http://pipeline.corante.com/archives...difluoride.php

And yes, what happens next is just what you think happens: you run a mixture of oxygen and fluorine through a 700-degree-heating block. "Oh, no you don't," is the common reaction of most chemists to that proposal, ". . .not unless I'm at least a mile away, two miles if I'm downwind." This, folks, is the bracingly direct route to preparing dioxygen difluoride, often referred to in the literature by its evocative formula of FOOF.

Well, "often" is sort of a relative term. Most of the references to this stuff are clearly from groups who've just been thinking about it, not making it. Rarely does an abstract that mentions density function theory ever lead to a paper featuring machine-shop diagrams, and so it is here. Once you strip away all the "calculated geometry of. . ." underbrush from the reference list, you're left with a much smaller core of experimental papers.