Triplet ground state singlet dynamics

Figure 1.1 Schematic picture of the simulation approach. Numbers denote the sequence of steps involved. (1) MD simulation on the ground state. (2) Vertical excitation of selected geometries and dynamics on the singlet excited state. (3) Assumption of intersystem crossing at the smallest singlet-triplet gap. (4) Dynamics on the triplet ground state. Reproduced with permission from Ref. [31]. Copyright 2013 American Chemical Society.

The interpretation of the PES leads to two important conclusions. First the ground state of 40 is in fact the singlet state, about 0.13 kcal mol below the triplet. This is corroborated by the subsequent high level computations (Table 5.9). Secondly, the broad peaks associated with the Aj ground state arise from the transition from the OXA radical anion to the Aj state, which is actually a transition state. The overtones observed in the spectrum are observations of the structure of this transition state. Wavepacket dynamics computations indicate a lifetime of about 100 fs for the Aj transition state, which corroborates the observed peak broadening. 

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