Local vs global approaches to treat two equivalent methyl internal rotations and 14N nuclear quadrupole coupling of 2,5-dimethylpyrrole.
Thuy NguyenWolfgang StahlHa Vinh Lam NguyenIsabelle KleinerPublished in: The Journal of chemical physics (2021)
The microwave spectrum of 2,5-dimethylpyrrole was recorded using a molecular jet Fourier transform microwave spectrometer operating in the frequency range from 2 to 26.5 GHz. Only one stable conformer was observed as expected and confirmed by quantum chemical calculations carried out to complement the experimental analysis. The two equivalent methyl groups cause each rotational transition to split into four torsional species, which is combined with the quadrupole hyperfine splittings in the same order of magnitude arising from the 14N nucleus. This results in a complicated spectrum feature. The spectral assignment was done separately for each torsional species. Two global fits were carried out using the XIAM code and the BELGI-C2v-2Tops-hyperfine code, a modified version of the BELGI-C2v-2Tops code, giving satisfactory root-mean-square deviations. The potential barriers to internal rotation of the two methyl groups were determined to be V3 = 317.208(16) cm-1. The molecular parameters were obtained with high accuracy, providing all necessary ground state information for further investigations in higher frequency ranges and on excited torsional-vibrational states.
Keyphrases
- mass spectrometry
- liquid chromatography
- density functional theory
- molecular dynamics
- tandem mass spectrometry
- high performance liquid chromatography
- energy transfer
- molecular dynamics simulations
- gas chromatography
- simultaneous determination
- radiofrequency ablation
- machine learning
- optical coherence tomography
- high frequency
- single molecule
- healthcare
- health information
- psychometric properties
- genetic diversity
- magnetic resonance imaging
- room temperature