Comparison of activation energies with barriers to rotation for ammonium and borohydride compounds

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Abstract
The activation energy observed experimentally by the study of the temperature dependence of the spin–lattice relaxation time has been determined from the hindered rotational energy levels of NH4+, ND4+, and BH4− in a number of their compounds. There are usually two anharmonic levels above the top of the barrier to rotation. The activation energy corresponds to the energy difference between the ground harmonic level and the energy levels just above the highest anharmonic level. The activation energy determined from the hindered rotational energy levels are in good agreement with the observed values.