Evidence of indirect spin–spin coupling in crystalline and glassy As–chalcogen compounds

Abstract Nuclear quadrupole resonance (NQR) studies on crystalline and glassy As–S/Se compounds reveal that the spin echo intensities as a function of pulse separation in the Hahn echo sequence exhibit oscillations superimposed on an exponential decay, given by the spin–spin relaxation time, T2. We have conducted systematic investigations of the nature of these T2 oscillations in glassy and crystalline As2S3 and As2Se3. T2 oscillations in c-As2S3 at 71.94 MHz are of the order of a kHz. T2 oscillations were also observed in glassy As2S3 and As2Se3. We will present calculations of indirect spin coupling between inequivalent As atoms to explain the nature of the T2 oscillations in glassy and crystalline As2S3 and As2Se3.