ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The stochastic classical trajectory method is used to calculate the energy relaxation of a highly excited diatomic rotor trapped in rare gas crystal at T=20 K. The friction kernels, which appear in the generalized Langevin equations characterizing the motions of the molecule and of nearest neighbor crystal atoms, are expressed in terms of the interaction potentials. The influence of the surrounding crystal on the relaxation mechanism and the efficiency of the various dissipation channels are analyzed by changing the rare gas species and by artificially switching off some channels. Within the limits of the model (classical two-dimensional rotation of the diatomic molecule, coupled on the one hand to a restricted number of first shell atoms themselves coupled to the bulk crystal and on the other hand to the other first shell atoms considered as pertaining to the bath), the results of the calculations show that, in the present case, rotational relaxation is a rapid process, over the picosecond scale, and that the local mode connected to the motions of the molecular center of mass plays a major role in the mechanism. This local mode is responsible, at short times t≤0.5 ps, for the relaxation of 95%, 75%, and 60% of the rotational energy excess in Ar, Kr, and Xe crystals, respectively.The remaining energy is then dissipated over longer times via the local mode or directly towards the crystal modes. A striking energy saturation phenomenon of the local mode is exhibited in xenon crystal.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.456752
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