Temperature-dependent decay of vibrational excitons in K2SO4 crystal measured by picosecond time-resolved CARS

Year: 1988

Authors: Angeloni L., Righini R., Castellucci E., Foggi P., Califano S.

Autors Affiliation: Dipartimento di Chimica, Università di Firenze, 50121 Firenze, Italy

Abstract: The relaxation times of five totally symmetric Davydov components of the internal vibrations of the SO4 2- ion in a K2SO4 single crystal have been measured between 10 and 120 K by means of picosecond time-resolved CARS. In all cases a strictly exponential decay is observed. At 10 K v1 (983 cm-1) and v2 (447 cm-1) show decay time constants of 294 and 21 ps, respectively; all other vibrations relax with time constants less than (or equal to) the time resolution of the experimental apparatus (~9 ps). Such behavior is interpreted in terms of population relaxation. In fact, in contrast to the other vibrations considered, no three-phonon down-conversion decay pathway is available to v1 and v2. The temperature dependence of the inverse lifetimes of the two modes is consistent with three-phonon up-conversion processes involving high-frequency (>135 cm-1) lattice phonons. Two possible explanations are given for the large difference in the lifetimes of v1 and v2 at 10 K: (a) the different efficiency of the four-phonon decay mechanism and (b) the different contribution of the dephasing due to scattering of the internal phonons by the 34S isotopic impurities.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY

Volume: 92 (4)      Pages from: 983  to: 988

KeyWords: potassium sulfate
DOI: 10.1021/j100315a025

Citations: 27
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