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Second-order rate constants k D , of the quenching of singlet oxygen in its a 1 Δ g state by toluene molecules in bulk solvent and four different solvent environments have been determined with the pressure dependence up to 1200 bar, using time-resolved phosphorescence. Experimental activation volumes Δ V ‡ exp were analysed taking into account contact complex formation as the initial step. The reaction volume of the formation of the contact complex Δ V C was evaluated using the hard-sphere model of Yoshimura and Nakahara. The data indicate that Δ V C is the main part of Δ V ‡ exp . A correlation was found between the k D values at 1 bar and the radial distribution function, as expected of the theory of Einwohner and Alder. The quenching rate constants for benzene and cyclohexane at normal pressure are in agreement with this correlation. |
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