Abstract: New methods of operating surface reactors, and such reactors, particularly spinning disk reactors, require that a first reactant is fed to a reactor surface (20) and forms a thin radially outward moving film (60) thereon in a reaction passage (42) formed between the reaction surface (20) and a parallel, closely spaced (less than 1 mm) retaining surface (40). The passage thickness is precisely controllable and the surfaces (20, 40) move relative to one another so that strong shear is applied to the material between them. A second reactant is fed to the surface (20) as a second thin film (65) that as it enters the first film (60), preferably perpendicularly, it is immediately merged therewith along a correspondingly very narrow interaction line (66) by the shear at a rate such as to break up molecular clusters in the films, so that their molecules can aggressively and completely interact by forced interdiffusion.