及30-60环大小的石墨团簇。这使得星际谷物地幔成为多环芳烃的潜在来源。

A set of laboratory experiments is presented that study the evolution of solid organic matter at low temperature as a result of exposure to photons and ions, with the aim of simulating the formation and evolution of organic refractory mantles on interstellar grains.Organic residue is a product of UV photolysed ice mantles in dense clouds and consists of 2-3 C atom containing compounds. From laboratory experiments, the efficiency of organic residue formation is given as a function of UV radiation dose.The yield of organic residue is so high that probably is the major source of solid carbonaceous matter in the interstellar medium.The processing into more complex carbonaceous matter has been simulated by irradiation with 10e VUV photons and bom-bardment with 3ke V He^+ions. The latter have a stopping power similar to cosmic ray 1 MeVprotons.The subesquent evolution of the residue is characterized by two processes : The loss of H,O.and N (carbonization) and the formation of polyaromatic clusters in the polymeric solid (polymerization) . Both processes are shown to occur, but notably polymerization by cosmic ray ions is found to be abbout 10^3 times more efficient than that by UV photons per unit energy absorbed. UV photons, however, will dominate the polymerization and carbonization, because in the diffuse medium UV photons deposit as much as 10^5 times more energy in the organic refractoy grain mantles than cosmic rays.After a typical lifetime in the diffusc medium, the processed organic refractory grain mantle becomes an hydrogenated amorphous carbon with a relatively large optical gap of about 0.6-1.le V,with small but significant amounts of H,O,and N,and graphitic clusters up to sizes of 30-60 rings. This makes interstellar grain mantles a potential source of PAHs.