Bret Halpern

The exciting oxidation of CO on Pt

Abstract An uncollimated molecular beam (free jet) of CO and O 2 molecules incident on a polycrystalline Pt surface at 775 K in vacuo produces vibrationally hot CO 2 molecules at a density sufficient for infrared emission spectrometry. Analysis of spectra at a resolution of 0.1 cm −1 clearly shows that nascent product molecules have much more internal excitation than would be the case for equilibrium at the surface temperature.

The mode of attack of oxygen atoms on the basal plane of graphite

Gold decoration of the basal lattice plane of graphite etched by atomic oxygen has been made possible by first desorbing the surface oxide layer on the basal plane. The formation of monolayer pits, as revealed by gold decoration, shows that anisotropy does exist, i.e., carbon atoms are preferentially attacked by atomic oxygen in the direction of a axes, rather than the direction of c axis. The monolayer pits are initiated from lattice vacancies which are continually formed by atomic oxygen. The monolayer pits created by atomic oxygen are, unlike the pits by O2 which are circular, hexagonal in shape, the sides of which are composed of 〈101l〉 lattice planes.

Vibrationally excited CO2 from the reaction of O atoms and adsorbed CO on platinum

Abstract Highly excited CO 2 is produced by the reaction O + CO ads / Pt CO 2 ↑ . Its infrared emission spectrum indicates that more than half of teh 4.1 eV exoergicity appears in asymmetric stretch vibration in a disiribution peaked roughly at level (009). CO 2 ↑ is destroyed by O atoms at high pressure (p  10 mTorr). The reaction dynamics and applications are discussed.

Vibrational energy distribution of CO in the oxidation of C on Pt

Abstract CO, excited to its seventh vibrational level, is generated by C oxidation on Pt at 1000–1400 K. Analysis of its Fourier transform IR emission spectrum suggests a non-equilibrium, yet statistical, vibrational distribution. A long-lived reaction complex involving 2–3 Pt atoms is postulated.

Fast flow deposition of metal atoms on liquid surfaces: Gold sol formation and surface lifetime

Abstract Gold atoms are deposited on liquid water surfaces by a low-pressure, fast-flow technique. This leads either to surface penetration with formation of a gold sol, or metal film growth on the liquid surface. The lifetime with respect to surface penetration is estimated, and several applications are discussed.

Chemical energy accommodation at catalyst surfaces. Flow reactor studies of the association of nitrogen atoms on metals at high temperatures

The fate of the energy release in highly exoergic surface-catalysed chemical reactions is of considerable fundamental interest and influences catalyst volatilization/sintering, the aerodynamic heating of hypersonic glide vehicles subject to bombardment by atomic nitrogen and atomic oxygen, etc. To provide the first available high temperature data (T > 800 K) on what fraction (β) of the equilibrium (bond) dissociation energy is delivered to the catalyst per atom association event, a coaxial filament flow reactor (CFFR) has been developed, well-suited to both precise atom mass balance and isothermal calorimetric measurements. Experimental results for the chemical energy accommodation (CEA) coefficient β, and the corresponding N-atom recombination probabilities, γ, are presented for the metals Pt, Ir, Rh, Pd, Co, W and Re at temperatures up to 2600 K. Catalyst energy deposition can be an order of magnitude less than the equilibrium reaction energy. However, since this is not true at all surface temperatures, simple rankings of β-values for metals (at, say, room temperature) or correlations based only on one or two relevant system parameters (e.g. bulk Debye temperature) are of limited application. Alternatively, for N/Re, N/W a Langmuir-type mass-action analysis of the operative elementary steps, combined with a simple postulate (viz. Rideal-produced molecules leave excited whereas Langmuir—Hinshelwood (LH) produced molecules do not) provides a semi-quantitative understanding of β-trends in terms of the adatom binding energy, the equilibrium bond dissociation energy of the product molecule and an elementary Rideal reaction probability. However, high β-values can be observed at low temperatures if the system admits LH-reaction, or Rideal-formed excited molecules are rapidly quenched prior to desorption. We postulate that low catalyst energy deposition occurs at high temperatures (N/Pt, N/Ir) if LH-reaction occurs prior to the complete accommodation of the reactant (atom) chemisorption energy.

Statistical energy partitioning in surface reactions: the Pt-catalyzed oxidations of C and CO

Abstract The fractions of energy partitioned between a desorbed product molecule and a solid catalyst are calculated for two surface-catalyzed reactions according to a simple statistical model. It is shown that the experimentally measured energy disposal in the oxidation of CO on Pt is, to a first approximation, statistical.

A surprisal analysis of the surface catalyzed reaction of atomic oxygen with CO adsorbed on Pt

Abstract The vibrational energy distribution of excited CO 2 produced in the exoergic reaction of gas-phase O atoms with CO adsorbed on Pt is analyzed according to surprisal theory. The result indicates that very few surface atoms participate in reaction energy disposal.

Thermionic emission from platinum in hydrocarbon flows at low pressure

Thermionic emission from Pt filaments is increased by a factor of 1000 in a flow of hydrocarbons at ∼1 Torr pressure and space‐charge‐free conditions. The effect can be used to trace the initial stages of hydrocarbon decomposition and carbon deposition, and it has possible application as an automobile exhaust sensor or a gas chromatograph detector.

Comment on “Desorption of carbon dioxide molecules from a Pt(111) surface: A stochastic classical trajectory approach”

Abstract We examine the claim of Kwong, De Leon and Haller that energy disposal in the Pt-catalyzed oxidation of CO is non-statistical. We find that their main arguments do not support that claim.