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Issue 14, 1999
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Analysis of internal rotations in ethyl nitrite using molecular beam Fourier transform microwave spectroscopy

Abstract

The microwave spectrum of ethyl nitrite (C2H5ONO) shows the presence of three rotational isomers, corresponding to cistrans, cisgauche, and transgauche structures. We have performed an investigation of the internal rotation of the methyl group in the cistrans and cisgauche rotamers and the motion of the ethyl group in the transgauche structure by using molecular beam-Fourier transform microwave (MB-FTMW) spectroscopy. Rotational spectra of these three isomers were recorded in the frequency regions 1–4 GHz and 7–26 GHz with two different spectrometers. For cistrans ethyl nitrite we observed µa- and µb-type and for the cisgauche form we detected µa-, µb-, and µc-type spectra. Due to the internal rotation of the methyl group, some lines were split and the torsional barriers could be determined, V3(CH3)=1082(2) cm-1 for the cistrans and V3(CH3)=918(10) cm-1 for the cisgauche form. For the transgauche form we found µa-, µb-, and µc-type spectra. The µb- and µc-type lines showed a doubling due to the interconversion between the two equivalent gauche conformers through rotation about the C–O axis. We determined the difference between the two lowest energy levels of the torsion around the C–O bond axis to be 68(3) kHz. Based on the observed splittings and the rotational constants, the Fourier coefficients of the potential hindering this internal rotation were determined to be V1=-1322 cm-1, V2=-1048 cm-1, V3=-412 cm-1, and V4=-109 cm-1 with a low barrier of 183(3) cm-1 in the trans position and a higher barrier of 1916(100) cm-1 in the cis position. Rotational, centrifugal distortion, and quadrupole coupling constants and some structural parameters have also been obtained from the analysis of spectra.

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Phys. Chem. Chem. Phys., 1999,1, 3219-3233
Article type
Paper

Analysis of internal rotations in ethyl nitrite using molecular beam Fourier transform microwave spectroscopy

N. Hansen, F. Temps, H. Mäder and N. W. Larsen, Phys. Chem. Chem. Phys., 1999, 1, 3219
DOI: 10.1039/A902413A

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