Ergodic properties of the multidimensional rayleigh gas with a semipermeable barrier

We consider a multidimensional system consisting of a particle of massM and radiusr (molecule), surrounded by an infinite ideal gas of point particles of massm (atoms). The molecule is confined to the unit ball and interacts with its boundary (barrier) via elastic collision, while the atoms are not affected by the boundary. We obtain convergence to equilibrium for the molecule from almost every initial distribution on its position and velocity. Furthermore, we prove that the infinite composite system of the molecule and the atoms is Bernoulli.