High resolution Raman measurements of the temperature variation of the bandwidth of some lattice phonons and of one internal vibron of alpha-oxalic acid

Using a tandem interferometer-spectrometer system we measured the bandwidth as a function of temperature of three lattice phonons and one internal vibron of α-oxalic acid over a broad temperature range. The temperature evolution of the bandwidth of the lattice phonons is linear with T in the classical regime. This proves that only three-phonon decay processes are responsible for the relaxation. We have found that the experimental data are easily interpreted in terms of one down- and one up-conversion three-phonon process. The bandwidth of the internal vibron at 819 cm-1 however, shows a clear non-linear behavior as a function of temperature. The experimental data are correctly reproduced assuming that the overall relaxation has two contributions, one due to a three-phonon down-conversion processes and one caused by a four-phonon dephasing mechanism.