The adsorption of NH3 on Rh(111)

R.M. van Hardeveld, R.A. Santen, van, J.W. Niemantsverdriet

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The adsorption of NH3 on Rh(111) has been investigated by temp. programmed desorption, work function measurements LEED and secondary ion mass spectrometry. TPD indicates the existence of three distinct desorption states; a1-a2- and b-NH3 with peak maxima at 320, 155 and 130 K, resp. For the most strongly chemisorbed state, a1-NH3, the desorption energy is 81.5 kJ mol-1. A (2x2) LEED pattern is obsd. after complete filling of the a1- and a2-NH3 states, which is attributed to satn. of the first adsorption layer, corresponding to an NH3 coverage of 0.25 ML. The sticking coeff. for NH3 adsorption at 120 K is on the order of unity and independent of coverage during filling of the first adsorption layer. NH3 adsorption causes a significant work function decrease of 2.4 eV below the value of clean Rh(111). The initial work function decrease corresponds to an av. dipole per NH3 mol. of 1.9 D, i.e. higher than that of the NH3 mol. in the gas phase. SIMS spectra of NH3 on Rh(111) contain Rh(NH3)+ as the predominant ammonia-derived cluster ion. The intensity of the Rh(NH3)+ cluster ion has a strong non-linear behavior with the NH3 coverage and indicates some changes in the NH3 adlayer at a coverage of ~ 0.12 ML
Original languageEnglish
Pages (from-to)23-25
Number of pages3
JournalSurface Science
Issue number1-3
Publication statusPublished - 1996


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