Theory of the Para-Ortho Conversion in Solid Deuterium
Abstract
The rate of para-ortho conversion in solid deuterium (D 2 ) is calculated taking two types of interactions, i.e., the magnetic dipole-dipole interaction between D 2 molecules and the coupling between the nuclear quadrupole moments of one D 2 molecule and the total quadrupole moment of the other molecule. It is found that both interactions make about the same contributions to the para-ortho conversion if only the interactions among para molecules are taken into account. However, the ortho molecules with I =2 also interact magnetically with para molecules and convert them into ortho molecules. The calculated conversion rate due to the para-para interactions is found to be 0.01 % per hour times c 2 , where c is the para concentration, while that due to the para-ortho interactions to be 0.01 % per hour times c (1- c ), so that the c 2 termes eventually cancel each other, leaving a total conversion rate which is proportional to c .