PRIMARY PROCESSES IN ISOLATED PHOTOSYSTEM-II REACTION CENTERS PROBED BY MAGIC-ANGLE TRANSIENT ABSORPTION-SPECTROSCOPY

There is currently some disagreement regarding the dominant time constant for formation of the radical pair state P680(+)Ph(-) in isolated photosystem two reaction centres. It has recently been suggested that this disagreement may originate, at least in part, from different polarisations of the pump and probe beams used in optical experiments. In this paper, we present data collected using a magic angle configuration of the pump and probe polarisations. We find that these data support our previous interpretation of data collected using a parallel polarisation configuration. Moreover, we present further evidence to support our conclusion that formation of the P680(+)Ph(-) state primarily occurs with a 21 ps time constant when P680 is directly excited. A 3 ps component is also observed; this component is not associated with a large proportion of the radical pair formation. We discuss our data and interpretation in comparison with those of other groups.