Thus optical transitions must preserve the total spin and occur between levels of the same total spin.

In fact this simply reflects the different internal couplings of total spin and spatial angular momentum.

This is the total spin of the deuterium nucleus.

The total spin is only one fourth of that which would be required.

All electrons have total spin 1/2, with two possible projection values, as we've seen.

The projection can be changed, but the total spin of 1/2 is fixed for all time.

Ortho-H has all three proton spins parallel, yielding a total nuclear spin of 3/2.

This means that their spins are guaranteed to cancel each other out to give a total spin of zero.

There is also a correlation related to the overall symmetry or total spin of the considered system.

Agüero was a real spinning top, putting Terry and company in a total spin.