The Higher Torsional States Of Methylamine - Preliminary Analysis

Gulaczyk, Iwona

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https://hdl.handle.net/2142/116814 Copy

Description

Title

The Higher Torsional States Of Methylamine - Preliminary Analysis

Author(s)

Gulaczyk, Iwona

Contributor(s)

Kreglewski, Marek

Issue Date

2022-06-23

Keyword(s)

Mini-symposium: Benchmarking in Spectroscopy

Abstract

Methylamine is a molecule performing two strongly coupled large amplitude motions: \chem{CH_3} internal rotation and \chem{NH_2} inversion. The rovibrational spectrum of the methylamine molecule has been extensively studied both experimentally and theoretically. The analyses of infrared bands such as \chem{NH_2} inversion or CN stretching show significant perturbations from highly excited torsional states. In order to untangle the interactions in the 700-1200 \wn region of the methylamine spectrum, it is crucial to assign the perturbing excited torsional states (3\nub{15} and 4\nub{15}). Both states are located well above the top of the torsional barrier. Thus, the splittings between the lower and upper sublevels are very large (80 to 180 \wn) and only low lying sublevels of 3\nub{15} or 4\nub{15} will be experimentally identified. The spectra were recorded with a resolution of 0.00125 \wn using Bruker IFS-120HR spectrometer at the University of Oulu. The accurate energy levels of the first excited torsional state, \nub{15}, \footnote{I. Gulaczyk, M. Kreglewski, V-M. Horneman, J. Mol. Spectrosc. 342 (2017) 25-30} \footnote{I. Gulaczyk, M. Kreglewski, JQSRT 252 (2020) 107097} were used as reference values for lower state combination differences in the assignments of the third and fourth torsional hot bands, 3\nub{15}-\nub{15} and 4\nub{15}-\nub{15}. After the complete analysis in the second torsional overtone region (360-720 \wn) was performed \footnote{I. Gulaczyk, M. Kreglewski, V-M. Horneman, JQSRT 217 (2018) 321–328}, many of the remaining unassigned lines in this region could be assigned to v=3-1 and v=4-1 bands. Earlier, about 200 transitions of B, E$_{1+1}$ and E$_{1-1}$ symmetry for the 3\nub{15} and 28 transitions of B symmetry for 4\nub{15} were found \footnote{N. Ohashi, H. Shimada, W. B. Olson, K. Kawaguchi, J. Mol. Spectrosc. 152 (1992) 298}. On the basis of the calculated energy levels for the third and fourth excited torsional states, many transitions of the hot band v=3-1, not assigned previously, have been identified (over 1500 transitions for all symmetry species). As for v=4-1, so far, the previously assigned series were only extended to higher J values (over 100 transitions assigned of B symmetry), but the analysis is in progress. All the assignments were confirmed by the LSCD. Each set of the experimental data was fit to a single state model based on the group theoretical formalism \footnote{N. Ohashi and J.T. Hougen, J. Mol. Spectrosc. 121 (1987) 474}.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Handle URL

https://hdl.handle.net/2142/116814&&

DOI

https://doi.org/10.15278/isms.2022.RI08

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Copyright 2022 held by the authors

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