Potential Energy and Absorption Spectrum of Oxygen

Light absorption by oxygen has been observed from the near infrared to the far ultraviolet. Absorption above about 2500 A. is of some interest in connection with proposed photochemical reactions of oxygen with some other molecules. For the formation of ozone, however, the middle and short ultraviolet region is of primary interest. 

From thermochemical considerations only, light of wavelength less than 8420 A. could possibly bring about ozone formation from oxygen. However, of the probable mechanisms, the one requiring the least energy is 

For this process, the minimum energy requirement corresponds to a wavelength of 3070 A. The decomposition of oxygen into atoms, 

From a consideration of the O2 absorption spectrum and the potential energy diagram, the following primary processes appear most likely. 

The upper limit corresponds to the transition from the lowest vibrational level in the ground state, v = 0, to the first vibrational level in the excited state, v = 1, the lowest vibrational level observed in absorption (17). 

---