The kinetics of geminate recombination of horse heart myoglobin with t
he diatomic ligands carbon monoxide, dioxygen, and nitric oxide have b
een reexamined. The new measurements are distinguished from previous s
tudies by (1) consideration of the complete time range longer than 1 p
s, (2) inclusion of the effect of temperature changes near ambient, (3
) attention to the relation between recombination kinetics and the yie
ld of dissociated partners on the millisecond time scale, and (4) use
of singular value decomposition in the analysis. These picosecond resu
lts, together with earlier nanosecond data, for O-2 prove that models
incorporating one, two, or even three discrete intermediates are not s
ufficient to account for all features of geminate recombination kineti
cs. Instead, a continuous evolution of the geminate pair distribution
is preferred.