Resonances in the scattering of atoms and molecules

It has been possible to resolve a number of resonance maxima in the low-energy (0.001 eV) cross sections for the scattering of H, H2 and He from other atoms and molecules. The observed resonances are attributed to the formation of metastable van der Waals molecules, which have long been postulated as intermediates in gas-phase recombination. Their energies and widths provide a sensitive probe of the long-range dispersion forces between atoms and molecules. The status of the search for Feshbach resonances involving molecular rotations and resonances associated with chemical complexes is also discussed.