ESR Spectra of NO2 in Inert Matrices

The ESR spectrum of NO2 in neon at 4°K has been re-examined at improved resolution. The spectrum is interpreted in terms of three distinct sites: (1) a rigid site with preferred molecular orientation as observed by Kasai et al. [J. Chem. Phys. 42, 1120 (1965)], (2) a rotational site with motion of the N atom about the O···O axis (which is oriented parallel to the matrix deposition surface), and (3) a hindered rotation about the C2v symmetry axis. The relative concentrations of these sites is estimated to be of the same order of magnitude. The NO2/argon spectra are irreversibly changed by annealing at 30°K, populating the latter rotational site at the expense of the former sites.