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

From the Big Bang to the Multiverse: Translations in Space and Time

Since 2004, I have been collaborating with artist Josiah McElheny on the design of cosmological sculptures, inspired originally by the chandeliers of the Metropolitan Opera House in New York. This article describes the science behind the four works that have emerged from this collaboration to date: An End to Modernity (2005), The Last Scattering Surface (2006), The End of the Dark Ages (2008), and Island Universe (2008). These works incorporate idealized representations of many fundamental aspects of contemporary cosmology, including expansion of the universe, the last scattering surface, cosmic microwave background anisotropies, the growth and morphological transformation of galaxies, the rise and fall of the quasar population, the development of large scale structure, and the possibility that our universe is one of many cosmic islands in an eternally inflating multiverse. A companion article describes the history of the collaboration.Comment: From "Josiah McElheny: A Prism," edited by L. Neri and J. McElheny, published by Skira/Rizzoli, New York, 2010. More information and higher resolution images available at http://www.astronomy.ohio-state.edu/~dhw/McElhen

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

Explaining Low Redshift Quasar Evolution

We have developed a flexible framework for constructing physical models of quasar evolution that can incorporate a wide variety of observational constraints, such as multi-wavelength quasar luminosity functions (QLFs), estimated masses and accretion rates of active black holes, space densities of quasar host galaxies, clustering measurements, and the mass function of black holes in the local universe. In this brief contribution we focus on the observed decline in the QLF break luminosity at $z<2$, which can be explained either by a shift toward lower characteristic accretion rates at low $z$ or by preferential suppression of activity in higher mass black holes.Comment: 2 pages, 1 figure, to be published in the Proceedings of "Multiwavelength AGN Surveys", Cozumel, Dec 8 - 12, 200