The different S3 lifetimes of the two isomers mainly reflect the time for moving from the S3 minimum to the region of S3→S2 hopping. As shown in Figure , the S3→S2 hopping geometries are farther away from the S3 minimum for 7-AIH + than for 6-AIH + . This happens because the planar S3 minimum of 6-AIH + provides easy access to the entire puckering conformational space, while the puckered pre-Dewar S3 minimum of 7-AIH + does not. To reach the hopping region, 7-AIH + either needs to increase the puckering degree in the 5-7a boat region (around  = 90º and  = 30º) or change the puckering conformation. Either way, these processes take time, delaying the internal conversion. For 6-AIH + (top-left graph in Figure ), the hoppings tend to happen with slightly puckered geometries. (Note the dominance of red and orange points.) On the other hand, for 7-AIH + (bottom-left graph in Figure ), there are many hoppings at strongly puckered geometries (green and blue points). The hypothesis that Dewar structures play a role in the S3 lifetime of 6-and 7-AIH + had already been raised in Ref. . However, in that paper, the discussion focused on Dewar bonds between atoms 4 and 7, while here, we see them between atoms 5 and 7a.