I was recently watching a video on the physics and chemistry in planetary accretion disks, and the speaker at a certain point mentioned 'freeze-out and UV dissociation'. Is freeze-out a purely chemical term, or is it specific for this process? Is it very important in planetary formation?
Freeze-out is indeed a chemical term. It happens in the midplane of accretion disks where density is high enough to block UV ionization/chemical dissociation and limit heating from the central star. No one seems to have gotten around to writing up a layman friendly article on the subject yet, but these refs give the gist:
From ref 2: