19 research outputs found
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DESIGN OF A MOLECULAR BEAM SURFACE SCATTERING APPARATUS FOR VELOCITY AND ANGULAR DISTRIBUTION MEASUREMENTS
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High Pressure Heterogeneous Catalysis in a Low Pressure Ultrahigh Vacuum Environment
An apparatus was been developed which couples high resolution electron energy loss spectroscopy with molecular beam and scattering techniques. Exposure of Ni(111) to atomic H results in H embedded within the Ni lattice and a monolayer of H adsorbed on the surface. This surface-bound H was removed by an Xe atom beam. Subsequent exposure to CH[sub 4] results in dissociative adsorption, producing adsorbed CH[sub 3] and adsorbed H. Results documents a new mechanism for a surface reaction, a reaction between an adsorbed and a bulk species, and demonstrates the importance of bulk H as a reactant in a heterogeneous catalytic reaction
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D2O PRODUCT ANGULAR AND TRANSLATIONAL ENERGY DISTRIBUTIONS FROM THE OXIDATION OF DEUTERIUM ON Pt(lll)
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High Pressure Heterogeneous Catalysis in a Low Pressure UHV Environment
The major thrust of our research is to carry out for the first time a heterogeneous catalytic reaction that normally is observed only at high pressures (>1 atm) of reactant gas at low pressures (<10{sup {minus}4} Torr) in an ultrahigh vacuum environment. The reaction we have chosen is the steam reforming of methane on a Ni(111) crystal
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SCATTERING OF THERMAL HELIUM BEAMS FROM HIGH-MILLER INDEX (STEPPED) PLATINUM CRYSTAL SURFACES
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MOLECULAR BEAM PHOTOIONIZATION AND GAS-SURFACE SCATTERING
The energetics of the ethylene ion-molecule reactions was investigated in more detail than previously possible in two body collision experiments by photoionization of the neutral van der Waals ethylene dimer. The stability of the (C/sub 2/H/sub 4/)/sup +/C/sub 2/H/sub 4/ ion-molecule collision complex has been determined to be 18.2 +- 0.5 kcal. The highest potential barriers along the reaction coordinate for decomposition of this collision complex into C/sub 4/H/sub 7//sup +/ + H and C/sub 3/H/sub 5//sup +/ + CH/sub 3/ have been determined to be 0 +- 1.5 and 8.7 +- 1.5 kcal. In a similar manner, the energetics of the solvated ethylene dimer ion was investigated by the photoionization of the ethylene trimer. The absolute proton affinity of NH/sub 3/ (203.6 +- 1.3 kcal/mole) and the proton solvation energies by more than one NH/sub 3/ have been determined by molecular beam photoionization. In addition, the NH/sub 3//sup +/-NH/sub 3/ interaction energy (0.79 +- 0.05 eV) was measured by photoionization of the neutral van der Waals dimer. These experiments have shown that photoionization of van der Waals clusters is a very powerful method of determining the energetics of gas phase proton solvation. The scattering of helium atomic beams from a high Miller index platinum surface that exhibits ordered, periodic steps on the atomic scale to probe the effect of atomic steps on the scattering distribution is explored. Rainbow scattering is observed when the step edges are perpendicular to the incident helium atoms. The design, construction and operation of a beam-surface scattering apparatus are described. The first data obtained in this apparatus are presented and the interesting dynamical aspects of the oxidation of D, D/sub 2/ and CO are discussed. 75 references
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