text: Both singlet oxygen states have no unpaired electrons and therefore no net electron spin. The Δ is however paramagnetic as shown by the observation of an electron paramagnetic resonance (EPR) spectrum. The paramagnetism of the Δ state is due to a net orbital (and not spin) electronic angular momentum. In a magnetic field the degeneracy of the  levels is split into two levels with z projections of angular momenta +1ħ and −1ħ around the molecular axis. The magnetic transition between these levels gives rise to the  EPR transition.