High resolution measurements of 14N, D quadrupole coupling in CH3CN and CD3CN

A molecular beam maser spectrometer was used to measure hyperfine structure on the J=1→ 0 rotational transitions in CH3CN and CD3CN. Measured nitrogen quadrupole coupling strengths are 1eqaaQ(N)=−4224.4 ± 1.5 kHz for CH3CN and eqaaQ(N)=−4229.3 ± 1.5 kHz for CD3CN. The deuterium quadrupole coupling strength along the C–D bond direction is eqzzQ(D)=167.5 ± 4.0 kHz Nitrogen quadrupole coupling is discussed in relation to the electronic structure. Spin‐rotation interaction strengths are reported. A convenient method for calculating matrix elements for hyperfine interactions in an arbitrary coupling scheme is presented.