Blanc's Law Research Articles

Setting the Separation Factor α for Ketone Monomers and Dimers by the Use of Different Drift Gases.

This study investigates the influence of different drift gases on ion mobility in ion mobility spectrometry (IMS) using ketones as model substances within a custom-built drift tube spectrometer. Different binary mixtures of nitrogen, helium, and argon were used as drift gases to investigate the influence of mobility on the monomers and dimers of the different ketones. Experimental results reveal shifts in ion drift times and separation factors (α) with varying gas compositions, in accordance with Blanc's Law. Furthermore, the study underscores the device-independent nature of α and the device-dependent resolution, emphasizing the importance of comparative analyses. Employing 2-hexanone and 2-decanone in the same sample but with different drift gases is used to show the impact of different drift gases. By changing the drift gas composition, total alignment of drift times and therefore no possible resolution or baseline resolution could be achieved. Through different experiments and analyses, this research provides insights into the interactions between gas composition and ion mobility, offering implications for diverse analytical applications from environmental monitoring to chemical detection.

Assessing the Impact of Drift Gas Polarizability in Polyatomic Ion Mobility Experiments.

Due to the core assumptions of kinetic theory and the drive toward realizing reproducible gas-phase measurements, ion mobility experiments are commonly conducted in the presence of an inert, neat buffer gas, usually nitrogen or helium. Mixing drift gases in defined, static ratios can provide useful information not only for optimizing the separation of analytes but also for defining the interaction between the ion and neutral particle. In a foundational effort, we seek to validate the role of the drift gas polarizability on the observed mobility of the ions by systematically mixing drift gases to discretely access a range of bulk gas polarizabilities not given by pure drift gases. Compared to historical efforts to probe the role of polarizability on the ion-neutral collisional cross section where a linear relationship was assumed, the data collected in the present effort clearly illustrate a quadratic dependency of the ion-neutral particle collision cross section and polarizability (R2 > 0.999). When translating these data into the mobility dimension, we illustrate that the gas-phase mobility of polyatomic ions conforms to Blanc's law. These observations combined with considerations related to Langevin's polarization limit provide an experimental mechanism to estimate to what degree an ion-neutral interaction conforms to either the hard-sphere or induced-dipole model. To support these observations, additional comparisons are made with the respective reduced masses, polarizabilities, and mobilities of ions in mixtures where different degrees of hard-sphere interactions are present.

Separation of Isotopologues in Ultra-High-Resolution Ion Mobility Spectrometry.

Ion mobility spectrometry provides ion separation in the gas phase mainly based on differing ion-neutral collision cross sections, enabling powerful analysis of many isomers. However, the separation also has a miniscule mass dependence due to the acceleration and collision properties. In this work, we show for the first time that using a compact ultra-high-resolution ion mobility spectrometer with a resolving power of 250 and an UV ionization source enables the separation of isotopologues with ion mobility spectrometry. This is demonstrated for regular and perdeuterated acetone, benzene, and toluene as well as toluene-13C7 in nitrogen and in purified air as drift gas. The observed peak shifts in the ion mobility spectrum agree with the basic ion mobility equation when using nitrogen as drift gas and also agree with a combination of this equation with Blanc's law when using purified air as drift gas. For benzene and toluene, a reduction in the ion-neutral collision cross section of the isotopically replaced species is observed. Furthermore, a third peak formed from regular and perdeuterated acetone is observed, which can most likely be attributed to the exchange of a methyl group.

Experimental ion mobility measurements in Xe-N2 mixtures

In this paper we present the results for the ion mobility measurements made in gaseous mixtures of xenon (Xe) and nitrogen (N2) for low reduced electric fields (in the 15 Td to 30 Td range), at room temperature. The choice of reduced electric fields was guided by typical gaseous detector's demands. In the 0–100% range of Xe concentrations in the mixture, only one peak was observed which was attributed to Xe2+; in fact its mobility was found to follow Blanc's law. A typical time-of-arrival spectrum for 90% Xe and 10% N2 is shown. The reduced mobilities, obtained from the peaks, are calculated and presented in this paper.

Transport properties of F− in SF6–Xe, SF6–Ar and SF6–He mixtures

F− mobility was calculated in the gas mixtures SF6–Xe, SF6–Ar and SF6–He from a Monte Carlo code for ion transport simulation. The elastic momentum transfer cross sections were determined from the semi-classical JWKB approximation while the inelastic ones (detachment and charge transfer) were taken from the literature. The resulting collision cross section sets were validated from the good agreement between the calculated F− mobilities in the individual gases and the measured ones. Moreover, the longitudinal and transverse density normalized diffusion coefficients and the reaction rate coefficients were calculated in these mixtures for the case where the share of SF6 is 50%. Finally, a comparison of our calculated F− mobilities in these mixtures obtained from the Monte Carlo code and those obtained from linear Blanc's law showed good agreement in the case of SF6–Xe at low field but strong disagreement in the case of SF6–He mixture. However, at 2000 Td, deviation from Blanc's law is obtained for F− mobility in both mixtures.

The Mobility of Negative Ions in $\hbox{CF}_{3} \hbox{I}$, $\hbox{CF}_{3}\hbox{I}{-}\hbox{N}_{2}$ , $\hbox{CF}_{3}\hbox{I}{-}\hbox{Ar}$, $\hbox{CF}_{3}\hbox{I}{-}\hbox{Xe}$, $\hbox{C}_{2}\hbox{F}_{6}$, and $\hbox{CHF}_{3}$, and of Positive Ions in $\hbox{C}_{2} \hbox{F}_{4}$ and $\hbox{c-C}_{4}\hbox{F}_{8}$

Using a pulsed Townsend technique, the drift velocity and the mobility of positive ions in C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> and those of negative ions in C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I and its mixtures with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , Ar, and Xe are reported. The overall range of the density-normalized electric field is 4-600 times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-17</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sup> ldrcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Ion identification is provided by means of previous studies on partial ionization and electron attachment. Thus, it is suggested that the predominant drifting ion in the discharge is C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> for C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and c-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> , F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> for C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> for CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I. The use of more comprehensive theories of ion motion considering the influence of a permanent dipole moment (CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I) has provided reasonable agreement between low-field measured and calculated mobilities. The mobility of negative ions in CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I-N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I-Ar, and CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I-Xe mixtures agrees reasonably well with the predicted values by Blanc's law.

Multi-Component Migration in the Gas Phase of Soil: Comparison between Results of Experiments and Simulation by Dusty Gas Model

Fick's law has been used to simulate gas systems within soil, although this law can be applied only to binary gas systems and the effect of the Knudsen diffusion is not considered. By contrast, the dusty gas model can be applied to multi-component gas systems with Knudsen diffusion. Blanc's law is a simplified version of the dusty gas model, but it can be used only for gas systems in which the tracer gas is dilute. Although the dusty gas model is superior to other methods for simulating gas systems within soil, it is not generally used because of its complexity. Numerical techniques such as the Eulerian-Lagrangian method for solving the advection-dispersion equation can be used to simulate the migration of chemical substance in the water or gas phases of soil within the range of every Péclet number. We derived the compound diffusion coefficient and compound velocity from the dusty gas model and formulated the advection-diffusion equation with these values by using the characteristic finite element scheme. Results of the model developed here were consistent with the results of column experiments conducted in this study, and the precision of the developed model was verified.

Transport properties of in SF6–Ne, SF6–N2 and SF6–O2 mixtures

The mobility of has been calculated for the gas mixtures SF6–Ne, SF6–N2 and SF6–O2 using an optimized Monte Carlo code for the ion transport simulation in a drift tube. The elastic momentum transfer collision cross sections needed for the calculation were determined from a semi-classical JWKB approximation, while the inelastic ones (detachment, dissociative charge transfer and conversion to and F−) were taken from the literature for the case of the collision system. The resulting sets of collision cross sections were validated by comparing the calculated mobilities with those measured in the above mixtures with a time-resolved pulsed Townsend technique. The longitudinal and transverse density-normalized diffusion coefficients were calculated for these mixtures for the case where the share of SF6 in the mixture was 50%. Finally, the validity of Blanc's law was discussed at low and high electric fields, whereby we show that it fails at high fields, where inelastic processes are dominant.

Calculations of ion-transport coefficients in gas mixtures in a space–time varying electric field and comparison with Blanc's law

The ion transport induced by the spatial and/or temporal variation of an electric field in gases is studied. Expressions for the corresponding transport coefficients in gas mixtures are obtained from the momentum-transfer theory and are given in terms of the coefficients in the pure component gases. The obtained results are used to calculate the considered transport coefficients for Na+ ions in an He–Ne mixture and their deviation from Blanc's law.

Theoretical analysis of ion kinetic energies and DLC film deposition by CH4+ Ar (He) dielectric barrier discharge plasmas

The kinetic energy of ions in dielectric barrier discharge plasmas are analysed theoretically using the model of binary collisions between ions and gas molecules. Langevin equation for ions in other gases, Blanc law for ions in mixed gases, and the two-temperature model for ions at higher reduced field are used to determine the ion mobility. The kinetic energies of ions in CH4 + Ar(He) dielectric barrier discharge plasma at a fixed total gas pressure and various Ar (He) concentrations are calculated. It is found that with increasing Ar (He) concentration in CH4 + Ar (He) from 20% to 83%, the CH4+ kinetic energy increases from 69.6 (43.9) to 92.1 (128.5) eV, while the Ar+ (He+) kinetic energy decreases from 97 (145.2) to 78.8 (75.5) eV. The increase of CH4+ kinetic energy is responsible for the increase of hardness of diamond-like carbon films deposited by CH4 + Ar (He) dielectric barrier discharge without bias voltage over substrates.

Swarm data of O−, NO−, He+, N2O+, and ions in N2O, He and N2O–He mixtures for PECVD applications

The aim is first to calculate and validate, from an ion swarm unfolding technique, the sets of collision cross sections of several ions (O−, NO−, He+, N2O+, , and ) colliding with N2O and He gases and their mixtures. The aim is then to calculate the corresponding ion swarm parameters in these pure gases and their mixtures in a large E/N range. These ion interactions and swarm data are very useful more particularly for the modelling of the electrical and energetic behaviour of RF discharge in N2O–He mixtures with a small admixture of SiH4 used in PECVD applications for thin film depositions. The sets of collision cross sections for these different ion/gas systems involve both elastic and inelastic processes in the case of an ion energy range varying from thermal energy up to about 100 eV. The elastic ion–gas interaction has been described by using a rigid core potential model which is well adapted for both polar and non-polar systems and also symmetric and asymmetric systems. Momentum transfer cross sections are then determined using a semi-classical JWKB approach while inelastic cross sections are taken from the literature and completed from empirical laws. Then by using these different cross section sets, it is possible to obtain the ion swarm data for different gas mixtures involving N2O and He whatever their relative proportions. These ion swarm data are obtained from an optimized Monte Carlo method well adapted for the ion transport in pure gas as well as gas mixtures. The specific behaviour of these swarm data (ion mobility or drift velocity, diffusion coefficient and reaction rates) is analysed in the case of each ion in different N2O–He mixtures over a quite large E/N range (1–1000 Td) showing more particularly the non-validity of the classical linear approximations such as Blanc law.

Analysis of ion mobility and diffusion in atmospheric gaseous mixtures from Monte Carlo simulation and macroscopic laws

The reduced mobility and diffusion coefficients of and O− are calculated with a Monte Carlo simulation for the gas mixtures N2–H2O (50%, 50%) and O2–N2 (80%N2, 20%O2), respectively, from measured and calculated elastic and inelastic cross sections. These mobility and longitudinal diffusion coefficients have been compared with the standard Blanc's law and with the common mean energy (CME) procedure. Good agreement between these three calculation methods was found for the mobility and diffusion of in the N2–H2O mixture at high reduced fields where inelastic processes are relatively uninfluential. However, a strong deviation between Blanc's law and both CME procedure and our Monte Carlo calculations for the reduced mobility and the diffusion coefficient of in this gas mixture N2–H2O was observed at low reduced fields, because inelastic processes are significant. On the contrary, for the case of the N2–O2 mixture, where inelastic processes are small over the reduced electric field range 1–8000 Td, the three calculation methods led to similar results. The elastic collision cross sections used were determined from a semi-classical JWKB approximation by using a rigid core potential model for both symmetric and asymmetric , O−/O2 and O−/N2 ion–neutral systems. Moreover, the inelastic cross sections were extended to low energies from appropriate approximations. These cross section sets were validated from the good agreement between our Monte Carlo calculated reduced mobilities in N2 and H2O, O− in O2 and N2 and either measured values for the systems and O−/O2 or physical properties of the systems and O−/N2.

Electron drift velocities in mixtures of helium and xenon and experimental verification of corrections to Blanc’s law

Measurements of electron drift velocities were performed in pure Xe and He and in a number of mixtures ranging up to 70% of Xe. The data were obtained by using a pulsed Townsend technique over the density-normalized electric field strength E/N between 1 and 100 Td . Even for pure gases there are no data in the entire range covered here, and these data represent an extension of accurate drift velocities to higher E/N. A selection of well-established cross sections for low energies, which was extended to higher energies, led to a reasonably good agreement of the calculated transport coefficients with the available data. At the same time we have applied the standard (common E/N) Blanc's law and two forms of common mean energy (CME, due to Chiflykian) procedures. Blanc's law fails for most mixtures at low and moderate E/N, while the CME procedure is capable of following the experimental data for the mixtures much more closely, and even predicting the negative differential conductivity region when such effect does not exist for pure gases. Thus the present paper also represents an experimental test of procedures to correct the standard Blanc's law. Finally, we have used the data for two mixtures to obtain results for the third mixture and in all cases this procedure gave excellent results even though only the standard Blanc's law was used in the process.

Measured and calculatedSF6−collision and swarm ion transport data inSF6-Ar andSF6-Xe mixtures

The measurement of the mobility of SF-6 in the mixtures SF6 -Ar and SF6 -Xe is reported over the density-reduced electric field strength E/N 1-180 Td (1 Townsend = 10(-17) V cm(2)), from a time-resolved pulsed Townsend technique. Simultaneously, the mobility of SF-6 in the same binary mixtures has been calculated from a set of collision cross sections for SF-6 -Ar, SF-6 -Xe, and SF-6 - SF6 using a Monte Carlo simulation procedure for ion transport. The good agreement between measured and calculated mobilities in these gas mixtures has led us to conclude that the validation of our cross section sets is confirmed. The elastic collision cross section, a predominant process for ion energies lower than about 10 eV, was determined from a semiclassical JWKB approximation using a rigid core potential model for the ion-neutral systems under consideration. This elastic cross section was then added to several other inelastic collision cross sections found in the literature for ion conversion, electron detachment of SF-6 and charge transfer. Moreover, the calculations of the mobility and the ratios of the transverse and longitudinal diffusion coefficients to the mobility were extended into a much wider E/N range from 1 to 4000 Td. Additionally, we have also calculated the energy distribution functions and the reaction coefficients for ion conversion and electron detachment. Finally, we have shown that the range of validity for the calculation of the mobility in gas mixtures from Blanc's law is only valid for the low E/N region, where the interaction is dominated by elastic collisions and the ion distribution function remains essentially Maxwellian.

Understanding and Designing Field Asymmetric Waveform Ion Mobility Spectrometry Separations in Gas Mixtures

Field asymmetric waveform ion mobility spectrometry (FAIMS) has significant potential for post-ionization separations in conjunction with MS analyses. FAIMS fractionates ion mixtures by exploiting the fact that ion mobilities in gases depend on the electric field in a manner specific to each ion. Nearly all previous work has used pure gases, for which FAIMS fundamentals are understood reasonably well; however, unexpected phenomena observed in some gas mixtures (e.g., N(2)/CO(2)) but not in others (N(2)/O(2)) remain unexplained. Here, we introduce and experimentally test a universal model for FAIMS separations in mixtures, derived from formalisms that determine high-field mobilities in heteromolecular gases. Overall, the theoretical findings are consistent with data for N(2)/CO(2) (although quantitative discrepancies remain), while results for N(2)/O(2) fit Blanc's law, in agreement with measurements. Calculations for He/N(2) and He/CO(2) are also consistent with observations and suggest why adding He to the working gas generally enhances FAIMS performance. As predicted, mixtures of gases with extremely disparate molecular masses and collision cross sections, such as He/SF(6), exhibit spectacular non-Blanc effects, which greatly improve the resolution and peak capacity of technique. Understanding FAIMS operation in gas mixtures is expected to enable the rational design of media for both targeted and global analyses.

Ion mobilities in Xe/Ne and other rare-gas mixtures.

The ion mobility or drift velocity data important for modeling glow discharges in rare gas mixtures are not generally available, nor are the ion-neutral scattering cross sections needed to calculate these data. In this paper we propose a set of cross sections for Xe+ and Ne+ collisions with Xe and Ne atoms. Ion mobilities at 300 K calculated using this cross section set in a Monte Carlo simulation are reported for reduced field strengths, E/N, up to 1500 x 10(-21) V m(2), in pure gases and in Xe/Ne mixtures containing 5% and 20% Xe/Ne, which are mixtures of interest for plasma display panels (PDPs). The calculated Xe+ mobilities depend strongly on the mixture composition, but the Ne+ mobility varies only slightly with increasing Xe in the mixture over the range studied here. The mobilities in pure gases compare well with available experimental values, and mobilities in gas mixtures at low E/N compare well with our recent measurements which will be published separately. Results from these calculations of ion mobilities are used to evaluate the predictions of Blanc's law and of the mixture rule proposed by Mason and Hahn [Phys. Rev. A 5, 438 (1972)] for determining the ion mobilities in mixtures from a knowledge of the mobilities in each of the pure gases. The mixture rule of Mason and Hahn is accurate to better than 10% at high field strengths over a wide range of conditions of interest for modeling PDPs. We conclude that a good estimate of ion mobilities at high E/N in Xe/Ne and other binary rare gas mixtures can be obtained using this mixture rule combined with known values of mobilities in parent gases and with the Langevin form for mobility of rare gas ions ion in other gases. This conclusion is supported by results in Ar/Ne mixtures which are also presented here.

Negative ion motion in the mixtures of SF6 with CF4 and CH4-Ar.

This paper deals with the measurement of the mobility of negative ions in the mixtures of SF6 with CF4 and the CH4-Ar (50:50) binary mixture with SF6 contents up to 50%. The pulsed Townsend technique was used to observe the integrated ionic avalanches over a range of the density-reduced electric field E/N for which ionization is either negligible or absent, and attachment processes are significant, leading to the formation of mostly SF-6. The E/N range of measurement was from 1 to 70 Td (1 Td=10(-17) V cm(2)), over which the measured mobilities were found to be almost constant. The mobility of the negative ions was also measured for trace amounts of SF6 in CH4 and Ar and 1% CF4, thereby providing a good value of the mobility of SF-6 in these pure gases, in order to test the measured mobilities with Blanc's law. We have found good agreement, within quoted experimental uncertainties, between calculated and measured values.

Test of Blanc's law for negative ion mobility in mixtures of SF6 with N2, O2 and air

We have measured the mobility of negative ion species drifting in mixtures of SF6 with N2, O2 and air. The pulsed Townsend experiment was used for this purpose. The conditions of the experiment, high pressures and low values of the reduced electric field, E/N, ensured that the majority species drifting in the gap was , to which the present mobilities are ascribed. The extrapolated, zero field mobilities for several mixture compositions were used to test them successfully with Blanc's law. Moreover, the measured zero field mobilities in air could also be explained in terms of the measured mobilities for this ionic species in N2 and O2.

Motion of SF+x (x=1-3,5) and ion conversion in SF6-N2 mixtures.

This paper reports on the mass-analyzed measurement of the drift velocity of the positive SF6 daughter ions, SF+x (x=1-3,5) in the mixture of SF6 with N2 for SF6 concentrations of 10% and 50%. A double mass spectrometer-drift tube was used for these measurements. The density-normalized electric field intensity E/N, was varied from 30 to 360 Td (1 Td=10(-17) V cm(2)). We have found an increasingly monotonic dependence of the drift velocity with E/N, and an inverse dependence of the above parameter with the decrease of the SF6 content in the mixture. A test of Blanc's law for the zero-field reduced mobilities of the above ions shows a fair qualitative agreement. No drift velocities of these ionic species could be measured in pure N2, since we found that these ions reacted strongly with the nitrogen molecules. The cases for SF+3 and SF+5 are discussed. A similar behavior was observed for the nitrogen ions drifting in pure SF6.

Effective ionization, electron and ion transport in SF6-Hemixtures

This paper reports on the measurement of the electron driftvelocity, the density normalized effective ionization coefficients (α-η)/N,and the ratio η/α (η and α are the attachment and ionization coefficients,respectively), over a wide range of the density-reduced field strength, E/N,from 40 to 560 Td (1 Td = 10-17 V cm2). From the measured values of(α-η)/N and η/α, the density normalized ionization and attachmentcoefficients were obtained. Further analysis of avalanche development past thefirst electron transit allowed us to derive the average mobility of bothpositive and negative ions. The mobility of negative ions was found toagree very well with Blanc's law at small fields, thereby indicating that themajority negative ion in the avalanche is SF6-. The critical field strengthwas found to vary almost linearly with the SF6 content in the mixture,comparing well with previous measurements.