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Dissociative ionization of methane in an elliptical pulse shaped laser field
, Article Journal of Molecular Structure ; Volume 1079 , January , 2015 , Pages 454-459 ; 00222860 (ISSN) ; Sadighi Bonabi, R ; Anvari, A ; Sharif University of Technology
Elsevier
2015
Abstract
The effect of strong femto-second laser pulses on the dissociation probability of methane has been investigated analytically in various arrangements. The ellipticity dependence of the dissociation probability at intensities from 1014 W cm-2 to 1016 W cm-2 for Ti:Sapphire laser is presented. A reliable calculation of the dissociation probability based on 3D time-dependent Schrodinger equation with an improved model of time-dependent density-functional theory is presented. These calculations are carried out for three different cases of elliptically polarized laser pulse, optimum convolution of dual short pulses, and two-color mixed nonresonant laser pulses. It is found that the rescattering...
Single-hydrogen dissociation paths for upright and flat acetophenone adsorbates on the Si(001) surface
, Article Journal of Physical Chemistry C ; Volume 118, Issue 41 , 16 October , 2014 , Pages 23682-23689 ; ISSN: 19327447 ; Sharif University of Technology
Abstract
Using cluster-based density functional theory we investigate adsorption configurations of an acetophenone molecule on a Si(001) surface and their follow-up proton transfer processes. We examine two possible types of dative-adsorption configurations, up-right standing and flat, as well as compute their follow-up kinetically preferable on-dimer, interdimer, and inter-row proton transfers. Energetics of possible conversions between the achieved adsorption configurations are computed as well. Using all the data obtained, we theoretically illustrate reaction pathways leading to detached hydrogen positions captured in STM imaging of a Si(001) surface exposed to acetophenone vapor at room...
Investigation of intense femto-second laser ionization and dissociation of methane with time-dependent density-functional approach
, Article Chemical Physics Letters ; Vol. 604 , 2014 , Pages 60-67 ; ISSN: 00092614 ; Sadighi Bonabi, R ; Anvari, A ; Sharif University of Technology
Abstract
Three dimensional calculations of electronic dynamics of CH4 in a strong laser field are presented with time-dependent density-functional theory. Time evolution of dipole moment and electron localization function is presented. The dependence of dissociation rate on the laser characters is shown and optimal effective parameters are evaluated. The optimum field leads to 76% dissociation probability for Gaussian envelope and 40 fs (FWHM) at 10 16 W cm-2. The dissociation probability is calculated by optimum convolution of dual short pulses. By combining of field assisted dissociation process and Ehrenfest molecular dynamics, time variation of bond length, velocity and orientation effect are...
Ab-Initio calculations of the CO adsorption and dissociation on substitutional Fe-Cu surface alloys relevant to Fischer-Tropsch Synthesis: Bcc-(Cu)Fe(100) and fcc-(Fe)Cu(100)
, Article Surface and Interface Analysis ; Volume 45, Issue 7 , 2013 , Pages 1081-1087 ; 01422421 (ISSN) ; Fazeli, E ; Joshani, A ; Gholami, M ; Sharif University of Technology
Abstract
Direct CO dissociation is seen the main path of the first step in the Fischer-Tropsch Synthesis (FTS) on the reactive iron surfaces. Cu/Fe alloy film is addressed with various applications over face-centered-cubic (fcc)-Cu and body-centered-cubic (bcc)-Fe in the FTS, i.e. preventing iron carbide formation (through direct CO dissociation) by moderating the surface reactivity and facilitating the reduction of iron surfaces, respectively. In this study by density functional theory, the stable configurations of CO molecule on various Cu/Fe alloys over fcc-Cu(100) and bcc-Fe(100) surfaces with different CO coverage (25% and 50%) have been evaluated. Our results showed that the ensemble effect...
DFT study of nitrogen monoxide adsorption and dissociation on Rh[sbnd]Cu nano clusters
, Article Journal of Alloys and Compounds ; Volume 695 , 2017 , Pages 1924-1929 ; 09258388 (ISSN) ; Nahali, M ; Gobal, F ; Sharif University of Technology
Abstract
Adsorption and dissociation of NO on RhxCu4-x(x = 0–4) nano clusters were investigated using density functional theory. Adsorption energy, total charge on NO, NO bond length, and NO vibrational frequency for various modes of NO adsorption were analyzed. Adsorption from the nitrogen end of NO on the Rh atom(s) of the clusters are more favored and adsorption energies are in the −1.02 eV to −2.59 eV range. NO binds stronger to Rh-Cu mixed clusters compared to pure Cu4 cluster, so N[sbnd]O bond is significantly weakened upon adsorption on the former. NO binding to more atoms of the clusters results in a corresponding decrease of the N[sbnd]O vibrational frequency. Dissociation of NO was also...
Selective photo-dissociative ionization of methane molecule with TDDFT study
, Article Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy ; Volume 171 , 2017 , Pages 325-329 ; 13861425 (ISSN) ; Anvari, A ; Sadighi Bonabi, R ; Sharif University of Technology
Elsevier B.V
2017
Abstract
Three dimensional calculation of control dynamics for finding the optimized laser filed is formulated using an iterative method and time-dependent density functional approach. An appropriate laser pulse is designed to control the desired products in the dissociation of methane molecule. The tailored laser pulse profile, eigenstate distributions and evolution of the efficient occupation numbers are predicted and exact energy levels of this five-atomic molecule is obtained. Dissociation rates of up to 78%, 80%, 90%, and 82% for CH2 +, CH+, C+ and C++ are achieved. Based on the present approach one can reduce the controlling costs. © 2016 Elsevier B.V
Interaction of Femtosecond Lasers with Molecule
, M.Sc. Thesis Sharif University of Technology ; Sadighi Bonabi, Rasul (Supervisor)
Abstract
Using field assisted dissociation model and with a classic view the dissociation probability is calculated when it a molecule is exposed with a Ti:sapphire laser with wavenumber of 800nm and the energy of . using gradient optimization method we find a tailored two rectangular laser pulse for controlling the dissociation of C-H bond of . Using classical method reduced the complicacy of solving schrodinger equation. In our optimization method in contrast with the usual controlling method experimental data is not needed and this reduced the controlling costs.
Phenylcyclopropane energetics and characterization of its conjugate base: Phenyl substituent effects and the C-H bond dissociation energy of cyclopropane
, Article Journal of Organic Chemistry ; Volume 81, Issue 19 , 2016 , Pages 9175-9179 ; 00223263 (ISSN) ; Lis, L ; Kass, S. R ; Sharif University of Technology
American Chemical Society
Abstract
The α-C-H bond dissociation energy (BDE) of phenylcyclopropane (1) was experimentally determined using Hess' law. An equilibrium acidity determination of 1 afforded ΔH°acid = 389.1 ± 0.8 kcal mol-1, and isotopic labeling established that the α-position of the three-membered ring is the favored deprotonation site. Interestingly, the structure of the base proved to be a key factor in correctly determining the proper ionization site (i.e., secondary amide ions are needed, and primary ones and OH- lead to incorrect conclusions since they scramble the deuterium label). An experimental measurement of the electron affinity of 1-phenylcyclopropyl radical (EA = 17.5 ± 2.8 kcal mol-1) was combined...
The formation and dissociation energy of vacancies in cementite: A first-principles study
, Article Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms ; Volume 502 , 2021 , Pages 157-163 ; 0168583X (ISSN) ; Amirhossein Feghhi, S ; Samadfam, M ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Because of the possibility of various types of vacancies in cementite due to its crystalline structure, the focus of this paper was only on vacancies. In this regard, the formation energies of single, two, three and four vacancies of over than 120 different cases were calculated using first-principles method. For the case of single vacancy, the results were in three values of ~1.63, 1.39 and 0.78 eV according to iron vacancies at general positions, iron vacancies located on mirror planes and carbon vacancies in the interstitial positions, respectively. The results for the case of two, three and four vacancies were between from 2.10 to 3.34 eV, from 3.92 to 5.10 eV and from 4.77 to 6.33 eV,...
Thermodynamic Modeling of Hydrogen Hydrate Formation with and without Help Molecules
, M.Sc. Thesis Sharif University of Technology ; Taghikhani, Vahid (Supervisor) ; Ghotbi, Siroos (Supervisor)
Abstract
In this study equilibrium condition of pure hydrogen hydrates is determined with Lee-Holder model. Two hydrogen molecules and four hydrogen molecules encaged in the small and large cavities respectively. Langmuir constant of hydrogen is calculated with the Exp-6 potential. Lee et al. reported parameter of this model by integrating ab initio calculation with classical statistical thermodynamics. This model reasonably predicts dissociation pressures of hydrogen hydrates.Calculated reference parameters are used in modeling of binary hydrogen hydrates. Lattice distortion model is used for modeling of binary hydrogen hydrates with tetrahydrofuran (THF) as a promoter. Cavity radius and parameters...
Styrene energetics and characterization of its conjugate base: An example of isotopic labeling gone awry
, Article International Journal of Mass Spectrometry ; 2016 ; 13873806 (ISSN) ; Lis, L ; Kass, S. R ; Sharif University of Technology
Elsevier
Abstract
The equilibrium acidity of styrene was measured (δH°acid(PhCHCH2)=390.6±0.5kcalmol-1) and its deprotonation site was revised from the ortho position on the aromatic ring to the α-hydrogen atom based upon deuterium-labeling studies and extensive computations. Somewhat surprisingly, the nature of the anionic base plays a critical role in properly determining the ionization site and avoiding misleading results due to extraordinary hydrogen-deuterium exchange. Bracketing the electron affinity of α-styryl radical (PhC CH2, 23.1±3.4kcalmol-1) enabled the α-CH bond dissociation energy (100.1±3.4kcalmol-1) of styrene and the effect of a phenyl substituent at an sp2-hybridized carbon to be...
Styrene energetics and characterization of its conjugate base: An example of isotopic labeling gone awry
, Article International Journal of Mass Spectrometry ; Volume 413 , 2017 , Pages 163-167 ; 13873806 (ISSN) ; Lis, L ; Kass, S. R ; Sharif University of Technology
Elsevier B.V
2017
Abstract
The equilibrium acidity of styrene was measured (ΔH°acid(PhCH[dbnd]CH2) = 390.6 ± 0.5 kcal mol−1) and its deprotonation site was revised from the ortho position on the aromatic ring to the α-hydrogen atom based upon deuterium-labeling studies and extensive computations. Somewhat surprisingly, the nature of the anionic base plays a critical role in properly determining the ionization site and avoiding misleading results due to extraordinary hydrogen–deuterium exchange. Bracketing the electron affinity of α-styryl radical (PhC[rad][dbnd]CH2, 23.1 ± 3.4 kcal mol−1) enabled the α-C[sbnd]H bond dissociation energy (100.1 ± 3.4 kcal mol−1) of styrene and the effect of a phenyl substituent at an...
Conversion of a weak organic acid to a super acid in the gas phase
, Article Journal of Physical Organic Chemistry ; Volume 21, Issue 2 , 2008 , Pages 112-118 ; 08943230 (ISSN) ; Tavasoli, E ; Sharif University of Technology
2008
Abstract
The effects of selected metal ions on the gas-phase acidity of weak organic acids have been explored using the DFT and Moller-Plesset Perturbation Theory (MP2) calculations. The three organic acids selected for this study were acetic acid (aliphatic), benzoic acid (aromatic), and glycine (amino acid). The acidities of these compounds are compared with the acidity of their Li +-, Na+-, and K+ -complexed species. The results indicate that upon complexation with Li+, Na+, and K+ at 298K, the gas-phase acidity of acetic acid, for example, varies from 345.3 to 218.8, 230.2, and 240.1 kcal/mol, respectively (i.e., its dissociation becomes much less endothermic). These values indicate that a weak...
Dissociation of C-H molecular bond of methane by pulse shaped ultra-intense laser field
, Article Chemical Physics Letters ; Volume 560 , 2013 , Pages 60-65 ; 00092614 (ISSN) ; Irani, E ; Navid, H. A ; Dehghani, Z ; Anvari, A ; Sadighi Bonabi, R ; Sharif University of Technology
2013
Abstract
The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability
Efficient photo-dissociation of CH4 and H2CO molecules with optimized ultra-short laser pulses
, Article AIP Advances ; Volume 5, Issue 11 , 2015 ; 21583226 (ISSN) ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
American Institute of Physics Inc
2015
Abstract
The fragmentation dynamics of CH4 and H2CO molecules have been studied with ultra-short pulses at laser intensityof up to 1015Wcm-2. Three dimensional molecular dynamics calculations for finding the optimized laser pulses are presented based on time-dependent density functional theory and quantum optimal control theory. A comparison of the results for orientation dependence in the ionization process shows that the electron distribution for CH4 is more isotropic than H2CO molecule. Total conversion yields of up to 70% at an orientation angle of 30o for CH4 and 65% at 900 for H2CO are achieved which lead to enhancement of dissociation probability
Effect of nanostructuring on thermal stability and decomposition of aluminium titanate (Al2TiO5): a phase transformation study
, Article Materials Characterization ; Volume 173 , 2021 ; 10445803 (ISSN) ; Madaah Hosseini, H. R ; Amutha, C ; Ramakrishna, S ; Sharif University of Technology
Elsevier Inc
2021
Abstract
As a refractory ceramic, the thermal instability of aluminium titanate (AT or Al2TiO5) has been in the crosshairs of research works in recent years. The studies have indicated that different parameters such as atmosphere, grain size, additives, oxygen pressure, and synthesis method can bilaterally affect the thermal decomposition of AT ceramic and resultant physicomechanical properties. In the present study, the AT nanostructure was synthesized by a citrate sol-gel method and influence of nanostructuring nature on its thermal instability and reaction pathway was explored in some details. It was shown that the reduction of grain size down to 30 nm can destabilize AT, so that the reaction...
Conversion of Methane into Heaviour Hydrocarbures using Nanosecond Lasers
, Ph.D. Dissertation Sharif University of Technology ; Sadighi Bonabi, Rasoul (Supervisor)
Abstract
In this thesis the conversion of methane into higher hydrocarbures using pulsed nanosecond lasers has been studied. The lasers of 532 nm of second harmonic of Nd: YAG, 355 nm of 3rd harmonic of Nd: YAG and 248 nm of KrF have been used in this project. Acetylene, ethylen and ethane have been detected using gas chromatography detection system, which showed acetylene as a dominant product. For each wavelength the amount of the laser energy and the fraction of secondary products have been measured. Also the dependence of amount of produced components on chamber pressure has been studied for 355 nm laser. During the irradiation time of methane no considerable changes in temperature and pressure...
Optimization of two tailored rectangular femtosecond laser pulses in methane dissociation
, Article Proceedings of SPIE - The International Society for Optical Engineering, 12 April 2010 through 16 April 2010 ; Volume 7721 , April , 2010 ; 0277786X (ISSN) ; 9780819481948 (ISBN) ; Dehghani, Z ; Irani, E ; The Society of Photo-Optical Instrumentation Engineers (SPIE); Brussels Photonics Team (B-PHOT); Brussels-Capital Region; Fonds Wetenschappelijk Onderzoek (FWO); International Commission for Optics (ICO) ; Sharif University of Technology
2010
Abstract
Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH4 + molecule exposed with a 100 femtosecond 8 Jcm-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH4 + molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and...
Mechanism of catalytic decomposition of CH3I on the Cu(111) surface: A UBI-QEP approach
, Article Langmuir, Washington, DC, United States ; Volume 16, Issue 21 , 2000 , Pages 8095-8099 ; 07437463 (ISSN) ; Gobal, F ; Sharif University of Technology
ACS
2000
Abstract
The method of unity bond index-quadratic exponential potential (UBI-QEP) and the computer simulation of the temperature programmed desorption (TPD) patterns are employed to derive the kinetic and thermodynamic parameters associated with the steps of the pathway we propose for the catalytic decomposition of methyl iodide on the Cu(111) surface. Assuming a highly reactive `hot methyl' surface intermediate and on the basis of our calculations it is concluded that the desorption of a part of this species is responsible for the reported methyl radical TPD peak at 140 K, while a part of this surface species is trapped in the three-fold sites of the Cu(111) surface and desorbs to form the reported...
The effect of intense short pulse laser shapes on generating of the optimum wakefield and dissociation of methane molecule
, Article Laser and Particle Beams ; Volume 30, Issue 3 , May , 2012 , Pages 357-367 ; 02630346 (ISSN) ; Zare, S ; Navid, H. A ; Dehghani, Z ; Sadighi Bonabi, R ; Sharif University of Technology
2012
Abstract
The optimum convolution of dual short pulse for producing the maximum wakefield and the highest dissociation probability of CH4 has been investigated. By using three fundamental shapes of pulses though four different arrangements, the generated wake are considered in plasma. It is found that when the first and second pulses were rectangular-triangular and sinusoidal pulse shapes, respectively, the resultant wakefield amplitude is the highest. This effect opens up a new novel way by pulse shaping mechanism in the photo dissociation dynamics of molecules and controlling of chemical reactions in the desired channels by short pulse intense lasers for reducing the computation time of genetic...