Conforming to present atomic physics, the two elementary particles in hydrogen atoms can have either parallel or antiparallel magnetic moments, and the energy differences between these two kinds of hydrogen atom are the cause of the hyperfine splitting of all S terms and all P, D, F fine subterms in the line spectrum assigned to atomic hydrogen.
Conforming to present molecular physics, the two electrons in all hydrogen molecules can only have antiparallel spins and magnetic moments, while their two protons can have spins and magnetic moments either antiparallel, as in diamagnetic parahydrogen, or parallel, as in orthohydrogen with nuclear magnetism.
Still the electronic spectrum of molecular hydrogen exhibits two distinct scales, one made of singlet terms, the other of triplets, and this fact can be explained only by admitting a diamagnetic orthohydrogen with a total spin number S = 0 of its electrons, but also a paramagnetic orthohydrogen with parallel magnetic moments of its electrons S = 1, at least in the excited states of molecular hydrogen. If this paramagnetism of orthohydrogen exits also in its fundamental state, even despite the Pauli’s principle of exclusion, it should have had to be cleared up for a long time by measuring experimentally the magnetic moment of orthohydrogen.
Unfortunately, even now we have no measured magnetic moment of orthohydrogen. In the 1930’s the proton magnetic moment was measured accurately enough in a Ster-Gerlach apparatus with adequate gradients of the non-uniform magnetic field, but in the case of orthohydrogen similar attempts failed for reasons never clearly explained, although the proton and orthohydrogen molecule with nuclear magnetism have the same ratio mass/magnetic moment, therefore the same trajectory in a non-uniform magnetic field. And after discovering magnetic resonance, many magnetic moments of particles with nuclear magnetism have been exactly measured through this method, but not that of orthohydrogen. Or, if that old failure in Stern-Gerlach installation could be explained now by a possible paramagnetism of orthohydrogen, which requires magnetic gradients much smaller than those used for particles with nuclear magnetism, this absence of an orthohydrogen magnetic moment measured by magnetic resonance remains a mystery.
Moreover, such a measured magnetic moment of orthohydrogen is necessary because paramagnetic orthohydrogen is supported also by other arguments. For example, a logical one: if two kinds of hydrogen atom really exist, one of smaller energy, the other of higher energy, then we ought to have three isomers of orthohydrogen: (1) made of two atoms of smaller energy, (2) made of two atoms of higher energy, and (3) made of different atoms. Still only two isomers of molecular hydrogen exist, and this is possible only if all hydrogen molecules are made of identical atoms, but whose electrons can have magnetic moments either parallel or antiparallel.
In these circumstances, I ask two questions:
Can someone give me a measured magnetic moment of orthohydrogen molecule?
If not, what could be the possible cause of this strange omission?