Rotational period of the system

It has become customary to divide reactive collisions on the basis of mechanism of reaction, i.e. into persistent complex and direct mechanisms. The criteria for complex or direct mechanisms are purely operational since a convenient time scale is the rotational period of the system. Consequently if the projectile and reactant form a complex which lives for more than a rotational period the angular distribution of the products will be symmetrical about a line 90° to the beam direction and passing through the centre of... 

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