Dynamics of the O-Atom Exchange Reaction 16O(3P) + 18O18O(3Σg–) → 16O18O(3Σg–) + 18O(3P) at Hyperthermal Energies

Lahankar, Sridhar A.; Zhang, Jianming; Minton, Timothy K.; Guo, Hua; Lendvay, György

doi:10.1021/acs.jpca.6b01855

Cited by 23 publications

(15 citation statements)

References 47 publications

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“…Previous studies (e.g., Dawes et al , and Powell et al) only focused on the set of singlet O 3 PESs, which has only a small statistical weight (1/9), or on the surfaces relevant to ozone photodissociation (e.g., Grebenshchikov et al). Recently, in their comparison to further validate Varga et al’s PESs, Geistfeld and Schwartzentruber found good agreement between their QCT calculations and the experimental data by Lahankar et al…”

Section: Introductionmentioning

confidence: 77%

Bayesian Machine Learning Approach to the Quantification of Uncertainties on Ab Initio Potential Energy Surfaces

2020

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This work introduces a novel methodology for the quantification of uncertainties associated with potential energy surfaces (PESs) computed from first-principles quantum mechanical calculations. The methodology relies on Bayesian inference and machine learning techniques to construct a stochastic PES and to express the inadequacies associated with the ab initio data points and their fit. By combining high fidelity calculations and reduced-order modeling, the resulting stochastic surface is efficiently forward propagated via quasi-classical trajectory and master equation calculations. In this way, the PES contribution to the uncertainty on predefined quantities of interest (QoIs) is explicitly determined. This study is done at both microscopic (e.g., rovibrational-specific rate coefficients) and macroscopic (e.g., thermal and chemical relaxation properties) levels. A correlation analysis is finally applied to identify the PES regions that require further refinement, based on their effects on the QoI reliability. The methodology is applied to the study of singlet (11A′) and quintet (25A′) PESs describing the interaction between O2 molecules and O atoms in their ground electronic state. The investigation of the singlet surface reveals a negligible uncertainty on the kinetic properties and relaxation times, which are found to be in excellent agreement with the ones previously published in the literature. On the other hand, the methodology demonstrated significant uncertainty on the quintet surface, due to inaccuracies in the description of the exchange barrier and the repulsive wall. When forward propagated, this uncertainty is responsible for the variability of 1 order of magnitude in the vibrational relaxation time and of factor four in the exchange reaction rate coefficient, both at 2500 K.

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Section: Introductionmentioning

confidence: 77%

Bayesian Machine Learning Approach to the Quantification of Uncertainties on Ab Initio Potential Energy Surfaces

2020

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“…Opacity functions were determined by running 50 000 trajectories at each impact parameter The statistical errors of the quantities obtained with the Monte Carlo QCT method were calculated using the standard prescription, , and in most cases are as small as the size of symbols shown in the plots. The calculations were performed using an extensively modified version ,− of the VENUS code . The potential energy surface developed earlier, , referred to as CGSL PES was used for the simulations of reaction , while the trajectory calculations for reaction were performed using the PES of de Oliveira et al…”

Section: Methodsmentioning

confidence: 99%

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 = CH₃, HO) Systems

et al. 2021

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The dynamics of the reactions CH 3 + HBr → CH 4 + Br and HO + HBr → H 2 O + 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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“…QCT calculations have been performed according to the standard methodology, with the specific features described in refs − . Similar to refs − , we used the PES developed by Babikov et al for the electronic ground state.…”

Section: Methodsmentioning

confidence: 99%

“…According to the calculated lifetime distributions, in the majority of collisions, the complex lives for only a few vibrational periods, which cannot be expected to be enough for efficient intramolecular energy scrambling and can be the origin of the inadequacy of the statistical theory. Another set of crossed-beam experiments has been performed at a much higher, hyperthermal collision energy (86 kcal mol −1 ) 20 and produced rather interesting results. In these experiments, the time-of-flight and the angular distributions of not only the products of isotope exchange (reactive) but also those of the inelastic collisions have been determined and compared with those obtained in QCT calculations.…”

Section: Introductionmentioning

confidence: 99%

“…An excellent example is the derivation of the celebrated Polanyi rules, which was based on extensive QCT calculations. Although studies of mechanistic questions are less popular because they are time-consuming, we have been engaged in using the method to understand the connection between the features of the potential energy surface (PES) and the dynamics of bimolecular reactions, − with particular interest to complex-forming reactions. − ,− In connection with the picture that emerged from the QCT calculations on the O + O 2 system at very high collision energies, we found intriguing the possibility of mechanism change of bimolecular reactions when E coll covers a wide range, such as the appearance of the dual mechanism that may arise at some energy threshold. It is not clear, either, whether the rotational excitation of the reactants influences the overall behavior of the reactive system and what happens in the reactive window observed in the earlier calculations.…”

Section: Introductionmentioning

confidence: 99%

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Mechanism Change in the Dynamics of the O′ + O₂ → O′O + O Atom Exchange Reaction at High Collision Energies

Lendvay

2019

J. Phys. Chem. A

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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 O 2 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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Dynamics of the O-Atom Exchange Reaction ¹⁶O(³P) + ¹⁸O¹⁸O(³Σ_g^–) → ¹⁶O¹⁸O(³Σ_g^–) + ¹⁸O(³P) at Hyperthermal Energies

Abstract: The O-atom exchange reaction, 16

Cited by 23 publications

References 47 publications

Bayesian Machine Learning Approach to the Quantification of Uncertainties on Ab Initio Potential Energy Surfaces

Bayesian Machine Learning Approach to the Quantification of Uncertainties on Ab Initio Potential Energy Surfaces

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 = CH₃, HO) Systems

Mechanism Change in the Dynamics of the O′ + O₂ → O′O + O Atom Exchange Reaction at High Collision Energies

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Dynamics of the O-Atom Exchange Reaction 16O(3P) + 18O18O(3Σg–) → 16O18O(3Σg–) + 18O(3P) at Hyperthermal Energies

Abstract: The O-atom exchange reaction, 16

Cited by 23 publications

References 47 publications

Bayesian Machine Learning Approach to the Quantification of Uncertainties on Ab Initio Potential Energy Surfaces

Bayesian Machine Learning Approach to the Quantification of Uncertainties on Ab Initio Potential Energy Surfaces

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 = CH3, HO) Systems

Mechanism Change in the Dynamics of the O′ + O2 → O′O + O Atom Exchange Reaction at High Collision Energies

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Dynamics of the O-Atom Exchange Reaction ¹⁶O(³P) + ¹⁸O¹⁸O(³Σ_g^–) → ¹⁶O¹⁸O(³Σ_g^–) + ¹⁸O(³P) at Hyperthermal Energies

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 = CH₃, HO) Systems

Mechanism Change in the Dynamics of the O′ + O₂ → O′O + O Atom Exchange Reaction at High Collision Energies