Quadrupole-inner electrical field gradient interaction

If the nucleus feels both a magnetic field and an electric field gradient, and the electric quadrupole interaction is small, then the excited levels shift as indicated in Fig. 10.20e. The result is that only the inner four lines of the sextet are equidistant. This type of spectrum is measured from bulk Fe2C>3, with a magnetic hyperfine field of 51.5 T and a small quadrupole shift on the absorption peaks of 0.10 mm/s. 

Energy shift and magnetic splitting of the / = 1/2 and / = 3/2 levels in the presence of an electric field gradient with rj = 0, and the corresponding Mossbauer spectrum (14 > 0). Note that due to quadrupole interaction, the symmetry center of the outmost peaks is shifted relative to the inner four peaks in contrast to Fig. 25.10... 

The nuclear electric quadrupole moment may also interact with the electric field gradient arising from the non-spherical distribution of the 4f electrons when the lanthanide ion is situated in a solid. The general form of the quadrupole interaction has been given in section 1.3.2. The principal value of the field gradient tensor, due to the 4f electrons is given by (18.73) in section 2.1.1.2, and as indicated there in (18.72) should be multiplied by the Sternheimer shielding factor (I-Rq) to take account of the distortion of the inner closed shells of the lanthanide ion by the open 4f shell. Other contributions to the total... 

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