Chemical reaction mechanism on the surafce of interstellar icy grains

我们开发了一种新的实验装置来研究星际冰粒表面的化学反应。该装置由三部分组成：1)冰和有机物的冷凝；2)紫外线高能离子和原子照射到冰或有机物上；3)质谱仪和红外光谱仪。利用该装置，我们进行了以下实验：(a)在10K条件下，在宽浓度范围内测量了CO和CO2在无定形水冰中的红外吸收光谱。CO和CO2的综合吸收系数在很大程度上取决于CO和CO2的浓度。(b)通过紫外线照射无定形冰，模拟星际分子云中有机物质形成的实验室实验。发现有机残留物的形成效率与紫外线辐射剂量有关。(c)利用紫外线和离子照射有机残留物，将其加工成更复杂的碳质物质。残渣的后续演化以H、C、N的损失（炭化）为特征。(d)将原子氢照射到非晶态冰表面，发现在非晶态冰表面反应形成氢分子。我们现在正在测量新形成的氢分子的动能和正对位比。

We have developed a new experimental set-up to investigate the chemical reaction on the surafce of interstellar icy grains. This set-up consists of three parts : i) condensation of ices and organic matter, ii) irradiation of UV high energy ions and atoms onto ices or organic matter, iii) mass spectrometer and infrared spectrometer. By the use of this set-up, we have performed following experiment :(a) Infrared absorption spectra of CO and CO2 in amorphous water ice have been measured at 10K over the wide concentration ranges. It is found that the integrated absorption coefficient of CO and CO2 graetly depends on the concentrations of CO and CO2.(b) A laboratory experiments to simulate the formation of organic matter in interstellar molecular cloud by the irradiation of UV rays onto the amorphous ices. It is found that the efficiency of oganic residue formation depends on the UV radiation dose.(c) The processing into more complex carbonaceous matter has been performed by the irradiation of UV and ions onto the oganic residue. The subsequent evolution of the residue is characterized by the loss of H,C,N (carbonization).(d) When atomic hydrogen is irradiated onto the surface of amorphous ice, it is found that hydrogen molecules have formed by the surface reaction on the amorphous ices. We are now measuring the kinetic energy and ortho/para ratio of newly formed hydrogen molecules.