What is the link between the modelling and the fundamental chemistry?
The two major areas of laboratory and theoretical study in the UCL Centre for Cosmic Chemistry and Physics are reactions of atomic hydrogen to form molecular hydrogen at cold surfaces, and the formation of more complex molecules at cold surfaces. Why have we chosen to concentrate on these types of surface reactions? Molecular hydrogen is an interesting case. This species is the most abundant molecule in the Universe, and a significant fraction of non-stellar baryonic matter is in this form. Although atomic hydrogen is abundant, the direct reaction of two hydrogen atoms to form H2 is strongly forbidden. Exchange reactions such as CH + H -> C + H2 can be shown to be far to slow to account for the high H2 abundance. Reaction networks via H- and H2+ can be important in some circumstances, though each has a slow rate-limiting step. Perforce, one must look for another mechanism, and the one that was proposed half a century ago, but without much experimental basis, was the reaction of hydroge
