ORBITAL PARAMAGNETISM AND O-P HYDROGEN CONVERSION

The orbital angular momenta of paramagnetic catalytic centres are show n to induce the ortho-para hydrogen conversion process. The considered hyperfine coupling includes the dipolar interactions between the two molecular nuclear spins and the orbital angular momenta of the catalys t electrons. The resulting orbital rates reach their magnetic dipole l imit for short-range components of the electron states. The rate analy sis is then restricted to the relative departures from this limit. The se are independent of the scatterings, and directly related to the fin ite electron spread of the catalytic centre. The tensorial algebra of this orbital mechanism is detailed, and applied by modelling the elect ron spread with Slater radial extensions. Spherical and C-4v one- and many-electron states are considered. Orbital conversion rates are foun d to be related to the orbital degeneracy and paramagnetism of the cat alytic centre. Important deviations from the magnetic dipole limit are obtained for open sub-shells and for optimal values of the parameters .