Absolute Rate Constants For Quenching Research Articles

Dynamic photoluminescence studies of vanadium oxide anchored on SiO2 and the effects of added O2 and H2O

Dynamcc photoluminescence studies of V-ozide anchored onto SiO2 are investigated in the absence and presence of O2 or H2O. It is found that the added O2 molecules interact with the charge transfer excited triplet state of tetrahedrally coordinaeed V-oxide species. This results in an efficient quenching of the phosphorescence due to an enhanced radiationless deactivation. On the other hand, the added H2O molecules interact with V-oxide in the ground state, resulting in the coordination change of V-species from tetrahedral to octahedral. These results obtained by dynamic photoluminescence spectroscopy are in good agreement with those obtained by ESR measurements of the photoreduced V4+ ions. From the Stern-Volmer plots for the quenching of the phosphorescence of V-oxide, the absolute quenching rate constants (reaction rate constants) of O2 for the charge transfer excited triplet state of V-oxide anchored onto SiO2 is first determined to be 3.2 × 108 g-cat./mol s at 77 K and 9.3 × 1012 g-cat./mol s at 298 K.

Kinetic study of electronically excited silicon atoms, Si(3p 2( 1S 0)), by time-resolved attenuation of atomic resonance radiation

The collisional behaviour of electronically excited silicon atoms in the 3p 2( 1S 0) state, 1.909 eV above the 3p 2( 3P 0) ground state, is investigated by time-resolved attenuation of atomic resonance radiation at λ = 390.53 nm (4s( 1P o 1)←3p 2 ( 1S 0)). The optically metastable Si(3 1S 0) atoms were generated by the repetitive pulsed irradiation of SiCl 4 and their decay monitored in the presence of added gases. Absolute quenching rate constants ( k Q, cm 3 molecule −1 s −1, 300 K) are reported for the following collision partners: He (⩽1.3 × 10 −15), SiCl 4 ((9.1 ± 1.4) × 10 −11), O 2 ((1.5 ± 0.2) × 10 −11) and N 2O ((4.3 ± 0.4) × 10 −11). The results for O 2 and N 2O are compared with analogous data reported hitherto for Si(3p 2( 3P J )) and with those for the other np 2( 1S 0) states of the group IV atoms C, Ge, Sn and Pb. The rate data for the silicon atoms are considered in terms of the nature of the potential surfaces arising from symmetry arguments based on the weak spin orbit coupling approximation.