The Bond-Energy Bond-Order (BEBO) Model of Chemisorption

The bond-energy bond-order (BEBO) model of chemisorption allows an estimate to be made of the interaction energy between a gaseous specie and a solid surface as a function of either bond length or bond order, i.e., the length or order of either the gas-surface bond being formed or the bond of the gaseous molecule being broken. The relationship between bond energy and either bond length or bond order is deduced from spectroscopic correlations for gaseous molecules, and a linear relationship between bond energy and bond order is assumed for the surface-adsorbate interaction. The geometry of the surface orbitals is taken to be that predicted by the crystal field model. The model allows a prediction of several relevant quantities in gas-surface interactions, namely: (1) binding energies for molecular adsorbed species, (2) binding energies for atomically adsorbed species, (3) activation energies to chemisorption, and (4) activation energies to dissociative chemisorption. The model is illustrated for the adsorption of H_2, CO, NO and O_2 on Pt, W and Ni surfaces

Atomic helium scattering and diffraction from solid surfaces

It is shown that whether or not diffractive scattering is observed from solid surfaces depends not only on the elastic scattering cross section, i.e. the normalized Debye-Waller factor, but also on the surface structure or local surface potential of the particular solid

Nitric oxide adsorption on Ru(001) at 78 and 120 K: Temperature dependence on the bonding geometry

The influence of surface temperature on NO adsorption on Ru(001) between 78 and 120 K has been investigated by high-resolution electron energy-loss spectroscopy (EELS) and thermal desorption mass spectrometry. Metastable NO adsorption states were isolated at 78 K and were identified by EELS. In all cases, heating of the NO overlayer from 78 to 120 K resulted in an irreversible conversion between adsites. All the measurements were performed in an UHV system that has been described in detail previously. Experimental techniques were employed that have also been documented thoroughly

Effective theory of excitations in a Feshbach resonant superfluid

A strongly interacting Fermi gas, such as that of cold atoms operative near a Feshbach resonance, is difficult to study by perturbative many-body theory to go beyond mean field approximation. Here I develop an effective field theory for the resonant superfluid based on broken symmetry. The theory retains both fermionic quasiparticles and superfluid phonons, the interaction between them being derived non-perturbatively. The theory converges and can be improved order by order, in a manner governed by a low energy expansion rather than by coupling constant. I apply the effective theory to calculate the specific heat and propose a mechanism of understanding the empirical power law of energy versus temperature recently measured in a heat capacity experiment.Comment: 4+ pages, 1 figure; Added references, corrected and clarified minor statements (v.2

Chemisorption on a model bcc metal

The system considered here is that of a single atom with one energy level chemisorbed on the (001) surface of a model bcc metal. We present the change in the density of electronic states Δn (E) due to chemisorption for two cases: one when the adatom is bound to a single substrate atom in the "on‐site" configuration and the other when it is bound to four substrate atoms in the "centered fourfold site." In principle, this change in the density of states Δn can be related to the results of photoemission measurements

Points of General Relativisitic Shock Wave Interaction are "Regularity Singularities" where Spacetime is Not Locally Flat

We show that the regularity of the gravitational metric tensor in spherically symmetric spacetimes cannot be lifted from $C^{0,1}$ to $C^{1,1}$ within the class of $C^{1,1}$ coordinate transformations in a neighborhood of a point of shock wave interaction in General Relativity, without forcing the determinant of the metric tensor to vanish at the point of interaction. This is in contrast to Israel's Theorem which states that such coordinate transformations always exist in a neighborhood of a point on a smooth single shock surface. The results thus imply that points of shock wave interaction represent a new kind of singularity for perfect fluids evolving in spacetime, singularities that make perfectly good sense physically, that can form from the evolution of smooth initial data, but at which the spacetime is not locally Minkowskian under any coordinate transformation. In particular, at such singularities, delta function sources in the second derivatives of the gravitational metric tensor exist in all coordinate systems of the $C^{1,1}$ atlas, but due to cancelation, the curvature tensor remains uniformly bounded.Comment: This article has been withdrawn since the main result is wrong due to an computational error. See arXiv:1506.04081 and arXiv:1409.5060 for a correction of this error and a proof of the opposite statemen

CO chemisorption on Ir(111)

The adsorption of carbon monoxide on the (111) crystallographic orientation of iridium both at and below room temperature has been investigated using both low‐energy electron diffraction (LEED) and thermal desorption mass spectrometry. At room temperature, CO adsorbs rapidly resulting in the appearance of a faint (√3×√3) R30° LEED pattern after only approximately 1.3×10^(−6) Torr s (1.72×10^(−4) Pa s) exposure. Upon further exposure to CO, the intensity of the overlayer LEED beams initially increases, but then decreases passing through a maximum at an exposure of approximately 2.4×10^(−6) Torr s (3.2×10^(−4) Pa s). By an exposure of 10^(−5) Torr s (1.3×10^(−3) Pa s) each of the (rather dim and diffuse) overlayer beams has split into two beams. These beams then move toward the substrate beams with increasing CO surface coverage, until near saturation coverage the angle between the split overlayer beams subtended at the (00) beam is greater than 30°

Kinetics of dissociative chemisorption of methane and ethane on Pt(110)-(1X2)

The initial probability of dissociative chemisorption Pr of methane and ethane on the highly corrugated, reconstructed Pt(110)‐(1×2) surface has been measured in a microreactor by counting the number of carbon atoms on the surface following the reaction of methane and ethane on the surface which was held at various constant temperatures between 450 and 900 K during the reaction. Methane dissociatively chemisorbs on the Pt(110)‐(1×2) surface with an apparent activation energy of 14.4 kcal/mol and an apparent preexponential factor of 0.6. Ethane chemisorbs dissociatively with an apparent activation energy of 2.8 kcal/mol and an apparent preexponential factor of 4.7×10^(−3). Kinetic isotope effects were observed for both reactions. The fact that P_r is a strong function of surface temperature implies that the dissociation reactions proceed via a trapping‐mediated mechanism. A model based on a trapping‐mediated mechanism is used to explain the observed kinetic behavior. Kinetic parameters for C–H bond dissociation of the thermally accommodated methane and ethane are extracted from the model

Thin solar cell and lightweight array

A thin, lightweight solar cell that utilizes front contact metallization is presented. Both the front light receiving surface of the solar cell and the facing surface of the cover glass are recessed to accommodate this metallization. This enables the two surfaces to meet flush for an optimum seal

CO on Ru(001): Formation and dissolution of islands of CO at low coverages

The present paper deals with the benefits and difficulties of using ion scattering spectroscopy as a spectrometric technique