  We derive the Boltzmann equation for the rotranslational dynamics of an
arbitrary convex rigid body in a rarefied gas. It yields as a limiting case the
Fokker-Planck equation accounting for friction, diffusion, and nonconservative
drift forces and torques. We provide the rotranslational friction and diffusion
tensors for specular and diffuse reflection off particles with spherical,
cylindrical, and cuboidal shape, and show that the theory describes
thermalization, photophoresis, and the inverse Magnus effect in the free
molecular regime.
