Formation of Interstellar OCS: Radiation Chemistry and IR Spectra of Precursor Ices
Formation of Interstellar OCS: Radiation Chemistry and IR Spectra of Precursor Ices
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星际 OCS 的形成：前体冰的辐射化学和红外光谱
DOI：
10.1086/590362
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
R. Hudson
中科院分区：
文献类型：
--
作者：
R. Ferrante;M. Moore;Morgan M. Spiliotis;R. Hudson
已经进行了大量的实验研究上的OCS分子在质子辐照的无水和水为主的冰含有CO或CO2作为碳源和H2S或SO2作为硫源的固态形成。在每种情况下，都容易形成OCS。生产效率遵循的趋势CO > CO2和H2S > SO2分别作为C，O-和S-源。在水为主的冰，OCS生产似乎是增强CO：H2S反应物。OCS的形成机制似乎是CO与游离S原子的反应，所述游离S原子由硫母体物种的断裂产生。虽然OCS很容易通过辐照形成，但它也最容易在持续暴露时被破坏。在以H2O为主的冰中，H2S、SO2和OCS的半衰期约为2 eV分子−1，相当于在宇宙射线质子处理的寒冷稠密星际云环境中约700万年。OCS的ν3波段的光谱轮廓高度依赖于温度和冰的成分，并随着辐射处理而变化。这些效应可以用于星际红外光谱的理论建模;加热到50 K的H2O：CO：H2S辐射光谱与W33 A光谱中2040 cm−1的特征非常吻合。在CO2占主导地位的冰OCS的识别提供了进一步的挑战，由于重叠的OCS频带与从照射的主机冰形成的CO 3。这两个特征可以通过曲线拟合过程来解开。2040 cm−1波段的宽度将帮助观测者确定富含CO2的冰的特征是由于OCS还是CO 3。
Extensive experimental studies have been performed on the solid-state formation of the OCS molecule in proton-irradiated water-free and water-dominated ices containing CO or CO2 as the carbon source and H2S or SO2 as the sulfur source. In each case OCS is readily formed. Production efficiency follows the trends CO > CO2 and H2S > SO2 as C,O- and S-sources, respectively. In water-dominated ices, OCS production appears to be enhanced for CO : H2S reactants. The mechanism of formation of OCS appears to be the reaction of CO with free S atoms produced by fragmentation of the sulfur parent species. While OCS is readily formed by irradiation, it is also the most easily destroyed on continued exposure. In H2O-dominated ices the half-life of H2S, SO2, and OCS is ~2 eV molecule−1, corresponding to ~7 million years in a cold dense interstellar cloud environment processed by cosmic-ray protons. The spectral profile of the ν3 band of OCS is highly dependent on temperature and ice composition, and changes with radiation processing. These effects can be used in theoretical modeling of interstellar infrared (IR) spectra; a laboratory spectrum of irradiated H2O : CO : H2S, warmed to 50 K, provides a good fit to the 2040 cm−1 feature in the W33A spectrum. The identification of OCS in CO2-dominated ices provides a further challenge, due to the overlap of the OCS band with that of CO3 formed from irradiation of the host ice. The two features can be unraveled by a curve-fitting procedure. It is the width of the 2040 cm−1 band that will help observers determine if features identified in CO2-rich ices are due to OCS or to CO3.