Ví dụ công khai
2003, Timothy M. Cox, 90: Protoporphyria, Karl M. Kadish, Kevin M. Smith, Roger Guilard, (editors), The Porphyrin Handbook, Volume 14: Medical Aspects of Porphyrins, page 132, When a ground state molecule absorbs a photon, the values of the electron spins are not altered and thus the primary excited state is the singlet state.