Wave functions for a quantum mechanical system of a charged particle
colliding with a model two-electron atom. The vertical axis represents
the coordinate of the incident particle, and the other two axes are the
electron coordinates. In the left panel, the collision energy is lower
than the breakup threshold; in the center panel, the collision energy
is sufficient to singly ionize the atom; in the right panel, the energy
is sufficient to cause complete fragmentation of the system.