Perturbations in the surface chemistry of hydrogen by nitrogen adatoms on platinum(110)-(1.times.2)

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The kinetics of adsorption and desorption of deuterium have been studied on Pt(110)-(1x2) surfaces on which various fractional coverages of nitrogen adatoms are present. The nitrogen was adsorbed via the decomposition of ammonia at 400 K, at which temperature the initial probability of dissociative adsorption is approximately 4 x 10/sup -3/. Nitrogen selectively blocks the high-temperature ..beta../sub 2/-state of deuterium prior to poisoning the low-temperature ..beta../sub 1/-state. No evidence of a long range electronic perturbation of the surface by the nitrogen adatoms was found. The adsorption kinetics of deuterium on both clean and nitrogen-precovered Pt(110)-(1x2) surfaces were Langmuirian. In particular, adsorption into the ..beta../sub 2/-state was first order with respect to the fraction of vacant surface sites, and adsorption into the ..beta../sub 1/-state was second order in all cases. The modification of the desorption rate coefficients of deuterium on Py(110)-(1x2) by the nitrogen adatoms was measured quantitatively. Nitrogen modifies the preexponential factor and the activation energy of desorption of deuterium on Pt(110)-(1x2) by essentially rescaling the effective coverage of the deuterium. For the ..beta../sub 2/-state, the activation energy and the preexponential factor of the rate coefficient of deuterium desorption from both clean and nitrogen-precovered Pt(110)-(1x2) display a compensation effect. Themore » activation energy of desorption of nitrogen from Pt(110)-(1x2) was determined to be 24 kcal x mol/sup -1/ and relatively independent of coverage, whereas the preexponential factor decreases from approximately 5 x 10/sup -5/ cm/sup 2/ x s/sup -1/ at low coverages (theta/sub N/ less than or equal to 0.15) to approximately 5 x 10/sup -7/ cm/sup 2/ x s/sup -1/ at higher coverages (theta/sub N/ greater than or equal to 0.3).« less