Threshold laws for collisional reorientation of electronic angular momentum

It is shown that the velocity dependence of cross sections for projection-changing transitions in collisions of paramagnetic atoms or molecules with structureless targets near threshold has the form v{sup 2{delta}}{sup m} when {delta}m is even and v{sup 2({delta}m+1)} when {delta}m is odd, where {delta}m is the change in the projection quantum number and v is the relative velocity.