Orbital processes in O-P H₂ conversion on noble metals

EELS experiments of H₂ physisorbed on noble metals at low temperature have indicated that the ortho-para (O-P) conversion can be very fast on non-magnetic catalysts. Two processes are described in which the molecular nuclear angular momenta are dissipated by the emission of metal electron-hole pairs through a metal-molecule spin-orbit coupling. Both processes rely on electron momentum transfer to the metal but in the second one the virtual electron jump-back and forth from the metal to the molecule as induced by the electron Coulomb interaction-considerably strengthens the O-P rate and brings it close to the experimental values observed on Cu catalysts.