A chemical process in which the @[email protected] has a @[email protected] that is longer than its period of rotation is called an indirect reaction (in contrast to a @[email protected]). In a @[email protected] experiment the products of such reactions are scattered at random with reference to the centre of mass of the system. Indirect reactions are also called @[email protected] (They are sometimes called complex reactions, but this usage is not recommended in view of the danger of confusion with @[email protected] reactions, which occur in more than one step).