Transition state theory requires a value of the transmission coefficient, called κ κ in that theory. This value is often taken to be unity (i.e., the species passing through the transition state A B ‡ ‡ always proceed directly to products AB and never revert to reactants A and B). To avoid specifying a value of κ κ , the rate constant can be compared to the value of the rate constant at some fixed reference temperature (i.e., k ( T ) / k ( T R e f ) ) which eliminates the κ κ factor in the resulting expression if one assumes that the transmission coefficient is independent of temperature.