Indirect (J) coupling of inequivalent 75As nuclei in crystalline and glassy As2Se3 and AS2S3

We present the results of nuclear quadrupole resonance (NQR) measurements in crystalline and glassy As2Se3 and As2S3. As a function of pulse separation, the decays of the NQR Hahn echoes following a 90°–180° pulse sequence exhibit damped oscillations superimposed on an exponential decay. These damped oscillations can be explained by an indirect coupling (J coupling) between two As nuclei through the polarized electrons on the chalcogen atom. Experimental values of the J couplings were obtained from the periods of the oscillations and calculations of the most probable transitions using second-order perturbation theory. The value estimated by this method for the 2J(75As–S–75As) in crystalline As2S3 compares well with empirical estimates, which are obtained using an existing value of 2J(31P–S–31P) and known scalings with atomic number from the literature. Unfortunately, there is insufficient experimental data on 2J(X–Se–X) couplings to make any empirical estimate of 2J(75As–Se–75As).