Changes in the infra-red spectra of molecules due to physical adsorption
Changes in the infra-red spectra of molecules due to physical adsorption
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由于物理吸附而导致分子红外光谱的变化
DOI：
10.1098/rspa.1956.0204
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发表时间：
1956
期刊：
影响因子：
--
通讯作者：
D. Yates
中科院分区：
文献类型：
--
作者：
N. Sheppard;D. Yates
本文研究了甲烷、乙烯、乙炔和氢分子在多孔石英玻璃上物理吸附的红外光谱。在所有情况下，当θ值远小于1时，很容易获得吸收带;对于甲烷，可以获得低至θ = 0.01的光谱。吸附时发生位移的吸收带中观察到的气相和吸附状态。在几种情况下，额外的频带发生在光谱的吸附分子，对应于已知的基本振动频率，禁止在气相中，因为分子的对称性。它们的出现直接是由于表面力使分子的对称性发生了畸变。用衍射光栅光谱仪获得的吸附甲烷和氢的高分辨率光谱，使频带的形状被准确地确定。虽然没有精细结构线，由于分子旋转可以解决，甲烷的广泛和不对称的v3带的整体形状可以解释作为一个理论模型的自由旋转的分子围绕一个单一的轴垂直于表面。带的形状是不一致的三维自由旋转轴平行以及垂直于表面。然而，它也可以用半宽为28 cm-1的洛伦兹曲线拟合，对应于没有旋转贡献的宽振动带，加上3050 cm-1附近的额外泛音吸收带。吸附的甲烷和氢的其他带的形状是不敏感的假设的自由或高度限制的表面上的旋转。通过比较强电场中吸附氢与气态氢的吸收带强度（Crawford & Dagg 1953），可以估算出玻璃表面的静电场。
Infra-red spectra of the molecules methane, ethylene, acetylene and hydrogen, physically adsorbed on porous silica glass have been studied at measured surface coverages, θ. In all cases absorption bands were readily obtained for θ values considerably less than unity; for methane it was possible to obtain spectra down to θ = 0.01. Shifts occurred on adsorption for the absorption bands that were observed in the gas phase and in the adsorbed state. In several cases additional bands occurred in the spectra of the adsorbed molecules which correspond to known fundamental vibration frequencies that are forbidden in the gas phase because of molecular symmetry. Their appearance results directly from the distortion of the symmetry of the molecules by surface forces. High-resolution spectra of adsorbed methane and hydrogen obtained with a diffraction grating spectrometer enabled the shapes of the bands to be accurately determined. Although no fine-structure lines due to molecular rotation could be resolved, the overall shape of the broad and asymmetrical v3 band of methane could be explained by using as a theoretical model free rotation of the molecule about a single axis normal to the surface. The band shape is not consistent with a three-dimensional free rotation about axes parallel as well as perpendicular to the surface. It could, however, alternatively be fitted by a Lorentz curve of half-width 28 cm-1, corresponding to a broad vibration band without rotational contribution, plus an extra overtone absorption band near 3050 cm-1. The shapes of the other bands of adsorbed methane and hydrogen are insensitive to the assumptions of free or highly restricted rotation on the surface. A comparison of the intensity of the absorption band due to adsorbed hydrogen with that of gaseous hydrogen in a strong electrical field (Crawford & Dagg 1953) has enabled an estimate to be made of the electrostatic field at the surface of the glass.