Re: O<sub>2</sub>
Three times, you wrote "atomic oxygen", over-riding my science-pedant restraint circuits, and so I am forced to point out that atomic oxygen is rather rare: one fifth of earth's atmosphere is composed of molecular oxygen, though.
I was responding to the suggestion that moon rocks should be tested on the International Space Station* and thus used "atomic oxygen" deliberately. At the ISS's altitude, atomic oxygen is a real and present problem for materials selection and design. The Long Duration Exposure Facility had many of its materials seriously degraded by atomic oxygen: silicone rubbers were converted to silica, Kapton was embrittled and degraded into brittle crap, durable solders corroded and flaked apart, and so on. Add the effects of large thermal expansion / contraction, UV light, and particle radiation to atomic oxygen, and LEO is a surprisingly aggressive environment.
http://esmat.esa.int/publications/published_papers/corrosion_in_space.pdf
If you want to perform a high-quality chemical analysis of microscopic grains of moon dust, then doing so outside the hull of the ISS is less ideal than in a terrestrial environment. As seen on ISS and LDEF materials, atomic oxygen modifies a thin layer of surface material in a short time (and thicker amounts over, well, long durations). When you're dealing with microscopic grain of moon dust, "thin layer" is similar to "radius of the grain," thus meaning your specimens are ruined. Or at least more challenging to analyze.
*As suggested earlier in this thread by "Your alien overlord - fear me"
Darn, that was only 5 uses. Atomic oxygen, atomic oxygen, atomic oxygen, atomic oxygen, atomic oxygen.