Consider the following elementary reaction: k + br2 → kbr + br. (a) use simple bimolecular collision theory to determine the value of "kmax" at 600 k. use d12 = 0.400 nm and express k in l mol-1 s -1 .

(b) the observed rate constant at 600 k is ~ 1.4 x 1012 l mol-1 s -1 . this value is larger than what you should have calculated in part (a). we account for this atypical result via a harpoon mechanism. as the k atom approaches a br2 molecule, an electron jumps from k to br2. the resulting cation (k+ ) and anion (br2 – ) are then drawn toward one another, potentially causing a collision that may not have occurred without the attraction. use the observed rate constant to find an effective d12 for this reaction; that is, calculate the value of d12 required for collision theory to agree with experiment. we can use this value as an estimate of the distance over which the electron transfer occurs.