Stern-Gerlach deflection spectra of nitrogen oxide radicals

Magnetic deflection spectra of beams of pure NO₂ and NO ₂ seeded into rare gases have been determined using a Stern-Gerlach apparatus. Using He as carrier, a simple two-line deflection pattern is observed, indicating the breakdown of spin-rotation coupling in fields of 10 kG or more. Use of the other rare gases as carriers yields the two satellites at positions dictated by the beam velocities, and in addition, a more-or-less intense component at zero deflection which we hold to be due to diamagnetic or weakly paramagnetic (NO₂)_x clusters. The deflection amplitudes and line shapes are in good agreement with calculations. Additional weak bands observed in the spectra are likely due to van der Waals clusters such as NO₂ · Ar and NO₂ · Ne. ¹⁴N/¹⁵N isotope effects in NO₂ were visible as changes of line shape. Zeeman level anticrossings are calculated quantum mechanically to occur for NO₂ in the 20-30 kG regime, however their effects are small and were not observed. Deflection spectra of NO in its ²Π_3/2 thermally excited state were obtained showing satellites at the positions predicted assuming pure Hund's case-á coupling. Modeling of the observed spectra shows that both the electronic and rotational temperatures of the NO in the beam are rather high (20-125 K). The observed magnetic deflection spectra of the dialkyl nitroxide TEMPO when combined with line-profile calculations do not support the suggestion of Amirav and Navon [Chem. Phys. 82, 253 (1983)] that this molecule undergoes significant intramolecular spin relaxation while in the magnetic gap. In contrast, the SG spectra of the related radical di-t-butyl nitroxide shows no magnetic deflection, suggesting a spin lifetime of 0.5 μs or less.