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Does the surface temperature influence the cross section of random isolated adsorbates in thermal He scattering?
A481 Surface Science 148 (1984) 117-125
North-Holland,
117
Amsterdam
DOES THE SURFACE TEMPERATURE INFLUENCE THE CROSS SECTION OF RANDOM ISOLATED ADSORBATES IN THERMAL SCATTERING?
Bene POELSEMA. Law-ens K. VERHEIJ and George COMSA lnstrrurftir Gren:Jl~~henJorschunR und Vakuumphysrk. Kernjorschungsanluge Jiihch. D 5170 J&h,
Received
He
Postjuch 1913.
Fed. Rep. OJ Germany
10 March
1984; accepted
for publication
4 June 1984
The question addressed in the title was investigated experimentally for low coverage CO and H on Pt(lll). The consistent result of two kinds of experiments is that the scattering cross section is in general not influenced by the surface temperature, except for H on Pt(ll1) in the limit of small changes of the normal component of the He wave vector, Ak,. The result simplifies substantially the use of He scattering as an analytical technique for surface dynamics investigations. Semi-classical arguments indicate that the lack of influence of the surface temperature at low coverages is related to two circumstances: (1) the small contribution to the specular He beam of the scattering from adsorbate induced disturbances of the repulsive potential and (2) the absence of long range modifications of the vibrational properties of Pt induced by adsorbed CO or H.
Surface Science 148 (1984) 126-138 North-Holland, Amsterdam
126
LIGHT ATOM SCATI’ERING COVERAGE
Hannes J6NSSON Department
oJ Chemistry,
FROM ADSORBATES
AT LOW
and John H. WEARE University of California
at San Diego, La Jolla, California
92093,
USA
and Andrea C. LEVI Dipartimenro
Received
di Fisica, Universid
di Geneva, Via Dodecaneso 33, I- I6146
Geneva, Italy
4 June 1984
A multiple scattering theory is developed for the scattering of light atoms from a disordered adsorbate on a smooth surface. Using gas phase potentials for adatom potentials, excellent agreement is found with data for He scattering from adsorbed Xe and surprisingly good agreement with the extensive data for He scattering from adsorbed CO. The attractive adatom potential must be included in the calculation if quantitative comparison with experimental data is to be made. An important contribution to the total cross section of an adatom are quantum mechanical oscillations similar to glory oscillations in gas phase scattering. The dependence of the total cross section on the incident angle is strongly influenced by the varying number of adatoms seen by the probe.
North-Holland,
117
Amsterdam
DOES THE SURFACE TEMPERATURE INFLUENCE THE CROSS SECTION OF RANDOM ISOLATED ADSORBATES IN THERMAL SCATTERING?
Bene POELSEMA. Law-ens K. VERHEIJ and George COMSA lnstrrurftir Gren:Jl~~henJorschunR und Vakuumphysrk. Kernjorschungsanluge Jiihch. D 5170 J&h,
Received
He
Postjuch 1913.
Fed. Rep. OJ Germany
10 March
1984; accepted
for publication
4 June 1984
The question addressed in the title was investigated experimentally for low coverage CO and H on Pt(lll). The consistent result of two kinds of experiments is that the scattering cross section is in general not influenced by the surface temperature, except for H on Pt(ll1) in the limit of small changes of the normal component of the He wave vector, Ak,. The result simplifies substantially the use of He scattering as an analytical technique for surface dynamics investigations. Semi-classical arguments indicate that the lack of influence of the surface temperature at low coverages is related to two circumstances: (1) the small contribution to the specular He beam of the scattering from adsorbate induced disturbances of the repulsive potential and (2) the absence of long range modifications of the vibrational properties of Pt induced by adsorbed CO or H.
Surface Science 148 (1984) 126-138 North-Holland, Amsterdam
126
LIGHT ATOM SCATI’ERING COVERAGE
Hannes J6NSSON Department
oJ Chemistry,
FROM ADSORBATES
AT LOW
and John H. WEARE University of California
at San Diego, La Jolla, California
92093,
USA
and Andrea C. LEVI Dipartimenro
Received
di Fisica, Universid
di Geneva, Via Dodecaneso 33, I- I6146
Geneva, Italy
4 June 1984
A multiple scattering theory is developed for the scattering of light atoms from a disordered adsorbate on a smooth surface. Using gas phase potentials for adatom potentials, excellent agreement is found with data for He scattering from adsorbed Xe and surprisingly good agreement with the extensive data for He scattering from adsorbed CO. The attractive adatom potential must be included in the calculation if quantitative comparison with experimental data is to be made. An important contribution to the total cross section of an adatom are quantum mechanical oscillations similar to glory oscillations in gas phase scattering. The dependence of the total cross section on the incident angle is strongly influenced by the varying number of adatoms seen by the probe.