Dynamic model of ortho-para conversion of water molecules

A quantum model of mutual conversion of spin isomers of the water molecule, involving a proton of a neighboring water molecule, is proposed. Molecules interact due to magnetic dipole-dipole forces which give rise to flip-flop processes. An additional adsorption energy different in magnitude and sign for singlets and triplets arises from a fast exchange of spin states within an acceptor molecule. A slower flip-flop process controls the simultaneous evolution of all three protons, which results in the transition between singlet and triplet states. Based on the developed model, experimental data on ortho-para-water are discussed.