Nuclear quadrupole shielding factors for trivalent rare earth ions

Abstract

The Sternheimer R factor, which takes account of the distortion of closed shells of electrons by the nuclear quadrupole moment and the consequent modification of the field gradient produced by the 4f electrons at the nuclear site, has been estimated theoretically for Pr3+ and Tm3+ ions. Both angular and radial excitations of the various closed orbitals have been calculated by numerical solution of corresponding first-order Schrodinger equations. The magnitudes of R factors for Pr3+ and Tm3+ ions come out as 0 20 and 0.15 respectively and the sign is positive for both indicating shielding rather than anti-shielding of the 4f field gradients. This magnitude for the Tm3+ ion is in good agreement with the semi-experimental value of 0 11 obtained by Barnes, Mossbauer, Kankeleit and Poindexter for Tm3+ in thulium ethyl sulphate from quadrupole splitting of Mossbauer lines. The possibility of change in the value of the R factor for rare earth ions due to covalent bonding is also pointed out.