BOUTHEINA KERKENI - Academia.edu (original) (raw)

Papers by BOUTHEINA KERKENI

arXiv (Cornell University), Jan 28, 2023

The Journal of Physical Chemistry A, 2022

In this contribution, we report a novel comprehensive investigation on negative ion formation fro... more In this contribution, we report a novel comprehensive investigation on negative ion formation from electron transfer processes mediated by neutral potassium atom collisions with neutral methanol molecules employing experimental and theoretical methodologies. Methanol collision-induced fragmentation yielding anion formation has been obtained by time-of-flight mass spectrometry in the wide energy range of 19 to 275 eV in the lab frame. The negative ions formed in such a collision process have been assigned to CH3O-, OH-, and O-, with a strong energy dependence especially at lower collision energies. The most intense fragment anions in the whole energy range investigated have been assigned to OH- and CH3O-. Additionally, the potassium cation energy loss spectrum in the forward scattering direction at 205 eV impact energy has revealed several features, where the two main electronic states accessible during the collision events have vertical electron affinities of -8.26 ± 0.20 and -10.36 ± 0.2 eV. Quantum chemical calculations have been performed for the lowest-lying unoccupied molecular orbitals of methanol in the presence of a potassium atom, lending strong support to the experimental findings.

Physical Chemistry Chemical Physics, 2022

A systematic theoretical analysis of calculated infrared spectra using density functional theory ... more A systematic theoretical analysis of calculated infrared spectra using density functional theory based calculations places new constraints on the interpretation of experimental spectra obtained for TiC-based nanoparticles.

The Journal of Physical Chemistry C, 2018

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Chemical Physics, 2016

This work reports a reduced dimensionality rate constant calculation of the H-abstraction reactio... more This work reports a reduced dimensionality rate constant calculation of the H-abstraction reaction from formaldehyde. Quantum scattering calculations are performed treating explicitly the bonds being broken and formed. Geometry optimisations and frequency calculations are done at the MP2/cc-pVTZ level while energies are calculated with the CCSD(T) method. An analytical potential energy surface was developed from a relatively small number of grid points. When compared to semi-classical approaches, the quantum scattering calculations show that quantum tunnelling yields large contributions at low temperatures. At 200 K, we note a difference of about 5 orders of magnitude between Transition State Theory (TST) and quantum rate constants. Our predicted results show that the quantum and the CVT/SCT rate constants are in reasonable agreement with the available experiment at high temperatures, but that the last one gives better agreement to experimental results at low temperatures.

Monthly Notices of the Royal Astronomical Society, 2021

Polycyclic Aromatic Hydrocarbons (PAHs) are carbon-based molecules resulting from the union of ar... more Polycyclic Aromatic Hydrocarbons (PAHs) are carbon-based molecules resulting from the union of aromatic rings and related species, which are likely responsible for strong infrared emission features. In this work, using a sample of 50 Seyfert galaxies (D L < 100 Mpc) we compare the circumnuclear (inner kpc) PAH emission of AGN to that of a control sample of star-forming galaxies (22 luminous infrared galaxies and 30 H II galaxies), and investigate the differences between central and extended PAH emission. Using Spitzer/InfraRed Spectrograph spectral data of Seyfert and star-forming galaxies and newly developed PAH diagnostic model grids, derived from theoretical spectra, we compare the predicted and observed PAH ratios. We find that star-forming galaxies and AGN-dominated systems are located in different regions of the PAH diagnostic diagrams. This suggests that not only are the size and charge of the PAH molecules different, but also the nature and hardness of the radiation field that excite them. We find tentative evidence that PAH ratios in AGN-dominated systems are consistent with emission from larger PAH molecules (N c > 300-400) as well as neutral species. By subtracting the spectrum of the central source from the total, we compare the PAH emission in the central versus extended region of a small sample of AGN. In contrast to the findings for the central regions of AGN-dominated systems, the PAH ratios measured in the e xtended re gions of both type 1 and type 2 Seyfert galaxies can be explained assuming similar PAH molecular size distribution and ionized fractions of molecules to those seen in central regions of star-forming galaxies (100 < N c < 300).

Based on theoretical spectra computed using Density Functional Theory we study the properties of ... more Based on theoretical spectra computed using Density Functional Theory we study the properties of polycyclic aromatic hydrocarbons (PAH). In particular using bin-average spectra of PAH molecules with varying number of carbons we investigate how the intensity of the mid-infrared emission bands, 3.3, 6.2, 7.7, and 11.3 μm, respond to changes in the number of carbons, charge of the molecule, and the hardness of the radiation field that impinges the molecule. We confirm that the 6.2/7.7 band ratio is a good predictor for the size of the PAH molecule (based on the number of carbons present). We also investigate the efficacy of the 11.3/3.3 ratio to trace the size of PAH molecules and note the dependence of this ratio on the hardness of the radiation field. While the ratio can potentially also be used to trace PAH molecular size, a better understanding of the impact of the underlying radiation field on the 3.3 μm feature and the effect of the extinction on the ratio should be evaluated. The newly developed diagnostics are compared to band ratios measured in a variety of galaxies observed with the Infrared Spectrograph on board the Spitzer Space Telescope. We demonstrate that the band ratios can be used to probe the conditions of the interstellar medium in galaxies and differentiate between environments encountered in normal star forming galaxies and active galactic nuclei. Our work highlights the immense potential that PAH observations with the James Webb Space Telescope will have on our understanding of the PAH emission itself and of the physical conditions in galaxies near and far.

Nanoscale titanium carbide (TiC) is widely used in composites and energy applications. In order t... more Nanoscale titanium carbide (TiC) is widely used in composites and energy applications. In order to design and optimize these systems and to gain a fundamental understanding of these nanomaterials, it is important to understand the atomistic structure of nano-TiC. Cluster beam experiments have provided detailed infrared vibrational spectra of numerous Ti x C y nanoparticles with well defined masses. However, these spectra have yet to be convincingly assigned to Ti x C y nanoparticle structures. Herein, using accurate density functional theory based calculations, we perform a systematic survey of likely candidate nanoparticle structures with masses corresponding to those in experiment. We calculate harmonic infrared vibrational spectra for a range of nanoparticles up to 100 atoms in size, with a focus on systems based on removing either four carbon atoms or a single titanium atom from rocksalt-structured stoichiometric TiC nanoparticles. Our calculations clearly show that Ti-deficient nanoparticles are unlikely candidates to explain the experimental spectra as such structures are highly susceptible to CC bonding, whose characteristic frequencies are not observed in experiment. However, our calculated infrared spectra for C-deficient nanoparticles have some matching features with the experimental spectra but tend to have more complex infrared spectra with more peaks than those obtained from experiment. We suggest that the discrepancy between experiment and theory may be largely due to thermally induced anharmonicities and broadening in the latter nanoparticles, which are not be accounted for in harmonic vibrational calculations.

In this contribution, we report a novel comprehensive investigation on negative ion formation fro... more In this contribution, we report a novel comprehensive investigation on negative ion formation from electron transfer processes mediated by neutral potassium atom collisions with neutral methanol molecules employing experimental and theoretical methodologies. Methanol collision-induced fragmentation yielding anion formation has been obtained by time-of-flight mass spectrometry in the wide energy range of 19 to 275 eV in the lab frame. The negative ions formed in such a collision process have been assigned to CH 3 O − , OH − , and O − , with a strong energy dependence especially at lower collision energies. The most intense fragment anions in the whole energy range investigated have been assigned to OH − and CH 3 O −. Additionally, the potassium cation energy loss spectrum in the forward scattering direction at 205 eV impact energy has revealed several features, where the two main electronic states accessible during the collision events have vertical electron affinities of −8.26 ± 0.20 and −10.36 ± 0.2 eV. Quantum chemical calculations have been performed for the lowest-lying unoccupied molecular orbitals of methanol in the presence of a potassium atom, lending strong support to the experimental findings.

In this study, the coordination sphere of copper in Cu−SSZ-13 as a catalyst for the selective cat... more In this study, the coordination sphere of copper in Cu−SSZ-13 as a catalyst for the selective catalytic reduction of NO x by ammonia is analyzed as a function of environmental parameters: temperature, partial pressure of water P(H 2 O), and partial pressure of ammonia P(NH 3). By periodic density functional theory calculations, we obtain stability domains for variable loadings of water and ammonia (nH 2 O + mNH 3 with (m + n ≤ 6)) close to Cu II ions, which are located at 6-membered ring (6MR) or 8-membered ring (8MR) of the zeolitic structure. Ab initio calculations and thermodynamic investigations were performed to build phase diagrams, with vibrational analysis, so as to provide Gibbs free energy, G, values. Copper located in the 8MR appears to be more reactive toward H 2 O and NH 3 adsorption than the one in the 6MR because of a lower coordination number of copper at 8MR in the absence of adsorbates. Depending on the operating conditions, structures containing adsorbed water and ammonia as ligands at the metal site can simultaneously be stabilized. The most widespread coordination number of Cu II is 4 even at m + n > 4. The theoretical predictions were validated by in situ X-ray absorption spectroscopy, in dehydration conditions and in two gas atmospheres: dry He with P(NH 3) = 10 −3 bar (1000 ppm) and He with P(NH 3) = 10 −3 bar and P(H 2 O) = 10 −2 bar. Trends in terms of ammonia desorption temperature as well as coordination numbers are well reproduced. Experimentally determined behaviors of Cu I and Cu II open new perspectives for the systematic computational investigation of the behavior of Cu I in a H 2 O/NH 3 atmosphere.

Physical Chemistry Chemical Physics

Recent detection of propyl cyanide (C$_3$H$_7$CN) with both linear and branched structures has st... more Recent detection of propyl cyanide (C$_3$H$_7$CN) with both linear and branched structures has stimulated many experimental and theoretical studies. In this theoretical work, we present spectroscopic properties of the far...

Journal of molecular modeling, 2016

A quantum chemistry study of mononuclear metal coordination with four 4-methylimidazole ligands (... more A quantum chemistry study of mononuclear metal coordination with four 4-methylimidazole ligands (4-MeIm) was investigated. The four complexes [Cu(4-MeIm)4](2+), [Cu(4-MeIm)4, H2O](2+), [Zn(4-MeIm)4](2+) and [Zn(4-MeIm)4, H2O](2+) were studied with particular attention to the Nπ or Nτ possible coordinations of the 4-MeIm ring with the metals, using different DFT methods. The results suggest that the Nτ coordination of 4-MeIm ring to Zn(II) or Cu(II) is more favorable whatever the level of calculation. In contrast, the addition of one water molecule in the first coordination sphere of the metal ions provides five-coordinated complexes showing no Nπ or Nτ preferences. There is good agreement between the DFT-calculated structure and those available experimentally. When metal ions are four-fold coordinated, they adopt a tetrahedral geometry. When Cu(II) and Zn(II) are five-fold coordinated, highly symmetric structures or intermediate structures are calculated. Similar energies are calcul...

Http Dx Doi Org 10 1080 00268970500044764, Mar 4, 2011

ABSTRACT The abstraction reaction of H atoms with propane molecules presents two concurrent chann... more ABSTRACT The abstraction reaction of H atoms with propane molecules presents two concurrent channels. In this work we have determined the specific rate constants and the product branching ratios (BRs) between the two channels using quantum chemistry calculations and reduced dimensionality quantum dynamics. The potential energy surfaces were computed by treating explicitly the forming and breaking bonds during the reaction, and optimizing the geometries of all the remaining degrees of freedom. In this way, the dynamics of the reaction occurs on an effective reduced dimensionality hyper-surface accounting for the zero-point energy of the optimized degrees of freedom. Energies are calculated with the CCSD(T) method and the cc-pVTZ basis set, while frequencies are calculated with the MP2 method and the same basis set. The calculations give barrier heights of 0.46 (0.36) eV and the reactions are exothermic by 0.13 (0.25) eV for primary (secondary) hydrogens in C3H8. At room temperature, quantum tunnelling and zero-point effects are found to contribute more than one order of magnitude to the rate constants, when compared to purely classical transition state theory (TST) computations. The branching ratios show the importance of abstraction of secondary hydrogen in propane more significantly at a lower temperature in accord with experimental investigations.

The Journal of Physical Chemistry a, 2004

Chemical Physics Letters, 2007

The abstraction reactions of H atoms from methylamine present two channels. In this work we repor... more The abstraction reactions of H atoms from methylamine present two channels. In this work we report quantum chemistry and reduced dimensionality quantum dynamical calculations of the rate constants and the branching ratios (Brs). The calculations give barrier heights of 0.41 (0.38) eV and the reactions are exothermic by À5.7 (À11.2) eV for H abstraction from the NH 2 group and H abstraction from the CH 3 group respectively. At room temperature, quantum tunneling and zero-point effects are found to contribute two orders of magnitude to the total rate constant, when compared to purely classical transition state theory (TST) computations. Abstraction of hydrogen from the methyl group is dominant and agreement with experiment is good.

The Journal of Chemical Physics, 2015

A permutationally invariant full-dimensional ab initio potential energy surface for the abstracti... more A permutationally invariant full-dimensional ab initio potential energy surface for the abstraction and exchange channels of the H + CH4 system

Phys. Chem. Chem. Phys., 2015

We investigate the potential role of ultrasmall silicate grains in interstellar hydrogen-based ch... more We investigate the potential role of ultrasmall silicate grains in interstellar hydrogen-based chemistry by modelling H adsorption and H2 formation/dissociation on nanosilicates.

arXiv (Cornell University), Jan 28, 2023

The Journal of Physical Chemistry A, 2022

Physical Chemistry Chemical Physics, 2022

The Journal of Physical Chemistry C, 2018

Chemical Physics, 2016

Monthly Notices of the Royal Astronomical Society, 2021

In this contribution, we report a novel comprehensive investigation on negative ion formation fro... more In this contribution, we report a novel comprehensive investigation on negative ion formation from electron transfer processes mediated by neutral potassium atom collisions with neutral methanol molecules employing experimental and theoretical methodologies. Methanol collision-induced fragmentation yielding anion formation has been obtained by time-of-flight mass spectrometry in the wide energy range of 19 to 275 eV in the lab frame. The negative ions formed in such a collision process have been assigned to CH 3 O − , OH − , and O − , with a strong energy dependence especially at lower collision energies. The most intense fragment anions in the whole energy range investigated have been assigned to OH − and CH 3 O −. Additionally, the potassium cation energy loss spectrum in the forward scattering direction at 205 eV impact energy has revealed several features, where the two main electronic states accessible during the collision events have vertical electron affinities of −8.26 ± 0.20 and −10.36 ± 0.2 eV. Quantum chemical calculations have been performed for the lowest-lying unoccupied molecular orbitals of methanol in the presence of a potassium atom, lending strong support to the experimental findings.

Physical Chemistry Chemical Physics

Journal of molecular modeling, 2016

Http Dx Doi Org 10 1080 00268970500044764, Mar 4, 2011

The Journal of Physical Chemistry a, 2004

Chemical Physics Letters, 2007

The Journal of Chemical Physics, 2015

Phys. Chem. Chem. Phys., 2015