Raman spectral characteristics of 12CO2/13CO2 and quantitative measurements of carbon isotopic compositions from 50 to 450 °C and 50 to 400 bar

Yuzhou Ge; Lianfu Li; Shichuan Xi; Liang Ma; Zhendong Luan; Xin Zhang

doi:10.1016/j.saa.2023.122651

Raman spectral characteristics of ¹²CO₂/¹³CO₂ and quantitative measurements of carbon isotopic compositions from 50 to 450 °C and 50 to 400 bar

Spectrochim Acta A Mol Biomol Spectrosc. 2023 Aug 5:296:122651. doi: 10.1016/j.saa.2023.122651. Epub 2023 Mar 23.

Authors

Yuzhou Ge¹, Lianfu Li², Shichuan Xi², Liang Ma², Zhendong Luan¹, Xin Zhang³

Affiliations

¹ CAS Key Laboratory of Marine Geology and Environment & Center of Deep Sea Research, Institute of Oceanology, Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266061, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² CAS Key Laboratory of Marine Geology and Environment & Center of Deep Sea Research, Institute of Oceanology, Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China.
³ CAS Key Laboratory of Marine Geology and Environment & Center of Deep Sea Research, Institute of Oceanology, Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266061, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: xzhang@qdio.ac.cn.

PMID: 37060650
DOI: 10.1016/j.saa.2023.122651

Abstract

The carbon isotopic composition of CO₂ 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 CO₂. In this work, Raman spectra of high-purity ¹³CO₂, ¹²CO₂, and six ¹²CO₂-¹³CO₂ 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 ¹³CO₂ and ¹²CO₂ shift to lower wavenumbers with increasing temperature and decreasing pressure, but the peak positions of ¹³CO₂ show a larger shift. The peak position difference of the corresponding characteristic peaks between ¹³CO₂ and ¹²CO₂ is greater than 15 cm^-1 under the above temperatures and pressures, and the peaks can be distinguished. However, ν_-¹³ overlays ν_H.B.¹² near 1265 cm^-1, ν₊¹² overlaps ν_H.B.¹³ near 1288 cm^-1. The existence of ¹³CO₂ can cause a change in the Fermi diad splitting of ¹²CO₂ and affect the establishment of CO₂ Raman densimeters. The positive correlation obtained between the peak intensity ratio and the content ratio is affected by temperature, pressure, and ¹³CO₂ content. I₊¹³/I₊¹² and I_-¹³/I_-¹² were selected as the quantitative indices to establish Raman quantitative analysis models for the determination of the carbon isotopic composition of CO₂, which can be applied to in-situ measurements of high-temperature and high-pressure systems.

Keywords: Carbon dioxide; Carbon isotopic; In situ measurement; Quantitative analysis; Raman spectroscopy.