Amorphous silicon hydride. Preparation, characterization, and photoelectrochemistry

Abstract

two branches of bistable states and rapid jumps during oscillation just as [Br"] crosses this critical value.In principle, either C102 or HC102 could also compete for HBr02 via reaction -T2 or T4, respectively. However, under the conditions employed in these studies both chlorine species concentrations always remain too low to compete with reaction B4. At higher [HC102], chlorous acid control could play a role, but the present experimental system must be viewed as a bromate-driven, bromidecontrolled oscillator.We have not explored the mechanism of the other bromate-chlorous acid-reductant systems in any detail. It seems clear, however, that the reducing agent must have the ability to replace the bromide flow by producing bromide from brómate at an appropriate rate. How this reduction may take place in the related bromate-catalyst-reductant systems will be discussed in a forthcoming paper.10We should also point out that, although the mechanism in Table II bears many similarities to that employed by Bar-Eli,6"7 there are differences of fundamental importance. In particular, though reactions -TI and T2 are analogous to the corresponding ceric and cerous reactions with Br02, kT1 is 4 orders of magnitude greater than the corresponding cerium rate constant. This large an increase in that rate would be sufficient to destroy the bistability in the cerium system.21 The additional reactions T3 and T4 must then play some essential role in the chlorous acid system.Acknowledgment. We thank Mohamed Alamgir and Patrick De Kepper for helpful discussions and Kenneth Kustin for a critical reading of the manuscript. This work was supported by National Science Foundation grants CHE7905911 and CHE8204085.