[Ron Hughes (OP)]

     If we had a hydrogen atom and an anti-hydrogen atom located in close proximity would the repulsion between the electron and anti-proton, and the repulsion between the anti-electron and proton be enough to prevent annihilation?

[LeeE]

I don't think so, because the atom and the anti-matter atom would both be electrically neutral.

[syhprum]

I all ways thought that it was magnetic forces that lead to the attraction of H atoms to form H2 molecules, these forces are identical between matter and anti matter versions of H so a molecule would form and rapidly disappear in a burst of Gamma radiation.

[Soul Surfer]

The magnetic forces would create an initial attraction at long range but as the atom and anti atom approached each other the attraction between the electron and the positron would take over.  What happens then is quite complex because a hydrogen atom is a composite structure of an electron and a proton which in turn is a composite structure of three quarks  each of these particles and anti particles will interact independently.  the electron and positron will probably be the first to go with a characteristic pair of photons being released.  The proton and anti proton annihilation can produce several outcomes which does include a range of particles as well as radiation.  I am not sure what the statistics of a low energy process id but I will see if I can look it up.

[Soul Surfer]

I have not found an article which states the result of a low energy annihilation but I think that it is likely to go something like this.

When the proton and anti proton interact only one of the quarks will annihilate first and this will result in the production of two mesons and the release of a lot of energy from the strong force field  this will result in the mesons flying apart quite quickly with a low probability of further interaction (although it could happen).  These mesons will decay in stages into  two electrons or positrons depending on which of the quarks annihilated

[LeeE]

Actually, this rings a very faint bell about some weird 'atoms' being formed from protons and anti-protons in mutual orbit about each other.  It was a long time ago though, and might just have been in fiction.