14N quadrupole coupling in the microwave spectra of n-vinylformamide

Nguyen, Ha Vinh Lam

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https://hdl.handle.net/2142/91198 Copy

Description

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

Issue Date

2016-06-22

Keyword(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, http://nqcc.wcbailey.net/index.html.} We conclude from this that f-polarization functions on heavy atoms hinder rather than help with modeling of conjugated $\pi$-electron systems.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

En

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http://hdl.handle.net/2142/91198

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Copyright 2016 by the authors

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