Itai Zakai’s research while affiliated with Hebrew University of Jerusalem and other places

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Publications (6)


Formation of Chlorine in the Atmosphere by Reaction of Hypochlorous Acid with Seawater
  • Article

January 2024

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43 Reads

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1 Citation

The Journal of Physical Chemistry Letters

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Itai Zakai

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The highly reactive dihalogens play a significant role in the oxidative chemistry of the troposphere. One of the main reservoirs of these halogens is hypohalous acids, HOX, which produce dihalogens in the presence of halides (Y–), where X, Y = Cl, Br, I. These reactions occur in and on aerosol particles and seawater surfaces and have been studied experimentally and by field observations. However, the mechanisms of these atmospheric reactions are still unknown. Here, we establish the atomistic mechanism of HOCl + Cl– → Cl2 + OH– at the surface of the water slab by performing ab initio molecular dynamics (AIMD) simulations. Main findings are (1) This reaction proceeds by halogen-bonded complexes of (HOCl)···(Cl–)aq surrounded with the neighboring water molecules. (2) The halogen bonded (HOCl)···(Cl–)aq complexes undergo charge transfer from Cl– to OH– to form transient Cl2 at neutral pH. (3) The addition of a proton to one proximal water greatly facilitates the Cl2 formation, which explains the enhanced rate at low pH.


Recent progress in understanding the dynamics of peroxy radical interactions and their impact on atmospheric new-particle formation
  • Conference Paper
  • Full-text available

January 2023

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33 Reads

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Itai Zakai

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[...]

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Theo Kurtén
Download

Figure 2. Correlation between τ L measured in collision simulations versus values of k expt . The data point for MeOO + AcOO is shown by the red × symbol and is not included in the fit. Experimental data used in the fit are the most recent available numbers from Table 1.
Figure 3. Three variants of α-pinene peroxy radicals that we studied. Structures are snapshots from LAMMPS simulations at T = 5 K.
Computed Pre-reactive Complex Association Lifetimes Explain Trends in Experimental Reaction Rates for Peroxy Radical Recombinations

September 2022

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44 Reads

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5 Citations

ACS Earth and Space Chemistry


Fig. 2 Snapshots taken from two MD trajectories showing the recombination reaction to form RO 4 R, and the decomposition reaction to form 2CH 3 O + O 2 , both calculated using the XMC-QDPT2 method.
Summary of the number of collision trajectories n traj generated for different peroxy radical systems, models and initial conditions
Probability of different durations of association times t assoc between two radicals during unreactive collisions with different collision velocities v z . 520 m s À1 for the methyl system and 378 for the larger systems correspond roughly to the most likely translational velocity from a Boltzmann distribution at 298 K
Energy transfer, pre-reactive complex formation and recombination reactions during the collision of peroxy radicals

April 2022

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79 Reads

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9 Citations

Physical Chemistry Chemical Physics

In this paper we study collisions between polyatomic radicals – an important process in fields ranging from biology to combustion. Energy transfer, formation of intermediate complexes and recombination reactions are treated, with applications to peroxy radicals in atmospheric chemistry. Multi-reference perturbation theory, supplemented by coupled-cluster calculations, describes the potential energy surfaces with high accuracy, including the interaction of singlet and triplet spin states during radical recombination. Our multi-reference molecular dynamics (MD) trajectories on methyl peroxy radicals confirm the reaction mechanism postulated in earlier studies. Specifically, they show that if suitable pre-reactive complexes are formed, they will rapidly lead to the formation and subsequent decomposition of tetroxide intermediates. However, generating multi-reference MD trajectories is exceedingly computationally demanding, and we cannot adequately sample the whole conformational space. To answer this challenge, we promote the use of a novel simplified semi-empirical MD methodology. It assumes the collision is governed by two states, a singlet (S0) and a triplet (T1) state. The method predicts differences between collisions on S0 and T1 surfaces, and qualitatively includes not only pre-reactive complex formation, but also recombination processes such as tetroxide formation. Finally, classical MD simulations using force-fields for non-reactive collisions are employed to generate thousands of collision trajectories, to verify that the semi-empirical method is sampling collisions adequately, and to carry out preliminary investigations of larger systems. For systems with low activation energies, the experimental rate coefficient is surprisingly well reproduced by simply multiplying the gas-kinetic collision rate by the simulated probability for long-lived complex formation.



Structures, Stability, and Decomposition Dynamics of the Polynitrogen Molecule N 5 + B(N 3 ) 4 – and Its Dimer [N 5 + ] 2 [B(N 3 ) 4 – ] 2

August 2019

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26 Reads

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8 Citations

The Journal of Physical Chemistry A

There is much current interest in materials that are made entirely or mostly of nitrogen atoms. Such materials, polynitrogens, may reveal new aspects of nitrogen chemistry, and are believed to provide a possible basis for novel energetic substances. An interesting family of such materials, in which the N5⁺group appears as a cation, was prepared by K. O. Christe and coworkers. Little is known as yet on the microscopic properties of these materials. In this paper, we report theoretical calculations to predict the structure, energetic stability and decomposition dynamics of the polynitrogen molecule N5⁺B(N3)4⁻, the building block of a solid prepared by K. O. Christe, and of the dimer of this molecule. The structures are computed at the B3LYP-D3 level of DFT. Ab Initio Molecular Dynamics simulations are used to explore the thermal stability of the species and the decomposition mechanism. It is found that the N5⁺B(N3)4⁻ molecule decomposes on a picosecond timescale at T=200K, with an ultrafast release of four N2 molecules, which is very exothermic. The species BN9 is a product. The dimer is considerably more stable. Sensitivity of the process to temperature and to an applied force is reported. Possible applications of this material are briefly discussed.

Citations (4)


... 3,6,7 Our research group, among others, has long been involved in using theoretical chemistry methods to understand bimolecular reactions between peroxy radicals. [8][9][10][11][12][13][14][15][16] In particular, we have been attempting to extend our studies to include the dynamics of the reactions. 13,14 In many cases, experimental results 5,17-21 show a decrease in overall reactivity as temperature is increased, consistent with a negative activation energy E a in the framework of an Arrhenius relation, ...

Reference:

Lifetimes of pre-reactive complexes of peroxy radicals revisited: thermostat effects, temperature dependence and highly oxygenated molecules
Computed Pre-reactive Complex Association Lifetimes Explain Trends in Experimental Reaction Rates for Peroxy Radical Recombinations

ACS Earth and Space Chemistry

... Density Functional Theory (DFT) is a powerful computational tool in quantum chemistry for investigating the electronic structure of molecules, ions, radicals and their reactions. [29][30][31][32][33][34][35] While DFT has been successful in studying various reaction mechanisms and optical properties, [36][37][38][39][40][41][42] complex open-shell systems can be challenging for DFT and may require the application of more expensive approaches such as the multireference method CASPT2 (Complete Active Space Second-Order Perturbation Theory). 43,44 CASPT2, despite its effectiveness, is computationally costly and challenging to apply. ...

Energy transfer, pre-reactive complex formation and recombination reactions during the collision of peroxy radicals

Physical Chemistry Chemical Physics

... The importance of halogen bonded complexes have also been reported for the halogen exchange reaction in (HOCl)···(I − ) aq and were explored spectroscopically. 27 Here, with AIMD simulations, we report the microscopic details of Cl 2 formation at acidic pH. Interestingly, under neutral pH condition, although Cl 2 forms transiently, it was not released in the subsequent process. ...

Preparation and Characterization of the Halogen-Bonding Motif in the Isolated Cl – ·IOH Complex with Cryogenic Ion Vibrational Spectroscopy
  • Citing Article
  • March 2022

The Journal of Physical Chemistry Letters

... [13] As of the N 5 + derivatives, N 5 + P(N 3 ) 6 - . [14] The structure, stability, and decomposition dynamics of the N 5 + B(N 3 ) 4 and its dimer [N 5 + ] 2 [B(N 3 ) 4 -] 2 were theoretically studied by Zakai et al. [15] A theoretical isomer study of N 5 + , N 5, and N 5 − indicates, the C 2v isomer is the most stable one of the N 5 + due to hyperconjugation. [16][17][18] The stability of N 5 + N 5 − and N 5 + N 3 − were intensively theoretically studied. ...

Structures, Stability, and Decomposition Dynamics of the Polynitrogen Molecule N 5 + B(N 3 ) 4 – and Its Dimer [N 5 + ] 2 [B(N 3 ) 4 – ] 2
  • Citing Article
  • August 2019

The Journal of Physical Chemistry A