ELECTRON PARAMAGNETIC RESONANCE OF NPO22+ IN CS2UO2CL4 AND CSUO2(NO3)3

The EPR spectra of NpO22+ in Cs2UO2Cl4 and CsUO2(NO3)3 have been observed at liquid-helium temperature. The Np6+ in its host crystals has been assumed to have an axial symmetry due to the strong NpO22+ complex. The resonances have been identified and fitted with the axial spin Hamiltonian H=gIIβHzSz+g β(HzSz+HySy)+AIzSz+B(IxSx+IySy)+P[I-13I(I+1)] For NpO22+ in Cs2UO2Cl4, the parameters are g=1.32±0.02, |A|=0.009±0.005 cm-1, gII=1.3±0.3, P=-0.016±0.005 cm-1, and B=0.0880±0.005 cm-1; for NpO22+ in CsUO2(NO3)3 they are gII=3.36±0.04, A=0.166±0.003 cm-1, g=0.20±0.20, P=-0.030±0.003 cm-1, and |B|=0.20±0.20 cm-1. The nuclear moment of Np237 has been calculated as 2.1μB and 2.9μB for Np6+ in Cs2UO2Cl4 and CsUO2(NO3)3, respectively. © 1969 The American Physical Society.