Preferred Label : microscopic diffusion control;
Detailed label : microscopic diffusion control (encounter control);
IUPAC definition : The observable consequence of the limitation that the rate of a bimolecular chemical
reaction in a homogeneous medium cannot exceed the rate of encounter of the reacting
molecular entities. If (hypothetically) a bimolecular reaction in a homogeneous medium
occurred instantaneously when two reactant molecular entities made an encounter, the
rate of reaction would be an encounter-controlled rate, determined solely by rates
of diffusion of reactants. Such a hypothetical 'fully diffusion controlled rate' is
also said to correspond to 'total microscopic diffusion control', and represents the
asymptotic limit of the rate of reaction as the rate constant for the chemical conversion
of the encounter pair into product (or products) becomes large relative to the rate
constant for separation (or dissociation) of the encounter pair. 'Partial microscopic
diffusion control' is said to operate in a homogeneous reaction when the rates of
chemical conversion and of separation are comparable. (The degree of microscopic diffusion
control cannot usually be determined with any precision.);
Origin ID : M03912;
See also
The observable consequence of the limitation that the rate of a bimolecular chemical
reaction in a homogeneous medium cannot exceed the rate of encounter of the reacting
molecular entities. If (hypothetically) a bimolecular reaction in a homogeneous medium
occurred instantaneously when two reactant molecular entities made an encounter, the
rate of reaction would be an encounter-controlled rate, determined solely by rates
of diffusion of reactants. Such a hypothetical 'fully diffusion controlled rate' is
also said to correspond to 'total microscopic diffusion control', and represents the
asymptotic limit of the rate of reaction as the rate constant for the chemical conversion
of the encounter pair into product (or products) becomes large relative to the rate
constant for separation (or dissociation) of the encounter pair. 'Partial microscopic
diffusion control' is said to operate in a homogeneous reaction when the rates of
chemical conversion and of separation are comparable. (The degree of microscopic diffusion
control cannot usually be determined with any precision.)
