UV Absorption Spectra and Photochemical Reactions of Simple Aromatic Hydrocarbons in the Cryogenic Oxygen Matrix

Article abstract of DOI:10.1021/j100339a017

The UV absorption spectra and photochemical properties of benzene, toluene, p-xylene, mesitylene, durene, styrene, and naphthalene in solid oxygen at 11 K have been studied.The well-resolved contact charge transfer (CCT) absorption spectra have been observed.Participation of valence interaction to the CT state has been discussed on the basis of the evidence that the spectra of the methyl-substituted benzenes consist of two absorption bands, and a vibrational structure of the intrinsic bands disappears.The vertical transition energy of the main CCT band plotted against the ionization potential correlates linearly with the slope of 0.46 +/- 0.13, which is far from unity.Photochemical excitation within the CCT absorption band for all the compounds studied (except styrene) causes oxidative cleavage of the aromatic ring to form the correponding dicarbonyl compounds and CO2 as main products.Styrene reacts as an alkene giving benzaldehyde and formaldehyde, which are specific for the oxidative cleavage of a side chain rather than an aromatic ring.It has been concluded that the oxidative cleavage of a double bond, either olefinic or aromatic, is the common reaction pathway characteristic of the ion-pair state or + ...O2^->.