Figure 3. Density differences for the Cope rearrangement of semibullvalene.

The total electron density at time zero is subtracted from the electron densities at later delay times during the course of the reaction via (a) tunnelling, and (b) for the over-the-barrier reaction. The density differences are presented in the y−z plane at pump-probe delay times T/4, T/2, 3T/4 and T.