Quenching of H2 Vibrations in Ultracold 3He and 4He Collisions

Abstract

We present results of quantum mechanical scattering calculations including full rovibrational coupling on the relaxation of vibrationally excited H2 molecules in collision with ultracold 3He and 4He atoms. The exothermic vibrational deactivation cross sections exhibit minima at translational temperatures near 10 K and show an inverse velocity dependence in accordance with Wigner's threshold law in the limit of zero kinetic energy. The corresponding rate coefficients exhibit minima before attaining constant values below 10-3 K. The rate coefficients increase by 3 orders of magnitude when the initial vibrational level of the molecule is raised from v = 1 to v = 10. The results suggest that quasibound resonance states of 3HeH2 and 4HeH2 exist, associated with each excited vibrational state of H2, and that both the triatomic species 3HeH2 and 4HeH2 have one bound vibrational state.