Dynamics of chemical reactions at cold and ultracold temperatures

The main characteristics of cold and ultracold chemical reactions are reviewed through the illustrative study of the O(P-3) + H-2 reaction dynamics. Using separate analytic representations of the lowest H2O((3)A) electronic state which differ essentially by their descriptions of long-range forces, quantumme-chanical scattering calculations show the crucial role played by the van der Waals interaction potential in chemical reactions at low temperatures. Furthermore, the presence of zero-energy resonances is found to significantly enhance chemical reactivity in the ultracold regime. At translational energies comparable to the well depth of the van der Waals potential, initial-state-selected probabilities and excitation functions are characterized by Feshbach resonances arising from the decay of quasibound states supported by the van der Waals well in the entrance channel of the reaction.