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 (designated as , an index of density), we performed theoretical calculations for the uncertainties of the peak positions of the Raman bands, and measured Raman spectra of under the conditions used for the calculations. The 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 by fitting a linear function to the data distribution improved the precision to ±0.0005 at best, corresponding to density precision as ±0.00015/ .