ELECTRIC-FIELD EFFECTS ON PROTON MAGNETIC SHIELDING IN SOME BINARY HYDRIDES

The coefficients which determine the electric field dependence of the mean proton shielding to second order in the field have been calculated by a finite field method at the SCF level for the binary hydrides CH4, NH3, H2O, HF, SiH4, PH3, H2S and HCl. The paramagnetic parts of the coefficients are considerably smaller in magnitude than those found previously for the coefficients for C-13, N-14, O-17 and F-19 shielding. As before, however, the largest paramagnetic terms occur when the electric and magnetic fields are perpendicular. The calculations show that some early experimental values of the coefficients were erroneous due probably to approximations in the rather crude models with which experimental data were interpreted.