Abstract: Flash desorption activation energies: DCOOH decomposition and CO desorption from Ni(110)

Abstract

Accurate values of activation energies were measured by flash desorption methods without assumptions about preexponential factors, reaction orders, or specific reaction mechanisms. The activation energies were determined by two methods; one method employed a new relationship for the shift in peak temperature with change in heating rate, and the other utilized the change in peak amplitude with shift in peak temperature for different heating rates. Agreement between the two methods was excellent. A series of flash curves at different heating rates were obtained for the CO2 and CO products from DCOOH flash decomposition following adsorption on Ni(110) at 37°C. Adsorbed DCOOH decomposed autocatalytically with an activation energy of 26.6 kcal/mol to form CO2 and D2. Carbon monoxide formation from DCOOH decomposition, which corresponded identically to CO desorption from this surface, showed a first order activation energy of 32.7 kcal/mol; this activation energy was used to fit a series of CO flash desorption curves obtained for CO adsorption at −55°C. The preexponential factor was found to be 8.5×1015 sec−1. The desorption was first order with a coverage dependent desorption energy. The results illustrate the sensitivity of flash desorption for the determination of binding energies over a wide range of coverages.