Quantitative Approaches in Estimating Crystal Field Effects

Quantitative Approaches in Estimating Crystal Field Effects 

Of the two main parts A) and B) of crystal field effects, effect B, the influence of lattice dynamics on NQR, can be excluded, at least to a large extent, by an appropriate experimental method, that is, by determining the nuclear quadru- 

In case of NQR in ionic crystals, particularly in crystals with approximately spherical ions, the determination of the crystal field is discussed above. For molecular crystals very little work has been done. 

Bersohn 76) has calculated the crystal field created by the molecular dipoles in the lattice of CH3C1. The static dipole moment of the molecules induces through the polarizability of the molecules an additional dipole moment which increases the dipole moment of the free molecule by a factor of about 1.05. This in turn means that the C—Cl bond has increased in ionic character under the influence of the intermolecular electric fields and therefore (see Eq. (II.9 the quadrupole coupling constant will be lower relative to the gaseous state. Besides the dipole moment induced in the direction of the static dipole, a perpendicular partial moment should be induced, too. Therefore the axial symmetry of the C—Cl bond will be disturbed and the asymmetry parameter 77 may become unequal zero. A small asymmetry parameter 17 = 0.028 has been observed for the nuclear quadrupole interaction in solid CH3I. Bersohn also calculated from the known crystal structure of 1,3,5-trichlorobenzene the induced 

For an absolute agreement between the observed and calculated crystal field effects in such dipolar crystal lattices, the zero point vibrations have to be considered, as Bersohn pointed out. Furthermore, we think that the part of the solid state shift is due to the contribution of the quadrupole polarization (antishielding factor). The inner shell electrons of the atom considered experience an induced quadrupole moment under the influence of the external fields. This 

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