Protoheme-carbon monoxide geminate kinetics

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Abstract
Recombination kinetics of CO to protoheme after laser photolysis have been measured vs. temperature and viscosity. A 25-ns laser pulse was focused on the sample to produce an excitation rate of 109/s per heme. This temporarily populates the heme.sbd.CO state of dissociated pairs which either separate or recombine on a picosecond time scale in viscous glycerol-water solutions. From the equilibrium amplitude of the fraction dissociated during the laser pulse, the geminate recombination rate constant is calculated to be 3 .times. 109/s. This rate coefficient is only weakly dependent on temperature or viscosity. As previously observed the fraction that escapes depends on the solvent viscosity [Marden, M. C. (1983) Ph.D. Thesis, University of Illinois-Urbana]. A model consisting of a single barrier plus diffusive escape is used to simulate the kinetics during and just after the flash.

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