Chemical reaction mechanism on the surafce of interstellar icy grains

我们研制了一套新的实验装置，用以研究星际冰粒表面的化学反应。该装置由三部分组成：i）冰和有机物的冷凝，ii）UV高能离子和原子照射到冰或有机物上，iii）质谱仪和红外光谱仪。（a）在10 K温度下测量了非晶态水冰中CO和CO_2在宽浓度范围内的红外吸收光谱。结果表明，CO和CO2的综合吸收系数与CO和CO2的浓度有很大关系。(b)利用紫外线照射无定形冰，模拟星际分子云中有机物形成的实验室实验。结果表明，有机残基的生成效率与紫外辐射剂量有关。(c)通过对有机残渣进行紫外线和离子辐照，可以将其加工成更复杂的含碳物质。残余物的后续演变的特征在于H、C、N的损失（碳化）。(d)当氢原子照射到非晶冰表面时，发现氢分子在非晶冰上通过表面反应形成。我们现在正在测量新形成的氢分子的动能和邻位/帕拉比。

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.