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Title:Next Level Achievement Of The xiam Code In Modeling Microwave Spectra Of Molecules With Very Low Torsional Barriers
Author(s):Nguyen, Ha Vinh Lam
Contributor(s):Grabow, Jens-Uwe; Nair, K.P. Rajappan; Herbers, Sven
Subject(s):Mini-symposium: Large Amplitude Motions
Abstract:The \textit{XIAM} code is one of the most frequently used programs to treat the microwave spectra of molecules with up to three methyl internal rotors. \textit{XIAM} is user-friendly and fast, but often shows difficulties in dealing with low torsional barriers. An example is the case of \textit{m}-methylanisole where the methyl group attached at the \textit{meta}-position of the ring undergoes internal rotation with a barrier height of about 56 \wn~for the \textit{cis} conformer and 37 \wn~for the \textit{trans} conformer.\footnote{L. Ferres, W. Stahl, H.V.L. Nguyen, \textit{J. Chem. Phys.} \textbf{148}, 124304 (2018).} The standard deviation obtained with \textit{XIAM} is much larger than the measurement accuracy for both conformers. Recently, the code has been modified, and two higher order effective parameters connected to the potential term cos(3$\alpha$) were implemented, which reduced the standard deviations of the fits to almost measurement accuracy.\footnote{S. Herbers, H.V.L. Nguyen, \textit{J. Mol. Spectrosc.} \textbf{370}, 111289 (2020).} The \textit{XIAM$_{mod}$} code also succeeded in modeling the microwave spectra of 3-fluorotoluene, 3,4-dimethylfluorotoluene,\footnote{K.P.R. Nair, S. Herbers, H.V.L. Nguyen, J.-U. Grabow, \textit{Spectro. Chim. Acta A} \textbf{242}, 118709 (2020).} and 4-methylacetophenone\footnote{S. Herbers, S.M. Fritz, P. Mishra, H.V.L. Nguyen, T.S. Zwier, \textit{J. Chem. Phys.} \textbf{152}, 074301 (2020).} with torsional barriers of 17 \wn, 32 \wn, and 22 \wn, respectively, to measurement accuracy.\\
Issue Date:2021-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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