Back to Volume 12 Issue 5	Article 5 of 11

Barriers, thresholds and negative ions

It is well known that a collision involving two heavy ions can be described exactly with classical mechanics. In a classical picture the motion of a particle is separated into two components: relative motion and centre-of-mass motion. However, it is not easy to generalize this technique to three or more particles, or to apply it when lighter particles, such as electrons, are involved. Electrons must be described by quantum mechanics, and their kinetic energy, for example, has to be calculated by applying a differential operator to the quantum wavefunction. In any case, the three-body collision problem cannot be solved exactly in either classical or quantum mechanics.

In the May issue of Physics World, Derrick Crothers from Queen's University in Belfast, Northern Ireland describes recent theoretical work by Jan Rost of the Max Planck Institute in Dresden on collisions between negative ions and electrons which result in a three-body system (J M Rost 1999 Phys. Rev. Lett. 82 1652).

Back to Volume 12 Issue 5	Article 5 of 11