Reliable Estimation of Wavenumbers for Calcite Peaks

ABSTRACT The Raman‐shift wavenumber ( ), which is calculated as the difference between the absolute wavenumbers of the excitation light and the Raman‐scattered light, is one of the most critical parameters in Raman spectroscopy. As the observed wavenumbers depend heavily on the spectrometer and measurement conditions, system calibration using a well‐characterised material is essential. In this study, we precisely determined the wavenumbers of calcite peaks—one of which is widely used to assess the spectral resolution of Raman spectrometers—and evaluated their associated uncertainties, using a He–Ne laser and Raman‐scattered light calibrated with Ne emission lines. We considered the following sources of uncertainty: the fitting and repeatability of the Ne emission lines and the Rayleigh/Raman‐scattered light; the wavenumber of the unstabilised He–Ne laser; and the pixel resolution. We also considered variations arising from differences among calcite grades and manufacturers, and changes in ambient temperature (15°C, 25°C and 35°C). The estimated wavenumbers for the five calcite peaks exhibited expanded uncertainties ranging from 1.1 to 1.2 cm −1 ( k = 2, coverage factor), which were confirmed using a 532‐nm diode‐pumped solid‐state (DPSS) laser. These values enable users to calibrate wavenumbers and assess spectral resolution simultaneously, and reagent‐grade calcite can also be used as a reference mineral for various research fields.