There are nuclear-spin isomers in diatomic molecules of the nuclides whose spin is
not zero. Especially in the case of a hydrogen molecule, the difference of properties is
significant. Spins of para-hydrogen are anti-parallel and the sum is 0 leading to a singlet
state. Spins of ortho-hydrogen are parallel and the sum is 1 resulting in a triplet state.
Since para-hydrogen is in a lower energy state, it is the stabler form at low temperatures.
The theoretical ratio of para-hydrogen is 100% at 0 K, but it decreases to about 25% at
room temperature, since the ratio of ortho-hydrogen increases at higher temperatures.
Gas chromatography and rotational lines in the electronic band spectrum of H2 can
distinguish two hydrogen isomers.