The boat conformation at the S2 minimum of 6-AIH + and S3 minimum of 7-AIH + indicates that the * orbital tends to form a weak Dewar bond between atoms 5 and 7a across the ring. Because the puckering degree is relatively small, we will refer to it as a pre-Dewar structure. The density differences in Figure show this bond is stronger in 6-than in 7-AIH + , explaining why the puckered * minimum is more stable in the former. This figure also shows that while the nitrogen atom in position 6 is an electron donor, it is an electron acceptor in position 7. These PES topographies give rise to the following dynamics. After 6-AIH + is vertically lifted to the S3 state, it relaxes to the planar S3 minimum within only 20 fs (Figure , left). This fast relaxation is due to the proximity between the S3 and S0 minima, which are only 0.03 Å apart, as measured by the root-mean-square deviation (RMSD) between them. Then, it undergoes S3→S2 hopping within 156 fs. In S2, it relaxes to the puckered S2 minimum. The population accumulates there, growing up to 30% before it transfers to the S1 state within 300 fs. In the case of 7-AIH + , it relaxes to the S3 minimum within about 40 fs (Figure , right). This minimum is located 0.19 Å from the S0 minimum. After that, the molecule takes longer to hop to S2, yielding an S3 lifetime of 268 fs. The population does not accumulate in S2, and it is immediately transferred to S1. The S3→S2 hopping geometries are characterized with the Cremer-Pople parameters Q, , and . The parameters  and  describe the type of puckering the 6-membered ring undergoes. Q, as mentioned, indicates the puckering intensity. Figure shows that the S3→S2 hoppings happen in the entire - space. Later we discuss how this distribution helps understand the S3 lifetimes of 6-and 7-AIH + .