CHARACTERIZATION OF ASYMMETRIC NITRIC-OXIDE DIMER O=N=O=N BY RESONANCE RAMAN AND INFRARED SPECTROSCOPY
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abstract
Nitric oxide reacts with Lewis acids [formula ommited] or SO2 to form a red species at 77 K. This species absorbs in the visible region near 500 nm and, thus, can be examined using resonance Raman spectroscopy when laser excitation lines near the absorption maximum are utilized. Both Raman and infrared spectra of the red species formed from four different isotopic forms of nitric oxide [formula ommited] and 15Nl8O) were recorded in order to ascertain the nature of the bonding. The results demonstrated that the asymmetric dimer 0=N-0=N was formed. The vibrational frequencies assigned to the normal isotopic species were v1(N=0 stretch) at 1778, v2(N=0 stretch) at 1690, v3(N-O stretch) at 482, v4(in-plane bend) at 184, and v5(in-plane bend) at 116 cm-1. In addition, also observed were [formula ommited] as well as other overtones and combinations. In infrared spectra only bands corresponding to to v1, v2, 2v2, and v1 + v2 were detected. No frequency shifts for the acid molecules were detected. The isotopic shifts observed for the v3 mode indicated that an O-N linkage was present. Force constant calculations showed that in this molecular species both N=0 groups retain strong multiple bond character and are joined by a weak N-O single bond. 1978, American Chemical Society. All rights reserved.
