Insight into why the Langmuir-Hinshelwood mechanism is generally preferred

In heterogeneous catalysis, the two main reaction mechanisms which have been proposed are the Langmuir-Hinshelwood and the Eley-Rideal. For the vast majority of surface catalytic reactions, it has been accepted that the Langmuir-Hinshelwood mechanism is preferred. In this study, we investigate catalytic CO oxidation on Pt(111). It is found that reaction barriers for Langmuir-Hinshelwood mechanisms actually tend to be higher than those for Eley-Rideal ones. An explanation is presented as to why it is still more probable for the reaction to proceed via the Langmuir-Hinshelwood mechanism, despite its higher reaction barrier. (C) 2002 American Institute of Physics.

The Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes

A Langmuir probe has been used as a diagnostic of the temporally evolving electron component within a laser ablated Cu plasma expanding into vacuum, for an incident laser power density on target similar to that used for the pulsed laser deposition of thin films. Electron temperature data were obtained from the retarding region of the probe current/voltage (I/V) characteristic, which was also used to calculate an associated electron number density. Additionally, electron number density data were obtained from the saturation electron current region of the probe (I/V) characteristic. Electron number density data, extracted by the two different techniques, were observed to show the same temporal form, with measured absolute values agreeing to within a factor of 2. The Langmuir probe, in the saturation current region, has been shown for the first time to be a convenient diagnostic of the electron component within relatively low temperature laser ablated plasma plumes. (C) 1999 American Institute of Physics. [S0034-6748(99)01503-8].

Langmuir probe measurements of plasma parameters in the late stages of a laser ablated plume

A simple Langmuir probe technique has been used to measure the electron density, electron temperature, and plasma potential in the late stages (>5 mu s) of a laser ablated plasma plume. In the plasma, formed following 248 nm laser irradiation of a copper target, in vacuum at a laser fluence of 2.5 J cm(-2), electron densities of similar to 10(18) m(-3) and temperatures of similar to 0.5 eV were measured. These values are comparable with those reported previously using Faraday cup detectors and optical emission spectroscopy, respectively. (C) 1997 American Institute of Physics.

Nonlinear hydrodynamic Langmuir waves in fully degenerate relativistic plasma

The combined effect of special relativity and electron degeneracy on Langmuir waves is analyzed by utilizing a rigorous fully relativistic hydrodynamic model. Assuming a traveling wave solution form, a set of conservation laws is identified, together with a pseudo-potential function depending on the relativistic parameter p<inf>F</inf>/(m c) (where p<inf>F</inf> is the Fermi momentum, m is the mass of the charge carriers and c the speed of light), as well as on the amplitude of the electrostatic energy perturbation.

A Revised Disrupted Langmuir-Adsorption Model of Photocatalysis

The increasingly popular disrupted Langmuir–adsorption (DLA) kinetic model of photocatalysis does not contain an explicit function for the dependence of rate on the irradiance, ρ, but instead has a term αρθ, where, α is a constant of the system, and θ is also a constant equal to 1 or 0.5 at low or high ρ values, respectively. Several groups have recently replaced the latter term with an explicit function of the form χ1(−1 + (1 + χ2ρ)1/2), where χ1 and χ2, are constants that can be related to a proposed reaction scheme. Here the latter schemes are investigated, and revised to create a more credible form by assuming an additional hole trapping step. The latter may be the oxidation of water or a surface saturated with O2–. Importantly, this revision suggests that it is only applicable for low quantum yield/efficiency processes. The revised disrupted Langmuir–adsorption model is used to provide good fits to the kinetic data reported for a number of different systems including the photocatalytic oxidation of nitric oxide (NO), phenol (PhOH), and formic acid (FA).