The polish American physicist Roman Smoluchowski showed that the rate constant for a diffusion controller reaction between molecules A and B, Kd is given by where rAB is the distance (in cm) between the molecules and DA and DB are their diffusion coefficients. Calcu- late kD, given that DA-6.0 x 10-5 cm2 s-1, DB = 2.5 × 10-5 cm 2 s-1 at 20°C and rAB-1.0 × 10-8 cm