Beam maser spectroscopy onJ= 1thinsp;rarr;thinsp;2,K= 1, andK= 0 transitions in CH3CN and CH3thinsp;13CN

摘要

J= 1thinsp;rarr;thinsp;2 transitions near 36.8 GHz in CH3CN and CH3thinsp;13CN were measured using a beam maser spectrometer.K= 1 transitions were observed with a 10 kHz linewidth (FWHM) andK= 0 transitions were observable with a twohyphen;cavity Ramsey system with about 3 kHz resolution. The measured difference betweenaaxis andcaxis nitrogen spinndash;rotation tensor components isCandash;Cc= 4.6plusmn;1.0 kHz for CH3CN and 4.5plusmn;1.0 kHz for CH3thinsp;13CN. Thecaxis nitrogen spinndash;rotation tensor component isCc= 2.0plusmn;0.4 kHz. Nitrogen chemical shift tensor components of sgr;a= 247 ppm and sgr;c= minus;165 ppm are obtained from the data and calculated diamagnetic contributions. The measured paramagnetic contributions to the nitrogen chemical shift tensor are sgr;ap= minus;98plusmn;15 ppm and sgr;cp= minus;600plusmn;120 ppm. Nitrogen quadrupole coupling strength is eqQ = minus;4224.3plusmn;4.0 kHz and rotational transition frequencies are: 36thinsp;795thinsp;476.9plusmn;3.0 kHz (CH3CN,thinsp;K= 0), 36thinsp;794thinsp;769.3plusmn;1.5 kHz (CH3CN,thinsp;K= 1), 36thinsp;777thinsp;282.6plusmn;3.4 kHz (CH3thinsp;13CN,thinsp;K= 0), and 36thinsp;776thinsp;573.3plusmn;1.6 kHz (CH3thinsp;13CN,thinsp;K= 1). This data, combined with previousJ= 0thinsp;rarr;thinsp;1 data yields accurate rotation and distortion constants for CH3CN and CH3thinsp;13CN as follows: thinsp; thinsp; thinsp; thinsp;