Direct measurement of vibrational level populations in CO2 produced during CO oxidation on Pd

Abstract

The dynamics of carbon monoxide oxidation by O2 on a Pd foil were probed under nearly collision free conditions using high resolution infrared chemiluminescence. Auger electron spectroscopy was used to verify the absence of impurities on the Pd surface. The reactants were supplied to the surface through a free jet nozzle source while a Fourier transform infrared spectrometer (Bomem DA3002) operating at 0.012 cm−1 resolution was used to fully resolve the rotational structure of 14 vibrational transitions in the product CO2. It was found for reaction on a 600 K surface that the (1001, 2001, 3001) symmetric stretch levels were populated consistent with an apparent vibrational temperature of Tsymmetric=3150 K. However, the populations of the levels with no symmetric component (0001, 0111, 0201, 0221, 0311, 0331, 0002, 0401, 0421, 0441, 0003) were better characterized by a temperature Tnonsymmetric=1900 K, with individual mode temperatures for bending and antisymmetric stretch being equal to 1820 and 2130 K, respectively. Increasing the surface temperature by 75 K resulted in a disproportionate increase in each of the temperatures, i.e., Tsymmetric=3700 K, Tanitsymmetric=2530 K and Tbend=2050 K. It is likely that the observed changes in the vibrational populations are due to changes in the reactant coverages as the surface temperature is increased.