14 N Nuclear quadrupole coupling and methyl internal rotation in the microwave spectrum of 2-methylpyrrole

• Published in: Molecular physics Vol. 118; no. 11; p. 1668572
• Main Authors: Nguyen, Thuy, Dindic, Christina, Stahl, Wolfgang, Nguyen, Ha Vinh Lam, Kleiner, Isabelle
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 02-06-2020
• Series: The 26th Colloquium on High-Resolution Molecular Spectroscopy
• Subjects: Chemical Sciences; or physical chemistry; Theoretical and; 2-methylpyrrole; nuclear hyperfine; microwave spectrum; internal rotation
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268976.2019.1668572

Using two molecular jet Fourier transform microwave spectrometers, the rotational spectrum of 2methylpyrrole was recorded in the frequency range from 2 to 40 GHz. From the torsional splittings due to the internal rotation of the methyl group a barrier height of 279.7183(26) cm −1 was deduced. Because of the 14 N nucleus, all lines show a quadrupole hyperfine structure. The microwave spectra were analyzed using the XIAM and BELGI-Cs-hyperfine codes. The XIAM code enabled us to reproduce the whole data set with a root-mean-square deviation of 5.6 kHz while the BELGI-Cshyperfine code could provide a better root-mean-square almost by a factor of 2 compared to that of XIAM. The experimental results were complemented by quantum chemical calculations. The values of the methyl torsional barrier and the 14 N nuclear quadrupole coupling constants are discussed and compared with other methyl substituted pyrroles as well as other aromatic five-membered rings.