Abstract
The mid-infrared (1500–3800 cm −1) absorption spectrum of gaseous nitric oxide has been studied at low temperature (99 K) with a long absorption path (160 m) in order to observe weak combination, difference, and overtone bands of the NO dimer. About ten new bands were assigned with greater or lesser certainty. Combined with previous results, they lead to a set of 12 secure and 7 tentative vibrational term values for (NO) 2, essentially doubling our knowledge of NO dimer vibrational states. The strongest non-fundamental bands in this region, other than the ν 1 (symmetric N–O stretch) + ν 5 (asymmetric N–O stretch) overtone, involve combinations of ν 5 with ν 3 (intermolecular stretch). Excitation of ν 5 results in increased frequencies for the intermolecular modes ν 2, ν 3, and ν 4. A new value of 155.5 cm −1 was obtained for ν 4, the elusive infrared-inactive out-of-plane fundamental vibration.
Published Version
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