Reinvestigation of the Fourier transform microwave spectrum of N-ethylacetamide: Pseudo a-type transitions

• Published in: Journal of molecular spectroscopy 2024-02, Vol.400, p.111871, Article 111871
• Main Authors: Kawashima, Yoshiyuki, Kuze, Nobuhiko, M. T. Yamada, Koichi, Hirota, Eizi
• Format: Article
• Language: English
• Subjects: Fourier transform microwave spectroscopy; N-ethylacetamide; Nitrogen nuclear quadrupole coupling constants; Potential barrier to CH3 internal rotation; Pseudo a-type transition
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/j.jms.2023.111871

[Display omitted] •Observation of ten pseudo a-type transitions and triplets due to the coupling with the internal rotation of the second methyl group.•Analysis of the observed transition frequencies.•Obtained barrier height V3(CH2-CH3) = 1078 (12) cm−1 using the splittings of the second methyl group.•Explanation for the abnormal intensities and the hyperfine structures of the E state using the wavefunctions. We observed ten pseudo a-type transitions in the E state of N-ethylacetamide (NEAA) using a Fourier transform microwave spectrometer. We found triplets caused by the coupling between the two methyl groups for the observed pseudo a-type transitions. Also, we succeeded in observing similar triplets for the 5 a-type Q-branch transitions, 20 b-type and 7 c-type transitions of the E state of NEAA. These observed triplets allowed us to determinate the potential barrier V3 to internal rotation of the ethyl-methyl group to be 1078 (12) cm−1. In addition, though the observed intensities of the c-type transitions in the A state were weak, the c-type transition in the E state were observed to be as intense as the b-type transitions of the E state. We explained in this paper the abnormal intensities of the c-type transitions and pseudo a-type transitions in the E state of NEAA.