Line strength measurements and relative isotopic ratio 13C/12C measurements in carbon dioxide using cavity ring down spectroscopy

- Cavity ring down spectroscopy was used for line intensity measurements in CO2.
- Line strength values for 12CO2 and 13CO2 lines were determined with 0.5% accuracy.
- Voigt and Galatry profiles were used during the line shape analysis.
- Results of relative isotopic ratio 13C/12C measurements in CO2 are presented.

Accurate intensity measurements were performed for several lines of the two main isotopologues of carbon dioxide, using cavity ring down spectroscopy. Absorption spectra of the R52e line at 6112.8902 cm-1 (30014←00001 band) of 12CO2 and the P6e line at 6114.8580 cm−1 (30013←00001 band) of 13CO2 were recorded at pressures between 15 and 50 mbar at 298 K. Line shape analysis shows that Galatry profile, taking into account Dicke narrowing of spectral lines, better describes the measured spectra at all pressures than the Voigt profile. The values of Dicke narrowing parameter for both lines were found to be significantly smaller than those predicted based on the mass diffusion constant. The values of the line strength for R52e line of 12CO2 and P6e line of 13CO2 were determined with an uncertainty of 0.5%. These values were found to be in good agreement with the corresponding data available in literature, in particular with the most recent ab initio calculations. The results of relative isotopic ratio 13CO2/12CO2 measurements are also presented in pure carbon dioxide samples and in 400 µmol/mol carbon dioxide in air samples, using cavity ring down spectroscopy.