Update: May 2017
I am currently writing up my findings, but have settled this question: N2 and O2 do absorb and emit IR radiation in space, at least the thermosphere. In the thermosphere there can only be radiation and these molecules are 'radiated' to a temp of some 2500C. Good for the goose, good for the gander: N2 and O2 radiate in the troposphere too.
The key assumption of climate science (to both proponents and skeptics of manmade climate change) is N2 and O2 – the non greenhouse gases; constituting 99% of the dry atmosphere – do not absorb or emit IR radiation. In space, there is only radiation to transfer heat energy. If it is true for the vacuum of space, then it must be true for the atmosphere. Space is the place to test that premise.