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Christopher J. Hogan - One of the best experts on this subject based on the ideXlab platform.
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calculation of the ion ion recombination Rate Coefficient via a hybrid continuum molecular dynamics approach
2020Co-Authors: Tomoya Tamadate, Hidenori Higashi, Takafumi Seto, Christopher J. HoganAbstract:AccuRate calculation of the ion–ion recombination Rate Coefficient has been of long-standing interest as it controls the ion concentration in gas phase systems and in aerosols. We describe the development of a hybrid continuum-molecular dynamics (MD) approach to determine the ion–ion recombination Rate Coefficient. This approach is based on the limiting sphere method classically used for transition regime collision phenomena in aerosols. When ions are sufficiently far from one another, the ion–ion relative motion is described by diffusion equations, while within a critical distance, MD simulations are used to model ion–ion motion. MD simulations are parameterized using the Assisted Model Building with Energy Refinement force-field as well as by considering partial charges on atoms. Ion–neutral gas collisions are modeled in two mutually exclusive cubic domains composed of 103 gas atoms each, which remain centered on the recombining ions throughout calculations. Example calculations are reported for NH4+ recombination with NO2− in He, across a pressure range from 10 kPa to 10 000 kPa. Excellent agreement is found in comparison with calculations to literature values for the 100 kPa recombination Rate Coefficient (1.0 × 10−12 m3 s−1) in He. We also recover the experimentally observed increase in the recombination Rate Coefficient with pressure at sub-atmospheric pressures, and the observed decrease in the recombination Rate Coefficient in the high pressure continuum limit. We additionally find that non-dimensionalized forms of Rate Coefficients are consistent with recently developed equations for the dimensionless charged particle–ion collision Rate Coefficient based on Langevin dynamics simulations.
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calculation of the ion ion recombination Rate Coefficient via a hybrid continuum molecular dynamics approach
2020Co-Authors: Tomoya Tamadate, Hidenori Higashi, Takafumi Seto, Christopher J. HoganAbstract:AccuRate calculation of the ion-ion recombination Rate Coefficient has been of long-standing interest, as it controls the ion concentration in gas phase systems and in aerosols. We describe the development of a hybrid continuum-molecular dynamics approach to determine the ion-ion recombination Rate Coefficient. The approach is based on the limiting sphere method classically used for transition regime collision phenomena in aerosols. When ions are sufficiently far from one another, ion-ion relative motion is described by diffusion equations while within a critical distance, molecular dynamics (MD) simulations are used to model ion-ion motion. MD simulations are parameterized using the AMBER force-field as well as by considering partial charges on atoms. Ion-neutral gas collisions are modeled in two mutually exclusive cubic domains composed of 103 gas atoms each, which remain centered on the recombining ions throughout calculations. Example calculations are reported for NH4+ recombination with NO2- in He, across a pressure range from 10 kPa to 10,000 kPa. Excellent agreement is found in comparison of calculations to literature values for the 100 kPa recombination Rate Coefficient (1.0 x 10-12 m3 s-1) in He. We also recover the experimentally observed increase in recombination Rate Coefficient with pressure at sub-atmospheric pressures, and the observed decrease in recombination Rate Coefficient in the high pressure continuum limit. We additionally find that non-dimensionalized forms of Rate Coefficients are consistent with recently developed equations for the dimensionless charged particle-ion collision Rate Coefficient based on Langevin dynamics simulations.
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Collision Rate Coefficient for charged dust grains in the presence of linear shear.
2017Co-Authors: Huan Yang, Christopher J. HoganAbstract:Like and oppositely charged particles or dust grains in linear shear flows are often driven to collide with one another by fluid and/or electrostatic forces, which can strongly influence particle-size distribution evolution. In gaseous media, collisions in shear are further complicated because particle inertia can influence differential motion. Expressions for the collision Rate Coefficient have not been developed previously which simultaneously account for the influences of linear shear, particle inertia, and electrostatic interactions. Here, we determine the collision Rate Coefficient accounting for the aforementioned effects by determining the collision area, i.e., the area of the plane perpendicular to the shear flow defining the relative initial locations of particles which will collide with one another. Integration of the particle flux over this area yields the collision Rate. Collision Rate calculations are parametrized as an enhancement factor, i.e., the ratio of the collision Rate considering potential interactions and inertia to the traditional collision Rate considering laminar shear only. For particles of constant surface charge density, the enhancement factor is found dependent only on the Stokes number (quantifying particle inertia), the electrostatic energy to shear energy ratio, and the ratio of colliding particle radii. Enhancement factors are determined for Stokes numbers in the 0-10 range and energy ratios up to 5. Calculations show that the influences of both electrostatic interactions and inertia are significant; for inertialess (St=0) equal-sized and oppositely charged particles, we find that even at energy ratios as low as 0.2, enhancement factors are in excess of 2. For the same situation but like-charged particles, enhancement factors fall below 0.5. Increasing the Stokes number acts to mitigate the influence of electrostatic potentials for both like and oppositely charged particles; i.e., inertia reduces the enhancement factor for oppositely charged particles and increases it for like-charged particles. Uniquely, at elevated Stokes numbers with attractive potentials we find collisionless "pockets" within the collision area, which are regions completely bounded by the collision area but within which collisions do not occur. Regression equations to results are provided, enabling calculation of the enhancement factor as a function of energy ratio and Stokes number. In total, this study both leads to insight into the collision dynamics of finite-inertia, charged particles in shear flows, and provides a means to simply calculate the particle-particle collision Rate Coefficient.
A Wolf - One of the best experts on this subject based on the ideXlab platform.
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the hd dissociative recombination Rate Coefficient at low temperature
2015Co-Authors: A Wolf, O Novotný, H Buhr, C Krantz, I F Schneider, O Motapon, Zs J MezeiAbstract:The effect of the rotational temperature of the ions is considered for low- energy dissociative recombination (DR) of HD + . Merged beams measurements with HD + ions of a rotational temperature near 300K are compared to multichannel quantum defect theory calculations. The thermal DR Rate Coefficient for a Maxwellian electron velocity distribution is derived from the merged-beams data and compared to theoretical results for a range of rotational temperatures. Good agreement is found for the theory with 300K rotational temperature. For a low-temperature plasma environment where also the rotational temperature assumes 10K, theory predicts a considerably higher thermal DR Rate Coefficient. The origin of this is traced to predicted resonant structures of the collision- energy dependent DR cross section at few-meV collision energies for the particular case of HD + ions in the rotational ground state.
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experimental Rate Coefficient for dielectronic recombination of neonlike iron forming sodiumlike iron
2009Co-Authors: E W Schmidt, S Schippers, A Muller, D Bernhardt, Jens Hoffmann, M Lestinsky, D Lukic, Dmitry A Orlov, D W Savin, A WolfAbstract:The Rate Coefficient for dielectronic recombination (DR) of Ne-like Fe16+ forming Na-like Fe15+ was measured employing the merged electron-ion beams technique at the heavy-ion storage-ring TSR of the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. In the electron-ion collision energy range of 240–840 eV the merged-beams recombination Rate Coefficient is dominated by DR associated with 2s2 2p6 1S0 → 2s2 2p5 3d 1P1 core excitation. The experimental Fe16+ DR plasma Rate Coefficient is derived from the measured merged-beams Rate Coefficient. It is in good agreement with recent theoretical results.
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towards state selective measurements of the h3 dissociative recombination Rate Coefficient
2005Co-Authors: H Kreckel, J Mikosch, Roland Wester, J Glosik, R Plasil, Michael Motsch, D Gerlich, D Schwalm, D Zajfman, A WolfAbstract:Ion storage and trapping techniques in connection with efficient internal state control and diagnostic for molecular ions offer the potential of providing Rate Coefficients for the dissociative recombination of H3+ for well-defined initial rotational states, required for understanding the role of this ion in the interstellar medium and other cold environments. Information on the vibrational and rotational excitation in stored H3+ ion beams, as obtained from experiments at the ion storage ring TSR, is reviewed. In addition, the arrangement of the TSR injector trap, using buffer gas cooling in a cryogenic radiofrequency multipole structure to inject pulses of internally cold H3+ ions into the TSR via a high-energy accelerator, is outlined. An account is given of tests towards the in-situ diagnostic of rotational level populations, where laser transitions between low-lying rovibrational levels could be detected in dilute H3+ ion ensembles using chemical probing in the radiofrequency multipole ion trap.
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experimental mg ix photorecombination Rate Coefficient
2004Co-Authors: S Schippers, C Brandau, A Muller, Matthias J Schnell, S Kieslich, A WolfAbstract:The Rate Coefficient for radiative and dielectronic recombination of beryllium-like magnesium ions was measured with high resolution at the Heidelberg heavy-ion storage ring TSR. In the electron-ion collision energy range 0-207 eV reso- nances due to 2s → 2p (∆N = 0) and 2s → 3l (∆N = 1) core excitations were detected. At low energies below 0.15 eV the recombination Rate Coefficient is dominated by strong 1s 2 (2s 2p 3 P) 7l resonances with the strongest one occuring at an energy of only 21 meV. These resonances decisively influence the Mg recombination Rate Coefficient in a low temperature plasma. The experimentally derived Mg dielectronic recombination Rate Coefficient (±15% systematical uncertainty) is compared with the recommendation by Mazzotta et al. (1998, A&AS, 133, 403) and the recent calculations by Gu (2003, ApJ, 590, 1131) and by Colgan et al. (2003, A&A, 412, 597). These results deviate from the experimental Rate Coefficient by 130%, 82% and 25%, respectively, at the temperature where the fractional abundance of Mg is expected to peak in a photoionized plasma. At this temperature a theoretical uncertainty in the 1s 2 (2s 2p 3 P) 7l resonance positions of only 100 meV would translate into an uncertainty of the plasma Rate Coefficient of almost a factor 3. This finding emphasizes that an accuRate theoretical calculation of the Mg recombination Rate Coefficient from first principles is challenging.
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storage ring measurement of the c iv recombination Rate Coefficient
2001Co-Authors: S Schippers, G Gwinner, J Linkemann, A Muller, A A Saghiri, A WolfAbstract:The low-energy C IV dielectronic recombination (DR) Rate Coefficient associated with 2s → 2p Δn = 0 excitations of this lithium-like ion has been measured with high-energy resolution at the heavy-ion storage ring TSR of the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. The experimental procedure and especially the experimental detection probabilities for the high Rydberg states produced by the recombination of this ion are discussed in detail. From the experimental data a Maxwellian plasma Rate Coefficient is derived with ±15% systematic uncertainty and parameterized for ready use in plasma-modeling codes. Our experimental result especially benchmarks the plasma Rate Coefficient below 104 K where DR occurs predominantly via C III (1s22p4l) intermediate states and where existing theories differ by orders of magnitude. Furthermore, we find that, to within our systematic uncertainty of 15%, the total dielectronic and radiative C IV recombination can be represented by the incoherent sum of our DR Rate Coefficient and the radiative recombination Rate Coefficient of Pequignot and coworkers.
Y Nakao - One of the best experts on this subject based on the ideXlab platform.
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distortion of bulk ion distribution function due to nuclear elastic scattering and its effect on t d n he4 reaction Rate Coefficient in neutral beam injected deuterium tritium plasmas
2007Co-Authors: Hideaki Matsuura, Y NakaoAbstract:An effect of nuclear elastic scattering on the Rate Coefficient of fusion reaction between field deuteron and triton in the presence of neutral beam injection heating is studied. Without assuming a Maxwellian for bulk-ion distribution function, the Boltzmann-Fokker-Planck (BFP) equations for field (bulk) deuteron, field (bulk) triton, α-particle, and beam deuteron are simultaneously solved in an ITER-like deuterium-tritium thermonuclear plasma [R. Aymar, Fusion Eng. Des. 55, 107 (2001)]. The BFP calculation shows that enhancement of the reaction Rate Coefficient due to knock-on tail formation in fuel-ion distribution functions becomes appreciable, especially in the case of low-density operations.
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distortion of bulk ion distribution function due to nuclear elastic scattering and its effect on t d n he4 reaction Rate Coefficient in neutral beam injected deuterium tritium plasmas
2007Co-Authors: Hideaki Matsuura, Y NakaoAbstract:An effect of nuclear elastic scattering on the Rate Coefficient of fusion reaction between field deuteron and triton in the presence of neutral beam injection heating is studied. Without assuming a Maxwellian for bulk-ion distribution function, the Boltzmann-Fokker-Planck (BFP) equations for field (bulk) deuteron, field (bulk) triton, α-particle, and beam deuteron are simultaneously solved in an ITER-like deuterium-tritium thermonuclear plasma [R. Aymar, Fusion Eng. Des. 55, 107 (2001)]. The BFP calculation shows that enhancement of the reaction Rate Coefficient due to knock-on tail formation in fuel-ion distribution functions becomes appreciable, especially in the case of low-density operations.
Georges Guiochon - One of the best experts on this subject based on the ideXlab platform.
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kinetic study of the concentration dependence of the mass transfer Rate Coefficient in enantiomeric separation on a polymeric imprinted stationary phase
2000Co-Authors: Kanji Miyabe, Georges GuiochonAbstract:Kinetic data previously acquired on the enantiomeric separation of L- and D-phenylalanine anilide (PA) on a polymeric stationary phase imprinted with L-PA were reinterpreted. The parameters characterizing the mass transport processes active in the column, i.e., axial dispersion, fluid-to-particle mass transfer, intraparticle diffusion, and adsorption/desorption were calculated. Intraparticle diffusion was shown to have a dominant contribution to band broadening. The surface diffusion Coefficient (Ds) showed a positive concentration dependence which could explain the dependence of the lumped mass transfer Rate Coefficient on the enantiomer concentration. It is likely that the positive concentration dependence of Ds could be explained by the heterogeneity of the surface of the stationary phase and that the distribution of adsorption energy on the surface of the imprinted polymer has an exponential decay profile.
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kinetic study of the concentration dependence of the mass transfer Rate Coefficient in anion exchange chromatography of bovine serum albumin
1999Co-Authors: Kanji Miyabe, Georges GuiochonAbstract:The experimental results of a previous study of the mass transfer kinetics of bovine serum albumin (BSA) in ion-exchange chromatography under nonlinear conditions are reevaluated. The analysis of the concentration dependence of the lumped mass-transfer Rate Coefficient (k{sub m,L}) provides information on the kinetics of axial dispersion, fluid-to-particle mass transfer, intraparticle mass transfer, and adsorption/desorption. The new analysis shows that the contribution of intraparticle mass transfer is the dominant one. Similar to k{sub m,L}, the surface diffusivity (D{sub s}) of BSA increases with increasing concentration. The linear concentration dependence of k{sub m,L} seems to originate in a similar dependence of D{sub s}. The use of a heterogeneous-surface model for the anion-exchange resin provides an explanation of the positive concentration dependence of D{sub s}. This work illustRates how frontal analysis data can be used for a detailed investigation of the kinetics of mass transfer between the phases of a chromatographic column, in addition to its conventional use in the determination of the thermodynamic characteristics of the phase equilibrium.
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application of the shock layer theory to the determination of the mass transfer Rate Coefficient and its concentration dependence for proteins on anion exchange columns
1997Co-Authors: Peter Sajonz, Hong Guansajonz, Guoming Zhong, Georges GuiochonAbstract:The extension of the shock layer theory to systems having a slow mass transfer kinetics and a concentration-dependent Rate Coefficient is discussed. Experiments were carried out with bovine serum albumin on two anion exchangers, TSK-GEL-DEAE-5PW and Resource-Q. The adsorption isotherm data, determined by single-step frontal analysis, could be fitted to simplified bi-Langmuir equations with very small residuals. A lumped kinetic model (solid film linear driving force model, with Rate Coefficient kf) was used to account for the mass transfer kinetics. The profile of each breakthrough curve (BC) was fitted to the curve calculated with this transport model and the Rate Coefficient kf obtained by identification. A linear dependence of kf on the average concentration of the step of the BC was found. The shock layer thicknesses (SLT) calculated for different relative concentrations agreed very well with the experimental results. This justifies the use of the SLT for the direct determination of Rate Coefficients.
S Schippers - One of the best experts on this subject based on the ideXlab platform.
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experimental Rate Coefficient for dielectronic recombination of neonlike iron forming sodiumlike iron
2009Co-Authors: E W Schmidt, S Schippers, A Muller, D Bernhardt, Jens Hoffmann, M Lestinsky, D Lukic, Dmitry A Orlov, D W Savin, A WolfAbstract:The Rate Coefficient for dielectronic recombination (DR) of Ne-like Fe16+ forming Na-like Fe15+ was measured employing the merged electron-ion beams technique at the heavy-ion storage-ring TSR of the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. In the electron-ion collision energy range of 240–840 eV the merged-beams recombination Rate Coefficient is dominated by DR associated with 2s2 2p6 1S0 → 2s2 2p5 3d 1P1 core excitation. The experimental Fe16+ DR plasma Rate Coefficient is derived from the measured merged-beams Rate Coefficient. It is in good agreement with recent theoretical results.
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experimental mg ix photorecombination Rate Coefficient
2004Co-Authors: S Schippers, C Brandau, A Muller, Matthias J Schnell, S Kieslich, A WolfAbstract:The Rate Coefficient for radiative and dielectronic recombination of beryllium-like magnesium ions was measured with high resolution at the Heidelberg heavy-ion storage ring TSR. In the electron-ion collision energy range 0-207 eV reso- nances due to 2s → 2p (∆N = 0) and 2s → 3l (∆N = 1) core excitations were detected. At low energies below 0.15 eV the recombination Rate Coefficient is dominated by strong 1s 2 (2s 2p 3 P) 7l resonances with the strongest one occuring at an energy of only 21 meV. These resonances decisively influence the Mg recombination Rate Coefficient in a low temperature plasma. The experimentally derived Mg dielectronic recombination Rate Coefficient (±15% systematical uncertainty) is compared with the recommendation by Mazzotta et al. (1998, A&AS, 133, 403) and the recent calculations by Gu (2003, ApJ, 590, 1131) and by Colgan et al. (2003, A&A, 412, 597). These results deviate from the experimental Rate Coefficient by 130%, 82% and 25%, respectively, at the temperature where the fractional abundance of Mg is expected to peak in a photoionized plasma. At this temperature a theoretical uncertainty in the 1s 2 (2s 2p 3 P) 7l resonance positions of only 100 meV would translate into an uncertainty of the plasma Rate Coefficient of almost a factor 3. This finding emphasizes that an accuRate theoretical calculation of the Mg recombination Rate Coefficient from first principles is challenging.
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experimental o vi dielectronic recombination Rate Coefficient and its enhancement by external electric fields
2003Co-Authors: S Bohm, S Schippers, A Muller, W Shi, N Eklow, R Schuch, H Danared, N R BadnellAbstract:The dielectronic recombination Rate Coefficient of $\ion{O}{vi}$ ions has been measured at the heavy ion storage ring cryring. The electron energy range covered all dielectronic recombination resonances attached to $\rm 2s \rightarrow 2p$ ($\Delta n=0$) core excitations. The Rate Coefficient in a plasma has been derived. It is compared to theoretical data. In addition the influence of external electric fields on the dielectronic recombination has been investigated. When increasing the electric field strength to 340 V/cm the experimental recombination Rate Coefficient is found to increase by up to a factor of 2.
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storage ring measurement of the c iv recombination Rate Coefficient
2001Co-Authors: S Schippers, G Gwinner, J Linkemann, A Muller, A A Saghiri, A WolfAbstract:The low-energy C IV dielectronic recombination (DR) Rate Coefficient associated with 2s → 2p Δn = 0 excitations of this lithium-like ion has been measured with high-energy resolution at the heavy-ion storage ring TSR of the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. The experimental procedure and especially the experimental detection probabilities for the high Rydberg states produced by the recombination of this ion are discussed in detail. From the experimental data a Maxwellian plasma Rate Coefficient is derived with ±15% systematic uncertainty and parameterized for ready use in plasma-modeling codes. Our experimental result especially benchmarks the plasma Rate Coefficient below 104 K where DR occurs predominantly via C III (1s22p4l) intermediate states and where existing theories differ by orders of magnitude. Furthermore, we find that, to within our systematic uncertainty of 15%, the total dielectronic and radiative C IV recombination can be represented by the incoherent sum of our DR Rate Coefficient and the radiative recombination Rate Coefficient of Pequignot and coworkers.
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storage ring measurement of the c iv recombination Rate Coefficient
2001Co-Authors: S Schippers, G Gwinner, J Linkemann, A A Saghiri, A Mueller, A WolfAbstract:The low energy C IV dielectronic recombination (DR) Rate Coefficient associated with 2s-2p Delta n=0 excitations of this lithiumlike ion has been measured with high energy-resolution at the heavy-ion storage-ring TSR of the Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany. The experimental procedure and especially the experimental detection probabilities for the high Rydberg states produced by the recombination of this ion are discussed in detail. From the experimental data a Maxwellian plasma Rate Coefficient is derived with 15% systematic uncertainty and parameterized for ready use in plasma modeling codes. Our experimental result especially benchmarks the plasma Rate Coefficient below 10000 K where DR occurs predominantly via C III (1s2 2p 4l) intermediate states and where existing theories differ by orders of magnitude. Furthermore, we find that the total dielectronic and radiative C IV recombination can be represented by the incoherent sum of our DR Rate Coefficient and the RR Rate Coefficient of Pequignot et al. (1991, Astron. Astrophys., 251, 680).
