The nitrogen oxides and nitrogen-containing acids are the most important compounds in this group. Ammonia and hydrazine are also members of the group, but their spectra have already been included in Chapter E, hydrides.

     Nitric oxide, NO, has a more complex spectrum than is normal for a diatomic molecule. There is a doubling of the lines and a weak Q-branch, which are a consequence of the molecule having an unpaired electron. In air, NO oxidizes spontaneously to NO2, but at low NO concentration this reaction is extremely slow.

     Nitrogen dioxide has its strongest band right in the middle of the main water vapor band, which complicates atmospheric measurements of the molecule. At atmospheric optical paths of 100 meters or less, however, there is enough infrared transmission for NO2 measurements to be made, providing that the water interference is properly subtracted. See SPECTRA, chapter M.

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