Microcanonical (NVE) trajectories were run using F-PES and employing a time step of 5 au, or about 0.121 fs. Except as noted below concerning Figure , at each of 6 total energies from 5000 cm -1 to 80,000 cm -1 , we initiated 100 trajectories of 10,000 steps with a recording of the energy, geometry, velocities, and gradients after every 10 steps. The starting geometry was the GM structure (at zero energy), so that the initial total energy was all randomly distributed as kinetic energy. Most trajectories finished, but at higher energies, 50,000 cm -1 and especially 80,000 cm -1 , many trajectories found "holes" which induced a break up of the molecule. Similar MD calculations were also run using the MB-PES, with a total internal energy of 50,000 cm -1 for 20,000 steps of the same duration, 5 au, as above.