ELECTRON-SPIN-RESONANCE LINE-SHAPE STUDIES OF THE ASO4(4-) CENTER IN RBH2ASO4 AND RBD2ASO4

A quantitative study of the electron-spin-resonance (ESR) line shapes of the AsO44- center in RbH2AsO4 and RbD2AsO4 is presented. Analysis o f the spectra at various temperatures, using a theoretical model and e lectron-nuclear double resonance (ENDOR) obtained superhyperfine (shf) couplings, shows the existence of a single correlation time with whic h the rubidium and hydrogen shf interactions are modulated. Further an alysis of the ENDOR- and ESR-deduced shf couplings is shown to disallo w any large-amplitude relative motions between the heavy atoms and the H4AsO4 units. It is suggested that fluctuations in the nonsymmetric d istribution of the electron density are responsible for the observed E SR features in potassium dihydrogen phosphate-type systems.