Laser induced transients

Laser induced transient spectra and decay kinetics have been observed from a wide variety of samples including fractions of monolayers of organic molecules adsorbed on catalytic metal oxide surfaces(3, 4), and included within zeolites(5), from... 

Abstract. A recently developed new method to monitor reaction kinetics of intermolecular interaction is reviewed. This method is based on the measurement of the time-dependent diffusion coefficient using the pulsed-laser-induced transient grating technique. Using this method, conformation change, transient association, and transient dissociation on reactions are successfully detected. The principle and some applications to studies on changes in the intermolecular interactions of photosensor proteins (e.g., photoactive yellow protein, phototropins, AppA) in the time domain are described. In particular, unique features of this time-dependent diffusion coefficient method are discussed. 

On the other hand, the contribution from charge-transfer processes to the laser-induced transients will only be significant if ... 

Alternatively, one can perform a full analysis of the laser-induced transients measured at several concentrations of charge-transfer adsorption species. In this way, one can characterize both... 

With this, the simulation of the laser-induced transients has been achieved as follows. As above mentioned, two main effects contribute to the measured laser-induced variation of potential, AE. On the one hand, the response from the double-layer is given by the product of the temperature coefficient of the double-layer po-... 

Consequently, the laser-induced potential transients can be simulated by the numerical solution of the combination of the Eqs. (88) to (92) and (94). This has been done with a fifth-order Runge-Kuta method with adaptative stepsize implemented in Fortran. As will be shown in Section V.3, this method of analysis is satisfactory for the simulation of laser induced transients for Pt(lll), Pt(lOO) and Pt(llO) in (0.1 - x) MKCIO4 + xM HCIO4 solutions, with X = 0.1, 10, 10 and lO ". From these simulations, both the temperature coefficient of the double-layer potential. 

On the other hand, at eertain selected potentials, the laser-induced transients for platinum electrodes in 0.1 M HCIO4 solutions exhibit elear eontributions from kinetics of charge-transfer processes. As a result, the laser-indueed transients exhibit a non-monopolar decay and, in some cases, a marked bipolar shape is observed. Figure 14 illustrates this behavior. Figure 14A shows that, for the three platinum basal planes, transients at = 0.10 V vs. RHE exhibit a bipolar shape, with a sharp negative peak at very short times, t < 0.5 ps, and a broader positive contribution at... 

The bipolar shape of the laser-induced transients within the hydrogen adsorption region (Fig. 14A), has been explained as follows. The negative fast contribution can be ascribed to the... 

Figure 15. Comparison of the simulated (A) with experimental (B) laser-induced transients for (111) at E = 0.10 V vs. RHE. A) Simulated curves with = 3 mV/K and = lO s. B) Experimental curves in...

Figure 16 compares the results of the simulations with the experimental laser-induced transients, for Pt(lll) at = 0.75 V vs. RHE in perchlorate solutions of pH = 1. For these calculations, constant values for the thermal coefficient of the double-layer... 

Finally, as above mentioned, it is observed that laser-induced transients forPt(llO) atE = 0.35 Vvs. RHE inO.l MHCIO4 solu-... 

In summary, the careful analysis of laser-induced transients for the three platinum basal planes in (0.1 - x) M KCIO4 + x M HCIO4 solutions have allowed decoupling the double-layer response and hydrogen and OH adsorption contributions. In this way, the thermal coefficient of the double-layer potential,... 

The careful analysis of the laser-induce transients for R(lll) stepped surfaces evidences the existence of two potential values where the double-layer temperature coefficient change sign from negative to positive. According to the preceding thermodynamic analysis, this implies the existence of two relative maxima in the entropy of formation of the double layer, or in brief, the presence of two The first pme is close to the peak potential of the... 

On the other hand, for both Pt(l 10) and Pt(lll) stepped surfaces, it is observed that the reorientation kinetics of the water adlayer becomes slower as the proton concentration decreases. This behavior could be explained by an acid-catalysis mechanism. In order to check this hypothesis, the laser-induced transients of Pt(llO) in (0.1 - x) M KCIO4 + X M HCIO4 solutions, where x equals 10 ", 10, 10 and 0.1, were fitted with expression (97). The result shows that, as expected for an acid-catalysis mechanism, the reaction rate is proportional to the proton concentration, and hence, the response time is inversely proportional to the proton concentration. Figure 21 compares the simulated and ejqrerimental curves. The good agreement between these curves corroborates the hypotheses of an acid-catalysis mechanism. 

Figure 22 shows selected laser-induced transients for a Pt(l 11) electrode modified by the deposition of selenium and lead in 0.1 M KCIO4 + 1 mM HCIO4 solutions. Under these conditions, the laser-induced transients essentially reflect the temperature coeffi-... 

Figure 22. Laser-induced transients for a bare, Se-modified and Pb-modified Pt(lll) electrodes in 0.1 M KCIO4 +1 mM HCIO4, at selected potentials vs. RHE. Adapted from Ref 21.

LASER-INDUCED TRANSIENTS WITH FIRST-ORDER KINETICS... 

Khoo I. C., and R. Normandin. 1984. Nanosecond laser-induced transient and erasable permanent grating dif actions and ultrasonic waves in a nematic film. Appl. Phys. 55 1416 see also Kiyano, K., and J. B. Ketterson. 1975. Ultrasonic study of liquid crystals. Plryw. Rev. A 12 615. 

Figure 9.5. Experimental setup for probing the dynamics of laser-induced transient refractive index changes in liquid crystals.

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