Abstract
In the last few years tunneling transitions have been observed for the highly symmetric groups CH4, CD4, NH +4 , and CH3 rotating in various environments. Typically the tunneling lines shift to lower energies with increasing temperatures. In this paper the shift of the tunneling energy is calculated in a microscopic approach to the problem. The coupling of the rotating groups to the lattice modes is studied in two stages. First the rotating group is coupled to a single oscillator, then to the modes of a Debye crystal. The first calculation leads to a set of discrete tunneling lines with an energy that diminishes as the oscillator is excited into higher levels. The second approach yields a single tunneling line shifted down-wards with increasing phonon population. The shiftΔ ω is proportional toT 4. The calculation explains the energy shift of the tunneling lines with reasonable values for the coupling parameters. In some cases also a broadening has been observed which does not follow from our calculations.
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Hüller, A. The temperature dependence of rotational tunneling. Z Physik B 36, 215–225 (1980). https://doi.org/10.1007/BF01325285
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DOI: https://doi.org/10.1007/BF01325285