Andersson M P, Hem C P, Schultz L N, Nielsen J W, Pedersen C S, Sand K K, Okhrimenko D V, Johnsson A, Stipp S L S
J Phys Chem A. 2014 Nov 13;118(45):10720-9. doi: 10.1021/jp5053858. Epub 2014 Oct 30.
We have measured infrared spectra from several types of calcite: chalk, freshly cultured coccoliths produced by three species of algae, natural calcite (Iceland Spar), and two types of synthetic calcite. The most intense infrared band, the asymmetric carbonate stretch vibration, is clearly asymmetric for the coccoliths and the synthetic calcite prepared using the carbonation method. It can be very well fitted by two peaks: a narrow Lorenzian at lower frequency and a broader Gaussian at higher frequency. These two samples both have a high specific surface area. Density functional theory for bulk calcite and several calcite surface systems allows for assignment of the infrared bands. The two peaks that make up the asymmetric carbonate stretch band come from the bulk (narrow Lorenzian) and from a combination of two effects (broad Gaussian): the surface or near surface of calcite and line broadening from macroscopic dielectric effects. We detect water adsorbed on the high surface area synthetic calcite, which permits observation of the chemistry of thin liquid films on calcite using transmission infrared spectroscopy. The combination of infrared spectroscopy and density functional theory also allowed us to quantify the amount of polysaccharides associated with the coccoliths. The amount of polysaccharides left in chalk, demonstrated to be present in other work, is below the IR detection limit, which is 0.5% by mass.
白垩、由三种藻类新培养的颗石藻、天然方解石（冰洲石）以及两种合成方解石。最强的红外波段，即不对称碳酸根伸缩振动，对于颗石藻和采用碳酸化法制备的合成方解石而言明显不对称。它可以很好地由两个峰拟合：低频处的窄洛伦兹峰和高频处的宽高斯峰。这两个样品都具有高比表面积。针对块状方解石和几种方解石表面体系的密度泛函理论能够对红外波段进行归属。构成不对称碳酸根伸缩带的两个峰分别来自块状（窄洛伦兹峰）以及两种效应的组合（宽高斯峰）：方解石的表面或近表面以及宏观介电效应导致的谱线展宽。我们检测到高比表面积合成方解石上吸附的水，这使得利用透射红外光谱观察方解石上的薄液膜化学成为可能。红外光谱和密度泛函理论的结合还使我们能够量化与颗石藻相关的多糖量。在其他研究中已证明存在于白垩中的多糖量低于红外检测限，该检测限为质量的0.5%。
