View Full Version : Hydrogen atoms in space

2010-Mar-28, 03:07 PM
Sorry I have not been able to be at this site for a long time. Spend more time at a site on more down to earth :shifty: physics, chemistry etc.

Where I would like the answer to the following question that came up.

Atomic hydrogen. H.

Where do you find it and where do you find on the other hand molecular hydrogen?

I am thinking of having heard of vast clouds of atomic hydrogen. (low temperature I think).

What are the typical and maximal densities? The temperatures? The atom collision frequencies?

Is it true that some/all of them exist in virtue not of the rarity of collisions, but of the rarity of third encounters to take away the energy given off by H2 molecule formation?

2010-Mar-30, 06:00 PM

I mean hydrogen is the majority of the ordinary matter in the Universe so it must be of some interest, somebody must know something about it. I confess I do not know offhand where most of it is or in what state now you were about to mention it. :confused:

2010-Mar-30, 06:15 PM
Most of it is in space...stars, interstellar medium, etc. In the atomic or plasma form. For the H2 gas, you need our sort of conditions.

That's all I know I'm afraid; no details (which is what I think you were looking for).

2010-Mar-31, 12:09 AM
Yeah, what you call space is mostly what I call the universe; I'll take it most of it is there.:lol: The non-astronomer might suppose most of it is in stars because that's what he mostly knows of. The stars are dense but the interstellar clouds are large, so I don't know where most of it is. Some figures like those mentioned above seem necessary to get a sense of it.

2010-Mar-31, 12:42 PM
There are whole books on these topics... so as not to spend a half hour typing, let me just point you to the Wikipedia articles on molecular clouds (http://en.wikipedia.org/wiki/Molecular_clouds) and the 21-cm neutral hydrogen emission (http://en.wikipedia.org/wiki/Hydrogen_line), although neither of them is all that complete; here's a bit more on gas in galaxies (http://www.astr.ua.edu/keel/galaxies/gas.html). The interstellar medium has multiple phases and rich structure in both temperature and density, so that "representative" values can end up meaning almost whatever one wants them to.

Indeed, such molecules as H2 seem to form on the surfaces of dust grains, as the grain can soak up momentum that would otherwise prevent the atoms from bonding. Otherwise they are limited to the small fraction formed via charge exchange reactions i the gas phase, which usually limits the fraction of molecules to parts per million.

2010-Apr-11, 08:35 PM
The sun and other stars eject large numbers of hydrogen nuclei = atomic hydrogen, often with no electron, so this may account for 80% of the hydrogen in the universe. Inside the stars, the temperature is too hot for molecular hydrogen to form, so again = hydrogen nuclei. In a molecular cloud, we expect from the name that at least part of the hydrogen is H2.
99.999999% of space has only a few particles per cubic meter, but almost half of the particles are electrons, so I will guess this space averages about 20% H2 = molecular hydrogen.
There are perhaps 50 kinds of hydrogen. Molecule with two protons and two electrons 2 molecule/ion with two protons and one electron 3 molecule with two protons, one neutron and two electrons = deuterium hydrogen pair 4 deuterium molecule that is ionized 5 etc.
Please if you have some real numbers instead of guesses. Neil