Proton-transfer-reaction mass intermediates

More experiments are needed to determine the yields of reactive oxygenated intermediates formed in aromatic degradation. Ideally these would be carried out with high time resolution as an aid to distinguishing primary and secondary oxidation products. Sensitive, on-line analytical techniques, such as proton-transfer-reaction mass spectrometry, should be employed to detect and quantify such intermediates in chamber experiments carried out under NOx conditions representative of atmospheric levels. 

The extension of analytical mass spectrometry from electron ionization (El) to chemical ionization (Cl) and then to the ion desorption (probably more correctly ion desolvation ) techniques terminating with ES, represents not only an increase of analytical capabilities, but also a broadening of the chemical horizon for the analytical mass spectrometrist. While Cl introduced the necessity for understanding ion—molecule reactions, such as proton transfer and acidities and basicities, the desolvation techniques bring the mass spectrometrist in touch with ions in solution, ion-ligand complexes, and intermediate states of ion solvation in the gas phase. Gas-phase ion chemistry can play a key role in this new interdisciplinary integration. 

Equation (115) is the same as (6) studied by James and co-workers (62) in the CO reduction of RhCl3.] The labeling experiment also revealed information on the stability of the hydroxycarbonyl intermediate in (115). If this species, Rh—COOH, was formed in an equilibrium concentration, then proton transfer and the reverse reaction would lead to incorporation of labeled oxygen in the carbonyl ligand and therefore to the observation of doubly labeled C02. However, comparison of the abundances of the three isotopic carbon dioxide molecules found (masses 44, 46 and 48) with distributions calculated assuming (i) equilibrium formation of the hydroxycarbonyl and (ii) immediate decomposition of the intermediate clearly showed that the hydroxycarbonyl intermediate reacts to form C02 immediately after it is formed, with no indication of a substantial equilibrium or incorporation of lsO in the carbonyl ligand. 

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