Abstract
The relaxation times of vibrational excitons in KClO 4 have been measured between 10 and 240 K by picosecond time-resolved CARS spectroscopy. The low temperature data are consistent with energy decay mechanisms based on three-phonon scattering processes. At higher temperature the linewidth of the symmetric stretching ν 1 has a well defined linear dependence on T, showing that three-phonon scattering is still the main relaxation mechanism. In contrast, the ν 2 bending mode has a marked T 2 dependence, showing that four-phonon and higher-order depopulation and dephasing mechanisms control the overall relaxation rate. Finally, the strong temperature dependence of the linewidth of the 2ν 2 overtone is interpreted in terms of the relaxation of an undispersed, quasi-free two-phonon state.
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