Nuclear Quadrupole Hyperfine Structure and Methyl Torsional Fine Structure in the Rotational Spectra of N,N-Dimethylformamide and N-Nitrosodimethylamine

Abstract

The complicated nuclear quadrupole hyperfine structure and methyl torsional fine structure in the rotational spectra of N,N-dimethylformamide and N-nitrosodimethylamine have been studied using microwave Fourier transform spectroscopy. It has been found that both molecules are rather similar in terms of their parameters of methyl group internal rotation as well as in terms of their amino nitrogen quadrupole coupling constants.

Reinvestigation of the Microwave Spectrum of Acetamide

“…) has long been of spectroscopic interest as a methyl-top molecule with a very low threefold barrier and an equilibrium structure in which all of its atoms except for two of the methyl hydrogens lie in the same plane (1)(2)(3)(4)(5). Acetamide is also of interest because of the importance of the -C(==O)-NH-linkage in polypeptides.…”

“…The data set treated here includes: (i) microwave measurements from Toyama University (4), where Stark effect measurements were carried out to verify assignments, but hyperfine splittings were not treated explicitly; (ii) Fourier transform microwave measurements from Kiel (5), where hyperfine effects were treated theoretically to generate hypothetical hyperfinefree transition frequencies; and (iii) new Fourier transform and new millimeter-wave measurements from NIST, which were again treated to give hyperfine-free torsion-rotation transition frequencies. The data set includes only rotational transitions within the lowest (v t = 0) torsional state, covering the rotational quantum number ranges 0 ≤ J ≤ 9 and 0 ≤ K a ≤ 7.…”

“…In this work we use neither the very common J K a,K c labeling scheme (8) nor the less common J τ labeling scheme (8) adopted in Refs. (3)(4)(5). As explained in Section 3, we use instead a new labeling scheme (9), which is designed to overcome some of the difficulties of the two older schemes.…”

“…Since hyperfine splittings can reach 1 MHz or more in this molecule, these measurements were assigned experimental uncertainties of 100 kHz in the fits. It was thus helpful to add the Heineking and Dreizler line centers determined after hyperfine interactions had been theoretically removed (5). Remeasurement of most of the Kiel transitions at NIST suggested that assigning a 4-kHz standard uncertainty to both the Kiel and the NIST hypothetical line centers was appropriate, except for the 3 −1 3 −3 transition in Table 1 of Ref.…”

14N Quadrupole Relaxation of DMF and DMF-d7 in DMSO at Infinite Dilution

“…Although the quadrupole coupling constant of 14N in gaseous D M F was reported recently [7], that for DMF-d7 is not yet available. Thus the isotope effects on the quadrupole coupling constants is not exactly known.…”