# How long would it take for a tank of same-spin hydrogen atoms to become a tank of H₂?

In the question Is there an energy cost associated with flipping the spin of an electron?, it is shown that it is very unlikely for two hydrogen atoms to bond if their electrons have the same spin. The reason is the very low rate at which such a system would be able to emit photons. This makes me think that a bottle of $$\ce{H1}$$ could be prepared if the spin-up hydrogen was separated from the spin-down hydrogen with an apparatus like the one used in the Stern-Gerlach experiment. Is it true that the spin transition can be ignored for "all practical purposes" (see linked question), or can tanks of spin-aligned $$\ce{H1}$$ only exist for times uninterestingly short for chemical purposes?

• Not long at all. – Ivan Neretin Oct 8 '19 at 15:41
• Assuming the tank survives ... – Ian Bush Oct 8 '19 at 16:21
• I doubt this experiment would be a valid "practical purpose". ;) Also spin relaxation typically occurs via energy exchange with the "lattice", not photon emission. Unless your tank had no walls and its content was infinitely dilute, it would present a suitably solid lattice for your electrons. – Karl Oct 8 '19 at 18:10
• And wouldnt one stray 21/cm photon self amplify like crazy? – Karl Oct 8 '19 at 18:19
• @Karl What if the vessel was lined with a compound that only exposed "spin-saturated" atoms to the gas, atoms whose electrons could not possibly accept any more spin? Is such a material possible? – Display Name Oct 8 '19 at 18:23