Negative Ion Mobility Research Articles

Bipolar Ion and Electron Diffusion Charging of Aerosol Particles in high purity argon and nitrogen

AbstractThe bipolar diffusion charging process is studied theoretically for aerosol particles in high purity argon and nitrogen. The Fuchs theory is extended by the incorporation of the free electron charging of the aerosol particles. The ion parameters for positive and negative ions are assumed to be identical. The influence of the free electrons explains the differences between the mean mobility and mean mass of negative and positive ions. The ratio of the electron number concentration to the number concentration of negative ions is used to fit the curves, calculated by the extended model, to the experimentally determined bipolar charge distribution in argon and nitrogen. The extended Fuchs model was found to be rather insensitive to variations in the mobility and mass compared with the model with four different ion parameters. Further experimental studies of the bipolar charge distribution in a gas mixture of pure nitrogen and sulfur hexafluoride, SF6, indicate the importance of the free electrons in the bipolar diffusion charging process.

Electrical conductivities, ion densities and mobilities in the middle atmosphere over India—balloon measurements

Polar conductivities, ion densities and mobilities measured in three balloon experiments are reported here. Of these, two were made with self-aspirated and one with pumped Gerdien condensers. These measurements were carried out over the period 1985–1986. Both positive and negative ion data were obtained only in the first flight. Positive ions were not collected in the other two flights. The conductivity profiles obtained from the self-aspirated condensers showed fluctuations around the tropopause. These were not seen when the pumped condenser was used. Reduced mobilities of both positive and negative ions agree well with those reported by other experimenters. The ion density profile from the pumped condenser measurement showed a broad maximum around 15 km, as expected from theory. The values were less than what are obtained using available ion pair production rates and recombination coefficients.

Ion mobility spectrometry of halothane, enflurane, and isoflurane anesthetics in air and respired gases

Three common gaseous anesthetics, halothane, enflurane, and isoflurane, were characterized by using ion mobility spectrometry (IMS)/mass spectrometry, and the dependence of product ion distributions on temperature and concentration was evaluated. At 40 degrees C and 500 ppb, negative ion mobility spectra in air largely consisted of monomer or dimer adducts with Br- or Cl- formed through dissociative electron capture of molecular neutrals. With increased temperature or decreased vapor concentrations, declustering and dissociation of product ions became pronounced. Ion-molecule reactions in the drift region of the IMS were evident as distortions in peak shape in the mass-resolved mobility spectra and in variable reduced mobilities for the same ions. A portable hand-held IMS was used for convenient, real-time detection of enflurane in respired gases following a controlled inhalation episode.

Ion mobility spectrometry and ion mobility spectrometry/mass spectrometric characterization of dimenhydrinate.

Positive and negative ion mobility spectra of dimenhydrinate are presented, and the calculated reduced mobility (K0) values for the most significant peaks are reported. Mass identification of the ionic species associated with the peaks in the ion mobility spectra was achieved by interfacing the ion mobility spectrometer to a mass spectrometer. The application of ion mobility spectrometry to the detection of dimenhydrinate and other drug residues on the hands of patients admitted to hospital with drug overdose is also discussed.

Influence of AC and DC fields on streaming electrification of transformer oil

A study conducted by flowing transformer oil through a coaxial cylinder system is discussed. In the case of AC voltage, the streaming current increases with the field strength and with temperature. The increase of the streaming current at low AC field strength is attributed to vibration of positive ions, diffused into the oil at the interface with the electrode. In the case of DC voltage application, the polarity of the streaming current varies from slightly positive at low DC field strength to negative at high field strength. The streaming current at low fields may be caused by the difference between positive and negative ion mobilities. >

Atmospheric ion mobility spectra near the ground

The mobility spectra of positive and negative ions artificially produced in the ambient air near the ground were measured by using a newly constructed mobility spectrometer having parallel plate electrodes. The negative mobility spectra obtained by this spectrometer have a very sharp peak at 1.80 cm 2 volt −1 s −1, and the average negative ion mobility is estimated to be 2.40 cm 2 volt −1 s −1. In the positive ion mobility spectra, on the other hand, a rather broad peak is seen at 1.25 cm 2 volt −1 s −1. The average positive ion mobility is estimated to be 1.69 cm 2 volt −1 s −1. By comparing the result with recent mass spectrometric measurements and a model calculation, detailed discussions are given. Additional experiments were made to test for changes of the mobility spectra by using nitric acid and ammonia vapours, and gases in tobacco smoke.

Transport coefficients of electrons and negative ions in SF6

A double-shutter drift tube, which was practically the same as that used in measurements of electron swarm parameters in gases, was used to measure the reduced mobility and longitudinal diffusion coefficient of negative ions and the electron drift velocity in SF6. The drift tube proved to be capable of forming three species of negative ion selectively and therefore of determining swarm parameters of the respective negative ions as well as the electrons in the gas. Measurements were carried out over a range of E/N from 20 to 600 Td on negative ions and from 280 to 700 Td on electrons. The three negative ions were identified as F-, SF5- and SF6- according to their reduced mobilities at low electric field.

Mobilities of several mass-identified positive and negative ions in air

The mobilities in dry air of the positive ions NO +, NO + 2, and O + 2 and the negative ions O −, O − 2, O − 3, Cl −, NO − 2, NO − 3, NO − 3 (HNO 3), and NO − 3 (HNO 3) 2 were measured at room temperature in a flow-drift tube apparatus. The measurements are reported as a function of E/ N in the range 3–250 Td (1 Td = 10 −17 V cm 2). The results are compared with previously published data for the mobilities of some of these ions in air, nitrogen, and oxygen. The reliability of previously published mass—mobility correlation curves for ions in air is also discussed.

Fast negative ion thermometer for 3He superfluids

Abstract A thermometer based on the temperature dependence of the negative ion mobility in superfluid 3 He is described. The device can be used for monitoring the temperature of an open geometry sample of 3 He in the range 0.4 ≲ T / T c ≤ 1. The ion thermometer is most sensitive immediately below T c , in the Ginzburg-Landau region; above T ≈ 0.95 T c a resolution of 0.1 μK can be achieved. The measuring technique provides an on-line display of the relative mobility, μ ( T )/ μ ( T c ), and the ions probe the temperature of the 3 He sample directly, which leads to a short time constant τ versus T / T c is insensitive to the external magnetic field and the pressure of the sample. Only a low electric field, E ≲ 10 V cm −1 , with essentially no homogeneity requirements is needed. Parasitic heating due to the flow of ions is of the order of 1 pW.

Modeling of corona characteristics in a wire-duct precipitator using the charge simulation technique

The charge simulation technique has been adapted to model the electrostatic and the corona characteristics in clean air of a duct-type electrostatic precipitator. The study involves the evaluation of the electric potential, electric field, and charge density in the interelectrode space as a function of corona current. The results show good agreement with published experimental data. The method developed can be applied to other geometries in the presence of space charge. The commonly used assumption that the space charge affects the magnitude but not the direction of the electric field is shown to be inadequate for large values of corona current. Also, the effect of using different values for the mobility of negative ions is presented.

Anisotropy of Negative Ion Mobility in Stationary and Rotating 3He–A

The mobility tensor for negative ions in 3He is calculated for the axisymmetric A and polar phases. The superfluid energy gap ΔA(T) is extracted from the A-phase mobility. In rotating 3He-A, our calculation, based on the assumption that polar phase occupies the core of a singular vortex, explains the measured high mobility along vortices in rotating 3He-A.

A Fast Negative Ion Thermometer for 3He Superfluids

A thermometer based on the temperature dependence of the negative ion mobility in superfluid 3He is described. The device can be used in the range 0.4<T/Tc< 1, and it is most sensitive immediately below Tc, where a resolution of 0.1 µK can be achieved, the measuring system includes an on-line display, and the ions probe the temperature of the sample directly. The thermometer is insensitive to the external magnetic field and to the pressure of the liquid. A low electric field, E< 10 V/cm with no homogeneity requirements is needed. The parasitic heating due to the flow of ions is of the order of 1 pW.

A Survey of the Electron and Ion Transport Properties of SF6

A compilation of the available data on some of the basic transport properties of sulfur hexafluoride (SF6) is presented. The properties considered are a) electron ionization, attachment, detachment and diffusion coefficients, and electron drift velocity; b) positive and negative ion mobilities, negative ion diffusion, and ion-ion recombination coefficients; and c) secondary ionization coefficients. Approximate analytical representations of the data are also given.

Negative ion mobility spectrometry for selected inorganic pollutant gases and gas mixtures in air

Spectra for inorganic gases common to combustion emissions were obtained in air by using negative ion mobility spectrometry (NIMS). Gases were characterized individually from 10 to over 4000 ppb in air and in two binary mixtures of SO/sub 2//NO/sub 2/ and HCl/SO/sub 2/. Spectra for HCl and SO/sup 2/ were distinguished by single intense peaks at reduced mobilities (K/sub 0/) of 2.98 cm/sup 2//(V s) and 2.30 cm/sup 2//(V s), respectively. The product ion for NO/sub 2/ had a K/sub 0/ of 2.80 cm/sup 2//(V s) as determined using binary mixture studies and was unresolved otherwise from reactant ions. In contrast, NIMS spectra for H/sub 2/S showed three peaks that were concentration dependent and had mobility values of 2.38, 2.28, and 1.70 cm/sup 2//(V s). Peak currents for H/sup 2/S ranged from 10 to 50 pA and the estimated limit of detection (LOD) was 10 ppb. Peak currents for SO/sub 2/ ranged from 15 to 65 pA and the estimated LOD was 2 ppb. The range of peak currents for HCl was comparatively large at 140-215 pA and estimated LOD was NO/sub 2/ > SO/sub 2/. 39 references, 5 figures, 1 table.« less

Ion Mobility Measurements in a 50 cSt Viscosity Polydimethylsiloxane Silicone Oil

Using two different time-of-flight techniques (pulse voltage and V.U.V. photon pulse) ion mobility measurements ents have been performed, at room temperature, on a purified 50 cSt polydimethylsiloxane silicone oil (Rhone Poulenc 604 V 50). These experiments have been carried out in a cell with planparallel electrodes, for electric field strengths ranging from 0.4 to 10 kV cm-1 and for four electrode gaps (0.15, 0.19, 0.22 and 0.3 cm). The effect of additives such as N2O and C7F14 has also been investigated. The positive ion mobilities (27.5xl0-5 cm2V-ls-1) are independent of the additives while the negative ion mobilities decrease from 7.3x 10-5 cm2V-1s-1 under N2 to 5.3x10-5 cm2V-1s-1 in the presence of C7F14.

A new technique for measuring negative ion mobilities at atmospheric pressure

The electrode system used for determination of negative ion mobilities consists of three electrodes: two parallel plane electrodes (C1 and C2) and a point electrode (A) perpendicular to C1 and C2. The central part of C1 is a wire mesh. The gap between C1 and C2 is an ion drift space and, that between C1 and A is used as a negative ion detector (detecting gap). C1 is earthed, C2 is kept at negative and A at positive potential. The potential across the detecting gap is kept at that corresponding to its Geiger counter region. When pulsed UV irradiation is directed at the mesh, perpendicular to it, photoelectrons are released simultaneously from the mesh and C2 and cause two burst pulses to appear in the detecting gap. As the time interval between the two pulses is equal to the time of flight of negative ions in the drift space, their mobilities can easily be determined. Advantages of this technique are: the determination can be done easily and quickly, and the device is of very simple construction and may be used even for high pressures. It is not capable of the determination of positive ion mobilities. Results obtained for negative ion mobilities for zero field at atmospheric pressure for dry air, humid air, O2 and SF6 are: 2.25, 1.9, 2.3 and 0.57 cm2 V-1 s-1 respectively.

D-region positive and negative ion concentration and mobilities during the February 1979 eclipse

Positive and negative ion concentrations and mobilities have been obtained from an analysis of Gerdien condenser measurements on rocket flights, A10.802-1 and A1O.802-2, during and after eclipse totality. The aerodynamic instrument calibration and the data analysis techniques are discussed. The measured concentrations on both flights were about 10 4 cm −3 in the altitude range, 45–80 km. These high concentrations at very low altitudes suggest that a relativistic electron precipitation event was occurring during the measurements. The ion concentration measurements along with electron density measurements made by other groups during the eclipse were used to calculate the negative ion: electron ratio, and the lumped parameter detachment rate. These results are compared with prior measurements during eclipse and solar proton events and code results. The analysis shows that the present negative ion model is incomplete. The reduced mobilities ( K 0) were also determined. The mobility distributions show that the heavy ions of both the positive and negative species dominate from 45 to 70 km. The data reveal more massive ions at higher al titudes than at low altitudes (1000 vs 300 a.m.u.) as well as possible evidence for multiply charged ions below about 60 km.

Positive and negative ion composition measurements in the D- and E-regions during the 26 February 1979 solar eclipse

Two rockets bearing quadrupole mass spectrometers capable of measuring both positive and negative ion composition were launched from Red Lake, Canada, during the solar eclipse. Both instruments had liquid helium cryopumps and shock-attaching conical samplers. The payloads also contained two Gerdien condensers to measure total positive and negative ion concentrations and ion mobilities. Attitude control systems aligned the payloads with the velocity vector throughout ascent and descent. The first rocket was launched so that the D-region was in darkness 35 ± 8 s on the upleg and about 150 ± 15 s on the downleg for the study of ionospheric decay processes. The second rocket was fired after totality into 75% solar illumination for the study of ionospheric recovery. The positive ion composition above 105 km exhibited a strongly increasing NO +/O 2 + ratio with time after second contact due to O 2 + charge transfer with NO and a sharply diminished ionization rate. However, in both nights, the ionization below 105 km was created mainly by energetic particle deposition as exemplified by the increased ion concentrations and the composition signatures of a particle event: asignificant enhancement of O 2 + below 105 km and large amounts of H 5O 2 + ions in the D-region which result from the O 2 + clustering scheme. H 5O 2 was the major ion in the upper D-region while H 7O + 3, H 9O 4 + and H 5O 2 + were dominant ions at lower altitudes. Numerous minor species were also detected. The negative ion distributions in both flights exhibited a distinct shelf at 83 ± 2 km, decreasing by more than an order of magnitude by 90 km and with minima near 75 km. In the 75–90 km range, a significant percentage of the negative ions had masses exceeding 160 a.m.u. Comparisons are made with prior negative ion measurements during similar daytime auroral zone absorption (AZA) events. Two striking characteristics of the precipitating particles were apparent from these and past observations in daytime AZA events: there is a near absence of low energy electrons capable of ionizing above about 105 km and there is'a significant spatial and/or temporal variability in the electron flux. This paper is devoted principally to a presentation of the ion composition measurements and associated uncertainties.

The mobility of negative ions in superfluid3He

Abstract This article reviews recent experimental and theoretical work on the mobility of negative ions in the superfluid A and B phases of liquid 3He. In the normal Fermi liquid at temperatures below ∼ 50 mK and also in the superfluid close to the superfluid transition temperature, Tc , the mobility of a negative ion may simply be considered as limited by the elastic scattering of 3He quasiparticles. This explains the constancy of the ion mobility in the normal phase. However, underlying the rapid increase of the measured mobility in the superfluid phases there is a subtle quantum-mechanical scattering effect. Detailed solutions of the 3He quasiparticle—negative ion scattering process in the pair-correlated state provide a simple physical picture of an energy-dependent forward-peaking phenomenon. This yields quantitative theoretical results for the ion mobility in the quasi-isotropic B phase and for the ion mobility tensor in the anisotropic A phase which agree with the experimental data.

Mobilities of negative halogen ions in various gases

The mobilities of SF−6 in He and of F−, Cl−, Br−, and I− in Ar, Xe, H2, N2, CO, and CH4, have been investigated over the field-strength (E/P) range of 5 to 25 V/cm Torr using time-resolved high pressure mass spectrometry and an ion source with coaxial electron entrance and ion drift fields. The reduced mobilities obtained by this method are in good agreement with those obtained in drift tubes when comparison is possible. Results are compared with ’’Langevin’’ polarization limits and with the drift properties of isoelectronic positive alkali ions measured previously.