Dynamics of hydroxyl radical desorption from a polycrystalline platinum surface

Laser-induced fluorescence was used to determine the internal energy distribution of OH radicals desorbing from a polycrystalline Pt surface at T = 1130 K. The measurements were performed in a low-pressure flow system under conditions which were shown to be nearly collisionless by determining the energy distribution as a function of pressure. A Cu surface surrounding the reaction zone removed OH radicals efficiently and prevented scattering back into the laser beam. Both the rotational and vibrational temperatures were found to be equal to that of the Pt catalyst, suggesting that the product OH reaches thermal equilibrium with the surface at a rate which is greater than the rate of desorption. For the systems investigated (H₂ + O₂, H ₂ + NO₂, H₂O), the energy distributions were independent of the source of OH radicals.