Igor Rahinov | The Open University of Israel (original) (raw)

Papers by Igor Rahinov

Physical Review E

The dynamics of ions in an electrostatic ion beam trap in the presence of an external time-depend... more The dynamics of ions in an electrostatic ion beam trap in the presence of an external time-dependent field is studied with a recently developed particle-in-cell simulation technique. The simulation technique, capable of accounting for space-charge effects, has reproduced all the experimental results on the bunch dynamics in the radio frequency mode. With simulation, the motion of ions is visualized in phase space and it is shown that the ion-ion interaction strongly affects the distribution of ions in phase space in the presence of an rf driving voltage.

Journal of the American Chemical Society

A detailed velocity-resolved kinetics study of NH 3 thermal desorption rates from p(2 × 2) O/Pt(1... more A detailed velocity-resolved kinetics study of NH 3 thermal desorption rates from p(2 × 2) O/Pt(111) is presented. We find a large reduction in the NH 3 desorption rate due to adsorption of O-atoms on Pt(111). A physical model describing the interactions between adsorbed NH 3 and O-atoms explains these observations. By fitting the model to the derived desorption rate constants, we find an NH 3 stabilization on p(2 × 2) O/Pt(111) of 0.147 −0.014 +0.023 eV compared to Pt(111) and a rotational barrier of 0.084 −0.022 +0.049 eV, which is not present on Pt(111). The model also quantitatively predicts the steric hindrance of NH 3 diffusion on Pt(111) due to co-adsorbed O-atoms. The derived diffusion barrier of NH 3 on p(2 × 2) O/Pt(111) is 1.10 −0.13 +0.22 eV, which is 0.39 −0.14 +0.22 eV higher than that on pristine Pt(111). We find that Perdew Burke Ernzerhof (PBE) and revised Perdew Burke Ernzerhof (RPBE) exchange−correlation functionals are unable to reproduce the experimentally observed NH 3 −O adsorbate−adsorbate interactions and NH 3 binding energies at Pt(111) and p(2 × 2) O/Pt(111), which indicates the importance of dispersion interactions for both systems.

Proceedings of the Combustion Institute, 2021

We report state-resolved absorption cross-section measurement and oscillator-strength evaluation ... more We report state-resolved absorption cross-section measurement and oscillator-strength evaluation of the gas-phase iron oxide (FeO) orange system near 611 nm. Intracavity absorption spectroscopy (ICAS) with a homemade broadband dye laser was applied for time-resolved measurements of absorption spectra of shockactivated mixtures of iron pentacarbonyl and carbon dioxide (diluted in argon), generating gas-phase FeO. The measurements were performed with a time resolution of 170 μs in the spectral range of 16,316-16,353 cm −1 that includes a large number of FeO absorption lines. Across the 8-cm diameter of the shock tube, ICAS leads to an effective absorption path length of 260 m. Absorption cross-section values of 0.5 × 10-18-4 × 10-18 cm 2 were determined for temperatures around 2200 K and pressures of ∼1.3 bar. Pressure-and temperature-independent oscillator strengths for individual ro-vibronic transitions within the 611-nm band of FeO orange system are reported for the first time. These data are generally applicable for quantitative absorption measurements of flame studies of iron chemistry, where FeO plays a key role as intermediate species.

Science, 2020

Nature of the molecule-surface encounter Adsorption is an important initial step in all heterogen... more Nature of the molecule-surface encounter Adsorption is an important initial step in all heterogeneous chemical processes. However, detailed adsorption dynamics are complex and challenging to follow experimentally. Using the fact that vibrationally excited carbon monoxide molecules can be trapped on the Au(111) surface with all degrees of freedom being equilibrated except the vibrational ones, Borodin et al. show that the vibrational relaxation time can serve as an internal clock to follow the microscopic pathways of adsorption and equilibration on the surface. On the basis of molecular beam experiments and theoretical modeling of this prototypical system, the authors reveal the intricate interplay between physisorption and chemisorption states. These observed characteristics are relevant to many other heterogeneous systems. Science , this issue p. 1461

Proceedings of the Combustion Institute, 2021

A sparkplug ion sensor can be used to measure the ion current in a homogeneous charge compression... more A sparkplug ion sensor can be used to measure the ion current in a homogeneous charge compression ignition (HCCI) engine, providing insight into the ion chemistry inside the cylinders during combustion. HCCI engines typically operate at lean equivalence ratios (/) at which the ion current becomes increasingly indistinguishable from background noise. This paper investigates the effect of fuel additives on the ion signal at low equivalence ratios, determines side effects of metal acetate addition, and validates numerical model for ionization chemistry. Cesium acetate (CsOAc) and potassium acetate (KOAc) were used as additives to ethanol as the primary fuel. Concentration levels of 100, 200, and 400 mg/L of metal acetate-in-ethanol are investigated at equivalence ratios of 0.08, 0.20, and 0.30. The engine experiments were conducted at a boosted intake pressure of 1.8 bar absolute and compared to naturally aspirated results. Combustion timing was maintained at 2.5°after top-dead-center (ATDC), as defined by the crank angle degree (CAD) where 50% of the cumulative heat release occurs (CA50). CsOAc consistently produced the strongest ion signals at all conditions when compared to KOAc. The ion signal was found to decrease with increased intake pressure; an increase in the additive concentration increased the ion signal for all cases. However, the addition of the metal acetates decreased the gross indicated mean effective pressure (IMEP g), maximum rate of heat release (ROHR), and peak cylinder pressure. Experimental results were used to validate ion chemistry mechanisms for cesium and potassium using a single-zone numerical engine model.

The Journal of Physical Chemistry C, 2021

We report nitric oxide (NO) desorption rates from Pd(111) and Pd(332) surfaces measured with velo... more We report nitric oxide (NO) desorption rates from Pd(111) and Pd(332) surfaces measured with velocity-resolved kinetics. The desorption rates at the surface temperatures from 620 to 800 K span more than 3 orders of magnitude, and competing processes, like dissociation, are absent. Applying transition state theory (TST) to model experimental data leads to the NO binding energy E 0 = 1.766 ± 0.024 eV and diffusion barrier D T = 0.29 ± 0.11 eV on the (111) terrace and the stabilization energy for (110)-steps ΔE ST = 0.060 −0.030 +0.015 eV. These parameters provide valuable benchmarks for theory.

Fuel, 2018

The experiments of Rahinov et al. (Combust. Flame, 145 (2006) 105-116) measuring NH 2 concentrati... more The experiments of Rahinov et al. (Combust. Flame, 145 (2006) 105-116) measuring NH 2 concentration profiles in methane-air laminar flat flames doped with ammonia were re-evaluated. The flames were simulated with the FlameMaster code using a modified NOx combustion mechanism of the CRECK Modeling Group. Based on local sensitivity analysis results, Arrhenius parameters A, n, E of reaction steps NH 2 + H = NH + H 2 and NH 3 + OH = NH 2 + H 2 O were selected for optimization, which took into account not only the experimental data of Rahinov et al., but also related direct measurements and theoretical determinations as optimization targets. The optimized mechanism described the measured concentration profiles better than the original one, while the new rate parameter values were within the prior uncertainty limits obtained from the evaluation of literature data. The optimization process also provided new posterior uncertainty limits, which are within the prior uncertainty limits.

Proceedings of the Combustion Institute, 2019

Nanoparticle formation in flames is strongly influenced by the residence-time-temperature history... more Nanoparticle formation in flames is strongly influenced by the residence-time-temperature history inside the flame. We study how the temperature history can be intentionally modified by orienting flames either in an upward-firing or downward-firing configuration. We also investigate the influence of unintended residence-time modifications caused by sampling nozzles. These phenomena are investigated by experiments and simulations for the synthesis of iron oxide nanoparticles from premixed iron-pentacarbonyl-doped hydrogen/oxygen flat flames. The experiments apply molecular-beam sampling with a particle mass spectrometer to measure particle sizes and a quartz microbalance to detect the presence of condensed matter. The simulations rely on a finite-rate chemistry approach with species-specific diffusion, particle dynamics are described by a bi-modal population balance model. It is demonstrated that the downward-burning flame forms a detached stagnation point, causing longer residence times at elevated temperature than an upwardor horizontally firing flame, permitting the growth of larger particles. These iron oxide particles are eventually formed in the recombination zone of the flame, but no condensed matter was found in the reaction zone. The experiments also observed the formation of particles in the preheat zone, but their composition and all aspects of their disappearance remain uncertain. Current models do, however, suggest the formation of iron particles and their subsequent evaporation and combustion.

Nature chemistry, Jan 26, 2018

The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH)... more The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH). In the LH mechanism, reactants adsorb, become thermalized with the surface, and subsequently react. The measured vibrational (relaxation) lifetimes of molecules adsorbed at metal surfaces are in the range of a few picoseconds. As a consequence, vibrational promotion of LH chemistry is rarely observed, with the exception of LH reactions occurring via a molecular physisorbed intermediate. Here, we directly detect adsorption and subsequent desorption of vibrationally excited CO molecules from a Au(111) surface. Our results show that CO (v = 1) survives on a Au(111) surface for ~1 × 10 s. Such long vibrational lifetimes for adsorbates on metal surfaces are unexpected and pose an interesting challenge to the current understanding of vibrational energy dissipation on metal surfaces. They also suggest that vibrational promotion of surface chemistry might be more common than is generally belie...

Journal of Instrumentation, 2017

Among the advantages of an electrostatic ion beam trap (EIBT), which is based on purely electrost... more Among the advantages of an electrostatic ion beam trap (EIBT), which is based on purely electrostatic fields, are mass-unlimited trapping and ease of operation. We have developed a new system that couples an electrospray ion source to an EIBT. Between the source and EIBT there is a Paul trap in which the ions are accumulated before being extracted and accelerated. After the ion bunch has entered the EIBT, the ions are trapped by rapidly raising the voltages on the entrance mirror. The oscillations of the bunch are detected by amplifying the charge induced on a pickup ring in the center of the trap, the ion mass being directly proportional to the square of the oscillation period. The trapping of biomolecules in the RF-bunching mode of the EIBT is used for measurement of mass spectra and collision cross sections. Coalescence of bunches of ions of nearby mass in the self-bunching mode is also demonstrated.

The Journal of Chemical Physics, 2016

In this work we seek to examine the nature of collisional energy transfer between HCl and Au(111)... more In this work we seek to examine the nature of collisional energy transfer between HCl and Au(111) for nonreactive scattering events that sample geometries near the transition state for dissociative adsorption by varying both the vibrational and translational energy of the incident HCl molecules in the range near the dissociation barrier. Specifically, we report absolute vibrational excitation probabilities for HCl(v = 0 → 1) and HCl(v = 1 → 2) scattering from clean Au(111) as a function of surface temperature and incidence translational energy. The HCl(v = 2 → 3) channel could not be observed—presumably due to the onset of dissociation. The excitation probabilities can be decomposed into adiabatic and nonadiabatic contributions. We find that both contributions strongly increase with incidence vibrational state by a factor of 24 and 9, respectively. This suggests that V-T as well as V-EHP coupling can be enhanced near the transition state for dissociative adsorption at a metal surfac...

The European Physical Journal D, 2016

Abstract The stability of anionic (SF6)-N clusters (in the range of N< 23), generated in a sup... more Abstract The stability of anionic (SF6)-N clusters (in the range of N< 23), generated in a supersonic expansion ion source with electron impact ionization, was investigated by measuring their blackbody induced radiative dissociation (BIRD) rates in an electrostatic ion beam trap (EIBT) at room temperature. The lifetime traces of EIBT-stored clusters were subjected to “master equation analysis” and the activation energies, Ea, for the evaporation of a SF6 monomer were extracted. We find that the decay rates of (SF6)-N anionic clusters are larger than those of cationic SF+5(SF6)N-1 measured previously by the same method, and their corresponding activation energies to be smaller. These observations provide further insight into the effect of localized charge on cluster stability. Graphical abstract

Combustion and Flame, 2016

Stoichiometric and very rich (1.5 ≤ ɸ ≤ 1.9) laminar flat flames of methane have been investigate... more Stoichiometric and very rich (1.5 ≤ ɸ ≤ 1.9) laminar flat flames of methane have been investigated using nonintrusive laser diagnostics. Premixed CH4 + O2 + N2 flames were stabilized at a pressure of 30 ± 0.3 Torr. Temperature profiles were obtained using laser-induced fluorescence of OH. Absolute concentration profiles of singlet methylene, 1CH2, were measured by intracavity laser absorption spectroscopy. Uncertainties of the relative and absolute concentrations of singlet methylene were evaluated to be about ±10% and ±30%, respectively. These new experimental data were compared with predictions of three detailed kinetic mechanisms: GRI-mech. 3.0, Aramco mech. 1.3, and the model under development in Lund. In the last mechanism 78 rate constants of reactions along the pathway CH3 → 1CH2 → 3CH2 → CH were reviewed and updated. No adjustment or tuning of the rate expressions to accommodate experimental results was attempted. GRI-mech. significantly overpredicts singlet methylene concentrations in all flames. Aramco mech. and the present model are in good agreement with the measurements in stoichiometric flame, while in all rich flames only the present mechanism reproduces spatial profiles of 1CH2. Detailed analysis of the behaviour of these models revealed that omission of the reaction 1CH2 + M = 3CH2 + M is the main reason of the discrepancy between predictions of the Aramco 1.3 and GRI-mech. 3.0 and experimental 1CH2 concentrations in rich flames.

The journal of physical chemistry letters, Jan 7, 2016

We report zero-coverage reaction probabilities (S0) for HCl dissociative adsorption on Au(111) ob... more We report zero-coverage reaction probabilities (S0) for HCl dissociative adsorption on Au(111) obtained by the seeded molecular beam hot-nozzle method. For measurements at normal incidence with mean translational energies ranging from 0.94 to 2.56 eV (nozzle temperatures 296 to 1060 K), S0 increased from 6 × 10(-6) to 2 × 10(-2). S0 also increased with increasing nozzle temperature for fixed incidence energy associated with the motion normal to the surface. Accounting for the influence of the vibrational state population and translational energy distributions in the incident beam, we are able to compare the experimental results to recent theoretical predictions. These calculations, performed employing 6-D quantum dynamics on an electronically adiabatic potential energy surface obtained using density functional theory at the level of the generalized gradient approximation and the static surface approximation, severely overestimate the reaction probabilities when compared with our exp...

Flow, Turbulence and Combustion, 2015

The behavior of pulsed flame (PF) and its potential application as a source for syngas production... more The behavior of pulsed flame (PF) and its potential application as a source for syngas production was investigated. Methane/oxygen mixtures of different compositions with and without nitrogen dilution in the temperature range of 278-673 K were studied. This allowed to study the influence of operating temperature, equivalence ratio and dilution on the PF behavior and syngas production efficiency. The PF exhibits two different modes of flame propagation: one relatively slow (several m/s) observed for CH4/O2 mixtures diluted by nitrogen and another, very fast, with flame speed of ∼1300 m/s, observed for the mixtures containing only CH4 and O2 without nitrogen dilution. The exhaust gases emerging from the PF were analyzed by Gas Chromatography (GC) and Fiber Laser Absorption Spectroscopy (FLICAS) for CO:CO2 ratio. The CO:CO2 ratio observed in the PF exhaust was found to be higher than that observed in continuous flame, suggesting additional advantages for employing PF for syngas production.

Applied Physics B, 2015

AbstractThe feasibility of temperature and concentration measurements using near-IR (∼1.5 μm) wat... more AbstractThe feasibility of temperature and concentration measurements using near-IR (∼1.5 μm) water spectra obtained by fiber laser intracavity spectroscopy was evaluated. The spectra were registered with water vapor heated in a tubular oven at temperatures between 1000 and 1300 K and in adiabatic flames where temperatures were above 1800 K. Adiabatic flames of methane were stabilized on the heat flux burner. For temperature and concentration evaluation, the observed spectra were fitted by simulated spectra calculated utilizing the HITEMP database. Several discrepancies between HITEMP data and the experiments leading to significant errors in evaluation were found. After small corrections to the database better, accuracy of the temperature (±70 K) and concentration (±20 %) measurements is obtained. A more precise spectroscopic assignment is needed to improve the accuracy of the results.

Energy & Fuels, 2015

Stoichiometric and very rich flames of methane have been investigated using nonintrusive laser di... more Stoichiometric and very rich flames of methane have been investigated using nonintrusive laser diagnostics. Absolute concentration profiles of HCO were measured by intracavity laser absorption spectroscopy, and temperature profiles were obtained with laser-induced fluorescence of OH. Premixed CH4 + O2 + N2 flames were stabilized at a pressure of 30 ± 0.3 Torr. These new experimental data were compared with predictions of two models: GRI-mech. 3.0 and Aramco mech. 1.3. GRI-mech. performs better in a stoichiometric flame, whereas Aramco mech. is in better agreement with experiments in the rich flames. Detailed analysis of the behavior of these two models revealed that similar performance is essentially fortuitous and explained by balancing of different reactions involved in HCO formation and consumption.

CrystEngComm, 2015

low-pressure flat flames doped with iron pentacarbonyl IJFeIJCO) 5) were used to investigate the in... more low-pressure flat flames doped with iron pentacarbonyl IJFeIJCO) 5) were used to investigate the initial steps towards the formation of iron-oxide nanoparticles. The particles were extracted from the flame using a molecular beam sampling probe and the mass flow rate of condensed material was measured by a quartz crystal microbalance (QCM). It was observed that particles are already formed on the cold side of the flame, and vanish quickly once they pass through the flame front. To understand the process and assess the perturbations caused by the sampling probe, spatially resolved laser-based measurements of temperature, Fe and FeO concentration as well as molecular-beam sampling with particle mass spectrometry (PMS) were carried out. Numerical flow simulations of the synthesis flames, the reactor, and the sampling were performed and the simulations confirmed the experimental findings of very early particle formation. The detailed knowledge of the perturbation caused by invasive probing enabled further insight into the iron-oxide nanoparticle formation mechanism. From the results it is concluded that neither Fe atoms nor FeO molecules belong to the growth species of iron-oxide nanoparticles from flame synthesis.

Physical Review E

The dynamics of ions in an electrostatic ion beam trap in the presence of an external time-depend... more The dynamics of ions in an electrostatic ion beam trap in the presence of an external time-dependent field is studied with a recently developed particle-in-cell simulation technique. The simulation technique, capable of accounting for space-charge effects, has reproduced all the experimental results on the bunch dynamics in the radio frequency mode. With simulation, the motion of ions is visualized in phase space and it is shown that the ion-ion interaction strongly affects the distribution of ions in phase space in the presence of an rf driving voltage.

Journal of the American Chemical Society

A detailed velocity-resolved kinetics study of NH 3 thermal desorption rates from p(2 × 2) O/Pt(1... more A detailed velocity-resolved kinetics study of NH 3 thermal desorption rates from p(2 × 2) O/Pt(111) is presented. We find a large reduction in the NH 3 desorption rate due to adsorption of O-atoms on Pt(111). A physical model describing the interactions between adsorbed NH 3 and O-atoms explains these observations. By fitting the model to the derived desorption rate constants, we find an NH 3 stabilization on p(2 × 2) O/Pt(111) of 0.147 −0.014 +0.023 eV compared to Pt(111) and a rotational barrier of 0.084 −0.022 +0.049 eV, which is not present on Pt(111). The model also quantitatively predicts the steric hindrance of NH 3 diffusion on Pt(111) due to co-adsorbed O-atoms. The derived diffusion barrier of NH 3 on p(2 × 2) O/Pt(111) is 1.10 −0.13 +0.22 eV, which is 0.39 −0.14 +0.22 eV higher than that on pristine Pt(111). We find that Perdew Burke Ernzerhof (PBE) and revised Perdew Burke Ernzerhof (RPBE) exchange−correlation functionals are unable to reproduce the experimentally observed NH 3 −O adsorbate−adsorbate interactions and NH 3 binding energies at Pt(111) and p(2 × 2) O/Pt(111), which indicates the importance of dispersion interactions for both systems.

Proceedings of the Combustion Institute, 2021

We report state-resolved absorption cross-section measurement and oscillator-strength evaluation ... more We report state-resolved absorption cross-section measurement and oscillator-strength evaluation of the gas-phase iron oxide (FeO) orange system near 611 nm. Intracavity absorption spectroscopy (ICAS) with a homemade broadband dye laser was applied for time-resolved measurements of absorption spectra of shockactivated mixtures of iron pentacarbonyl and carbon dioxide (diluted in argon), generating gas-phase FeO. The measurements were performed with a time resolution of 170 μs in the spectral range of 16,316-16,353 cm −1 that includes a large number of FeO absorption lines. Across the 8-cm diameter of the shock tube, ICAS leads to an effective absorption path length of 260 m. Absorption cross-section values of 0.5 × 10-18-4 × 10-18 cm 2 were determined for temperatures around 2200 K and pressures of ∼1.3 bar. Pressure-and temperature-independent oscillator strengths for individual ro-vibronic transitions within the 611-nm band of FeO orange system are reported for the first time. These data are generally applicable for quantitative absorption measurements of flame studies of iron chemistry, where FeO plays a key role as intermediate species.

Science, 2020

Nature of the molecule-surface encounter Adsorption is an important initial step in all heterogen... more Nature of the molecule-surface encounter Adsorption is an important initial step in all heterogeneous chemical processes. However, detailed adsorption dynamics are complex and challenging to follow experimentally. Using the fact that vibrationally excited carbon monoxide molecules can be trapped on the Au(111) surface with all degrees of freedom being equilibrated except the vibrational ones, Borodin et al. show that the vibrational relaxation time can serve as an internal clock to follow the microscopic pathways of adsorption and equilibration on the surface. On the basis of molecular beam experiments and theoretical modeling of this prototypical system, the authors reveal the intricate interplay between physisorption and chemisorption states. These observed characteristics are relevant to many other heterogeneous systems. Science , this issue p. 1461

Proceedings of the Combustion Institute, 2021

A sparkplug ion sensor can be used to measure the ion current in a homogeneous charge compression... more A sparkplug ion sensor can be used to measure the ion current in a homogeneous charge compression ignition (HCCI) engine, providing insight into the ion chemistry inside the cylinders during combustion. HCCI engines typically operate at lean equivalence ratios (/) at which the ion current becomes increasingly indistinguishable from background noise. This paper investigates the effect of fuel additives on the ion signal at low equivalence ratios, determines side effects of metal acetate addition, and validates numerical model for ionization chemistry. Cesium acetate (CsOAc) and potassium acetate (KOAc) were used as additives to ethanol as the primary fuel. Concentration levels of 100, 200, and 400 mg/L of metal acetate-in-ethanol are investigated at equivalence ratios of 0.08, 0.20, and 0.30. The engine experiments were conducted at a boosted intake pressure of 1.8 bar absolute and compared to naturally aspirated results. Combustion timing was maintained at 2.5°after top-dead-center (ATDC), as defined by the crank angle degree (CAD) where 50% of the cumulative heat release occurs (CA50). CsOAc consistently produced the strongest ion signals at all conditions when compared to KOAc. The ion signal was found to decrease with increased intake pressure; an increase in the additive concentration increased the ion signal for all cases. However, the addition of the metal acetates decreased the gross indicated mean effective pressure (IMEP g), maximum rate of heat release (ROHR), and peak cylinder pressure. Experimental results were used to validate ion chemistry mechanisms for cesium and potassium using a single-zone numerical engine model.

The Journal of Physical Chemistry C, 2021

We report nitric oxide (NO) desorption rates from Pd(111) and Pd(332) surfaces measured with velo... more We report nitric oxide (NO) desorption rates from Pd(111) and Pd(332) surfaces measured with velocity-resolved kinetics. The desorption rates at the surface temperatures from 620 to 800 K span more than 3 orders of magnitude, and competing processes, like dissociation, are absent. Applying transition state theory (TST) to model experimental data leads to the NO binding energy E 0 = 1.766 ± 0.024 eV and diffusion barrier D T = 0.29 ± 0.11 eV on the (111) terrace and the stabilization energy for (110)-steps ΔE ST = 0.060 −0.030 +0.015 eV. These parameters provide valuable benchmarks for theory.

Fuel, 2018

The experiments of Rahinov et al. (Combust. Flame, 145 (2006) 105-116) measuring NH 2 concentrati... more The experiments of Rahinov et al. (Combust. Flame, 145 (2006) 105-116) measuring NH 2 concentration profiles in methane-air laminar flat flames doped with ammonia were re-evaluated. The flames were simulated with the FlameMaster code using a modified NOx combustion mechanism of the CRECK Modeling Group. Based on local sensitivity analysis results, Arrhenius parameters A, n, E of reaction steps NH 2 + H = NH + H 2 and NH 3 + OH = NH 2 + H 2 O were selected for optimization, which took into account not only the experimental data of Rahinov et al., but also related direct measurements and theoretical determinations as optimization targets. The optimized mechanism described the measured concentration profiles better than the original one, while the new rate parameter values were within the prior uncertainty limits obtained from the evaluation of literature data. The optimization process also provided new posterior uncertainty limits, which are within the prior uncertainty limits.

Proceedings of the Combustion Institute, 2019

Nanoparticle formation in flames is strongly influenced by the residence-time-temperature history... more Nanoparticle formation in flames is strongly influenced by the residence-time-temperature history inside the flame. We study how the temperature history can be intentionally modified by orienting flames either in an upward-firing or downward-firing configuration. We also investigate the influence of unintended residence-time modifications caused by sampling nozzles. These phenomena are investigated by experiments and simulations for the synthesis of iron oxide nanoparticles from premixed iron-pentacarbonyl-doped hydrogen/oxygen flat flames. The experiments apply molecular-beam sampling with a particle mass spectrometer to measure particle sizes and a quartz microbalance to detect the presence of condensed matter. The simulations rely on a finite-rate chemistry approach with species-specific diffusion, particle dynamics are described by a bi-modal population balance model. It is demonstrated that the downward-burning flame forms a detached stagnation point, causing longer residence times at elevated temperature than an upwardor horizontally firing flame, permitting the growth of larger particles. These iron oxide particles are eventually formed in the recombination zone of the flame, but no condensed matter was found in the reaction zone. The experiments also observed the formation of particles in the preheat zone, but their composition and all aspects of their disappearance remain uncertain. Current models do, however, suggest the formation of iron particles and their subsequent evaporation and combustion.

Nature chemistry, Jan 26, 2018

The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH)... more The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH). In the LH mechanism, reactants adsorb, become thermalized with the surface, and subsequently react. The measured vibrational (relaxation) lifetimes of molecules adsorbed at metal surfaces are in the range of a few picoseconds. As a consequence, vibrational promotion of LH chemistry is rarely observed, with the exception of LH reactions occurring via a molecular physisorbed intermediate. Here, we directly detect adsorption and subsequent desorption of vibrationally excited CO molecules from a Au(111) surface. Our results show that CO (v = 1) survives on a Au(111) surface for ~1 × 10 s. Such long vibrational lifetimes for adsorbates on metal surfaces are unexpected and pose an interesting challenge to the current understanding of vibrational energy dissipation on metal surfaces. They also suggest that vibrational promotion of surface chemistry might be more common than is generally belie...

Journal of Instrumentation, 2017

Among the advantages of an electrostatic ion beam trap (EIBT), which is based on purely electrost... more Among the advantages of an electrostatic ion beam trap (EIBT), which is based on purely electrostatic fields, are mass-unlimited trapping and ease of operation. We have developed a new system that couples an electrospray ion source to an EIBT. Between the source and EIBT there is a Paul trap in which the ions are accumulated before being extracted and accelerated. After the ion bunch has entered the EIBT, the ions are trapped by rapidly raising the voltages on the entrance mirror. The oscillations of the bunch are detected by amplifying the charge induced on a pickup ring in the center of the trap, the ion mass being directly proportional to the square of the oscillation period. The trapping of biomolecules in the RF-bunching mode of the EIBT is used for measurement of mass spectra and collision cross sections. Coalescence of bunches of ions of nearby mass in the self-bunching mode is also demonstrated.

The Journal of Chemical Physics, 2016

In this work we seek to examine the nature of collisional energy transfer between HCl and Au(111)... more In this work we seek to examine the nature of collisional energy transfer between HCl and Au(111) for nonreactive scattering events that sample geometries near the transition state for dissociative adsorption by varying both the vibrational and translational energy of the incident HCl molecules in the range near the dissociation barrier. Specifically, we report absolute vibrational excitation probabilities for HCl(v = 0 → 1) and HCl(v = 1 → 2) scattering from clean Au(111) as a function of surface temperature and incidence translational energy. The HCl(v = 2 → 3) channel could not be observed—presumably due to the onset of dissociation. The excitation probabilities can be decomposed into adiabatic and nonadiabatic contributions. We find that both contributions strongly increase with incidence vibrational state by a factor of 24 and 9, respectively. This suggests that V-T as well as V-EHP coupling can be enhanced near the transition state for dissociative adsorption at a metal surfac...

The European Physical Journal D, 2016

Abstract The stability of anionic (SF6)-N clusters (in the range of N< 23), generated in a sup... more Abstract The stability of anionic (SF6)-N clusters (in the range of N< 23), generated in a supersonic expansion ion source with electron impact ionization, was investigated by measuring their blackbody induced radiative dissociation (BIRD) rates in an electrostatic ion beam trap (EIBT) at room temperature. The lifetime traces of EIBT-stored clusters were subjected to “master equation analysis” and the activation energies, Ea, for the evaporation of a SF6 monomer were extracted. We find that the decay rates of (SF6)-N anionic clusters are larger than those of cationic SF+5(SF6)N-1 measured previously by the same method, and their corresponding activation energies to be smaller. These observations provide further insight into the effect of localized charge on cluster stability. Graphical abstract

Combustion and Flame, 2016

Stoichiometric and very rich (1.5 ≤ ɸ ≤ 1.9) laminar flat flames of methane have been investigate... more Stoichiometric and very rich (1.5 ≤ ɸ ≤ 1.9) laminar flat flames of methane have been investigated using nonintrusive laser diagnostics. Premixed CH4 + O2 + N2 flames were stabilized at a pressure of 30 ± 0.3 Torr. Temperature profiles were obtained using laser-induced fluorescence of OH. Absolute concentration profiles of singlet methylene, 1CH2, were measured by intracavity laser absorption spectroscopy. Uncertainties of the relative and absolute concentrations of singlet methylene were evaluated to be about ±10% and ±30%, respectively. These new experimental data were compared with predictions of three detailed kinetic mechanisms: GRI-mech. 3.0, Aramco mech. 1.3, and the model under development in Lund. In the last mechanism 78 rate constants of reactions along the pathway CH3 → 1CH2 → 3CH2 → CH were reviewed and updated. No adjustment or tuning of the rate expressions to accommodate experimental results was attempted. GRI-mech. significantly overpredicts singlet methylene concentrations in all flames. Aramco mech. and the present model are in good agreement with the measurements in stoichiometric flame, while in all rich flames only the present mechanism reproduces spatial profiles of 1CH2. Detailed analysis of the behaviour of these models revealed that omission of the reaction 1CH2 + M = 3CH2 + M is the main reason of the discrepancy between predictions of the Aramco 1.3 and GRI-mech. 3.0 and experimental 1CH2 concentrations in rich flames.

The journal of physical chemistry letters, Jan 7, 2016

We report zero-coverage reaction probabilities (S0) for HCl dissociative adsorption on Au(111) ob... more We report zero-coverage reaction probabilities (S0) for HCl dissociative adsorption on Au(111) obtained by the seeded molecular beam hot-nozzle method. For measurements at normal incidence with mean translational energies ranging from 0.94 to 2.56 eV (nozzle temperatures 296 to 1060 K), S0 increased from 6 × 10(-6) to 2 × 10(-2). S0 also increased with increasing nozzle temperature for fixed incidence energy associated with the motion normal to the surface. Accounting for the influence of the vibrational state population and translational energy distributions in the incident beam, we are able to compare the experimental results to recent theoretical predictions. These calculations, performed employing 6-D quantum dynamics on an electronically adiabatic potential energy surface obtained using density functional theory at the level of the generalized gradient approximation and the static surface approximation, severely overestimate the reaction probabilities when compared with our exp...

Flow, Turbulence and Combustion, 2015

The behavior of pulsed flame (PF) and its potential application as a source for syngas production... more The behavior of pulsed flame (PF) and its potential application as a source for syngas production was investigated. Methane/oxygen mixtures of different compositions with and without nitrogen dilution in the temperature range of 278-673 K were studied. This allowed to study the influence of operating temperature, equivalence ratio and dilution on the PF behavior and syngas production efficiency. The PF exhibits two different modes of flame propagation: one relatively slow (several m/s) observed for CH4/O2 mixtures diluted by nitrogen and another, very fast, with flame speed of ∼1300 m/s, observed for the mixtures containing only CH4 and O2 without nitrogen dilution. The exhaust gases emerging from the PF were analyzed by Gas Chromatography (GC) and Fiber Laser Absorption Spectroscopy (FLICAS) for CO:CO2 ratio. The CO:CO2 ratio observed in the PF exhaust was found to be higher than that observed in continuous flame, suggesting additional advantages for employing PF for syngas production.

Applied Physics B, 2015

AbstractThe feasibility of temperature and concentration measurements using near-IR (∼1.5 μm) wat... more AbstractThe feasibility of temperature and concentration measurements using near-IR (∼1.5 μm) water spectra obtained by fiber laser intracavity spectroscopy was evaluated. The spectra were registered with water vapor heated in a tubular oven at temperatures between 1000 and 1300 K and in adiabatic flames where temperatures were above 1800 K. Adiabatic flames of methane were stabilized on the heat flux burner. For temperature and concentration evaluation, the observed spectra were fitted by simulated spectra calculated utilizing the HITEMP database. Several discrepancies between HITEMP data and the experiments leading to significant errors in evaluation were found. After small corrections to the database better, accuracy of the temperature (±70 K) and concentration (±20 %) measurements is obtained. A more precise spectroscopic assignment is needed to improve the accuracy of the results.

Energy & Fuels, 2015

Stoichiometric and very rich flames of methane have been investigated using nonintrusive laser di... more Stoichiometric and very rich flames of methane have been investigated using nonintrusive laser diagnostics. Absolute concentration profiles of HCO were measured by intracavity laser absorption spectroscopy, and temperature profiles were obtained with laser-induced fluorescence of OH. Premixed CH4 + O2 + N2 flames were stabilized at a pressure of 30 ± 0.3 Torr. These new experimental data were compared with predictions of two models: GRI-mech. 3.0 and Aramco mech. 1.3. GRI-mech. performs better in a stoichiometric flame, whereas Aramco mech. is in better agreement with experiments in the rich flames. Detailed analysis of the behavior of these two models revealed that similar performance is essentially fortuitous and explained by balancing of different reactions involved in HCO formation and consumption.

CrystEngComm, 2015

low-pressure flat flames doped with iron pentacarbonyl IJFeIJCO) 5) were used to investigate the in... more low-pressure flat flames doped with iron pentacarbonyl IJFeIJCO) 5) were used to investigate the initial steps towards the formation of iron-oxide nanoparticles. The particles were extracted from the flame using a molecular beam sampling probe and the mass flow rate of condensed material was measured by a quartz crystal microbalance (QCM). It was observed that particles are already formed on the cold side of the flame, and vanish quickly once they pass through the flame front. To understand the process and assess the perturbations caused by the sampling probe, spatially resolved laser-based measurements of temperature, Fe and FeO concentration as well as molecular-beam sampling with particle mass spectrometry (PMS) were carried out. Numerical flow simulations of the synthesis flames, the reactor, and the sampling were performed and the simulations confirmed the experimental findings of very early particle formation. The detailed knowledge of the perturbation caused by invasive probing enabled further insight into the iron-oxide nanoparticle formation mechanism. From the results it is concluded that neither Fe atoms nor FeO molecules belong to the growth species of iron-oxide nanoparticles from flame synthesis.