Probing model interstellar grain surfaces with small molecules
Probing model interstellar grain surfaces with small molecules
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DOI：
10.1093/mnras/stv425
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发表时间：
2015-05-11
影响因子：
4.8
通讯作者：
McCoustra, M. R. S.
中科院分区：
文献类型：
--
作者：
Collings, M. P.;Frankland, V. L.;McCoustra, M. R. S.
程序升温脱附和反射-吸收红外光谱已被用来探索氧（O-2），氮（N-2），一氧化碳（CO）和水（H2O）与无定形二氧化硅薄膜的相互作用，作为演示的详细表征的硅酸盐表面，可能存在于星际介质。简单的双原子吸附物被发现润湿二氧化硅表面，并表现出一级脱附动力学的政权单层覆盖。除此之外，它们表现出零级动力学，如散装固体升华所预期的那样。相反，水不润湿二氧化硅表面，并且在与形成岛状结构一致的所有覆盖率下表现出零级解吸动力学。动力学参数用于天体物理建模获得的实验数据在亚单层覆盖和比较模型在多层制度。在亚单层制度的光谱研究表明，C-O伸缩模式是在约2137厘米（-1）（5.43 μ m），与线性表面CO相互作用一致的位置，并不均匀地扩大，从表面的异质性。这些研究还揭示了，第一次，直接的证据扩散的热激活，因此去湿，二氧化硅表面上的水。这些发现的天体物理意义可以解释致密星际云中缺少的氧气预算的一部分，并表明这些简单分子的亚单层吸附研究可能是更复杂的硅酸盐材料表面化学的有用探针。
Temperature-programmed desorption and reflection-absorption infrared spectroscopy have been used to explore the interaction of oxygen (O-2), nitrogen (N-2), carbon monoxide (CO) and water (H2O) with an amorphous silica film as a demonstration of the detailed characterization of the silicate surfaces that might be present in the interstellar medium. The simple diatomic adsorbates are found to wet the silica surface and exhibit first-order desorption kinetics in the regime up to monolayer coverage. Beyond that, they exhibit zero-order kinetics as might be expected for sublimation of bulk solids. Water, in contrast, does not wet the silica surface and exhibits zero-order desorption kinetics at all coverages consistent with the formation of an islanded structure. Kinetic parameters for use in astrophysical modelling were obtained by inversion of the experimental data at sub-monolayer coverages and by comparison with models in the multilayer regime. Spectroscopic studies in the sub-monolayer regime show that the C-O stretching mode is at around 2137 cm(-1) (5.43 mu m), a position consistent with a linear surface-CO interaction, and is inhomogenously broadened as resulting from the heterogeneity of the surface. These studies also reveal, for the first time, direct evidence for the thermal activation of diffusion, and hence de-wetting, of H2O on the silica surface. Astrophysical implications of these findings could account for a part of the missing oxygen budget in dense interstellar clouds, and suggest that studies of the sub-monolayer adsorption of these simple molecules might be a useful probe of surface chemistry on more complex silicate materials.