We consider the quantum theory of two atomic fields interacting coherently to form a molecular field via Raman photoassociation. This can be applied to treat interactions in either atomic Bose condensates or quantum Fermi gases, describing coherent molecule formation together with s-wave scattering This new type of super-chemical reaction (or nonlinear atom optics) has never been observed on Earth-and temperature even in space would be far too hot to observe it naturally. Thus, it would represent a breakthrough into a completely new type of low-temperature physics, only accessible at the temperatures that have been recently obtained experimentally. The theory required is also new, yet surprisingly relatively simple.