J=1→2 transitions near 36.8 GHz in CH3CN and CH3 13CN were measured using a beam maser spectrometer. K=1 transitions were observed with a 10 kHz linewidth (FWHM) and K=0 transitions were observable with a two-cavity Ramsey system with about 3 kHz resolution. The measured difference between a axis and c axis nitrogen spin-rotation tensor components is Ca-Cc=4.6±1.0 kHz for CH3CN and 4.5±1.0 kHz for CH3 13CN. The c axis nitrogen spin-rotation tensor component is Cc=2.0±0.4 kHz. Nitrogen chemical shift tensor components of σa=247 ppm and σc=-165 ppm are obtained from the data and calculated diamagnetic contributions. The measured paramagnetic contributions to the nitrogen chemical shift tensor are σap=-98±15 ppm and σcp=-600±120 ppm. Nitrogen quadrupole coupling strength is eqQ=-4224.3±4.0 kHz and rotational transition frequencies are: 36 795 476.9±3.0 kHz (CH3CN, K=0), 36 794 769.3±1.5 kHz (CH3CN, K=1), 36 777 282.6±3.4 kHz (CH3 13CN, K=0), and 36 776 573.3±1.6 kHz (CH3 13CN, K=1). This data, combined with previous J=0→1 data yields accurate rotation and distortion constants for CH 3CN and CH3 13CN as follows: CH3CN CH313CN B 9 198 899.3±1.0 9 194 347.1±0.7 KHz DJ 3.7±0.3 3.3±0.3 KHz DJK 176.9±1.0 177.3±0.7 KHz.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry