# EPR spin selection rules

1. Jan 27, 2008

### Albex

hello

I got al little bit confused about spins flipping in an EPR experiment. As far as I know, the idea of EPR is to measure the absorption of an electromagnetic wave induced by spin flips if the energy is conserved by
$$\hbar \omega = g_{spin} \mu_B B_0$$.
But now I heard several times that a spin cannot be flipped by an electromagnetic dipole field and only optical transitions that include
$$\Delta m_s = 0$$
are permitted if there is zeeman splitting.
So how do spins flip then?