Measurements of Townsend's Energy Factor k1 for Electrons in Carbon Dioxide

Rees, J A

doi:10.1071/ph640462

Cited by 26 publications

(11 citation statements)

References 10 publications

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“…Although the results of a number of workers (Townsend and Bailey 1921;Crompton and Sutton 1952;Cochran and Forester 1962;Warren and Parker 1962;Rees 1964;Rees and Jory 1(64) are in reasonable agreement when the mean energy of the electron swarm is in excess of about 0·5 e V, the agreement is not satisfactory when the electron energy approaches the energy of the gas molecules. Our own experience and that of Warren and Parker (1962) have shown that considerable difficulties exist in obtaining reliable, and therefore significant, data in this low energy region.…”

Section: (I)mentioning

confidence: 84%

Precision Measurements of the Townsend Energy Ratio for Electron Swarms in Highly Uniform Electric Fields

Crompton¹,

Elford²,

Gascoigne³

1965

Aust. J. Phys.

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SummaryA detailed account is given of the solution to the problems associated with the use of the Townsend-Huxley method of measuring the ratio of drift speed to diffusion coefficient for very low energy electron swarms. The elimination of radial components of the electric field within the diffusion chamber is shown to be the major experimental problem, especially in the case of the comparatively weak electric fields which must be used for some of the measurements in the near· thermal region. The experimental techniques and procedures, which are described in some detail, enable measurements to be made in this region with an accuracy comparable to that which has been achieved at higher electron energies. I. INTRODUOTIONOne of the methods of examining collision phenomena between low energy electrons and gas molecules is to measure the ratio of the drift velocity W to the diffusion coefficient D of an electron swarm moving under the influence of an electric field E in a gas at a pressure p. Since WjD is a pressure-dependent quantity, the experimental results are always given either in terms of DjfL, where fL is defined as the ratio WjE, or of kv a parameter closely related to the Townsend energy factor, k T , which is defined as the ratio of the mean energy of agitation of the electrons to the mean thermal energy of the molecules of the gas through which the electron swarm moves. These quantities are related by the expression whereBoth k1 and DjfL are functions of the ratio EjN and are also, in general, functions of the gas temperature.An examination of a number of possible sources of error in the TownsendHuxley method for measuring k1 has been made by Crompton and Jory (1962), who showed that, by careful attention to the choice of experimental parameters and conditions, results with errors of less than I % can be achieved for measurements of k1 in hydrogen at 293°K over the range in E jp of O· 1-5·0 V cm -1 torr-I, for which the lowest value of k1 is approximately 2. If the measurements are to be extended to lower values of E jp, the data lose much of their significance unless

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Section: (I)mentioning

confidence: 84%

Precision Measurements of the Townsend Energy Ratio for Electron Swarms in Highly Uniform Electric Fields

Crompton¹,

Elford²,

Gascoigne³

1965

Aust. J. Phys.

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“…Figure 4 shows such a comparison between Buchel'nikova's data and the data from our experiments where the data have been analysed on the basis of a Maxwellian distribution, using the values of kl given in Table 1 * The values of c1a computed from data for aa/P for dry air and carbon dioxide by Rees (1964) and Rees and Jory (1964) are in error by 7%, the correct values being 7% higher than those quoted. This systematic error does not in any way affect the conclusions drawn from the compari- from a recalculation of these data using the newer data for kl and W is also shown.…”

Section: (4)mentioning

confidence: 91%

“…Prasad and Craggs 1961;Rees 1964;Rees and Jory 1964) have shown discrepancies no greater than might be expected as a result of imprecise knowledge of the appropriate energy distributions, the comparisons for water vapour (Prasad and Craggs 1960) were a notable exception. For this gas, values of ua calculated from swarm experiments exceeded the corresponding values calculated from Buchel'nikova's data by a factor of 5 in some instances.…”

Section: Comparison Of Attachment Data From Beam and Swarm Experimentioning

confidence: 99%

“…Frequently, however, comparisons have been made (e.g. Craggs, Thorburn, and Tozer 1957;Bhalla and Craggs 1960;Prasad and Craggs 1960;Chanin, Phelps, and Biondi 1962;Rees 1964;Rees and Jory 1964) by comparing a "mean attachment cross section" ua, derived from the swarm data, with values of the same quantity calculated by averaging the monoenergetic attachment cross section over the energy distribution of the swarm. This procedure is perhaps less satisfactory because of the difficulty in assigning a physical significance to ua (see equation (6)).…”

Section: Comparison Of Attachment Data From Beam and Swarm Experimentioning

confidence: 99%

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The Diffusion and Attachment of Electrons in Water Vapour

Crompton¹,

Rees²,

Jory³

1965

Aust. J. Phys.

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SummaryThe energy ratio and attachment coefficient for electrons in water vapour have been determined in the range 20 < Elp < 60 V cm-l torr-l. The results for the attachment coefficient are in general agreement with other recent determina· tions, but those for the energy ratio differ significantly from the results of Bailey and Duncanson. The use of these new data, in conjunction with values of the drift velocity determined by Pack, Voshall, and Phelps, is shown to remove the serious discrepancy which previously existed between the results of single-collision and swarm experiments. r. INTRODUCTIONWhen electrons having energies of the order of 5 e V pass through water vapour at a pressure of a few torr, an appreciable fraction of the electrons form negative ions by electron attachment. According to Laidler (1954), Craggs and McDowell (1955), and others, the dominant attachment process for energies up to about lO e V is the following resonance capture process:(1)Laidler states that the water molecule is first raised to a repulsive 2Al or 2A2 state of H 2 0-which at once dissociates into H -(IS) and OH(27T). The appearance potential is of the order of 5·5 e V, and the cross section is a maximum for electrons having energies of about 6·5 eV.The curve showing the variation with electron energy of the rate of production of H -ions from H 2 0 shows a second, smaller peak which has a maximum value at an energy of about 8·5 eV (Mann, Hustrulid, and Tate 1940; Buchel'nikova 1959). For electrons of energy greater than about 7·5 eV, 0-ions may also be produced, the reaction being (2) It is widely believed (see, for example, Cottin 1959) that the H-ions formed as above are rapidly converted to negative hydroxyl ions by the following process:At gas pressures of the order of 1 torr, Branscomb and Smith (1955) and Muschlitz and Bailey (1956) observed that the OH-ions so formed were considerably more abundant than either H -or 0-ions.

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“…1·2 3·64 6·533 6·539 6·536 6'536 1·0 3·03 5·421 5·425 5·421 5'421 0·9 2·73 4·869 4·865 4·871 4'868 0·8 2·43 4·322 4·327 4·322 4'32, 0·7 2·124 3·780 3·785 3'783 3·786 3'78, 0·6 1·820 3·236 3·240 3·245 3·244 3.24 1 0·5 1·517 2·698 2·700 2·699 2·704 2'700 0·4 1·214 2·158 2·158 2·162 2·162 2.16 0 0·3 0·910 1·621 1·620 1·621 1·621 0·25 0·759 1·350 1·351 1·352 1·351 0·2 0·607 1·080 1·081 1·081 0·18 0·546 0·972 0·972 0·972 0·15 0·455 0'811 0·811 0·811 0·12 0·364 0·649 0·651 0·650 0·1 0·303 0·541 0·541 The error has been calculated for all values of E /P293 and E used in the present measurements, using the values of W/pD measured by Rees (1964). With the exception of the values at E /p = 6 and 7, the maximum difference between W a.nd W' is less tha.n 0·2%.…”

Section: Resultsmentioning

confidence: 99%