RATE CONSTANTS FOR THE IONIZATION AND ELECTROCHEMICAL DESORPTION OF HYDROGEN-ATOMS ON THE MERCURY-ELECTRODE - THE INFLUENCE OF SPECIFICALLYADSORBING BR- AND I- ANIONS

Rate constants for the ionization (W-2) and electrochemical desorption (W-3) Of hydrogen atoms adsorbed on the mercury electrode from 1 M Na 2SO4, KBr, and KI solutions are measured using the method of laser-ind uced photoelectron emission. The specific adsorption of anions is foun d to increase W-2 decreasing at the same time W-3 Potential dependence s of the rate constant W-1 for the hydrogen ion discharge in the same solutions are derived utilizing the known Tafel dependence for the dis charge current of hydrogen ions and employing the voltammograms for hy drogen atoms, From a comparison of W-1 and W-2 it follows that the fre e energy Delta G = RTIn (W-1/W-2) of the reaction H-aq(+) + e --> H-ad s, in accordance with Frumkin's hypothesis, does not depend on the sur face excess Gamma(1) of the anions. In all three solutions, a transiti on from a normal ionization mode (with a transfer coefficient of 0.5) to an activationless one, where maximum values of W-2 are (2 - 4) x 10 (7) s(-1), is observed. The discharge plane of hydrogen ions is assume d to be located within the compact part of the electrical double layer .