通过红外光谱与量子化学建模的结合揭示HCN与宇宙硅酸盐之间的界面化学
Unraveling the Interface Chemistry between HCN and Cosmic Silicates by the Interplay of Infrared Spectroscopy and Quantum Chemical Modeling
AI总结：
本研究结合低温红外光谱与周期性DFT模拟，表征了HCN在宇宙硅酸盐镁橄榄石不同晶面的吸附特征，通过非线性拟合解卷积光谱并推断样品形貌，为无机表面吸附物红外光谱表征提供通用方法。
摘要：
理解氰化氢（HCN）与硅酸盐表面的相互作用，对于阐明星际颗粒核心以及彗星和陨石基质中发生的益生元过程至关重要。本研究结合低温（100-150 K）实验红外光谱与周期性DFT（密度泛函理论）模拟，表征了HCN在结晶镁橄榄石（Mg₂SiO₄，宇宙中丰度最高的硅酸盐之一）表面的吸附特征。结果表明，随着所研究的镁橄榄石晶面的不同，HCN的分子吸附络合物与解离吸附络合物共存。分子吸附在最稳定的表面上占主导，而解离吸附主要发生在稳定性较低的表面上，这一过程由表面暴露的Mg²⁺-O²⁻离子对增强的路易斯酸碱行为所催化。针对所有吸附情况，研究开展了谐振频率计算，并与实验红外谱带进行了对比。为厘清构成实验宽谱带的各振动模式，研究在预测频率集与实验谱带之间进行了最优非线性拟合。该流程的结果使我们能够：i）通过将计算得到的简正振动模式归属到各谱带的主要特征，对实验红外光谱进行解卷积；ii）揭示哪些晶面对吸附质振动谱带的贡献最大，从而提供样品形貌相关信息。本研究提出的这一直接流程具有很强的普适性，对复杂无机材料表面吸附物红外光谱的精细表征具有广泛参考价值。
英文摘要：
Understanding the interaction between hydrogen cyanide (HCN) and silicate surfaces is crucial for elucidating the prebiotic processes occurring on interstellar grain cores, as well as in cometary and meteoritic matrices. In this study, we characterized the adsorption features of HCN on crystalline forsterite (Mg2SiO4) surfaces, one of the most abundant cosmic silicates, by combining experimental infrared spectra at low temperatures (100-150 K) with periodic DFT simulations. Results showed the coexistence of both molecular and dissociative HCN adsorption complexes as a function of the considered forsterite crystalline face. Molecular adsorptions dominate on the most stable surfaces, while dissociative adsorptions occur predominantly on surfaces of lower stability, catalyzed by the enhanced Lewis acid-base behavior of surface-exposed Mg2+-O2- ion pairs. On the whole set of adsorption cases, harmonic frequency calculations were carried out and compared with the experimental infrared bands. To disentangle each vibrational mode contributing to the experimental broad bands, we run a best non-linear fit between the predicted set of frequencies and the experimental bands. The outcome of this procedure allowed us to: i) deconvolute the experimental IR spectrum by assigning computed normal modes of vibrations to the main features of each band; ii) reveal which crystal faces are responsible of the largest contribution to the adsorbate vibrational bands, giving information about the morphology of the samples. The present straigthforward procedure is quite general and of broad interest in the fine characterization of the infrared spectra of adsorbates on complex inorganic material surfaces.
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