Biexponential decay, second-order

In comparison, photolysis of 83 in protic solvents such as methanol, ethanol, and water yields 84 as expected, but 84 forms mainly 87 rather than 85. Furthermore, in these solvents, the transient absorption (Amax 425 nm) due to 84 decays not with a second-order rate law but by biexponential decay. For example, the decay of transient absorption of 84 (A ax 420 nm) in water at pH 7 had rate constants of 2 x 10 and 3 x lO s Subsequent to the decay of 84, a transient absorption was formed with Amax 330 nm and a weak absorption band at 740 nm. However, this transient was formed much slower than 84 decayed. The absorption at 330 nm was described as a biexponential growth with rate constants of 584 and 21 s h The authors assigned this absorption to 88. Since 84 and 88 do not form and decay at the same rate, the authors theorized that 84 decays into 87, which then furnishes 88. Even though intermediate 87 does not absorb in the near UV, the authors characterized it with time-resolved IR spectroscopy. The authors demonstrated that, in hexane and a strongly acidic or basic aqueous solution, the photorelease from 83 goes through the formation of 87, whereas in near neutral aqueous solution, formation of 85 predominates. The authors concluded that the dehydration of intermediates 85 and... 

The second phase of the reaction occurs over a longer time period and can be analyzed by fitting to a biexponential decay. The rates are given in Table III. Interestingly, the rates for a single complex do not vary outside of experimental error as a function of either R or the absolute concentrations of metal complex or DNA. In addition, the rates are the same within experimental error for both Ru(tpy)(bpy)02+ and Ru(tpy)(phen)02+. However, the rates are an order of magnitude slower for Ru(tpy)(dppz)02+ than for the other two complexes. 

Maintaining polar order in a poled pol5uner is of great importance for second-order applications (88,89). The dielectric relaxation process leading to decay in the orientation of ordered polymers has been studied extensively and is the subject of another article (see Dielectric Relaxation). Several models that describe the chromophore reorientation for NLO materials have been proposed, including the Kohlrausch-Williams-Watts (KWW) model (90,91), biexponential and triexponential decay models (92), time-dependent Debye relaxation time models (93), and the Liu-Ramkrishna-Lackritz (LRL) model (94). For further information on... 

Stacy and Van Duyne report time-resolved investigation of SERS of pyridine on silver. They find that at -0.7 V and cathodic to it the signal decays in a biexponential manner, with characteristic times of the order of 0.1 s and tens of seconds. At -0.6 V there is a time-dependent increase of the signal which saturates with the longer time constant. 

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