cCold collisions between atoms and diatomic molecules

Collision cross sections are calculated for the three systems O-2-He, Na-2-Na and K-2-K at cold and ultracold temperatures. We discuss their relevance for cold molecule formation by buffer-gas cooling and by other cooling methods where collisions between molecules and atoms are important, e. g photoassociation. The molecule is treated as a rigid rotator in the electronic and vibrational ground state. We have calculated ab initio the potential energy surfaces for the three systems with special emphasis on the long range potential which is very important at low energies. With relevance to buffer gas cooling, we have also studied the thermalization process between O-2 molecules and He atoms as determined by the calculated cross sections.