SYMMETRY-SPECIES CONVERSION IN CD3 SYSTEMS

The rates for symmetry-species conversion of CD3 groups are calculated using a model in which the interaction between the quadrupolar moment of the deuterons with electric-field gradient at the site of the nucl eus causes symmetry-changing transitions. Just the same phonons are co nsidered for energy conservation as are used to describe the temperatu re dependence of inelastic neutron scattering experiments. For the con version rate, a similar temperature dependence is found as has already been obtained for CH3. For temperatures around the tunnelling energy, a behaviour is predicted for CD3 that is different from the behaviour in protonated systems according to all theories known to us. In compa rison with the corresponding protonated species embedded in the same s urroundings, the conversion rate at elevated temperatures turns out to be larger by orders of magnitude. Only the low-temperature conversion mte is suppressed owing to the lack of resonance phonons at the usual ly smaller tunnelling frequency in CD3. The relative increase of the c onversion rate with deuteration due to Raman processes is predicted to be independent of temperature but strongly dependent on the height of die orientational potential in the case of shallow potentials. If the tunnelling energy is smaller than 25 mueV, the conversion rates incre ase by a constant factor of approximately 10 compared to the protonate d species at a given temperature.