HYPERFINE AND LIGAND HYPERFINE (PERPENDICULAR) PARAMETERS OF CU2- A NEW ASSIGNMENT(NH4BR (BASIC) FROM EPR )

Ammonium bromide crystals doped with Cu2+ and grown in basic solution (pH similar or equal to 8) were studied at 300 K and 77 K with X-band EPR to elucidate divergent spin Hamiltonian parameters. Careful measur ements of the perpendicular part of the spectra indicated resolved 16 lines (300 K) and 19 lines (77 K). They were interpreted combining 4 h yperfine and 13 ligand (Br) hyperfine lines. We obtained A perpendicul ar to =(33 +/- 2) x 10(-4) cm(-1) (300 K) and A perpendicular to =(67 +/- 2) x 10(-4) cm(-1) (77 K). These values are not so different from the known values assigned to the analogous centre in NH4Cl and ND4Cl. The discrepancy reported is due to the difficulty in ascribing the Br hyperfine parameter now determined as A'perpendicular to = (47 +/- 3) x 10(-4) cm(-1) (300 and 77 K). Compared with that of CI compounds it is about five times greater, which is of the same order as the hyperfi ne interaction ratio for free Br and Cl atoms.