Spin-lattice relaxation of the O2 − molecule-ion in the potassium halides

An experimental and theoretical study of the spin-lattice relaxation (SLR) of the O₂ ^? molecule-ion in the potassium halides has been made. The SLR rate was measured by several methods between 1.32°K and 36°K with a 3 cm. ESR spectrometer. The results indicate a one phonon process with a large anisotropy dominates forT<2°K.T ₁ is much longer for the magnetic field parallel to the molecular axis. Detailed theoretical calculations indicate a new SLR process, namely phonon-induced libration of the molecular axis, can probably explain the field parallel case. The Van Vleck SLR process can account for the field-perpendicular case.