The nature of the NO x species produced during the adsorption of NO at room temperature and during its coadsorption with oxygen on pure and sulfated zirconia has been investigated by means of in situ FTIR spectroscopy. The adsorption of NO on both samples occurs through disproportionation leading to the formation of nitrous acid; water molecules; nitro species; and anionic nitrosyls, NO -. A mechanism for the formation of these adsorption forms is proposed. The NO -species are stable on the surface of zirconia, whereas on the sulfated sample, they are readily oxidized by the SO 4 2-groups. The process of NO disproportionation is favored by wet surfaces and occurs with participation of the tribridged (ZrO 2 ) and terminal (ZrO 2 -SO 4 2-) hydroxyl groups. Coadsorption of NO and O 2 on pure zirconia leads to the formation of various kinds of nitrate species. The presence of sulfate ions reduces the amount of surface nitrates and decreases their thermal stability. An analysis of the combination bands of the nitrate species shows that this spectral region can be used for structural identification of bidentate and bridged nitrates.

Adsorption of CO on Mn-ZSM-5 zeolite at 85 K results in formation of physically adsorbed CO, several kinds of Hbonded CO and Mn 2þ ðCOÞ x geminal species ð2202 cm À1 Þ. Decreasing the coverage during evacuation results in disappearance of the physically adsorbed CO and the H-bonded forms and in conversion of the dicarbonyls to linear Mn 2þ -CO species ð2214 cm À1 Þ. The latter are quite stable at 85 K. Coadsorption 12 CO and 13 CO reveals that the CO molecules in the geminal polycarbonyls behave as independent oscillators. In contrast, CO adsorption at 85 K on MnNaY zeolite only leads to formation of linear Mn 2þ -CO species (2210 cm À1 ) and mono-and di-carbonyls associated with residual sodium cations. The results are interpreted as evidence that site-specified geminal carbonyls are formed with cations possessing an ionic radius bigger than a critical value. This value is different for different positions in various zeolites and is bigger for cations in S II positions in Y zeolites than is the case of cations in a ZSM-5 matrix. Ó

We report on the application of a novel nondestructive in-vacuum technique for relative work function measurements, employing a grazing incidence electron deflection above a sample with a planar surface. Two deflected electron beam detectors are used as a position sensitive detector to control feedback to the sample potential as the sample work function changes. With feedback the sample potential exactly follows the surface sample-size averaged work function variation, so that the deflected beam trajectory remains stable. We also discuss methods to optimize the initial electron trajectories for this method, so as to minimize unwanted effects such as from uncontrolled external magnetic fields. As the electron beam does not impinge on the surface in this new technique electron induced desorption, ionization, dissociation, and/or decomposition is not induced at the interface. Importantly also the technique allows for free access to the surfaces enabling simultaneous deposition/evaporation and/or application of other surface characterization methods. We demonstrate its application in concurrent measurements of helium atom reflectivity and work function changes taking place during molecular oxygen exposure of a Cu(001) surface. A work function measurement sensitivity and stability is demonstrated at ∼10 mV at a sampling rate of 1 Hz and after application of an ∼7 s smoothing routine. In comparison to the helium atom reflectivity measurements, the work function measurements are more sensitive to the initial O uptake, and less so to the final coverage variations and possible surface reordering at higher O coverages.

The interactions of cyanide species with a copper (001) surface were studied with temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Adsorbed cyanide species (CN(a)) undergo recombinative desorption evolving molecular cyanogen (C(2)N(2)). As the adsorbed CN species charge upon adsorption, mutually repulsive dipolar interactions lead to a marked desorption energy reduction with increasing CN(a) coverages. Two new TPD analysis approaches were developed, which used only accurately discernible observables and which do not assume constant desorption energies, E(d), and pre-exponential values, ν. These two approaches demonstrated a linear variation of E(d) with instantaneous coverage. The first approach involved an analysis of the variations of desorption peak asymmetry with initial CN coverages. The second quantitative approach utilized only temperatures and intensities of TPD peaks, together with deduced surface coverages at the peak maxima, also as a function of initial surface coverages. Parameters derived from the latter approach were utilized as initial inputs for a comprehensive curve fit analysis technique. Excellent fits for all experimental desorption curves were produced in simulations. The curve fit analysis confirms that the activation energy of desorption of 170-180 kJ/mol at low coverage decreases by up to 14-15 kJ/mol at CN saturation.

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