By oxygen perturbation

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. 

Evans, D. F. Perturbation of singlet-triplet transitions of aromatic molecules by oxygen under pressure. J. Chem. Soc. 7957, 1351. 

In practice, handling Sq- transitions is often simpler (though less satisfactory), since absorption spectra are not normally available and the maxima of the B and BH+ phosphorescence bands must then be used in the Forster cycle. However Sq-Tj absorption spectra can sometimes be obtained, especially if perturbation methods can be used to enhance the singlet to triplet transition probability. For example, Grabowska and Pakula (1966) induced Sq-Tj absorption in a series of nitrogen-containing heterocyclic compounds by the oxygen perturbation method of Evans (1957). Hence, for these compounds, by combination of absorption and phosphorescence spectral results, the 0-0 transitions could be located more accurately. 

Water may perturb directly the activity of the catalysts by competitive adsorption on active sites. In that case, the inhibition will be a function of the adsorption strength. It was reported in previous papers [7,8] that the inhibition by oxygenated compounds is moderate. Water caused... 

The low-lying triplet states of BD were investigated optically by Evans [128] using the high pressure oxygen perturbation technique. The broad absorption band with... 

Devlin and coworkers (24,25,26) studied the interaction between metal nitrate and chlorate ion pairs and water, and concluded that the interaction is between the metal cation and the oxygen on the coordinated H2O. In addition, they observed some evidence for hydrogen bonding in the second coordination sphere similar to the results here. These researchers worked in a quite different concentration regime and monitored the coitplex by observing perturbed bands of the anion rather than the water molecule, but the results were nonetheless consistent. 

A key question is whether the diatomic molecule in its interaction with metal surfaces remains molecular or dissociates into carbon and oxygen. Broden et al. (3) predicted, by the perturbation of molecular orbitals for CO adsorbed, that only iron could dissociate CO. However, other metals in Group VIII such as nickel (A) ruthenium (5) and rhodium (6) can dissociate CO. Recently Ichikawa et al.(7) observed that disproportionation of CO to CO2 and carbon occurs on small particles of silica-supported palladium. These results show that carbon deposition phenomena may occur via either dissociation of CO on the metals used or disproportionation of CO to CO and carbon on small platinum particles. Cant and Angove (8) studied the apparent deactivation of Pt/Si02 catalyst for the oxidation of carbon monoxide and they suggested that adsorbed CO forms patches and that oxygen atoms are gradually consumed. 

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