Following the microscopic pathway to adsorption through chemisorption and physisorption wells

Adsorption involves molecules colliding at the surface of a solid and losing their incidence energy by traversing a dynamical pathway to equilibrium. The interactions responsible for energy loss generally include both chemical bond formation (chemisorption) and nonbonding interactions (physisorption). In this work, we present experiments that revealed a quantitative energy landscape and the microscopic pathways underlying a molecule’s equilibration with a surface in a prototypical system: CO adsorption on Au(111). Although the minimum energy state was physisorbed, initial capture of the gas-phase molecule, dosed with an energetic molecular beam, was into a metastable chemisorption state. Subsequent thermal decay of the chemisorbed state led molecules to the physisorption minimum. We found, through detailed balance, that thermal adsorption into both binding states was important at all temperatures.

Pairwise tidal equilibrium states and the architecture of extrasolar planetary systems

ABSTRACT Current observations indicate that the planet formation process often produces multiple planet systems with nearly circular orbits, regular spacing, a narrow range of inclination angles, and similar planetary masses of order mp ∼ 10 M⊕. Motivated by the observational sample, this paper determines the tidal equilibrium states for this class of extrasolar planetary systems. We start by considering two-planet systems with fixed orbital spacing and variable mass ratios. The basic conjecture explored in this paper is that the planet formation process will act to distribute planetary masses in order to achieve a minimum energy state. The resulting minimum energy configuration – subject to the constraint of constant angular momentum – corresponds to circular orbits confined to a plane, with nearly equal planetary masses (as observed). We then generalize the treatment to include multiple planet systems, where each adjacent pair of planets attains its (local) tidal equilibrium state. The properties of observed planetary systems are close to those expected from this pairwise equilibrium configuration. In contrast, observed systems do not reside in a global minimum energy state. Both the equilibrium states of this paper and observed multiplanet systems, with planets of nearly equal mass on regularly spaced orbits, have an effective surface density of the form σ ∝ r−2, much steeper than most disc models.

Formation of Solid TiC from Thermal Plasma: Thermodynamic Consideration

The synthesis process of solid TiC in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixture containing titanium and chlorine (titanium as a reactant is assumed to be in the form of titanium tetrachloride) with argon, hydrogen and carbon (carbon as a reactant is assumed to be in the form of methane). The calculation was performed for the temperature range between 500 and 6000 K and the total pressure in the system of 1 bar. The fact that thermal plasma is plasma in (local) thermodynamic equilibrium made possible the theoretical determination (by employing the Gibbs free energy data for the compounds present in the system and assuming that the equilibrium of the system corresponds to its minimum energy state) of its equilibrium composition. From the calculated compositions of the investigated gas systems the temperature zones with saturated and/or oversaturated vapor of Ti, TiC and C were determined and the mechanism of the formation of TiC in solid state was proposed.