Magneto-optical absorbance difference spectroscopy. A new tool for the study of radical recombination reactions. An application to bacterial photosynthesis

Abstract A new spectroscopic technique is presented for measuring triplet-minus-singlet absorbance difference (T - S) spectra, making use of the effect of a small, modulated magnetic field on the yield of triplet states that are produced by radical recombination. The technique is applied to reaction centers of the photosynthetic bacterium Rhodopseudomonas viridis . T - S spectra have been measured from 280 to 110 K and it is shown that spectral changes induced by cooling are caused by spectral broadening and not by decreasing admixture of a charge-transfer state.