氢原子轰击含冰的CO2、HCOOH和CH3CHO
H-atom bombardment of CO2, HCOOH and CH3CHO containing ices
摘要：
氢化反应被认为是星际冰最重要的表面反应之一。然而，关于氢原子与常见星际冰成分反应的固态天体化学实验室数据在很大程度上缺乏。目的：我们实验室工作的目标是确定二氧化碳（CO2）、甲酸（HCOOH）和乙醛（CH 3CHO）是否以及如何在低温下与固态H原子反应，并推导出反应速率和产率。方法：在超高真空实验中，用氢原子轰击纯CO2、HCOOH和CH 3CHO星际冰模拟物。通过反射吸收红外光谱法监测冰，并通过程序升温脱附在气相中检测反应产物，以确定破坏和形成产率以及相应的反应速率。结果如下：在我们设置的灵敏度内，我们得出结论，纯CO2和HCOOH冰的H原子轰击不会导致可检测的反应产物。反应速率的上限小于或等于7 e（-17）cm ^2/s，这使得这些物质不太可能在星际冰中由于与H原子反应而形成更复杂有机物的过程中发挥主要作用。相比之下，CH 3CHO不与H原子反应。最多20%被氢化成乙醇（C2 H5 OH），第二反应途径导致C-C键断裂以形成固态CH 4（~20%）以及H2 CO和CH 3OH（15-50%）。甲烷的产率预计等于H2 CO和CH 3OH的总产率，因此由于反应的高挥发性，CH 4很可能在形成后部分蒸发。CH 3CHO破坏的反应速率取决于冰温而不是冰厚。
英文摘要：
Context: Hydrogenation reactions are expected to be among the most important surface reactions on interstellar ices. However, solid state astrochemical laboratory data on reactions of H-atoms with common interstellar ice constituents are largely lacking. Aims: The goal of our laboratory work is to determine whether and how carbon dioxide (CO2), formic acid (HCOOH) and acetaldehyde (CH3CHO) react with H-atoms in the solid state at low temperatures and to derive reaction rates and production yields. Methods: Pure CO2, HCOOH and CH3CHO interstellar ice analogues are bombarded by H-atoms in an ultra-high vacuum experiment. The ices are monitored by reflection absorption infrared spectroscopy and the reaction products are detected in the gas phase through temperature programmed desorption to determine the destruction and formation yields as well as the corresponding reaction rates. Results: Within the sensitivity of our set-up we conclude that H-atom bombardment of pure CO2 and HCOOH ice does not result in detectable reaction products. The upper limits on the reaction rates are less or equal to 7e(-17) cm^2/s which make it unlikely that these species play a major role in the formation of more complex organics in interstellar ices due to reactions with H-atoms. In contrast, CH3CHO does react with H-atoms. At most 20% is hydrogenated to ethanol (C2H5OH) and a second reaction route leads to the break-up of the C-C bond to form solid state CH4 (~20%) as well as H2CO and CH3OH (15-50%). The methane production yield is expected to be equal to the summed yield of H2CO and CH3OH and therefore CH4 most likely evaporates partly after formation due to the high exothermicity of the reaction. The reaction rates for CH3CHO destruction depend on ice temperature and not on ice thickness.
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