CO 2 Raman thermometer improvement: Comparing hot band and Stokes and anti‐Stokes Raman scattering thermometers

CO 2 fluid inclusions are popular in the mantle‐derived rock. CO 2 Raman densimeter is widely used for estimating depth provenance and magma plumbing system. However, in order to obtain precise CO 2 density, we should also measure CO 2 temperature simultaneously because the densimeter has temperature dependency. In this study, we measured CO 2 Raman spectra with densities of 0.8–1.0 g/cm 3 at temperatures of 15, 25, 35, 45, and 55°C using a high‐pressure optical cell. We propose a new equation relating hot bands to the Fermi diad intensity ratio, temperature, and distance between the Fermi diad (delta, cm −1 ), which has higher accuracy than those of previous studies (±3.9–4.7°C) across all measurement conditions. The change in temperature engenders thermal expansion or shrinkage of mineral, resulting in change in CO 2 density of fluid inclusion. Simultaneous measurement of both density and temperature of CO 2 will be a probe for elastic property of minerals.