Methyl andterthyphen;butyl reorientation and distributions of activation energies in molecular solids. A nuclear spinhyphen;relaxation study in 2,4hyphen; and 2,5hyphen;dihyphen;terthyphen;butylhydroxybenzene

摘要

We have measured proton Zeeman relaxation ratesRin the 2,4hyphen; and 2,5hyphen;isomers of dihyphen;terthyphen;butylhydroxybenzene (DTHB) in the solid state.Rwas measured as a function of temperatureTat proton Larmor frequencies of ohgr;/2pgr;=8.50, 22.5, and 53.0 MHz. TheTranges were from 78 K to just below the melting points of 2,4hyphen; and 2,5hyphen;DTHB, 385 and 323 K, respectively. The 2,5hyphen;DTHBRvsTand ohgr; can be interpreted qualitatively in terms of three Bloembergenndash;Purcellndash;Pound (BPP) spectral densities, one for each of the three types of rotors in the molecule. The quantitative agreement is poor but a good fit is obtained using either a Davidsonndash;Cole (DC) or Frouml;lich spectral density, still preserving the three rotor types. The implications of this are discussed. The BPP and DC spectral densities fail completely in interpretingRvsTand ohgr; for 2,4hyphen;DTHB whereas good quantitative fits are obtained using a Frouml;lich spectral density. The distributions of activation energies characterizing the three rotor types are so wide for the Frouml;lich spectral density fit of the 2,4hyphen;DTHB data that the individual rotor types lose their identity.