Vibrational spectroscopy of nitrogen oxides

Abstract

The first laser Raman spectra of both asymmetric dinitrogen trioxide (ONNO(,2)) and symmetric dinitrogen trioxide (ONONO) have been collected by stabilizing these species in nitric oxide matrices at 12 K. Laser irradiation at wavelength from 568.2 to 752.6 nm converts asym-N(,2)O(,3) to sym-N(,2)O(,3) but wavelengths of 514.5 or 488.0 nm convert the symmetric isomer back to the asymmetric one. The Raman and infrared data of several isotopic species (with ('15)N and/or ('18)O) for both molecules demonstrated that the N-N stretching frequency occurs at 266 cm('-1) for asym-N(,2)O(,3). This resolved the previous ambiguities in the vibrational assignments of this species. The N-O single bond stretching force constant for sym-N(,2)O(,3) was determined to be 3.61 mdyne/A. The Raman spectra of the solid nitric oxide dimer (('16)O('14)N('14)N('16)O) and two of its isotopic species (('16)O('15)N('15)N('16)O and ('18)O('14)N('14)N('18)O) at 12 K have been recorded and analyzed. The observed isotopic shifts demonstrate that fundamental vibrational frequencies for the normal isotopic species are at 1866((nu)(,1)), 1762((nu)(,5)), 268((nu)(,2)), 215((nu)(,6)), and 189((nu)(,3)) cm('-1). A band at 97 cm('-1) may be due to the sixth vibration ((nu)(,4)). The 495 cm('-1) band is a combination band, (nu)(,2) + (nu)(,6), and not a fundamental. The products of the reactions of HCl or HBr with nitrogen dioxide at 12 K have been examined using Raman spectroscopy. Cl(,3)('+) and Br(,3)('+) are produced from these two reactions, respectively. The Raman frequencies for Cl(,3)('+) were observed at 515((nu)(,3)), 462((nu)(,1)), and 236((nu)(,2)) cm('-1). The Br(,3)('+) resonance Raman species, which represent the first well documented spectra for this species, show strong fundamental bands at 281((nu)(,1)) and 227 & 238 cm('-1) (doublet for (nu)(,2)) as well as an overtone doublet 471 & 487 cm('-1). Laser Raman spectra of trans-sodium hyponitrite Na(,2)N(,2)O(,2) as a solid and in aqueous solution have been recorded along with its infrared spectrum. Polarization data for the aqueous solution Raman spectra were also determined for the first time. The results confirm the trans structure of the hyponitrite ion and also have led to a new vibrational assignment.