Analysis of Transient Absorption Data from Reaction Centers of Purple Bacteria

Abstract

The primary reaction in photosynthetic bacteria is an ultrafast charge separation and electron transfer process which proceeds on the timescale of 10⁻¹²s. In order to understand the molecular mechanisms different spectroscopic techniques with very high time resolution are used. The most common spectroscopic method is the so-called “pump and probe” technique. A strong excitation pulse (wavelength favourable in the lowest absorption band of the special pair P) starts the photosynthetic reaction which induces absorption changes in the sample. These changes are monitored by a second, properly delayed weak probing pulse of variable wavelength. The experiment yields the absorbance change ΔA as a function of delay time t_D and probing wavelength λ_pr.