The transient effect in a diffusion limited reaction is described by a time-dependent rate coefficient: k(t) = a + b exp(c 2 t)erfc(ct 1/2), where a, b, and c are expressed in terms of the diffusion coefficient (D), the encounter distance (R), and the absolute rate coefficient (k a ); and for ionic reactions, the Onsager length (r e ). Time resolved fluorescence quenching studies on cresyl violet-potassium iodide system in water confirm the validity of the above equation. The values of D and R obtained from the fluorescence quenching studies are in good agreement with the values inferred from other sources, and the value of ka is reasonable
