Carbon monoxide (CO) is the second most abundant gas-phase molecule after molecular hydrogen (H₂) of the interstellar medium (ISM). In molecular clouds, an important component of the ISM, it adsorbs at the surface of core grains, usually made of Mg/Fe silicates, and originates complex organic molecules through the catalytic power of active sites at the grain surfaces. To understand the atomistic, energetic, and spectroscopic details of the CO adsorption on core grains, we resorted to density functional theory based on the hybrid B3LYP-D* functional inclusive of dispersion contribution. We modeled the complexity of interstellar silicate grains by studying adsorption events on a large set of infinite extended surfaces cut out from the bulk Mg₂SiO₄ forsterite, the Mg end-member of olivines (Mg_2xFe_2–2xSiO₄), also a very common mineral on the Earth’s crust. Energetic and structural features indicate that CO is exclusively physisorbed with binding energy values in the 23–68 kJ mol^–1 range. Detailed analysis of data revealed that dispersive interactions are relevant together with the important electrostatic contribution due to the quadrupolar nature of the CO molecule. We performed a full thermodynamic treatment of the CO adsorption at the very low temperature typical of the ISM as well as a full spectroscopic characterization of the CO stretching frequency, which we prove to be extremely sensitive to the local nature of the surface-active site of adsorption. We also performed a detailed kinetic analysis of CO desorption from the surface models at different temperatures characterizing the colder regions of the ISM. Our computed data could be incorporated in the various astrochemical models of interstellar grains developed so far and thus contribute to improve the description of the complex chemical network occurring at their surfaces.

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镁橄榄石表面作为星际核心粉尘颗粒的模型：一氧化碳吸附的计算研究

一氧化碳（CO）是星际介质（ISM）的氢分子（H ₂）之后第二高的气相分子。在分子云中，它是ISM的重要组成部分，它吸附在通常由Mg / Fe硅酸盐制成的核心晶粒表面上，并通过晶粒表面活性位点的催化作用产生复杂的有机分子。为了了解CO在核心颗粒上的吸附的原子，能级和光谱学细节，我们诉诸于基于杂散B3LYP-D *功能的含杂散贡献的密度泛函理论。我们通过研究从大量Mg ₂ SiO ₄切出的大量无限延伸表面上的吸附事件，对星际硅酸盐颗粒的复杂性进行了建模。镁橄榄石，橄榄石的Mg末端成员（Mg _{2 x} Fe _{2–2 x} SiO ₄），也是地壳上非常常见的矿物。能量和结构特征表明，CO仅以23–68 kJ mol ^–1的结合能值被物理吸附。范围。数据的详细分析表明，由于CO分子的四极性质，色散相互作用与重要的静电作用相关。我们对ISM典型的非常低的温度下的CO吸附进行了完整的热力学处理，并对CO的拉伸频率进行了全光谱表征，我们证明对CO的表面活性部位的局部性质极为敏感。吸附。我们还对ISM较冷区域在不同温度下从表面模型中解吸出的CO进行了详细的动力学分析。