1
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Chen W, Xie H, Chen Z, Qu Z, Ren H, Li X. Influence of Singlet Oxygen in H + O 2 Collision Reaction. J Phys Chem A 2024; 128:7226-7234. [PMID: 39140992 DOI: 10.1021/acs.jpca.4c03317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/15/2024]
Abstract
The collision reaction of H + O2 = OH + O is a pivotal step in combustion. To investigate the influence of singlet oxygen on this reaction, we computed potential energy surfaces (PESs) for all six lowest states using high-level ab initio methods and coupled them with embedded atom neural network (EANN) fitting. By integrating quasi-classical trajectory (QCT) with trajectory surface hopping (TSH) based on the fitted PESs, we simulated the dynamics of both ground- and excited-states to derive the reaction rate constants for the forward and reverse processes. The results reveal that the forward reaction facilitates radical generation, promoting combustion reactions. Furthermore, calculations of reverse reaction rate constants indicate that all electronic states ultimately yield ground-state oxygen, leading to radical deactivation and exerting an inhibitory effect on combustion processes.
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Affiliation(s)
- Wenlan Chen
- School of Chemical Engineering, Sichuan University, Chengdu 610065, China
| | - Haohan Xie
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130023, China
| | - Zhizhou Chen
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130023, China
| | - Zexing Qu
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130023, China
| | - Haisheng Ren
- School of Chemical Engineering, Sichuan University, Chengdu 610065, China
- Engineering Research Center of Combustion and Cooling for Aerospace Power, Ministry of Education, Sichuan University, Chengdu 610065, China
| | - Xiangyuan Li
- School of Chemical Engineering, Sichuan University, Chengdu 610065, China
- Engineering Research Center of Combustion and Cooling for Aerospace Power, Ministry of Education, Sichuan University, Chengdu 610065, China
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2
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Szabó P, Lendvay G. Theoretical dynamics studies of the CH 3 + HBr → CH 4 + Br reaction: effects of isotope substitution and vibrational excitation of CH 3. Phys Chem Chem Phys 2024; 26:10530-10537. [PMID: 38512242 DOI: 10.1039/d3cp05610d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/22/2024]
Abstract
The rate coefficient for two deuterium substituted isotopologues of reaction CH3 + HBr → CH4 + Br has been determined using the quasiclassical trajectory (QCT) method. We used the analytical potential energy surface (PES) fitted to high-level ab initio points in earlier work. The PES exhibits a pre-reaction van der Waals complex and a submerged potential barrier. The rate coefficients of the deuterated isotopologue reactions, similarly to the pure-protium isotopologue, show significant deviation from the Arrhenius law, namely, the activation energy is negative below about 600 K and positive above it: k[CH3 + DBr] = 1.35 × 10-11 exp(- 2472/T) + 5.85 × 10-13 exp(335/T) and k[CD3 + HBr] = 2.73 × 10-11 exp(- 2739/T) + 1.46 × 10-12 exp(363/T). The CH3 + DBr reaction is slower by a factor of 1.8, whereas CD3 + HBr isotopologue is faster by a factor of 1.4 compared to the HBr + CH3 system across a wide temperature range. The isotope effects are interpreted in terms of the properties of various regions of the PES. Quantum state-resolved simulations revealed that the reaction of CH3 with HBr becomes slower when any of the vibrational modes of the methyl radical is excited. This contradicts the assumption that vibrational excitation of methyl radicals enhances its reactivity, which is of historical importance: this assumption was used as an argument against the existence of negative activation energy in a decade-long controversy in the 1980s and 1990s.
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Affiliation(s)
- Péter Szabó
- Department of Chemistry, KU Leuven, Celestijnenlaan, 200F, Leuven, 3001, Belgium.
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Avenue Circulaire 3, Brussels, 1180, Belgium
| | - György Lendvay
- Institute of Materials and Environmental Chemistry, HUN-REN Research Centre for Natural Sciences, Magyar tudósok krt. 2., H-1117 Budapest, Hungary.
- Center for Natural Sciences, Faculty of Engineering, University of Pannonia, Egyetem u. 10, Veszprém, 8200, Hungary
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3
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Szabó P, Gustafsson M. Polyatomic radiative association by quasiclassical trajectory calculations: Formation of HCN and HNC molecules in H + CN collisions. J Chem Phys 2023; 159:144112. [PMID: 37831719 DOI: 10.1063/5.0170577] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 08/21/2023] [Indexed: 10/15/2023] Open
Abstract
We have developed the polyatomic extension of the established [M. Gustafsson, J. Chem. Phys. 138, 074308 (2013)] classical theory of radiative association in the absence of electronic transitions. The cross section and the emission spectrum of the process is calculated by a quasiclassical trajectory method combined with the classical Larmor formula which can provide the radiated power in collisions. We have also proposed a Monte Carlo scheme for efficient computation of ro-vibrationally quantum state resolved cross sections for radiative association. Besides the method development, the global potential energy and dipole surfaces for H + CN collisions have been calculated and fitted to test our polyatomic semiclassical method.
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Affiliation(s)
- Péter Szabó
- Department of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Avenue Circulaire 3, 1180 Brussels, Belgium
- Applied Physics, Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden
| | - Magnus Gustafsson
- Applied Physics, Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden
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4
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Bedjanian Y, Szabó P, Lendvay G. Experimental and Theoretical Study of the Kinetics of the CH 3 + HBr → CH 4 + Br Reaction and the Temperature Dependence of the Activation Energy of CH 4 + Br → CH 3 + HBr. J Phys Chem A 2023; 127:6916-6923. [PMID: 37561546 PMCID: PMC10461296 DOI: 10.1021/acs.jpca.3c03685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 07/26/2023] [Indexed: 08/11/2023]
Abstract
The rate coefficient of the reaction of CH3 with HBr was measured and calculated in the temperature range 225-960 K. The results of the measurements performed in a flow apparatus with mass spectrometric detection agree very well with the quasiclassical trajectory calculations performed on a previously developed potential energy surface. The experimental rate coefficients are described well with a double-exponential fit, k1(exp) = [1.44 × 10-12 exp(219/T) + 6.18 × 10-11 exp(-3730/T)] cm3 molecule-1 s-1. The individual rate coefficients below 500 K accord with the available experimental data as does the slightly negative activation energy in this temperature range, -1.82 kJ/mol. At higher temperatures, the activation energy was found to switch sign and it rises up to about an order of magnitude larger positive value than that below 500 K, and the rate coefficient is about 50% larger at 960 K than that around room temperature. The rate coefficients calculated with the quasiclassical trajectory method display the same tendencies and are within about 8% of the experimental data between 960 and 300 K and within 25% below that temperature. The significant variation of the magnitude of the activation energy can be reconciled with the tabulated heats of formation only if the activation energy of the reverse CH4 + Br reaction also significantly increases with the temperature.
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Affiliation(s)
- Yuri Bedjanian
- Institut
de Combustion, Aérothermique, Réactivité et Environnement
(ICARE), CNRS, Orléans Cedex
2 45071, France
| | - Péter Szabó
- Department
of Chemistry, KU Leuven, Celestijnenlaan, 200F, Leuven 3001, Belgium
- Royal
Belgian Institute for Space Aeronomy (BIRA-IASB), Avenue Circulaire 3, Brussels 1180, Belgium
| | - György Lendvay
- Institute
of Materials and Environmental Chemistry, Research Centre for Natural
Sciences, Magyar tudósok
krt. 2., Budapest H-1117, Hungary
- Center
for Natural Sciences, Faculty of Engineering, University of Pannonia, Egyetem u. 10., Veszprém 8200, Hungary
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5
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Gao D, Xin X, Wang D, Szabó P, Lendvay G. Theoretical dynamics studies of the CH 3 + HBr → CH 4 + Br reaction: integral cross sections, rate constants and microscopic mechanism. Phys Chem Chem Phys 2022; 24:10548-10560. [PMID: 35445671 DOI: 10.1039/d2cp00066k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Quantum and quasi-classical dynamics calculations have been performed for the reaction of HBr with CH3. The accurate ab initio-based potential energy surface function developed earlier for this reaction displays a potential well corresponding to a reactant complex and a submerged potential barrier. The integral cross sections were calculated on this potential energy surface using both a six-degree-of-freedom reduced dimensional quantum dynamics and the quasi-classical trajectory method and very good agreement was found between the two approaches. The cross sections were found to diverge when the collision energy decreases, indicating that the reactant attraction is responsible for the dynamics at low collision energy. The quantum mechanical and the quasi-classical rate constants also agree very well and almost exactly reproduce the experimental results at low temperatures up to 540 K. The negative activation energy observed experimentally is confirmed by the calculations and is a consequence of the long-range attraction between the reactants. From the classical trajectories mechanistic details have been extracted. It is found that at very low collision energy, the reacting system crosses the potential barrier because the forces within the complex guide them, although some 30% is reflected from the product side of the barrier. When the collision energy increases, the system does not follow the most favorable path and the reactants are, with increasing probability, reflected from the repulsive walls of the nonreactive parts of the reactants, providing a picture beyond the decreasing excitation function.
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Affiliation(s)
- Delu Gao
- College of Physics and Electronics, Shandong Normal University, Jinan 250014, Shandong, China.
| | - Xin Xin
- College of Physics and Electronics, Shandong Normal University, Jinan 250014, Shandong, China.
| | - Dunyou Wang
- College of Physics and Electronics, Shandong Normal University, Jinan 250014, Shandong, China.
| | - Péter Szabó
- Faculté des Sciences, des Technologies et de Médecine, Département Physique et sciences des matériaux, Campus Limpertsberg, Université du Luxembourg 162 A, avenue de la, Faïencerie L-1511, Luxembourg
| | - György Lendvay
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar Tudósok krt. 2, H-1117 Budapest, Hungary. .,Department of General and Inorganic Chemistry, University of Pannonia, Egyetem utca 10, Veszprém, H-8200, Hungary
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6
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Csorba B, Szabó P, Góger S, Lendvay G. The Role of Zero-Point Vibration and Reactant Attraction in Exothermic Bimolecular Reactions with Submerged Potential Barriers: Theoretical Studies of the R + HBr → RH + Br (R = CH 3, HO) Systems. J Phys Chem A 2021; 125:8386-8396. [PMID: 34543008 PMCID: PMC8488937 DOI: 10.1021/acs.jpca.1c05839] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The dynamics of the reactions CH3 + HBr → CH4 + Br and HO + HBr → H2O + Br have been studied using the quasiclassical trajectory method to explore the interplay of the vibrational excitation of the breaking bond and the potential energy surface characterized by a prereaction van der Waals well and a submerged barrier to reaction. The attraction between the reactants is favorable for the reaction, because it brings together the reactants without any energy investment. The reaction can be thought to be controlled by capture. The trajectory calculations indeed provide excitation functions typical to capture: the reaction cross sections diverge when the collision energy is reduced toward zero. Excitation of reactant vibration accelerates both reactions. The barrier on the potential surface is so early that the coupling between the degrees of freedom at the saddle point geometry is negligible. However, the trajectory calculations show that when the breaking bond is stretched at the time of the encounter, an attractive force arises, as if the radical approached a HBr molecule whose bond is partially broken. As a result, the dynamics of the reaction are controlled more by the temporary "dynamical", vibrationally induced than by the "static" van der Waals attraction even when the reactants are in vibrational ground state. The cross sections are shown to drop to very small values when the amplitude of the breaking bond's vibration is artificially reduced, which provides an estimate of the reactivity due to the "static" attraction. Without zero-point vibration these reactions would be very slow, which is a manifestation of a unique quantum effect. Reactions where the reactivity is determined by dynamical factors such as the vibrationally enhanced attraction are found to be beyond the range of applicability of Polanyi's rules.
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Affiliation(s)
- Benjámin Csorba
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok krt. 2., H-1117 Budapest, Hungary
| | - Péter Szabó
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok krt. 2., H-1117 Budapest, Hungary
| | - Szabolcs Góger
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok krt. 2., H-1117 Budapest, Hungary
| | - György Lendvay
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok krt. 2., H-1117 Budapest, Hungary.,Center for Natural Sciences, Faculty of Engineering, University of Pannonia, Egyetem u. 10. Veszprém, 8200 Hungary
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7
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Lendvay G. Mechanism Change in the Dynamics of the O' + O 2 → O'O + O Atom Exchange Reaction at High Collision Energies. J Phys Chem A 2019; 123:10230-10239. [PMID: 31647868 DOI: 10.1021/acs.jpca.9b07393] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The extreme velocity and the large available energy of atoms with hyperthermal kinetic energies can give rise to novel mechanisms and behavior of chemical reactions unseen at thermal conditions. Crossed-molecular-beams experiments combined with isotope labeling on the reaction of hyperthermal O atoms with O2 molecules have provided an example of the arising complexity of such systems. Quasiclassical trajectory (QCT) calculations proved to be instructive in the exploration of the microscopic mechanism of the reactive and inelastic scattering observed, and a new mechanism has been identified: there are reactive collisions in which the potential energy remains repulsive during the entire encounter ("direct" reactions in which, in a sense, no complex is formed). In this work, the effect of the magnitude of the collision energy on this mechanism is explored. At hyperthermal collision energies, the reaction is characterized by a unique impact parameter window favorable for reaction through complex formation, while the direct collisions take place exclusively at small impact parameters. In direct reactive collisions, contributing as much as 12% to the reaction cross section, first the existing bond is broken, and the new bond is formed afterward. This kind of collision is unique to extremely high collision energies. Analysis of various correlations was used to find out the details of the reaction dynamics. The observed phenomena indicate that when the collision energy is extremely high, one can expect deviation from what an extrapolation from the more familiar energy ranges would predict.
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Affiliation(s)
- György Lendvay
- Institute of Materials and Environmental Chemistry , Research Centre for Natural Sciences , Magyar tudósok krt. 2 , H-1117 Budapest , Hungary
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8
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Ghosh S, Sharma R, Adhikari S, Varandas AJC. Fully coupled (J > 0) time-dependent wave-packet calculations using hyperspherical coordinates for the H + O2 reaction on the CHIPR potential energy surface. Phys Chem Chem Phys 2019; 21:20166-20176. [DOI: 10.1039/c9cp03171e] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
ICS calculation by time dependent wavepacket approach for H + O2 reaction using non-zero J values.
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Affiliation(s)
- Sandip Ghosh
- School of Chemical Sciences
- Indian Association for the Cultivation of Science
- Kolkata-700032
- India
| | - Rahul Sharma
- Department of Chemistry
- St. Xaviers' College
- Kolkata-700016
- India
| | - Satrajit Adhikari
- School of Chemical Sciences
- Indian Association for the Cultivation of Science
- Kolkata-700032
- India
| | - António J. C. Varandas
- School of Physics and Physical Engineering
- Qufu Normal University
- 273165 Qufu
- China
- Departamento de Química, and Centro de Química
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9
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Simulation of experimental imaging results for four isotopic variants of the OH + CH4 reaction with a simple and relatively accurate theoretical approach. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2018.09.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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10
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Bonnet L. Semiclassical initial value theory of rotationally inelastic scattering: Some remarks on the phase index in the interaction picture. J Chem Phys 2018; 148:194104. [PMID: 30307190 DOI: 10.1063/1.5024785] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This paper deals with the treatment of quantum interferences in the semiclassical initial value theory of rotationally inelastic scattering in the interaction picture. Like many semiclassical methods, the previous approach involves a phase index related to sign changes of a Jacobian whose square root is involved in the calculations. It is shown that replacing the original phase index by a new one extends the range of applicability of the theory. The resulting predictions are in close agreement with exact quantum scattering results for a model of atom-rigid diatom collision involving strong interferences. The developments are performed within the framework of the planar rotor model, but are readily applicable to three-dimensional collisions.
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Affiliation(s)
- L Bonnet
- CNRS, ISM, UMR 5255, F-33400 Talence, France and Université de Bordeaux, ISM, UMR 5255, F-33400 Talence, France
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11
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Zuo JX, Hu XX, Xie DQ. Quantum Dynamics of Oxyhydrogen Complex-Forming Reactions for the HO2 and HO3 Systems. CHINESE J CHEM PHYS 2018. [DOI: 10.1063/1674-0068/31/cjcp1804060] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
- Jun-xiang Zuo
- Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
| | - Xi-xi Hu
- Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
| | - Dai-qian Xie
- Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
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12
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Szabó P, Gustafsson M. A surface-hopping method for semiclassical calculations of cross sections for radiative association with electronic transitions. J Chem Phys 2017; 147:094308. [DOI: 10.1063/1.5000573] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Affiliation(s)
- Péter Szabó
- Applied Physics, Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden
| | - Magnus Gustafsson
- Applied Physics, Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden
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13
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Vikár A, Nagy T, Lendvay G. Testing the Palma-Clary Reduced Dimensionality Model Using Classical Mechanics on the CH4 + H → CH3 + H2 Reaction. J Phys Chem A 2016; 120:5083-93. [PMID: 26918703 DOI: 10.1021/acs.jpca.6b00346] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Application of exact quantum scattering methods in theoretical reaction dynamics of bimolecular reactions is limited by the complexity of the equations of nuclear motion to be solved. Simplification is often achieved by reducing the number of degrees of freedom to be explicitly handled by freezing the less important spectator modes. The reaction cross sections obtained in reduced-dimensionality (RD) quantum scattering methods can be used in the calculation of rate coefficients, but their physical meaning is limited. The accurate test of the performance of a reduced-dimensionality method would be a comparison of the RD cross sections with those obtained in accurate full-dimensional (FD) calculations, which is not feasible because of the lack of complete full-dimensional results. However, classical mechanics allows one to perform reaction dynamics calculations using both the RD and the FD model. In this paper, an RD versus FD comparison is made for the 8-dimensional Palma-Clary model on the example of four isotopologs of the CH4 + H → CH3 + H2 reaction, which has 12 internal dimensions. In the Palma-Clary model, the only restriction is that the methyl group is confined to maintain C3v symmetry. Both RD and FD opacity and excitation functions as well as differential cross sections were calculated using the quasiclassical trajectory method. The initial reactant separation has been handled according to our one-period averaging method [ Nagy et al. J. Chem. Phys. 2016, 144, 014104 ]. The RD and FD excitation functions were found to be close to each other for some isotopologs, but in general, the RD reactivity parameters are lower than the FD reactivity parameters beyond statistical error, and for one of the isotopologs, the deviation is significant. This indicates that the goodness of RD cross sections cannot be taken for granted.
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Affiliation(s)
- Anna Vikár
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar tudósok körútja 2, H-1117 Budapest, Hungary
| | - Tibor Nagy
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar tudósok körútja 2, H-1117 Budapest, Hungary
| | - György Lendvay
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar tudósok körútja 2, H-1117 Budapest, Hungary
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14
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Szabó P, Lendvay G. Dynamics of Complex-Forming Bimolecular Reactions: A Comparative Theoretical Study of the Reactions of H Atoms with O2((3)Σg(-)) and O2((1)Δg). J Phys Chem A 2015; 119:12485-97. [PMID: 26517427 DOI: 10.1021/acs.jpca.5b07938] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The atomic-level mechanism of the reaction of H atoms with triplet and singlet molecular oxygen, H((2)S) + O2((3)Σg(-)) → O((3)P) + OH((2)Πg) ( R1 ) and H((2)S) + O2((1)Δg) → O((3)P) + OH((2)Πg) ( R2 ) is analyzed in terms of the topology of the potential energy surfaces (PES) of the two reactions. Both PES exhibit a deep potential well corresponding to the ground and first excited electronic state of HO2. The ground-state reaction is endothermic with no barrier on either side of the well; the excited-state reaction is exothermic with a barrier in the entrance valley of the PES. The differences of the PES are manifested in properties such as the excitation functions, which show reaction R1 to be much slower and the effect of rotational excitation on reactivity, which speeds up reaction R1 and has little effect on R2 . Numerous common dynamics features arise from the presence of the deep potential well on the PES. Such are the significant role of isomerization (for example, 90% of reactive collisions in R2 involve at least one H atom transfer from one of the O atoms to the other in reaction R2 ), which is shown to give rise to a significant rotational excitation of the product OH radicals. Common is the significant sideways scattering of the products that originates from collisions in propeller-type arrangements induced by the presence of two bands of acceptance around the O2 molecule. The HO2 complex in both reactions proves to behave nonstatistically, with signatures of the dynamics in lifetime distributions, angular distributions, opacity functions, and product quantum-state distributions.
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Affiliation(s)
- Péter Szabó
- Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia , P.O.B. 158, Veszprém H-8201, Hungary
| | - György Lendvay
- Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia , P.O.B. 158, Veszprém H-8201, Hungary.,Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar Tudósok krt. 2., Budapest H-1117, Hungary
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