I. Chronopotentiometry in thin layers of solution. II. Application of thin layer chronopotentiometry to kinetic studies. III. Proton spin relaxation in hydrogen deuteride.

Abstract

Part I: The theory of chronopotentiometry of an electroactive species confined in a thin layer of solution next to the electrode is presented. The potential-time and transition time relationships are verified for the reduction of iron(III) in 1F perchloric acid for solution layer thicknesses from 2 X 10^(-3) to 1 X 10^(-2) cm . The technique is shown to be especially useful for studying irreversible systems that give poor diffusion chronopotentiograms and for determining the number of electrons transferred in electrochemical reactions. Application of the technique to the oxidation of N,N-dimethyl-p-phenylenediamine in 1F sulfuric acid is demonstrated. Part II: A chronopotentiometric procedure is described for studying the rates of chemical reactions that occur subsequent to the electrochemical generation of a species that is confined in a thin layer of solution next to an electrode. The theory is verified for the hydrolysis of p-benzoquinoneimine , and the technique is shown to be especially useful for the study of reactions too slow to be investigated conveniently by other voltammetric methods. Applicability of the technique to the study of ligand exchange reactions is demonstrated. Part III: The HD proton spin-lattice relaxation time T_1 has been measured in pure HD and in mixtures with eight other gases as a function of composition at room temperature. Probabilities per collision for Δ m_J transitions are determined from the Schwinger relation and compared with the values for pure H_2 and H_2 in the same gases. The differences are interpreted in terms of the displacement of the HD center of mass from the charge center of the molecule, and show up in a way correlated with the strengths of the interactions. With the assumptions that Δ J transitions do not contribute to the nuclear spin relaxation and that the isotropic part of the H_2 intermolecular interaction is described by the Lennard-Jones potential, it is found that the Bloom-Oppenheim theory does not explain the large difference in relaxation times for HD and H_2. A method of testing the form of isotropic intermolecular potential functions is proposed.