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Title:14N quadrupole coupling in the microwave spectra of n-vinylformamide
Author(s):Nguyen, Ha Vinh Lam
Contributor(s):Bailey, William C.; Stahl, Wolfgang; Kannengießer, Raphaela
Subject(s):(Hyper)fine structure, tunneling
Abstract:The microwave spectra of two conformers, \emph{trans} and \emph{cis}, of the title compound were recorded using two molecular beam Fourier transform microwave spectrometers operating in the frequency range 2 GHz to 40 GHz, and aimed at analysis of their $^{14}$N quadrupole hyperfine structures. Rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants (NQCCs) $\chi$$_{aa}$ and $\chi$$_{bb}$ - $\chi$$_{cc}$, were all determined with very high accuracy. Two fits including 176 and 117 hyperfine transitions were performed for the \emph{trans} and \emph{cis} conformers, respectively. Standard deviations of both fits are close to the measurement accuracy of 2 kHz. The NQCCs of the two conformers are almost exactly the same, and are compared with values found for other saturated and unsaturated formamides. \newline \indent Complementary quantum chemical calculations - MP2/6-311++G(d,p) rotational constants, MP2/cc-pVTZ centrifugal distortion constants, and B3PW91/6-311+G(d,p)//MP2/6-311++G(d,p) nuclear quadrupole coupling constants - give spectroscopic parameters in excellent agreement with the experimental parameters. B3PW91/6-311+G(d,p) calculated electric field gradients, in conjunction with eQ/h = 4.599(12) MHz/a.u., yields more reliable NQCCs for formamides possessing conjugated $\pi$-electron systems than does the B3PW91/6-311+G(df,pd) model recommended in Ref. \footnote{W. C. Bailey, \emph{Chem. Phys.}, \textbf{2000}, \emph{252}, 57.}, whereas this latter performs better for aliphatic formamides.\footnote{W. C. Bailey, Calculation of Nuclear Quadrupole Coupling Constants in Gaseous State Molecules,} We conclude from this that f-polarization functions on heavy atoms hinder rather than help with modeling of conjugated $\pi$-electron systems.
Issue Date:2016-06-22
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper/Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2017-01-26

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