Perturbation by Paramagnetic Species, the Oxygen Pressure Method

Perturbation by Paramagnetic Species, the Oxygen Pressure Method 

A very simple and effective method of increasing the intensity of Ti So transitions by several orders of magnitude was introduced by Evans 53-s5) Either the pure liquid or concentrated solutions of an aromatic hydrocarbon in chloroform were saturated with oxygen or nitric oxid at high pressures. The newly appearing absorption bands are proportional to the applied gas pressures from 0—100 atm. The So absorptions are in general well structured and the posi- 

Compound Oxygen perturbation (CHCI3 soln.) Phorsphorescence (low-temp, glass) 

The oxygen-perturbed singlet-triplet spectra of aromatic carbonyl compounds were investigated by Warwick and Wells (Fig. 23). Transitions to states were enhanced by the perturbing agent while transitions to (n,7t ) states remained unaffected. It should be mentioned, however, that Evans also observed an oxygen-perturbed increase of the intensity of the Tnn So transitions in pyrazine and acridine. 

A theoretical explanation of the influence of paramagnetic molecules on singlet-triplet intensities involving an exchange interaction between the absorbing molecule and the paramagnetic species was advanced by Hoijtink 

---