Pressure and temperature dependence of H-atom tunneling in the Debye approximation. Barrier preparation and media reorganization.

In the frame of the radiationless transitions modified theory, the analytical expression of a rate constant of the chemical reaction with an atom tunneling is found for the case of a continuous spectrum of a phonon subsystem. Two mechanisms of temperature dependence of a rate constant are taken into account, the oscillations of the potential barrier of the reaction at the intermolecular vibrations and media reorganization. The simple expressions for temperature and pressure dependencies of a rate constant are obtained in the special case of lattice motion-the Debye model. The well-known Marcus expression for the rate constant of an electron transfer in the Debye phonon spectrum is deduced first. The pressure dependence of the reorganization energy of the media is derived. Comparison of the theoretical results with the literature experimental data on H-atom tunneling in the fluorene-acridine crystal, taking into account four promotive modes (translational, librational, and two low-frequency intramolecular modes at 95 and 238 cm(-1)) and the frequency dependence of the Grueneisen parameter, is fulfilled. Good agreement of the theory and experiments is observed.