| Popis: |
A newly developed optical technique gives direct access to the rate of nuclear spin conversion, i.e. the rate of relaxation between tunneling levels, for methyl groups in the solid state. In dimethyl-s-tetrazine (DMST) doped single crystals of durene, spin conversion times as long as 7.0×10 6 s (81 days) could be measured with an estimated error less than 25%. Study of the temperature dependence of the spin conversion rate shows that an Orbach type temperature law predominates down to 2 K, while existing theories predict Raman or direct processes to become predominant below 4 to 6 K. The assumptions of the theoretical predictions are questioned, based on the assignment of librational modes of the methyl group in the fluorescence spectra of protonated and perdeuterated DMST. |
