Intermolecular potential for Ar+NH3 from differential cross sections

¹H- {¹³C} and ¹H- {¹⁵N} heteronuclear double resonance experiments are used to determine the transition frequencies in the ¹³C and ¹⁵N N.M.R. spectra of isotopically entriched samples of methyl cyanide dissolved in the nematic mesophase of p-ethoxybenzylidene-p-butyl aniline. It is found that σ_∥ - σ_⊥ in the -C ≡ N group has values of 307 and 452 p.p.m. for ¹³C and ¹⁵N respectively, and these are rationalized in terms of Pople's LCAO theory of nuclear shielding.