Excited-state oxygen, definition

The triplet state of the unpaired electrons of oxygen play a key role in both the photon excitation and the potential relaxation mode of the excited chromophores of vision. The paramagnetic properties of oxygen provide a definitive method of determining whether oxygen is present in the chromophores of vision, a condition that would eliminate the Shiff-base theory of retinol reaction with opsin to form rhodopsin. The evaluation of the electron paramagnetic resonance of the chromophores of vision is discussed in Chapter 7. 

UV excited valence-band spectra (UPS) are not often used in the characterization of real catalyst systems. In the present study they were measured for two purposes. First, in a mixture of iron metal and iron oxide, UPS allows accurate definition of the zero of the energy scale and the detection of charging phenomena. In addition, the characteristic dependence of spectral features on excitation energy permits the qualitative separation of the valence band features due to oxygen-derived states from those of the iron 3d valence states. It is therefore possible to follow the reduction process of the surface. In addition, these spectra can indicate that there are no small molecules such as molecular oxygen, water, or carbon monoxide on the activated surface, by the absence of characteristic fingerprint patterns. 

---