The purpose of this article is to give a set of recommendations to producers of assessed thermodynamic data, who may be involved in either the critical evaluation of limited chemical systems or the creation and dissemination of larger thermodynamic databases. Also, it is hoped that reviewers and editors of scientific publications in this field will find some of the information useful. Good practice in the assessment process is essential, particularly as datasets from many different sources may be combined together into a single database. With this in mind, we highlight some problems that can arise during the assessment process and we propose a quality assurance procedure. It is worth mentioning at this point, that the provision of reliable assessed thermodynamic data relies heavily on the availability of high quality experimental information. The different software packages for thermodynamics and diffusion are described here only briefly.

We use the Newns-Anderson Hamiltonian to describe many-body electronic processes that occur when hyperthermal alkali atoms scatter off metallic surfaces.Following Brako and Newns, we expand the electronic many-body wavefunction in the number of particle-hole pairs (we keep terms up to and including a single particle-hole pair). We extend their earlier work by including level crossings, excited neutrals and negative ions. The full set of equations of motion are integrated numerically, without further approximations, to obtain the many-body amplitudes as a function of time. The velocity and work-function dependence of final state quantities such as the distribution of ion charges and excited atomic occupancies are compared with experiment. In particular, experiments that scatter alkali ions off clean Cu(001) surfaces in the energy range 5 to 1600 eV constrain the theory quantitatively. The neutralization probability of Na + ions shows a minimum at intermediate velocity in agreement with the theory. This behavior contrasts with that of K + , which shows virtually no neutralization, and with Li + , which exhibits a monotonically increasing neutral fraction with decreasing velocity. Particle-hole excitations are left behind in the metal during a fraction of the collision events; this dissipated energy is predicted to be quite small (on the order of tenths of an electron volt). Indeed, classical trajectory simulations of the surface dynamics account well for the observed energy loss, and thus provide some justification for our truncation of the equations of motion at the single particle-hole pair level. Li + scattering experiments off low work-function surfaces provide qualitative information on the importance of many-body effects. At sufficiently low work function, the negative ions predicted to occur are in fact observed. Excited neutral Li atoms (observed via the optical 2p → 2s transition) also emerge from the collision. A peak in the calculated Li(2p) → Li(2s) photon intensity occurs at intermediate work function in accordance with measurements.

Strong electric double layers are produced in a low-density plasma column confined by an axial magnetic field and maintained by single-ended inflow of plasma along the magnetic field. The double layer evolves from an anode sheath, and ionisation within the sheath is shown to be a significant process in this conversion. Once the double layer has been formed, its axial position can be controlled by the external electric circuit. The layer exhibits an axial motion back and forth with amplitudes somewhat larger than the layer thickness.

No abstract

Double layers in a current-carrying magnetised argon plasma are studied experimentally. The layer evolves from an unstable anode sheath when the anode voltage has reached a critical value which depends on the neutral gas pressure. The double layer is an oscillating, three-dimensional structure enclosing both axially and radially a plasma at higher potential which is maintained by a low rate of ionisation due to the accelerated electrons. Axially accelerated electrons and radially accelerated ions have been detected, but not axially accelerated ions. High frequency is detected on the anode side of the layer. Double layers have also been observed in helium and xenon plasmas. Time independent numerical solutions of Maxwell's equation div D= rho in one dimension including ionisation are discussed.

No abstract

No abstract

No abstract