Orientational order in solid hydrogen at reduced ortho concentration

The splitting of the NMR line in solid hydrogen has been observed during 145 h while it aged at temperatures below 0.1°K. For ortho-hydrogen mole fractions X less than 0.55, the NMR splitting is present but disappears abruptly at transition temperatures fitting a straight line Tc=(0.54 0.06)X+(0.02 0.02). The concentration dependence of the splitting is compared to a model which includes only a zero-point admixture to the J=0 ground state from the J=1 wave functions of the libron band, and a zero-point admixture of the J=3 state, both of which admixtures scale according to the observed concentration dependence of the transition temperature.