J. Phys. Colloques
Volume 50, Numéro C8, Novembre 198936th International Field Emission Symposium
|Page(s)||C8-147 - C8-151|
J. Phys. Colloques 50 (1989) C8-147-C8-151
KINETICS OF ADSORPTION, THERMAL DESORPTION AND DISSOCIATION OF NO ON RHODIUM, STUDIED BY PULSED FIELD DESORPTIONN. KRUSE1, G. ABEND2 et J.H. BLOCK2
1 Technisch-Chemisches Laboratorium, ETH Zentrum, CH-8092 Zürich, Switzerland
2 Fritz-Haber-Institut der Max-Plank-Gesellschaft, Faradayweg 4-6, D-1000 Berlin 33, F.R.G.
The interaction of NO with stepped surfaces of a Rh field emitter has been studied by means of pulsed field desorption mass spectrometry (PFDMS). At temperatures 300<T<550 K and pressures p<1.3·10-3 Pa, the PFD mass spectra of the adsorbed layer were always dominated by NO+, RhxNn+ and RhOn+ ions (n,x = 1.2). We conclude that part of the adsorbed NO undergoes dissociation with subsequent deposition of oxygen and nitrogen atoms on the surface. At low coverages, i.e. Θ<0.1 monolayer, NO adsorption was found to be predominantly molecular. Using a probe-hole, ~150 atomic sites close to the (100) pole of the Rh tip surface were analyzed by varying the field-free reaction interval, tR, between the field pulses (100µs<tR<1s. The equilibration between NO adsorption and thermal desorption was monitored. The temperature dependence of the mean lifetimes, τ before thermal desorption was evaluated, assuming first order thermal desorption kinetics, yielding an activation energy Ed = 102 kj/mol and a preexponential τ0 = 4·10-14 s.