THE $\nu_{1}$ BANDS OF $Br^{14}NO_{2}$ AND $Br^{15}NO_{2}$ AROUND $7.8 \mu M$ STUDIED BY HIGH-RESOLUTION FOURIER-TRANSFORM ABSORPTION SPECTROSCOPY
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Date
1998
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Publisher
Ohio State University
Abstract
Nitryl bromide $(BrNO_{2})$ is a molecule of atmospheric interest. It is probably formed by heterogeneous reactions on polar stratospheric clouds and on sea-salt aerosol particles in the marine $tropospher^{a}$, and by gas-phase reactions of bromine atoms with $NO_{2}{^{b}}. BrNO_{2}$ is chemically unstable and difficult to synthesize. From the spectroscopic point of view, $BrNO_{2}$ is a heavy asymmetric top with small rotational constants and some low-energy fundamental vibrations, leading to a rather congested spectrum in the mid-infrared. Recently, we have presented the first high-resolution infrared spectrum of gascous $BrNO_{2}$ in the region of the b-type $\nu_{4}$ bands around $6 \mu m.^{c}$ The ground-state rotational constants of $BrNO_{2}$ were determined from the infrared spectra using ground-state combination differences. Although it is possible to estimate the molecular structure using the ground-state rotational constants of $^{79}BrNO_{2}$ and $^{81}BrNO_{2}$, the small displacement of the center-of-mass between these isotopomers causes a strong correlation between the Br-N bond length and the O-N-O angle. Therefore, high-resolution absorption spectra of the a-type $\nu_{1}$ bands of $Br^{14}NO_{2}$ and $Br^{15}NO_{2}$ were recorded with a spectral resolution of $0.0002 cm^{-1}$ using the Bruker IFS-120HR FTS at the University of Hannover. The bands were analyzed using a Watson-type A-reduced Hamiltonian in the $I^{r} representation^{d}$. The analysis confirms the rotational constants derived from line assignments in the $\nu_{4}$ bands, and allows for an accurate determination of the ground-state substitution structure of $BrNO_{2}$.
Description
$^{a}$B.J. Finlayson-Pitts, F.E. Livingston, and H.N. Berko, Nature 343, 622 (1990) $^{b}$W.B. DeMore et al., JPL. Publ. 97-4 (1997) $^{c}$J. Orphal, A. Frenzel, H. Grothe, B. Redlich, D. Scheffler. H. Willner, and C. Zetzsch, submitted to J. Mol. Spectrosc. (1998) $^{d}$J. K. G. Watson, in vibrational Spectra and Structure (Ed. J.R. Durig), 1-89, Elsevier, Amsterdam (1997)
Author Institution: Institute of Environmental Physics and Institute of Remote Sensing, University of Bremen; Institute of Physical Chemistry and Institute of Anorganic Chemistry, University of Hannover
Author Institution: Institute of Environmental Physics and Institute of Remote Sensing, University of Bremen; Institute of Physical Chemistry and Institute of Anorganic Chemistry, University of Hannover