Structure and physical properties of impure amorphous interstellar icy grains

利用新研制的超高真空极低温原子力显微镜和现有设备，对非晶态冰粒的形成、变质和彗星的起源演化进行了以下研究：1)通过紫外照射非晶态冰薄膜，定量分析氢分子的形成。测定了反应截面，确定了反应机理。2)对非纯非晶冰的物理性能进行了测量。研究发现，不纯净的非晶冰的导热系数比没有缺陷的非晶冰的导热系数小2-3个数量级。通过差热分析，我们发现含杂质的非晶态冰的结晶是吸热反应。3)研究结果清楚地表明，非纯非晶冰的某些性能在很大程度上取决于其在非晶冰中的缺陷结构。4)在上述结果的基础上，我们计算了彗星核的热历史。我们发现，到目前为止认为的失控结晶不可能发生在实际的彗星核中。

The following research was carried out on the formation and metamorphism of amorphous icy grains and origin and evolution of comets using newly developed ultrahigh-vacuum very low temperature atomic force microscope and existing equipments :1) By irradiating the ultraviolet rays onto amorphous ice thin film, we analyze the formation of hydrogen molecule quantitatively. In addition, the reaction cross section was measured, and the reaction mechanism was decided.2) The measurements on physical properties of impure amorphous ices were carried out. The thermal conductivity of impure amorphous ice was found to be 2-3 orders of magnitude smaller than that of the amorphous ice without the defect. As a result of the differential thermal analysis, we found that the crystallization of amorphous ices including impurities were endothermic reaction.3) There results clearly shows that the some properties of impure amorphous ices strongly depends on their defect structure in amorphous ices.4) On the basis of the above results, we have calculated the thermal history of comet nucleus. We found that runaway crystallization considered until now could not be occurred in the actual comet nucleus.