Reflectivity-potential curves

Figure 3.6 Reflectivity-potential curve(top)and corresponding current-potential cyclic voltammograms (bottom) for a platinum electrode in t.GM HjS04. The reflectivity curve was taken at 546 nm using S-polarised light at a 70° angle of incidence. The potential limits for both the reflectivity and cyclic voltammetry experiments were + 0,535V and -0.006V vs. NHE, and the scan rate was 26.46 Vs" . From Bewick and Tuxford (1973).

Reflectivity-Potential Curve. RIRq—E curves of gold in a phosphate buffer solution (pH 8.30) containing two different concentrations of NAD are shown in Fig. 25. Addition of NAD to the solution scarcely affects the R/Rq values between —0.8 and —1.0 V but causes a marked decrease in reflectivity in potential regions more positive than about —0.8 V (curves b and c in Fig. 25, in which the curves are drawn separately as in... 

Zhu and Nakamura proved that the intriguing phenomenon of complete reflection occurs in the ID NT type potential curve crossing [1, 14]. At certain discrete energies higher than the bottom of the upper adiabatic potential, the particle cannot transmit through the potential from right to left or vice versa. The overall transmission probability P (see Fig. 45) is given by... 

FIGURE 27.26 Cyclic voltammogram obtained on An electrode in O.IM NaCI04 (a) and reflectivity change-potential curves for O.IM NaC104 (b), O.IM LiCI04 (c), O.IM NaNOj (d), and 0.1 M NaOH (e). Scan rate 0.1 V/s. (From Aral et al., 1997, with permission from... 

The current response is also reversible electrochemically in the sense that electron transfer is fast enough to remain unconditionally at equilibrium, diffusion being the sole kinetic limitation. This is also reflected by superposition of the forward and reverse traces after the above-mentioned transformations have been completed. The same test of reversibility may be performed on the charge-time or charge-potential curves by means of the same transformations (see Section 6.1.2). 

Figure 3.16A shows spectra of o-tolidine in an optically transparent thin-layer electrode (OTTLE) for a series of applied potentials. Curve a was recorded after application of +0.800 V, which caused complete oxidation of o-tolidine ([0]/[R] > 1000). Curve g was recorded after application of +0.400 V, causing complete reduction ([0]/[R] < 0.001). The intermediate spectra correspond to intermediate values of Eapplied. Since the absorbance at 438 nm reflects the amount of o-tolidine in the oxidized form via Beer s law, the ratio [0]/[RJ that corresponds to each value of Eapplied can be calculated from the spectra by Equation 3.18. 

Secondly, if the first oxidation wave cannot be attributed to metallic copper oxidation, only one oxidisable compound is left, namely Cu(I). Indications for this can be found in the fact that in Cu(I)-containing styrene solutions, the limiting-current of this first oxidation wave is much higher than for Cu(II)-containing solutions. As a matter of fact, the first oxidation wave is expected to be absent in Cu(II) solutions. Apparently, the presence of this wave has to be attributed to the fact that some Cu(I) is present in the vicinity of the electrode surface. When the position of the current-potential curves in Fig. 12.2 reflects the standard potentials of the... 

Fig. 3.5. Adiabatic potential curves en(R), defined in (3.31), for the model system illustrated in Figure 2.3. The right-hand side depicts three selected partial photo dissociation cross sections cr(Ef,n) for the vibrational states n = 0 (short dashes), n = 2 (long dashes), and n = 4 (long and short dashes). The vertical and the horizontal arrows illustrate the reflection principle (see Chapter 6). Also shown is the total cross section (Jtot Ef) ...

Fig. 6.4. Schematic illustration of the multi-dimensional reflection principle in the adiabatic limit. The left-hand side shows the vibrationally adiabatic potential curves en(R). The independent part of the bound-state wavefunction in the ground electronic state is denoted by

Here E,j, is the energy of the initial state and R is the nuclear geometry. The division by 3 in (14) comes from orientational averaging. In this form, calculation of the absorption cross section requires the initial vibrational wave function, the transition dipole moment surface and the excited state potential. The reflection principle can be employed for direct or near direct photodissociation. It is again an approximation where the ground state wave function is reflected off the upper potential curve or surface. Prakash et al and Blake et al. [84-86] have used this theory to calculate isotope effects in N2O photolysis. 

All the curves discussed in this chapter have been assigned to the general Herschbach ionic Morse potential curves classification. While many of these curves are speculative, they reflect the data. As stated by Robert Sanderson Mulliken in offering curves for I2 in 1971, While the curves shown cannot possibly be quantitatively correct, they should be useful as forming a sort of zeroth approximation to the true curves. [128]. 

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