Frozen-in disorder probed by electron spin relaxation

Here we demonstrate that two extreme cases of molecular packing, i.e. the crystalline and glassy state of solid ethanol, which define the complete experimental span of attainable host matrix frustration, can be efficiently probed by measuring the electron spin phase memory relaxation time, TM, of an incorporated TEMPO nitroxyl radical at X-band EPR frequency. The sensitivity of TM is based on the spectral and spin diffusion effects which reflect the spatial distribution of involved spins as a function of molecular frozen-in disorder. By keeping the excited region of the EPR spectrum fixed one can monitor the changes in the density of spin packets, upon the state transformation of the host. EPR experiments performed at 94 GHz show a clear difference in local distribution of paramagnetic centers in ethanol glass as compared to crystalline ethanol. The results support the idea that, by measuring TM and properties of density of spin packets, one can explore the extent of molecular disorder.