Accurate Determination of Absolute Raman Cross Sections of Carbon Dioxide Using H2 as a Reference

The accurate determination of Raman cross sections is challenging for multiple reasons, the major one being the incomplete intensity calibration of experimental setups. In this work, the absolute Raman cross sections of CO2, a molecule important in environmental science and chemical engineering, are determined to high accuracy. To achieve this, we utilized a Raman instrument calibrated for precise intensity measurements using the rotational bands of H2. Supported by rigorous quantum mechanical data on H2 and a careful analysis of uncertainties introduced by various experimental factors, we reduced the uncertainty in the determined cross sections for the Fermi doublet of CO2 to 6% (3σ), with the primary sources of experimental uncertainty stemming from the detectors' digitization error and thermal fluctuations. This report marks the most precise determination of Raman cross-section values to date, paving the way for improved quantitative Raman analysis of a wide range of samples and the retrieval of experimental transition polarizabilities for benchmarking ab initio methods.