Abstract

Picosecond absorption spectroscopy has been extensively used in recent years to probe both the transient species and the ligand rebinding process after photoexcitation of the liganded heme proteins. From most of these experiments, it appears that the photodissociation process occurs in less than 6 ps^1-3 or even in a subpicosecond time scale.⁴ This conclusion is supported by the appearance of a deoxy-like difference spectrum with kinetics limited by the pulse duration ( 6 - 8 ps ). As it has been pointed out by others⁵, most of the transient spectra reported differ significantly from the equilibrium spectra. Broaden, red shifted Δ A spectra seems to be the most common characteristic of these picosecond studies. Multiphoton excited species¹ and possible systematic errors in the picosecond spectroscopic methods,⁵ could explain the poor agreement among the various published studies, concerning the precise shape and the time evolution of the transient spectra.⁵,⁶

© 1984 Optical Society of America