Abstract: Methods of operating surface reactors, and such reactors, particularly spinning disc reactors require that a first reactant is fed to the reactor surface and forms a thin film on the surface. A second reactant is fed to the surface in the form of a second thin film to interact with the first film so as to overcome the impedance to interaction between the two films imposed by the existence of molecular clusters in the films. Thus, each film is fed into the receiving film at a rate such as to break up the molecular clusters in the film and thereby permit the molecules to aggressively and completely interact with one another. In the spinning disc apparatus the films are fed at respective distances from the spin axis.