The g = 2 multiline EPR signal of the S2 state of the photosynthetic oxygen-evolving complex originates from a ground spin state.

@article{Britt1992TheG,
  title={The g = 2 multiline EPR signal of the S2 state of the photosynthetic oxygen-evolving complex originates from a ground spin state.},
  author={R David Britt and Gary A Lorigan and Kenneth Sauer and Melvin Klein and Julia L Zimmermann},
  journal={Biochimica et biophysica acta},
  year={1992},
  volume={1140 1},
  pages={95-101}
}
The amplitude of the g = 2 Mn 'multiline' EPR signal of the S2 state of the photosynthetic oxygen-evolving complex varies inversely with temperature, indicating that this signal arises from a ground spin state. Electron spin echo experiments at temperatures of 4.2 K and 1.4 K show such Curie-law behavior of the g = 2 multiline EPR signal, as do continuous-wave EPR experiments performed at a non-saturating microwave power in the range from 15.0 K to 4.2 K.