Low-intensity transient absorption spectroscopy has been performed on the isolated D1-D2-cyt-b559 reaction center complex of photosystem II from spinach. The excitation intensity was low enough to keep annihilation at a relatively low level (similar to 11%) and still maintain a very high signal/noise ratio. The kinetics has been measured with similar to 200 fs resolution over two time ranges extending up to 200 ps for two different excitation wavelengths (680 nm, preferential primary donor excitation, and 670 nm, preferential external chlorophyll excitation). Detection wavelengths both in the pheophytin Q(x) region (535-555 nm) and in the chlorin Q(y) region, including the stimulated emission range (660-760 nm) have been employed. The data for all excitation/ detection wavelength pairs and from both time ranges have been analyzed by combined global analysis. A highly complex kinetics, i.e. six lifetimes, has been found necessary for a good description of the data over the entire excitation/detection matrix and time range. These lifetimes are T-1 = 2.4 +/- 0.3 ps, T-2 = 8.9 +/- 1 ps, T-3 = 19.8 +/- 3 ps, T-4 = 56 +/- 10 ps, and T-5 greater than or equal to 1 ns (long-lived, nondecaying). The fastest component (T-6) in these fits had an ca. 300 +/- 50 fs lifetime. Decay-associated spectra of these components are presented for both excitation wavelengths. In a preliminary analysis the 2.4 ps component is assigned to primary charge separation; the 8.9 and 19.8 ps components, to slow energy transfer from external chlorophylls; and the 56 ps component, to a relaxation process among different radical pairs. The ultrafast component most likely reflects the excited-state equilibration within the reaction center core. This assignment is supported by a minimal-yet incomplete-kinetic model which provides rate constants and species-associated difference spectra for the intermediates. In this modeling the apparent rate constant for primary charge separation from the excited reaction center core is 120 +/- 30 ns(-1). In this minimal kinetic model the formation of the primary radical pair occurs exclusively with a 2.8 ps lifetime. Two radical pair states and two external chlorophylls have to be included in the minimal kinetic model for a reasonable description of the data. The data is compared with transient absorption data from other groups and with the results from our previously reported fluorescence study. The high apparent rate constant of 120 ns(-1) for charge separation found in the kinetic models as well as other data exclude the possibility that primary charge separation could be associated primarily with a similar to 21 ps lifetime.