Identification of a Jahn-Teller Tunneling Level

The effects of a nearby tunneling level are observed in the ESR of the lowest optically excited ${\Gamma }_8$ level of ${\mathrm{Eu}}^{2+}$ in Ca${\mathrm{F}}_2$. These results are substantiated by the previous observation of this level by other workers using piezospectroscopic techniques. The ESR evidence for such a level can be found in other systems and may allow its approximate position and symmetry to be determined in these cases.