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A simple model of the photosynthetic unit has been constructed and used for simulated Forster-type energy migration, fluorescence and intersystem crossing, in order to gain insight into the conditions that influence both the form and the lifetime of the fluorescence decay in vivo. The model consists of a two-dimensional random lattice with one central trap. The simulation was done by means of repetitive Monte Carlo-type computations. The results obtained show that the form of the decay curve changes from exponential to non-exponential, as the chlorophyll concentration (molecules/nm2) is increased. The fluorescence lifetimes (tau 1/e) were also found to decrease substantially with only slight increases inc concentration. At a concentration comparable to that of chlorophyll in the chloroplast, both the form of the fluorescence decay and the lifetime are in fair agreement with experiment in vivo. The reasons for non-exponentially of the decay as well as the properties of energy migration are discussed. Preliminary work involving the dependence of trapping rate on donor concentration is also presented.

As the first part of a systematic theoretical study of oxacarbene rearrangement, ab initio SCF MO calculations employing a split valence shell basis set have been carried out for the model conversion of formaldehyde to the corresponding oxacarbene. The various cross‐sections of the reaction hypersurface were obtained by complete geometry optimization. The results suggest that, at least for the present model system, the reaction takes place preferentially in the first triplet (T1) state via a concerted pathway.

The energy profiles for the decomposition of the first triplet of acetaldehyde via the reactions: CH 3 CHO ν → CH 3 CO° + H°, CH 3 CHO * → CH . 3 + HCO . , have been computed using a non-empirical LCAO MO SCF procedure. Both reactions were found to have energy barriers of similar height (245 KJ mole −1 ) and at similar extensions of the respective rupturing bonds (0.71–0.76 A). The energy profile for internal rotation about the C-C bond was also calculated and showed a small barrier (3.5 kJ mole −1 ).