First-order spectra pseudo

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

Irradiation of DMDAF in benzene solution at room temperature generates a transient intermediate that appears within the rise-time of the laser and decays by a pseudo first-order kinetic path with a half-life of 51 ns. The optical spectrum of the intermediate is essentially the same as that observed in the low temperature irradiation experiment. 

Small differences in light sources have definite effects on photochemical processes. Some irradiation systems match the solar spectrum poorly, thus affecting the relative importance of the various photodissociation processes occurring in the atmosphere. Ambient variations in the nitrogen dioxide photolysis pseudo-first-order rate constant,... 

It was found possible to measure the kinetics of cleavage of protonated sec-butyl methyl ether 24 by following the disappearance of the methoxy doublet in the NMR spectrum with simultaneous formation of protonated methanol and ferf-butyl cation. The cleavage shows pseudo-first-order kinetics. Presumably, the rate-determining step is the formation of sec-butyl cation followed by rapid rearrangement to the more stable ferf-butyl cation... 

B, then the fluorescence of A would be dominated by the acceptor emission spectrum and that of B by the donor spectrum. Thus, the reaction would cause a blue shift, which, if it were big enough, would enable a cross-correlation measurement. The reverse process with FRET large for B and small for A, would work equally well. For the bimolecular reaction A 4- L B, the flux could be measured if the binding caused a large enough shift in the fluorescence spectrum of A. The analysis for the bimolecular reaction is the same as given earlier in a steady state, the concentration of L is constant and so can be absorbed into a pseudo-first-order rate constant. 

The spectra of alkene selenides persists for several minutes after flashing. A spectrum observed in flashed COSe and ethylene mixture is identical to that produced in flashed CSe2 and ethylene mixture. In Ar or N2, flash photolysis of COSe produces Se2 but no CSe. An added alkene inhibits Se2 formation in experiments either with COSe or CSe2. In flashed CSe2, the rate of decay of Se (4 P) is identical to the rate of appearance of the far ultraviolet bands, within an experimental scatter of + 20% in the pseudo first-order rate constant. Therefore the absorption in the far... 

Cyclohexene was dried and vacuum-distilled before use. It was degassed by three freeze-punp-thaw cycles and stored over activated molecular sieves in a glass bulb. It was introduced into the reactor via vapor phase transfer through a high vacuum manifold (base pressure <10 Torr). After 30 mins, the epoxide yield was quantified on an HP 6890 GC/MS equipped with a J W Scientific DBl capilary column. At the end of each experiment, Ti analysis was performed (15) and epoxide/Ti ratios were calculated. For kinetics experiments, silica powder containing the /ert-butylperoxotitanium complex was prepared in an in situ reactor and the reaction initiated by addition of olefin. The IR spectrum of the gas phase above the silica was recorded at timed intervals. Pseudo-first-order rate constants... 

Furthermore, if the reaction is not truly first order, k values compared at different conversions will be different. When the species are adsorbed on the catalyst, first-order kinetics would be rather unlikely. Even if each species reacted according to first-order kinetics, the lumping of a spectrum of species with different reactivities into one pseudo-component would lead to an overall order higher than 1. 

Picket-fence porphyrin (TpivPP)-iron-V-methylimidazole-02 complex is used as an artificial P-450, and the decomposition rates are investigated in details in the presence of HCl and H2-colloidal platinum supported on poly(vinylpyrrolidone) with or without addition of benzoic anhydride. From the decay rates of the oxy complex followed by electronic spectrum under a variety of conditions, pseudo-first-order rate (with the complex) constants are obtained. ( Kinetics and Mechanism of Reductive Dioxygen Activation Catalyzed by P-450 Model System. Iron Picket... 

Depending on the half-life of the reaction, one may decide whether the mass-transfer delay should be included in data analysis. For the MIMS system that has generated the CNCl spectrum in Figure 27.4, the total delay is approximately 2 min. If a 5% measurement discrepancy is assumed to occur in this period, then a pseudo-first-order reaction with a half-Ufe greater than 27 min would not require consideration of the delay (i.e., tm 2 min x [ln(0.5)/ln(0.95)]). This is the case for CNCl decay in the presence of free chlorine, which has a half-life of ca. 60 min [16]. 

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