UV-photoprocessing of interstellar ice analogs: New infrared spectroscopic results
UV-photoprocessing of interstellar ice analogs: New infrared spectroscopic results
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DOI：
10.1051/0004-6361:20031408
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发表时间：
2003-12-01
影响因子：
6.5
通讯作者：
Schutte, WA
中科院分区：
文献类型：
--
作者：
Caro, GMM;Schutte, WA
我们利用高真空实验装置，在接近12 K的低温条件下，模拟了稠密云中存在的物理条件。用以下方法模拟了颗粒表面冰的吸积和光处理过程：在基底窗口上沉积一层成分类似星际冰的冰层，同时受到紫外线（UV）光子的照射。随后将样品缓慢加热至室温；残留物中含有光和热处理的大部分难熔产物。本文报道了在各种初始条件（冰成分、紫外光谱、紫外剂量和样品温度）下形成的难熔有机材料的傅里叶变换红外光谱。对实验中得到的耐火产物进行了鉴定，并给出了相应的生成效率。第一个证据表明羧酸盐是耐火产品的一部分。耐火材料的红外光谱特征由六亚甲基四胺(HMT, [（CH2)(6) n -4]）、羧酸铵盐[(R- coo -)(NH4+)]、酰胺类[H2NC(= O) - R]、酯类[R -C (= O) - O- R']和聚甲醛(POM, [（- ch2o -)(n)]）组成。此外，还提供了室温下HMT形成的证据，以及H2O冰作为复杂有机分子形成催化剂的重要作用。这些物种也可能存在于星际介质（ISM）中，并构成彗星的一部分。正在进行的和未来的彗星任务，如星尘号和罗塞塔号，将允许与实验室结果进行比较，为我们太阳系形成期间的物理化学条件提供新的见解。
We simulate experimentally the physical conditions present in dense clouds by means of a high vacuum experimental setup at low temperature T approximate to 12 K. The accretion and photoprocessing of ices on grain surfaces is simulated in the following way: an ice layer with composition analogous to that of interstellar ices is deposited on a substrate window, while being irradiated by ultraviolet (UV) photons. Subsequently the sample is slowly warmed up to room temperature; a residue remains containing the most refractory products of photo- and thermal processing. In this paper we report on the Fourier transform-infrared (FT-IR) spectroscopy of the refractory organic material formed under a wide variety of initial conditions ( ice composition, UV spectrum, UV dose and sample temperature). The refractory products obtained in these experiments are identified and the corresponding efficiencies of formation are given. The first evidence for carboxylic acid salts as part of the refractory products is shown. The features in the IR spectrum of the refractory material are attributed to hexamethylenetetramine (HMT, [(CH2)(6)N-4]), ammonium salts of carboxylic acids [(R-COO-)(NH4+)], amides [H2NC(= O) - R], esters [R - C(= O) - O - R'] and species related to polyoxymethylene (POM, [(-CH2O-)(n)]). Furthermore, evidence is presented for the formation of HMT at room temperature, and the important role of H2O ice as a catalyst for the formation of complex organic molecules. These species might also be present in the interstellar medium (ISM) and form part of comets. Ongoing and future cometary missions, such as Stardust and Rosetta, will allow a comparison with the laboratory results, providing new insight into the physico-chemical conditions present during the formation of our solar system.