Precision evaluation of nitrogen isotope ratios by Raman spectrometry

Precision evaluation of Raman densimetry for carbon dioxide: improvement by correction for the drift effect

To evaluate the precision of the wavenumber difference between the two main Raman bands of C O 2 (designated as Δ, an index of C O 2 density), we performed theoretical calculations for the uncertainties of the peak positions of the C O 2 Raman bands, and measured Raman spectra of C O 2 under the conditions used for the calculations. The Δ precision improves with increased peak intensity, but the peak intensity-precision relation does not hold beyond an intensity threshold corresponding to the measurement time of 1-2 min. Correction for temporal variation of Δ by fitting a linear function to the data distribution improved the Δ precision to ±0.0005c m -1 at best, corresponding to C O 2 density precision as ±0.00015g/c m 3.