Angular dependence of rotational and vibrational energies of product CO2 in CO oxidation on Pd(110)

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Rotational and vibrational energies of product CO2 in CO oxidation on Pd(110) surfaces were measured as functions of desorption angles. The antisymmetric vibrational temperature (Ta) was separately determined from the other vibrational modes from the normalized chemiluminescence intensity. The rotational temperature (Trot) and vibrational temperature averaged over the symmetric and bending modes (Tsb) were then determined by the position and width of spectra by comparison with simulated spectra. On Pd(110)-(111), with increases in desorption angle, Ta, Tsb and Trot decreased in the [001] direction but remained constant in [110]. However, such anisotropy disappeared when the ratio of exposure of O2 to that of CO decreased, resulting in a gradual decrease of the three temperatures with increases in the desorption angle. On Pd(110) with missing-rows, the three temperatures increased in [001] but decreased in [110], indicating that the transition state changes with the geometry of the substrate. On Pd(110) with missing-rows, Ta was significantly lower than Tsb, although Ta was close to or higher than Tsb on Pd(110)-(111). However, there was no significant difference in angular dependence between Ta, Tsb and Trot.
2008-07-08