A possible mechanism for a bimolecular process catalyzed at a solid surface. It is envisaged that one of the molecules is adsorbed and then reacts with a second molecule that is not adsorbed. This mechanism was suggested by the US chemist Irving Langmuir in 1921 and developed by the British chemist Sir Eric Rideal (1890–1974) in 1939. The Langmuir–Rideal mechanism is not common but certain reactions involving hydrogen atoms probably occur by this mechanism.