Diffuse reflectance triplet–triplet absorption spectroscopy of aromatic hydrocarbons chemisorbed on γ-alumina

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Abstract
An apparatus developed to enable diffuse reflectance flash photolysis measurements to be made is described. Transient spectra observed from five aromatic hydrocarbons adsorbed at less than monolayer levels on activated γ-alumina powder are shown to be due to triplet–triplet absorption. These spectra are strikingly different from the triplet–triplet spectra of these same hydrocarbons in homogeneous media and these differences are interpreted as arising mainly from transitions to charge-transfer states of the surface–adsorbate systems. The potential of this method for investigating photocatalytic reactions and excited states properties on surfaces is demonstrated.