Abstract Anomalous peaks were observed during attempts to measure micro-ATR infrared spectra of small domains (>30 μm) of the mineral apatite that were associated with coal particles in polished epoxy grain mounts. The peaks were sharp, variable in intensity, and appeared near the high wavenumber edge of the broad ν3 band of the phosphate. Similar effects were observed in single crystals of quartz, garnet and calcite. The manifestation of these peaks was associated with experimental factors that rendered a small gap between the ATR tip and the sample. They were assigned to surface phonon polaritons (SPhPs) owing to their explicit requirement of non-contact between sample and ATR objective, their position in relation to the longitudinal optic limit of the reststrahlen bands of the crystalline materials, and their wavenumber dependence on the refractive index of the intermediating dielectric, as predicted by SPhP theory. In this paper we establish three conditions under which SPhPs can be accidentally or unintentionally excited: when the IR beam of the microscope is not well aligned; when optical contact between the mineral and ATR objective is poor; and when the surface of the sample is not normal to the optical axis of the microscope. The object of this paper was not to study SPhPs as such, but to raise awareness amongst FT-IR ATR practitioners that SPhP peaks can interfere if their experimental conditions are less than ideal, particularly in the case of polished geological sections and minerals.

中文翻译：

---

地质样品的 ATR-FTIR 光谱中表面声子极化子的无意激发

摘要 在尝试测量与抛光环氧树脂颗粒支架中的煤颗粒相关的矿物磷灰石的小区域 (>30 μm) 的微 ATR 红外光谱期间观察到异常峰。峰很尖锐，强度可变，并出现在磷酸盐宽 ν3 带的高波数边缘附近。在石英、石榴石和方解石的单晶中观察到类似的效果。这些峰的表现与在 ATR 尖端和样品之间呈现小间隙的实验因素有关。由于它们明确要求样品和 ATR 物镜之间不接触，它们相对于晶体材料的剩余光谱带的纵向光学极限的位置，它们被分配给表面声子极化子 (SPhP)，正如 SPhP 理论所预测的那样，它们的波数依赖于中间电介质的折射率。在本文中，我们建立了 SPhP 可能被意外或无意激发的三个条件：当显微镜的红外光束没有很好地对准时；当矿物和 ATR 物镜之间的光学接触不良时；当样品表面与显微镜光轴不垂直时。本文的目的不是研究 SPhP，而是提高 FT-IR ATR 从业者的意识，即如果实验条件不理想，SPhP 峰会干扰，特别是在抛光地质剖面和矿物的情况下。在本文中，我们建立了 SPhP 可能被意外或无意激发的三个条件：当显微镜的红外光束没有很好地对准时；当矿物和 ATR 物镜之间的光学接触不良时；当样品表面与显微镜光轴不垂直时。本文的目的不是研究 SPhP，而是提高 FT-IR ATR 从业者的意识，即如果实验条件不理想，SPhP 峰会干扰，特别是在抛光地质剖面和矿物的情况下。在本文中，我们建立了 SPhP 可能被意外或无意激发的三个条件：当显微镜的红外光束没有很好地对准时；当矿物和 ATR 物镜之间的光学接触不良时；当样品表面与显微镜光轴不垂直时。本文的目的不是研究 SPhP，而是提高 FT-IR ATR 从业者的意识，即如果实验条件不理想，SPhP 峰会干扰，特别是在抛光地质剖面和矿物的情况下。