THE MICROWAVE SPECTRUM AND STRUCTURE OF THE $CH_{3}NO_{2}-H_{2} O$ DIMFR
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Date
1994
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Journal ISSN
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Publisher
Ohio State University
Abstract
The microwave spectrum of the nitromethane-water, $CH_{3}NO_{2}-H_{2}O,$ complex has been studied with a pulsed-beam Fourier-transform Fabry-Perot-cavity spectrometer. The dominant spectrum is {b}-type with a weaker {a}-type spectrum. Critical to the rotational assignments were well resolved $^{14}N$ nuclear electric quadruple transitions, and the incorporation of the pulsed nuzzle in one of the mirrors which provided a beam co-axial with the cavity axis to attain linewidths of about 2 kHz. In order to provide structural data, substitutions of HDO and $D_{2}O$, and $CD_{3}NO_{2}$ in the complex were assigned. Thu molecular structure derived from the moments of inertia has a center of mass separation of 3.506(7) {\AA}. The moments of inertia can not distinguish two possible forms of the complex, one with the monomer dipole moment vectors aligned and the other with them anti-aligned. Measurement of the dipole moment components in the complex, $\mu_{a} = 1.243(11) D$ and $\mu_{b} = 1.706(12) $D, resolves this difficulty and shows that the dipole vector are anti-aligned. The {ab initio} results are in excellent agreement with the experimental structure and also show that the form with aligned dipoles has no energy minimum. The complex is quite strongly bonded with a harmonic pseudodiatomic stretching force constant $k_{3} = 9.30 N/m$ and evidence for two hydrogen bonds of approximately 2.1 {\AA} between the water O atom and a $CH_{3}$ H atom and a water H atom and an O atom of the $NO_{2}$ group. Comparison with The transition state geometry in the water catalyzed conversion of nitromethane to its aci form, $CH_{2}N(O)OH$ by $Melius^{1}$ will be presented.
Description
$^{1}$C. F. Melius, Phil. Trans. R. Soc. London, A 339, 365 (1992).
Author Institution: Molecular Physics Division, National Institute of Standards and Technology; Molecular Physics Division, Molecular Spectroscopy Laboratory Applied Physics Institute; Center for Advanced Research in Biotechnology, National Institute of Standards and Technology
Author Institution: Molecular Physics Division, National Institute of Standards and Technology; Molecular Physics Division, Molecular Spectroscopy Laboratory Applied Physics Institute; Center for Advanced Research in Biotechnology, National Institute of Standards and Technology