# Can the atomic liquid Hydrogen exist?

#### Eagle9

Imagine that we have got some vessel under standard temperature and pressure filled with atomic Hydrogen inside and the electrons of these atoms have got the same spin and therefore they cannot join into Hydrogen molecules, so the process of recombination does not occur. Then we begin cooling the vessel lower 20.28 K (boiling point for molecular Hydrogen) temperature. The question is-what will happen? Will the atomic Hydrogen liquefy or will it remain in gaseous condition? Or maybe it will be turned into molecular Hydrogen?

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#### chill_factor

How do those electrons have the same spin? Its more like "if there are 2 electrons in 1 orbital, they WILL have antiparallel spins". What you said is just not possible.

#### Eagle9

chill_factor
How do those electrons have the same spin?
I do not know if it possible to achieve this from the technical point of view, but just imagine that it is done. I would like to know:
The question is-what will happen? Will the atomic Hydrogen liquefy or will it remain in gaseous condition? Or maybe it will be turned into molecular Hydrogen?
Its more like "if there are 2 electrons in 1 orbital, they WILL have antiparallel spins".
Well, this can happen in case of heavier elements, but not Hydrogen.

#### snorkack

How do those electrons have the same spin? Its more like "if there are 2 electrons in 1 orbital, they WILL have antiparallel spins". What you said is just not possible.
No, the reasoning is "if 2 electrons have parallel spins, they CANNOT go to the same orbital".

Example in case - ortohelium.

Both electrons have the same spin.
THEREFORE they CANNOT share an orbital, such as the lowest, 1s one. If one electron winds up in 1s orbital, the lowest available one for the other is 2s orbital.

This is an excited state - about 20 eV above the ground state where the electrons have opposite spins and both fit in 1s.

It is possible to change the spin of an electron so as to go to 1s ground state. This, however, is extremely hard.

The lifetime of orthohelium is quoted in the region of 8000 seconds - which is 2 hours. Does someone know what the decay process actually is?

Now suppose you could somehow produce atomic hydrogen gas with aligned spins.

Unless two hydrogen atoms can somehow change one electron spin to fit the electrons into a common orbital, they cannot form a bond - they repel and scatter off each other. And when they are not interacting, they have no reason to change spin. Thus spin aligned hydrogen cannot be described by single lifetime like orthohelium, because the specific speed of the process of spin reorientation events would depend on the specific frequency of interactions - temperature and density. In any case, it could be expected that the spin reorientation would be slow.

If spin aligned hydrogen could be produced in large quantities, could it be cooled, in face of the infrequent spin flip caused recombinations releasing heat, to the extent that the atoms would under van der Waals forces condense into liquid or solid?

#### Eagle9

DrDu
Nasa has a patent on it:
Thanks! Very interesting! :shy:
I also remember about an article on experiments to generate liquid atomic hydrogen in Scientific American, maybe in the 1980's.
And did they succeed in it?

snorkack
This is an excited state - about 20 eV above the ground state where the electrons have opposite spins and both fit in 1s.
And how this Helium is excited? By means of lasers? Magnetic field? Other methods?
The lifetime of orthohelium is quoted in the region of 8000 seconds - which is 2 hours. Does someone know what the decay process actually is?

Now suppose you could somehow produce atomic hydrogen gas with aligned spins.

Unless two hydrogen atoms can somehow change one electron spin to fit the electrons into a common orbital, they cannot form a bond - they repel and scatter off each other. And when they are not interacting, they have no reason to change spin. Thus spin aligned hydrogen cannot be described by single lifetime like orthohelium, because the specific speed of the process of spin reorientation events would depend on the specific frequency of interactions - temperature and density. In any case, it could be expected that the spin reorientation would be slow.
Well…….can you tell me how to calculate the necessary time for recombination? I opened the topic here https://www.physicsforums.com/showthread.php?t=624890 but nobody answered.
If spin aligned hydrogen could be produced in large quantities, could it be cooled, in face of the infrequent spin flip caused recombinations releasing heat, to the extent that the atoms would under van der Waals forces condense into liquid or solid?
Well, the recombination will slowly occur, the heat will be emitted and dispersed, so probably hydrogen will be cooled

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#### DrDu

And did they succeed in it?
No, if I remember well, the problem was that spin flip is to rapid. This whole subject became a turn with the generation of Bose Einstein Condensates in the nineties in magnetic traps. AFAIK, BECs of Hydrogen atoms have not been prepared, yet.

#### Eagle9

No, if I remember well, the problem was that spin flip is to rapid. This whole subject became a turn with the generation of Bose Einstein Condensates in the nineties in magnetic traps. AFAIK, BECs of Hydrogen atoms have not been prepared, yet.
But what about the NASA patent the link of which you posted here? I read it, they say that it is possible to store solid atomic Hydrogen (page 3, BACKGROUND OF THE INVENTION). Why it is so difficult to store liquid atomic Hydrogen and relatively easy-solid one? :uhh:

#### DrDu

Because the atoms are bound to the surface which creates an energetic barrier for recombination.

#### DrDu

Oh, that's interesting. Good you found it!

#### snorkack

snorkack

And how this Helium is excited? By means of lasers? Magnetic field? Other methods?
Trivially easy. Just about anything that ionizes helium and allows it to recombine.

There is no guarantee that an electron which comes across a helium ion has opposite spin to the lone electron of the ion. Once the electron has recombined, even to a higher orbital than 2s, all decays changing electron spin are extremely unlikely, so orthohelium states will decay to the lowest available orthohelium state... which is long lived.

#### Eagle9

DrDu
Because the atoms are bound to the surface which creates an energetic barrier for recombination
And why it is difficult/impossible to do the same with liquid atomic Hydrogen?

snorkack
Trivially easy. Just about anything that ionizes helium and allows it to recombine.

There is no guarantee that an electron which comes across a helium ion has opposite spin to the lone electron of the ion. Once the electron has recombined, even to a higher orbital than 2s, all decays changing electron spin are extremely unlikely, so orthohelium states will decay to the lowest available orthohelium state... which is long lived.

#### M Quack

The density and thus collision rate in a liquid (any liquid) is much higher than in the gas.

The life time of the metastable state will be strongly affected by that.

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