Calculations of dipole moments, optical spectra, and second-order hyperpolarizability coefficients of some mono- and disubstituted stilbene models for the design of nonlinear optical materials

Abstract

Conclusion In this study we have gained additional insight into the mechanism of Hz production from water mediated by colloidal metal catalysts. The differing rates of decay of MV+ and of the conductiity signal observed in this investigation show that charging of the Ptc by electrons is followed by a slower uptake of protons and that the reducing species loading the Ptc above pH 7 cannot be assigned a simple formula like H-, although once equilibrium is established on the catalyst, the ratios of protons to electrons do not differ greatly from 0.5 predicted by this formula. Although both initial [MV'] and [Ptc] strongly affect the fractional decay of MV' , the concentration of MV2+ has little effect. An equilibrium with a Ptc surface saturated with adsorbed MV2+ is suggested. Slow changes in optical absorption and conductivity were found which can be attributed to equilibration of the Ptc with hydrogen (produced with G = 1.0). The ratio of protons to electrons loading the Pt was found for this process to be similar to that in the case of reduction of the Ptc by MV+. The results described above therefore allow us to obtain a more complete understanding of the role played by colloidal metal catalysts in water reduction to hydrogen and have demonstrated the value of using the pulse radiolysis technique together with optical and conductivity detection methods in enabling us to probe such reaction systems.