OBSERVATION OF TWO COMBINATION BANDS INVOLVING TORSION AND ASYMMETRIC BENDING MODES OF THE NON-POLAR N$_2$O DIMER
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Date
2008
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Publisher
Ohio State University
Abstract
The non-polar N$_{2}$O dimer has four low frequency intermolecular vibrational modes: van der Waals stretch (A$_{g}$ symmetry), symmetric and asymmetric in-plane bends (A$_{g}$ and B$_{u}$ symmetry, respectively), and out-of-plane torsion (A$_{u}$ symmetry). There are two possible intramolecular dimer vibrations which correlate with the $\nu _{1}$ monomer stretch. One of these is an in-phase vibration of the two monomers, which has A$_{g}$ symmetry and is not infrared active. The other is an out-of-phase vibration, which has B$_{u}$ symmetry and gives rise to the infrared active dimer band at 2229.48 cm$^{-1}$. In the present work, we report the observation of an N$_{2}$O dimer band with c-type rotational structure, assigned as a combination of the A$_{g}$ intramolecular N$_{2}$O $% \nu _{1}$ stretching vibration and the A$_{u}$ intermolecular out-of-plane dimer torsional vibration. The vibrational origin for this band is measured to be 2249.360 cm$^{-1}$, giving an estimated torsional frequency of 21.5 cm$% ^{-1}$. A second combination band with a- and b-type rotational transitions has also been measured and assigned as the combination of the same A$_{g}$ intramolecular vibration and the B$_{u}$ asymmetric van der Waals bend. The measured band center is 2264.37 cm$^{-1}$, giving an asymmetric bending frequency of about 36.5 cm$^{-1}$. A search for the other two combination bands is currently underway.
Description
Author Institution: Department of Physics and Astronomy, 2500 University Drive NW, Calgary, ALberta T2N 1N4, Canada; Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A OR6, Canada