Raman spectral characteristics of CO/CO and quantitative measurements of carbon isotopic compositions from 50 to 450 °C and 50 to 400 bar.

The carbon isotopic composition of CO is traced to its different origins and widely used in the fields of geology, biology, and chemistry. Raman spectroscopy can be performed in situ, is nondestructive, and requires no sample preparation; these characteristics enable Raman spectroscopy to be considered a new alternative method to measure the carbon isotopic composition of CO. In this work, Raman spectra of high-purity CO, CO, and six CO-CO binary mixtures with known mixing ratios were collected using a High Pressure Optical Cell (HPOC) at 50-450 °C and 50-400 bar. The results showed that the characteristic peak positions of both CO and CO shift to lower wavenumbers with increasing temperature and decreasing pressure, but the peak positions of CO show a larger shift. The peak position difference of the corresponding characteristic peaks between CO and CO is greater than 15 cm under the above temperatures and pressures, and the peaks can be distinguished. However, ν overlays ν near 1265 cm, ν overlaps ν near 1288 cm. The existence of CO can cause a change in the Fermi diad splitting of CO and affect the establishment of CO Raman densimeters. The positive correlation obtained between the peak intensity ratio and the content ratio is affected by temperature, pressure, and CO content. I/I and I/I were selected as the quantitative indices to establish Raman quantitative analysis models for the determination of the carbon isotopic composition of CO, which can be applied to in-situ measurements of high-temperature and high-pressure systems.