Para States Research Articles

Experiments on heavy hydrogen. II.―The ortho-para conversion

Ortho- and para-modifications should exist in all diatomic molecules of identical atoms with nuclear spin, since the law of prohibition of the ortho-para intercombination is generally applicable. The rotational states consist alternately of ortho- and para-levels: the ortho-levels being those which possess on the average the higher quantum weight and represent the states with the symmetrical nuclear-spin eigenfunctions, whereas the para-levels correspond to the antisymmetrical nuclear-Spin function. The rotational quantum numbers possessed by the ortho- and para-levels depend on the statistics valid for the nuclei and on the symmetry of the electronic eigenfunctions. For even electronic eigenfunction (for hydrogen and diplogen the ground states of which are 1 Σ g ) if the Fermi-Dirac statistics are valid the ortho-modifications are in the rotational states with odd quantum numbers and the para states in the even ones, whilst the Bose-Einstein statistics lead one to expect the reverse to be true.