THE NO DIMER: ISOTOPIC INFRARED SPECTRA, LINE WIDTHS, AND FORCE FIELD
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Date
1995
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Publisher
Ohio State University
Abstract
Continuing our earlier $study^{1}$ of $(^{14}N{^{16}O})_{2}$. We have now obtained spectra of the $\nu_{1}$ bands (symmetric N-O stretch) of $(^{15}N{^{16}O})_{2}$ and $^{14}N{^{16}O} - {^{15}}N{^{16}O}$. These were recorded at a resolution of $0.005 cm^{-1}$ using a Bomem FTIR spectrometer and a new 5 m cooled multiple-traversal cell. The absorption path was 200 m with T = 84 K and P = 0.5 Torr. The $\nu_{1}$ band origins are found to be 1835.359 and $1854.869 cm^{-1}$ for the $^{15}N$ and mixed isotopes, respectively, and a full set of rotational and quartic centrifugal distortion parameters is obtained for each. Observed predissociation line widths, which show no strong rotational dependence, are $0.0056 cm^{-1}$ for $(^{14}N{^{16}O})2$, and $0.0044 cm^{-1}$ for $(^{15}N{^{16}O})_{2}$. This is somewhat narrower than reported by $Matsumoto et al.,^{1}$ who did not detect any significant difference in line width between the two isotopes. Our observed width of $0.014 cm^{-1}$ for the mixed dimer is significantly larger than those of the symmetric dimers. $Nour et al.^{3}$ have determined a harmonic force field for $(NO)_{2}$ based on observed frequencies and isotope shifts in the Raman spectrum of solid NO. However, their result is not compatible with our observed centrifugal distortion parameters. We are thus investigating further the force field and its consequences for the assignment of the low frequency intermolecular vibrational modes of the dimer, which are yet to be detected in the gas phase.
Description
1. B.J. Howard and A.R.W. McKellar, Mol. Phys. 78, 55 (1993). 2. Y. Matsumoto, Y. Ohshima, and M. Takami, J. Chem. Phys. 92, 937 (1990). 3. E.M. Nour, L.-H. Chen, M.M. Strube, and J. Laane, J. Phys. Chem. 88, 756 (1984).
Author Institution: National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.; Oxford University, South Parks Road, Oxford OX1 3QZ, U.K.
Author Institution: National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.; Oxford University, South Parks Road, Oxford OX1 3QZ, U.K.