Can H2O form with out an atmosphere?
Define "form", define "without an atmosphere" - while it may seem obvious to you what you mean, question is very ambiguous.
Well, there's a lot of interstellar water, most of which probably formed out there in space (novae? supernovae?) That's the likely source for much of the early water on Earth: ice comets raining down upon earth (as opposed to stuff 'outgassing' out of the Earth's core). Unfortunately, I can't find a good source for this last assertion, beyond what I remember and the Wikipedia article:
Separate names with a comma.