We have developed a potential-energy surface for spin-polarized $\mathrm{K}\left({}^{2}S\right)+{\mathrm{K}}_2\left({}^3\Sigma _u^{+}\right)$ collisions and carried out quantum dynamical calculations of vibrational quenching at low and ultralow collision energies for both bosons ${}^{39}\mathrm{K}$ and ${}^{41}\mathrm{K}$ and fermions ${}^{40}\mathrm{K}$. At collision energies above about $0.1\mathrm{mK}$ the quenching rates are well described by a classical Langevin model, but at lower energies a fully quantal treatment is essential. We find that for the low initial vibrational state considered here $(v=1)$, the ultracold quenching rates are not substantially suppressed for fermionic atoms. For both bosons and fermions, vibrational quenching is much faster than elastic scattering in the ultralow-temperature regime. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states.

• Received 4 November 2004

DOI:https://doi.org/10.1103/PhysRevA.71.032722