Photoluminescence and the Reactivities of Catalysts

QuiiNCniNG AND AbSOLUI E RA I E CoNSTANI S 1. Supported Vanadium Oxide 

As shown in Fig. 19, vanadium oxide supported on Vycor glass exhibits a photoluminescence spectrum at about 400-600 nm upon excitation of the absorption band at about 320 nm (33, 34, 63, 69,115,116). The absorption and photoluminescence spectra are represented by Eq. (12). The addition of 62, CO, N2O, C2H4, CsHg, or QHjj to the catalyst led to the quenching of the photoluminescence with differing efficiencies but without any changes in the shape of the spectrum. 

The results obtained from such dynamic photoluminescence studies shown in Fig. 41, together with the results obtained for O2 and CO. permit calculation of the absolute rate constants of quenching for the various molecules, as follows 9.34 x 10 for O2, 3.52 x 10 for C2H4, 2.24 x 10 for rram -2-butene, and 1.51 x 10 for N2O, all in units of (g/mol s), respectively (33,34,56,69,115-117). Consequently, the reactivities of these molecules toward the charge-transfer excited state of the vanadyl species decrease in the order O2 CO C2H4 CsHg trans-l-C Wg N2O (120, 208-210). 

The Stern-Vohner equation (Eq. 24) has also been observed to pertain to both the yields (i.e., intensity) and the lifetimes of the photoluminescence spectra of the anchored molybdenmn oxide. 

These absolute quenching rate constants are larger than the values for the excited triplet state of the tetrahedral oxo-vanadyl species of the supported vanadium oxide but decrease in the same order 2.56 x 1(T, 4.35 x 10,  

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