scholarly journals Some Recent Studies of Electron Swarms in Gases

1992 ◽  
Vol 45 (3) ◽  
pp. 365 ◽  
Author(s):  
H Tagashira
Keyword(s):  
Boltzmann Equation ◽  
Cross Section ◽  
Electric Fields ◽  
Cross Sections ◽  
Collision Cross Section ◽  
Vibrational Excitation ◽  
Time Spectrum ◽  
Electron Collision ◽  
Electron Drift ◽  
Radio Frequency Electric Fields

Some recent studies of electron swarms in gases under the action of an electric field are introduced. The studies include a new type of continuity equation for electrons having a form in which the partial derivative of the electron density with respect to position and to time are interchanged, a method to deduce the time-of-flight and arrival-time-spectrum swarm parameters based on a Fourier-transformed Boltzmann equation, an examination of the correspondence between experimental and theoretical electron drift velocities, and an automatic technique to deduce the electron-gas molecule collision cross section from electron drift velocity data. We also briefly introduce a method for the deduction of electron collision cross sections with gas molecules having vibrational excitation cross sections greater than the elastic momentum transfer cross section by using a gas mixture technique, an integral type of method for solution of the Boltzmann equation with salient numerical stability, a quantitative analysis of the effect of Penning ionisation, and the behaviour of electron swarms under radio frequency electric fields.

scholarly journals Drift Velocity and Longitudinal Diffusion Coefficient of Electrons in CO2?Ar Mixtures and Electron Collision Cross Sections for CO2 Molecules

1995 ◽  
Vol 48 (3) ◽  
pp. 357 ◽  
Author(s):  
Y Nakamura
Keyword(s):  
Diffusion Coefficient ◽  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Vibrational Excitation ◽  
Electron Collision ◽  
Longitudinal Diffusion ◽  
Excitation Cross Sections ◽  
Momentum Transfer Cross Section

The drift velocity and longitudinal diffusion coefficient of electrons in 0�2503% and 1� 97% C02-Ar mixtures were measured for 0�03 ~ E/N ~ 20 Td. The measured electron swarm parameters in the mixtures were used to derive a set of consistent vibrational excitation cross sections for the C02 molecule. Analysis of electron swarms in pure C02 using the present vibrational excitation cross sections was also carried out in order to determine a new momentum transfer cross section for the C02 molecule.

Electron energy distributions in uniform electric fields and the Townsend ionization coefficient

1958 ◽  
Vol 244 (1237) ◽  
pp. 166-185 ◽  
Keyword(s):  
Differential Equation ◽  
Cross Section ◽  
Electric Fields ◽  
Cross Sections ◽  
Collision Cross Section ◽  
Present Theory ◽  
Uniform Electric Field ◽  
Ionization Coefficient ◽  
Special Cases ◽  
Wide Range

The second-order differential equation which expresses the equilibrium condition of an electron swarm in a uniform electric field in a gas, the electrons suffering both elastic and inelastic collisions with the gas molecules, is solved by the Jeffreys or W.K.B. method of approximation. The distribution function F(ε) of electrons of energy ε is obtained immediately in a general form involving the elastic and inelastic collision cross-sections and without any restriction on the range of E/p (electric strength/gas pressure) save that introduced in the original differential equation. In almost all applications the approximation is likely to be of high accuracy, and easy to use. Several of the earlier derivations of F(ε) are obtained as special cases. Using the function F(ε) an attempt is made to relate the Townsend ionization coefficient a to the properties of the gas in a more general manner than hitherto, using realistic functions for the collision cross-section. It is finally expressed by the equation α/ p = A exp ( — Bp/E ) in which A and B are functions involving the properties of the gas and the ratio E/p . The important coefficient B is directly related to the form and magnitude of the total inelastic cross-section below the ionization potential and can be evaluated for a particular gas once the cross-section is known experimentally. The present theory shows clearly the influence of E/p on both A and B, a matter which has not been satisfactorily discussed previously. The theory is illustrated by calculations of F (ε) and a/p for hydrogen over a range of E/p from 10 to 1000. The agreement between the calculated results and recent reliable observations of α/ p is surprisingly good considering the nature of the calculations and the wide range of E/p .

Determination of Positronium – Atom Collision Cross Section

1975 ◽  
Vol 53 (1) ◽  
pp. 13-22 ◽  
Author(s):  
D. M. Spektor ◽  
D. A. L. Paul
Keyword(s):  
Monte Carlo ◽  
Cross Section ◽  
Cross Sections ◽  
Collision Cross Section ◽  
Diffusion Theory ◽  
Correction Term ◽  
Time Spectrum ◽  
Free Positron ◽  
Atom Collision

We have determined the collision cross section of positronium in He, Ne, Ar, Kr, Xe, N2, and isobutane gases at thermal energies by studying the diffusion of positronium to the walls of a specially designed chamber. The time distribution of annihilations is measured as a function of pressure for each gas. The presence of an admixture of 20 Torr of isobutane in the chamber quenches the free positron component so that the orthopositronium component is the only exponential decay in the time spectrum of annihilations. Diffusion theory is used to obtain theoretical values of the orthopositronium decay constant λ2. These values are a function of three parameters, two of which are common to all results; the third one is σc, the collision cross section. Monte Carlo simulations of the isobutane experiments verify the theoretical results and determine the wall annihilation parameter which is common to all experiments. The Monte Carlo calculations also enable the determination of the second parameter common to all the experiments, which occurs in a correction term in the diffusion theory. The entire analysis has been carried out twice, one in each of the following extreme cases: (1) assuming that no triplet to singlet conversion takes place at the walls of the cells, and (2) assuming that the maximum conversion takes place at the walls.The cross sections in case (1) are, in units of πa02: He, 0.0166 ± 0.0017; Ne, 0.042 ± 0.003; Ar, 0.086 ± 0.005; Kr, 0.099 ± 0.006; Xe, 0.128 ± 0.008; N2, 0.238 ± 0.014; and isobutane, 0.534 ± 0.016. The implications for other types of experiment and theory are briefly discussed, in particular the bubble model for positronium in liquids.

scholarly journals Cross Sections for Electron Scattering in Nitrogen

1984 ◽  
Vol 37 (5) ◽  
pp. 487 ◽  
Author(s):  
GN Haddad
Keyword(s):  
Boltzmann Equation ◽  
Electron Scattering ◽  
Cross Sections ◽  
Vibrational Excitation ◽  
Electron Drift ◽  
Normalization Factor ◽  
Pure Nitrogen ◽  
The Boltzmann Equation ◽  
Excitation Cross Sections

New measurements of electron drift velocities in mixtures of nitrogen and argon have been analysed to determine the normalization factor for the vibrational excitation cross sections for nitrogen. The validity of applying a two-term solution of the Boltzmann equation in these mixtures is demonstrated. The derived cross sections are shown to be consistent with earlier transport data in pure nitrogen.

scholarly journals The Cross Section for the J = 0 → 2 Rotational Excitation of Hydrogen by Slow Electrons

1969 ◽  
Vol 22 (6) ◽  
pp. 715 ◽  
Author(s):  
RW Crompton ◽  
DK Gibson ◽  
AI McIntosh
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Vibrational Excitation ◽  
The Cross ◽  
Excitation Processes ◽  
Slow Electrons ◽  
And Diffusion ◽  
Momentum Transfer Cross Section ◽  
Section Analysis

The results of electron drift and diffusion measurements in parahydrogen have been analysed to determine the cross sections for momentum transfer and for rotational and vibrational excitation. The limited number of possible excitation processes in parahydrogen and the wide separation of the thresholds for these processes make it possible to determine uniquely the J = 0 → 2 rotational cross section from threshold to 0.3 eV. In addition, the momentum transfer cross section has been determined for energies less than 2 eV and it is shown that, near threshold, a vibrational cross section compatible with the data must lie within relatively narrow limits. The problems of uniqueness and accuracy inherent in the swarm method of cross section analysis are discussed. The present results are compared with other recent theoretical and experimental determinations; the agreement with the most recent calculations of Henry and Lane is excellent.

Screened Collision-Induced Quantum Interference in Collisional Plasmas

2009 ◽  
Vol 64 (3-4) ◽  
pp. 233-236 ◽  
Author(s):  
Sang-Chul Na ◽  
Young-Dae Jung
Keyword(s):  
Cross Section ◽  
Quantum Interference ◽  
Potential Model ◽  
Collision Cross Section ◽  
Electron Collision ◽  
Particle Collision ◽  
Interference Effects ◽  
Particle Collisions ◽  
Collision System ◽  
Electron Collisions

Abstract The effects of neutral particle collisions on the quantum interference in electron-electron collisions are investigated in collisional plasmas. The effective potential model taking into account the electronneutral particle collision effects is employed in order to obtain the electron-electron collision cross section including the total spin states of the collision system. It is found that the collision effects significantly enhance the cross section. In addition, the collision-induced quantum interference effects are found to be significant in the singlet spin state. It is shown that the quantum interference effects decrease with increasing the thermal energy of the plasma. It is also shown that the quantum interference effects increase with an increase of the collision energy

scholarly journals A Study of the Vibrational Excitation of H2 by Measurements of the Drift Velocity of Electrons in H2−Ne Mixtures

1988 ◽  
Vol 41 (4) ◽  
pp. 573 ◽  
Author(s):  
JP England ◽  
MT Elford ◽  
RW Crompton
Keyword(s):  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Excitation Cross Section ◽  
Vibrational Excitation ◽  
Pure Hydrogen ◽  
Velocity Data ◽  
Highly Sensitive ◽  
Hydrogen Mixtures ◽  
Made In

Measurements of electron drift velocities have been made in 1�160% and 2�892% hydrogen-neon mixtures at 294 K and values of EI N from 0�12 to 1�7 Td. The measurements are highly sensitive to the region of the threshold of the v = 0 → 1 vibrational excitation cross section for hydrogen and have enabled more definitive tests of proposed cross sections to be made than was possible using drift velocity data for H2−He and H2−Ar mixtures. The theoretical v = 0 → 1 vibrational excitation cross section of Morrison et al. (1987) is shown to be incompatible with the present measurements. A new set of hydrogen cross sections has been derived from the available electron swarm measurements in pure hydrogen and hydrogen mixtures.

scholarly journals THE EINSTEIN–BOLTZMANN SYSTEM AND POSITIVITY

2013 ◽  
Vol 10 (01) ◽  
pp. 77-104 ◽  
Author(s):  
HO LEE ◽  
ALAN D. RENDALL
Keyword(s):  
Cauchy Problem ◽  
General Relativity ◽  
Boltzmann Equation ◽  
Cross Section ◽  
Collision Cross Section ◽  
Curved Spacetime ◽  
The Boltzmann Equation ◽  
The Cauchy Problem

The Einstein–Boltzmann (EB) system is studied, with particular attention to the non-negativity of the solution of the Boltzmann equation. A new parametrization of post-collisional momenta in general relativity is introduced and then used to simplify the conditions on the collision cross-section given by Bancel and Choquet-Bruhat. The non-negativity of solutions of the Boltzmann equation on a given curved spacetime has been studied by Bichteler and Tadmon. By examining to what extent the results of these authors apply in the framework of Bancel and Choquet-Bruhat, the non-negativity problem for the EB system is resolved for a certain class of scattering kernels. It is emphasized that it is a challenge to extend the existing theory of the Cauchy problem for the EB system so as to include scattering kernels which are physically well-motivated.

Characterisation of Calmodulin Structural Transitions by Ion Mobility Mass Spectrometry

2012 ◽  
Vol 65 (5) ◽  
pp. 504 ◽  
Author(s):  
Antonio N. Calabrese ◽  
Lauren A. Speechley ◽  
Tara L. Pukala
Keyword(s):  
Mass Spectrometry ◽  
Cross Section ◽  
Cross Sections ◽  
Ion Mobility ◽  
Collision Cross Section ◽  
Travelling Wave ◽  
Ion Mobility Mass Spectrometry ◽  
Structural Transitions ◽  
Calmodulin Binding ◽  
Negative Mode

This study demonstrates the ability of travelling wave ion mobility-mass spectrometry to measure collision cross-sections of ions in the negative mode, using a calibration based approach. Here, negative mode ion mobility-mass spectrometry was utilised to understand structural transitions of calmodulin upon Ca2+ binding and complexation with model peptides melittin and the plasma membrane Ca2+ pump C20W peptide. Coexisting calmodulin conformers were distinguished on the basis of their mass and cross-section, and identified as relatively folded and unfolded populations, with good agreement in collision cross-section to known calmodulin geometries. Titration of calcium tartrate to physiologically relevant Ca2+ levels provided evidence for intermediately metalated species during the transition from apo- to holo-calmodulin, with collision cross-section measurements indicating that higher Ca2+ occupancy is correlated with more compact structures. The binding of two representative peptides which exemplify canonical compact (melittin) and extended (C20W) peptide-calmodulin binding models has also been interrogated by ion mobility mass spectrometry. Peptide binding to calmodulin involves intermediates with metalation states from 1–4 Ca2+, which demonstrate relatively collapsed structures, suggesting neither the existence of holo-calmodulin or a pre-folded calmodulin conformation is a prerequisite for binding target peptides or proteins. The biological importance of the different metal unsaturated calmodulin complexes, if any, is yet to be understood.

Sign in / Sign up

Export Citation Format

Share Document