No abstract available

No abstract available

No abstract available

No abstract available

[en] The drift velocity of electrons in mercury vapour at 573 K has been measured using the Bradbury-Nielsen time-of-flight method at vapour number densities ranging from 3.40x10¹⁷ to 1.83x 10¹⁸cm^-3 and at E/N values from 0.1 to 3.0 Td. The measured drift velocities increase linearly with mercury vapour number density, the magnitude of the dependence being a function of E/N. This number density dependence has been attributed to the presence of mercury dimers and the drift velocity corresponding to dimer-free mercury vapour has been obtained by extrapolation. Sources of error are examined and the present results are compared with those of previous workers

[en] 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 180A²(1.8x10^-18m²) 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

[en] The total (He⁺, He) and Ar⁺, Ar) charge-exchange cross sections have been measured in the energy range 1 keV < Esub(lab) < 10 keV, using the condenser-plate method. Special emphasis was placed on accurately controlling and measuring the target gas pressure, and this resulted in an uncertainty of less than 0.5% in the relative values of the cross section and 2.5% in their absolute values. The measured cross sections fit the expression (sigma)sup(1/2) = k₁ - k₂ 1n upsilon to within the experimental errors, and no oscillatory behaviour was observed. The cross section for (He⁺, He) has been calculated in the JWKB approximation, using published ²Σ⁺sub(g) and ²Σ⁺sub(u) potential curves. The calculated and experimental values agree within 10%. The experimental data have been analysed in order to obtain the cross section for electron loss in neutral (Ar, Ar) collisions, and this cross section was found to increase monotonically from (0.39 +- 10%) x 10^-16 cm² at 1.5 keV to (2.47 +- 10%) x 10^-16 cm² at 10 keV. (author)

[en] The mass discrimination errors introduced when ions are sampled from a drift tube and mass analysed have been studied as a function of various experimental parameters such as the diameter of the sampling aperture, the gas pressure, the nature of the gas and the mass of the ion. It is shown that mass discrimination can be reduced by working with low gas pressures and with small sampling apertures. The formation and dissociation of product ions in the sampling system are discussed. (Auth.)

[en] The analysis of mobility data is a valuable technique for deriving ion-atom interaction potentials or testing at initio potentials particularly at relatively large internuclear separations. In order to obtain the most complete information on the long range part of the potential it is necessary to have mobility data at sufficiently low gas temperatures and small values of E/N that the mobility is determined only by the dipole polarization force. Although this condition can be reasonably well met at room temperature for gases of high polarizability, this is not the case for ions in helium and in particular for the most well studied case, that of Li⁺ in helium. The prime purpose of the present measurements was to obtain low temperature data for Li⁺ in helium in order to determine more accurately the attractive long range tail of the potential. The measurements were also extended to argon to demonstrate the effect of the polarizability on the derivation of potentials. The mobility measurements were made using a drift tube-mass spectrometer system employing the Bradbury-Nielsen time of flight technique. Measurements were performed at 294 K and 80 K. The 'three temperature' theory of Lin, Viehland and Mason was used to fit interaction potentials to the present data. Detailed comparisons are made here only for the case of Li⁺ ions in helium. The new data for 80 K provide additional information on the potential at internuclear separations which cover the range to 5 A. (Authors)

[en] The drift velocity of electrons in water vapour at 294 K has been measured over the E/N range 1.4 to 40 Td with an error estimated to be <±0.5% for 5 < E/N (Td) <35 and ± 0.7% for E/N < 5 Td and E/N > 35 Td. The present data show that μN decreases monotonically with decreasing E/N at low E/N values as observed by Wilson et al. (1975) and does not become independent of E/N as indicated by Lowke and Rees (1963). The present values although lower than those of Lowke and Rees, lie within the combined error limits, except for values below 2 Td. The present data suggested that the momentum transfer cross section at low energies is approximately 10% larger than that obtained by Pack et al. (1962) from their drift velocity measurements. 13 refs., 2 tabs., 5 figs