Relaxation processes in molecular crystals. Temperature dependence of the bandwidth of Raman active lattice phonons of crystalline CO2

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Abstract
We have measured the bandwidth of the three Raman active lattice phonons of crystalline CO2 as a function of temperature in the range 6–130 K. For bandwidths narrower than 1 cm−1 we used a high resolution tandem interferometer–spectrometer instrument and for broader bands a standard Raman instrument. We found that our measurements, made at constant pressure, differ considerably from those obtained previously by other authors at constant volume. These differences are explained as due to the deconvolution procedure utilized for the constant volume measurements. The evolution with temperature of the phonon bandwidth shows that fourth‐order processes play a significant role in the phonon relaxation.