Electron spin couplings in ion-atom collisions

The Dirac equation in a 'tumbling frame' is shown to yield, in its non-relativistic form, a non-inertial rotational coupling, quadratic in angular velocity of the frame, besides the usual Coriolis potential. The new 'quadratic Coriolis coupling' contains spin-orbit interaction and is numerically important for problems involving fast-rotating frames. The customary analysis of radiative transitions in rotating diatomic molecules and quasi-molecular x-ray emission in ion-atom collisions is generalised to include the effects of the new coupling term. (author)