In situ investigation of the catalytic reaction H-2+1/2O(2)->H2O on Pt(111) with second-harmonic generation

Application of adsorbate specific second-harmonic generation to the quantitative determination of adsorbed species in situ during a catalytic reaction is presented. At a reactant pressure of 10(-5) mbar less than or equal to p less than or equal to 10(-3) mbar the method is applied, taking the catalytic reaction H-2 + 1/2 O-2 --> H2O as an example. The experimentally found coverages in the temperature range 300 K less than or equal to T less than or equal to 700 K can successfully be reproduced with calculations using a kinetic reaction model. The activation energies obtained for the two main routes of water formation are found to be in excellent agreement with previous studies using the modulated molecular-beam reactive scattering technique.