Electron scattering on molecules: search for semi-empirical indications

Reliable cross-sections for electron-molecule collisions are urgently needed for numerical modeling of various processes important from technological point of view. Unfortunately, a significant progress in theory and experiment over the last decade is not usually accompanied by the convergence of cross-sections measured at different laboratories and calculated with different methods. Moreover the most advanced contemporary theories involve such large basis sets and complicated equations that they are not easily applied to each specific molecule for which data are needed. For these reasons the search for semi-empirical indications in angular and energy dependencies of scattering cross-section becomes important. In this paper we make a brief review of the applicability of the Born-dipole approximation for elastic, rotational, vibrational and ionization processes that can occur during electron-molecule collisions. We take into account the most recent experimental findings as the reference points

Characterization of sputtered W–Si–N thin films by a monoenergetic positron beam

A monoenergetic positron beam was employed to characterize the uniformity and the microstructural variation of thermally treated W–Si–N thin film. As the annealing temperature is increased, positrons are found to be progressively trapped in sites rich in silicon. This behavior is explained by the formation of W clusters from which positrons are favorably trapped into the Si–N amorphous matrix. Positron results are discussed together with information obtained on similar samples by Rutheford backscattering, infrared spectroscopy and transmission electron microscopy measurements

FCHgo : fuel cells hydrogen educational model for schools, an imaginative approach to hydrogen and fuel cell technology for young students and their teachers

In this paper we will describe didactic elements in the Horizon 2020 project FCHgo. This project is directed at children and adolescents between 8 and 18 years old. Its ultimate goal is to raise awareness for renewable energy sources, in particular hydrogen as a fuel and fuel cells for electric power. As part of the project, we are developing a toolkit for teachers and pupils, based upon a narrative approach to physical science and engineering. We believe the narrative approach to be best suited for this project because it allows us to take into account the cognitive tools available to pupils at various stages of their development

Cross Sections for Electron Collisions with H2O

Electron collision cross section data for the water molecule are compiled from the literature. Cross sections are collected and reviewed for totalscattering, elastic scattering, momentum transfer, excitations of rotational and vibrational states, electronic excitation, dissociation, ionization,and dissociative attachment. For each of these processes, the recommended values of the cross sections are presented. The literature has beensurveyed up to the end of 2019

Spectroscopic Studies of Intramolecular Proton Transfer in 2-(4-Fluorophenylamino)-5-(2,4-Dihydroxybenzeno)-1,3,4-Thiadiazole

Spectroscopic studies of the biologically active compound 2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole (FABT), have been performed. Absorption studies in the UV-Vis region for FABT in polar solvents, like water or ethanol, exhibit the domination of the enol form over its keto counterpart, with a broad absorption band centered around 340 nm. In non-polar solvents such as n-heptane or heavier alkanes the 340 nm absorption band disappears and an increase of the band related to the keto form (approximately 270 nm) is observed. Fluorescence spectra (with 270 nm and 340 nm excitation energies used) show a similar dependence: for FABT in 2-propanol a peak at about 400 nm dominates over that at 330 nm while in n-heptane this relation is reversed. The solvent dependent equilibrium between the keto and enol forms is further confirmed by FTIR and Raman spectroscopies. As can be expected, this equilibrium also shows some temperature dependences. We note that the changes between the two tautomeric forms of FABT are not related to the permanent dipole moment of the solvent but rather to its dipole polarizability

Between Physics and Metaphysics — on Determinism, Arrow of Time and Causality

Contemporary physics, with two Einstein’s theories (called “relativity” what can be interpreted erroneously) and with Heisenberg’s principle of indeterminacy (better: “lack of epistemic determinism”) are frequently interpreted as a removal of the causality from physics. We argue that this is wrong. There are no indications in physics, either classical or quantum, that physical laws are indeterministic, on the ontological level. On the other hand, both classical and quantum physics are, practically, indeterministic on the epistemic level: there are no means for us to predict the detailed future of the world. Additionally, essentially all physical principles, including the arrow of time and the conservation of energy could be, hypothetically, violated (with some exceptions in the world of heavier quarks, and probably, the cosmological arrow of time). However, in contrast to Hume’s skepticism, we have no experimental evidence that the causality can be removed or even “hung on” in any case. The text contains some didactical-like issues, as well

“Atoms” Special Issue (Electron Scattering in Gases—From Cross Sections to Plasma Modeling)

Experimental studies of electron scattering in gases, under the name of “cathode rays”, started before the “official” discovery of the electron by J [...

Ramsauer-Townsend minimum in methane – modified effective range analysis

Electron-scattering cross sections in methane are analysed in the very-low energy region. The correspondence between integral elastic, elastic differential and momentum transfer cross sections is checked via a novel approach to modified effective range theory, in order to determine the depth and position of the Ramsauer-Townsend minimum. Phase shifts of the two lowest partial waves are obtained explicitly and parameterized by four coefficients with the physical meaning of the scattering lengths and the effective ranges. Using recent experiments on vibrational cross sections performed over an extended (0–180°) angular range and comparing several theories, an agreement within 10% has been obtained between experimental total and present summed (elastic + vibrational) cross sections in the whole 0.1–2.0 eV energy range. An additional check for consistency is done using two-term Boltzmann analysis to derive electron diffusion coefficients. Calculated drift velocities and transversal diffusion coefficients at 0–10 Td reduced electric field agree within 5% with experiments