The twisted arc model for chiral molecules

We present a simple model for chiral molecules which yields the frequency-dependent multipole-multipole polarizabilities required for calculating the dispersive van der Waals constants in a simple, closed, and consistent form. The model consists of a single effective charge confined to a one-dimensional wire formed by two circular arcs, which are twisted with respect to each other by an angle characterizing the chirality. The resulting polarizabilities show a simple functional dependence on the model parameters, and they serve to mimic the chiral properties of small molecules, such as H2S2, in a reasonably realistic way.Comment: 21 pages, 4 figure

Using atomic interference to probe atom-surface interaction

We show that atomic interference in the reflection from two suitably polarized evanescent waves is sensitive to retardation effects in the atom-surface interaction for specific experimental parameters. We study the limit of short and long atomic de Broglie wavelength. The former case is analyzed in the semiclassical approximation (Landau-Zener model). The latter represents a quantum regime and is analyzed by solving numerically the associated coupled Schroedinger equations. We consider a specific experimental scheme and show the results for rubidium (short wavelength) and the much lighter meta-stable helium atom (long wavelength). The merits of each case are then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX sourc

Unified Treatment of Asymptotic van der Waals Forces

In a framework for long-range density-functional theory we present a unified full-field treatment of the asymptotic van der Waals interaction for atoms, molecules, surfaces, and other objects. The only input needed consists of the electron densities of the interacting fragments and the static polarizability or the static image plane, which can be easily evaluated in a ground-state density-functional calculation for each fragment. Results for separated atoms, molecules, and for atoms/molecules outside surfaces are in agreement with those of other, more elaborate, calculations.Comment: 6 pages, 5 figure

The reactions of active nitrogen with molecular oxygen, atomic oxygen and hydrogen.

For the reaction of nitrogen atoms with molecular oxygen, the nitrogen and oxygen atom concentrations were estimated, at different temperatures and pressures, by addition of excess N0 and measurement of N2O and NO produced. The rate constant was given by 2.3 x 10^12 exp(-5,900/RT) cc mole^-1 sec^-1. The maximum production of oxygen atoms was found to correspond to the maximum amount of HCN produced in the active nitrogen-ethylene reaction. A rate constant of 1.83(+- 0.2) x 10^15 cc^2 mole^-2 sec^-1 was determined for the reaction of nitrogen atoms with oxygen atoms, in the absence of molecular oxygen, at pressures of 3, 3.5 and 4 mm, in an unheated reaction tube. The nitrogen atom consumption was estimated by titrating active nitrogen with NO at different positions along the reaction tube. Using the same titration method, the rate constant for the decay of nitrogen atoms, in an unheated vessel, was found to have the value of 5.2 x 10^15 cc^2 mole^-2 sec^-1, with y= 7.5 (-+ 0.6) x 10^-5, in the pressure range from 0.5 to 4 mm. Under similar conditions, and by similar methods, a value of 4.87(+- 0.8) x 10^14 cc^2 mole^-2 sec^-l was obtained for the rate constant of the reaction between nitrogen atoms and hydrogen atoms, over the pressure range from 2.5 mm to 4.5 mm