Electric field effects on the ¹³C and ¹⁹F nuclear shielding in HF and CH₃F

Abstract

In a uniform electric field changes take place in some or all of the tensor components of nuclear shielding. For small fields a Taylor series expansion of each component in terms of the field can be formulated. Coefficients of such expansions have been calculated for the ¹H and ¹⁹F nuclei of HF and the ¹³C and ¹⁹F nuclei of CH₃F. The calculations have been carried out at the SCF level with moderately large basis sets. The resulting coefficients (a) are the first ab initio results for the electric field dependence of carbon-13 shielding and (b) permit the first comparison of ab initio results for the electric field dependence of ¹⁹F shielding in two molecules. The ¹⁹F coefficients are found to be quite different for the two molecules—especially at quadratic level. The ¹³C coefficients are smaller than the ¹⁹F coefficients for the CH₃F molecule.