Ultracold collisions of oxygen molecules

Collision cross sections and rate constants between two ground-state oxygen molecules are investigated theoretically at translational energies below ~1 K and in zero magnetic field. We present calculations for elastic and spin-changing inelastic collision rates for different isotopic combinations of oxygen atoms as a prelude to understanding their collisional stability in ultracold magnetic traps. A numerical analysis has been made in the framework of a rigid-rotor model that accounts fully for the singlet, triplet, and quintet potential-energy surfaces in this system. The results offer insights into the effectiveness of evaporative cooling and the properties of molecular Bose-Einstein condensates, as well as estimates of collisional lifetimes in magnetic traps. Specifically, ¹⁷O₂ looks like a good candidate for ultracold studies, while ¹⁶O₂ is unlikely to survive evaporative cooling. Since ¹⁷O₂ is representative of a wide class of molecules that are paramagnetic in their ground state we conclude that many molecules can be successfully magnetically trapped at ultralow temperatures.