scholarly journals The Diffusion Coefficient for Thermal Electrons in Mercury Vapour at 470 K

1980 ◽  
Vol 33 (6) ◽  
pp. 989 ◽  
Author(s):  
R Hegerberg ◽  
RW Crompton
Keyword(s):  
Diffusion Coefficient ◽  
Momentum Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Theoretical Calculations ◽  
Sampling Technique ◽  
Mercury Vapour ◽  
Velocity Data ◽  
Average Momentum ◽  
Momentum Transfer Cross Section

The diffusion coefficient for thermal electrons in mercury vapour has been measured using the CavaIIeri electron density sampling technique. The result indicates that the average momentum transfer cross section for electrons is ~27 x 10−16 cm2, a result which favours previously derived cross sections from drift velocity data over recent theoretical calculations.

scholarly journals The Momentum Transfer Cross Section for Electrons in Mercury Vapour from 0·1 to 5 eV

1980 ◽  
Vol 33 (2) ◽  
pp. 259 ◽  
Author(s):  
MT Elford
Keyword(s):  
Experimental Data ◽  
Energy Range ◽  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Mercury Vapour ◽  
Velocity Data ◽  
Maximum Value ◽  
Momentum Transfer Cross Section

The momentum transfer cross section for electrons in mercury vapour has been derived over the energy range 0�1-5 eV from the drift velocity data of Elford (1980). The cross section has a resonance at 0�5 eV with a maximum value of 180 A 2 (1� 8 x 10-18 m2). It is shown that previous cross sections derived either from experimental data or obtained by ab initio calculations are incompatible with the drift velocity data.

scholarly journals Momentum Transfer Cross Section for e??Kr Scattering

1993 ◽  
Vol 46 (2) ◽  
pp. 249 ◽  
Author(s):  
MJ Brennan ◽  
KF Ness
Keyword(s):  
Energy Range ◽  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Theoretical Calculations ◽  
Transport Coefficients ◽  
Velocity Data ◽  
Experimental Errors ◽  
Momentum Transfer Cross Section

The momentum transfer cross section for electrons in krypton has been derived over the energy range Q-4 eV from an analysis of drift velocity and DT/I-' data for hydrogen-krypton mixtures. At energies in the vicinity of the Ramsauer-Townsend minimum, the present work differs significantly from derivations based on analyses of drift velocity data alone. The overall uncertainty in the derived cross section reflects the experimental errors in the transport coefficients, the uncertainty in the cross sections used to represent the hydrogen component in the mixtures, and the uncertainty associated with the X2 minimisation. The present cross section is compared with recent theoretical calculations and other experimental derivations.

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.

scholarly journals Momentum Transfer Cross Section for Electrons in Mercury Vapour Derived from Drift Velocity Measurements in Mercury Vapour?Gas Mixtures

1991 ◽  
Vol 44 (6) ◽  
pp. 647 ◽  
Author(s):  
JP England ◽  
MT Elford
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Personal Communication ◽  
Mercury Vapour ◽  
Semi Empirical ◽  
Time Of Flight Method ◽  
Momentum Transfer Cross Section ◽  
Good Agreement

The Bradbury-Nielsen time-of-flight method has been used to measure electron drift velocities at 573 K in pure mercury vapour, a mixture of 46�80% helium-53� 20% mercury vapour and a mixture of 9�37% nitrogen-90� 63% mercury vapour. The E/N and pressure ranges used were O� 2 to 1� 5 Td and 5�4 to 15�2 kPa for pure mercury vapour, 0 �08 to 3�0 Td and 5 �40 to 26�88kPa for the mixture containing helium and 0�06 to 5�0Td and 3�33 to 16�67kPa for the mixture containing nitrogen. It is shown that the use of mixtures significantly reduces the dependence of the measured drift velocity on the pressure, due to the effect of mercury dimers, from that measured in pure mercury vapour. An iterative procedure to derive the momentum transfer cross section for electrons in mercury vapour over the range 0�04 to 4 eV with an uncertainty between �5 and 10% is described. It is concluded that previously published momentum transfer cross sections for mercury vapour derived from drift velocity data are significantly in error, due to diffusion effects and the procedure used to correct for the influence of dimers. The present cross section is in good agreement with the semi-empirical calculations of Walker (personal communication).

scholarly journals Momentum Transfer Cross Section for Electrons in Krypton Derived from Measurements of the Drift Velocity in H2?Kr Mixtures

1988 ◽  
Vol 41 (5) ◽  
pp. 701 ◽  
Author(s):  
JP England ◽  
MT Elford
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Personal Communication ◽  
Electron Drift ◽  
Velocity Data ◽  
The Cross ◽  
Momentum Transfer Cross Section ◽  
Made In

Measurements of electron drift velocities have been made in 0�4673% and 1�686% hydrogenkrypton mixtures at 293 K and values of E/ N from 0�08 to 2�5 Td with an estimated uncertainty of <�0�7%. The data have been used in conjunction with the H2 cross sections of England et aL (1988) to derive the momentum transfer cross section for krypton over the energy range 0�05 to 6�0 eV. The drift velocity data have also been used to test the Kr momentum transfer cross sections of Koizumi et aL (1986) and Hunter (personal communication 1988). The cross section of Koizumi et aL is clearly incompatible with the present measurements while the cross section of Hunter has been used to predict these measurements to within 1% to 3%.

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.

Energy transfer from excited mercury atoms to electrons

1971 ◽  
Vol 324 (1557) ◽  
pp. 183-200 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Light Flux ◽  
Rate Equations ◽  
Mercury Vapour ◽  
Collector Current ◽  
Torr Pressure ◽  
Associative Ionization ◽  
Detailed Balancing ◽  
Momentum Transfer Cross Section

This work verifies experimentally the principle of detailed balancing pertaining to the interdependence of the forward and reverse cross-sections q 12 and q 21 for electron-atom collisions. Previous experiments on superelastic collisions in excited mercury vapour, namely Hg*( 3 P 1 or 3 P 0 ) + e slow → Hg ( 1 S 0 ) + e fast show that electrons can acquire energies less or equal to the sum of the atom’s excitation energy and the initial electron energy ϵ . However, the cross-sections q 21 were found to be about two orders of magnitude smaller than those theoretically predicted. The major cause of this discrepancy was the use of estimated values of the u. v. resonance light flux. It is measured here in situ by chemical actinometry. In the experiment, electrons are accelerated into a field-free space, while the Hg vapour is irradiated with its resonance light. Some electrons, colliding with Hg*, become fast enough to reach a collector kept at a retarding potential. To find q 21, besides collector current and light flux, the concentrations of atoms in the resonance ( 3 P 1 ) and the lower metastable state ( 3 P 0 ) must be known. These are calculated from the rate equations; 3 P 2 atoms are neglected. It is found that between 5 mTorr and 5 Torr pressure (1 Torr ≈ 133 Pa) the 3 P 1 concentra­tion is nearly independent of p whereas that of the 3 P 0 atoms rises with p until it reaches at ca . 1 Torr a high maximum. This results from collisions with ground state atoms ( 1 S 0 ): at low p they induce transitions downwards from the 3 P 1 to the 3 P 0 state; at high p the fast 1 S 0 atoms in the tail of the distribution collide with the numerous 3 P 0 atoms lifting more up to the 3 P 1 level than arrive. At pressures p > 30 mTorr collisions between 3 P 1 and 3 P 0 atoms contri­bute to the collector current through ‘associative ionization’ which dominates at large p . The corresponding cross-section is q a85 = 4.6 x 10 -14 cm 2 , valid between 383 and 424 K. The superelastic cross-section q 2l = f ( ϵ ) in the pressure range 20-40 mTorr for ϵ = ½ to 5 eV is found to decrease with increasing ϵ , showing branches corresponding to the fine struc­ture of the P state; the position of the two maxima is probably near ½ eV. At low p , when the concentrations of 3 P 1 and 3 P 0 are comparable, the curve for q 21 corresponds to collisions with a mixture of the two states, whereas at high p , when 3 P 0 atoms predominate, a lower q 21 curve is found. The agreement with various theories is reasonable. In addition, approximate values of the momentum transfer cross-section for ½ - 5 eV electrons in Hg are obtained by measuring the current of elastically scattered electrons as a function of ϵ . The result compares satisfactorily with earlier determinations.

scholarly journals The Ratio DL/ for Electrons in Helium at 293 K

1974 ◽  
Vol 27 (2) ◽  
pp. 235 ◽  
Author(s):  
MT Elford
Keyword(s):  
Diffusion Coefficient ◽  
Momentum Transfer ◽  
Cross Section ◽  
Electron Mobility ◽  
Absolute Error ◽  
Longitudinal Diffusion ◽  
Experimental Errors ◽  
The Common ◽  
The Absolute ◽  
Momentum Transfer Cross Section

The Bradbury–Nielsen method has been used to measure the ratio of the longitudinal diffusion coefficient DL to the electron mobility μ in helium at 293 K over the E/N range 0024–0.607 Td. The absolute error is estimated to be less than � 3 %. The present results agree with those of Wagner et al. (1967), to within the combined experimental errors over the common range of E/N values, and are also compatible with the values predicted by Lowke and Parker (1969) from calculations based on the momentum transfer cross section of Crompton et al. (1967).

scholarly journals The Momentum Transfer Cross Section for Electrons in Argon in the Energy Range 0 - 4 eV

1977 ◽  
Vol 30 (1) ◽  
pp. 61 ◽  
Author(s):  
HB Milloy ◽  
RW Crompton ◽  
JA Rees ◽  
AG Robertson
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Scattering Length ◽  
Effective Range ◽  
Fitting Procedure ◽  
Low Energies ◽  
Range Theory ◽  
The Cross ◽  
Momentum Transfer Cross Section

The momentum transfer cross section for electron-argon collisions in the range 0–4 eV has been derived from an analysis of recent measurements of DT/μ as a function of E/N at 294 K (Milloy and Crompton 1977a) and W as a function of E/N at 90 and 293 K (Robertson 1977). Modified effective range theory was used in the fitting procedure at low energies. An investigation of the range of validity of this theory indicated that the scattering length and effective range were uniquely determined ,and hence the cross section could be accurately extrapolated to zero energy. It is concluded that for ε ≤ 0.1 eV the error in !he cross section is less than � 6 % and in the range 0.4 ≤ ε (eV) ≤ 0.4 the error is less than � 8 %. In the range 0.1 < ε (eV) < 0.4 the presence of the minimum makes it difficult to determine the errors in the cross section but it is estimated that they are less than −20 %, +12 %. It is demonstrated that no other reported cross sections are compatible with the experimental results used in the present derivation.

Momentum transfer cross section of argon deduced from electron drift velocity data

1990 ◽  
Vol 23 (7) ◽  
pp. 842-850 ◽  
Author(s):  
M Suzuki ◽  
T Taniguchi ◽  
H Tagashira
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Electron Drift Velocity ◽  
Electron Drift ◽  
Velocity Data ◽  
Momentum Transfer Cross Section
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