Quantum Dynamics of Ultracold [Formula presented] Collisions

Abstract

Ultracold collisions between spin-polarized Na atoms and vibrationally excited [Formula presented] molecules are investigated theoretically, using a reactive scattering formalism (including atom exchange). Calculations are carried out on both pairwise additive and nonadditive potential energy surfaces for the quartet electronic state. The Wigner threshold laws are followed for energies below [Formula presented]. Vibrational relaxation processes dominate elastic processes for temperatures below [Formula presented]. For temperatures below [Formula presented], the rate coefficients for vibrational relaxation ([Formula presented]) are [Formula presented] and [Formula presented] for the additive and nonadditive potentials, respectively. The large difference emphasizes the importance of using accurate potential energy surfaces for such calculations. © 2002 The American Physical Society.