Spin-flipping transitions in 2Σ molecules induced by collisions with structureless atoms -: art. no. 060703

It is shown that spin-flipping transitions in low energy collisions of (2)Sigma diatomic molecules in the lowest rotational N=0 level with structureless atoms proceed through coupling to the rotationally excited N>0 levels, and are determined by the spin-rotation interaction in the rotationally excited molecule. We carry out calculations for collisions of CaH and He-3. For the spin-flip rate coefficient corresponding to an interaction potential that does not generate a shape resonance, we obtain 1.20x10(-17) cm(3) s(-1) at a temperature of 0.4 K consistent with the measured value of 10(-17+/-1) cm(3) s(-1). We make predictions as to which molecules should have the least probability of spin-flipping in collisions with atoms.