A product branching ratio controlled by vibrational adiabaticity and variational effects: Kinetics of the H + <i>trans-</i>N2H2 reactions

Zheng, Jingjing; Rocha, Roberta Jachura; Pelegrini, Marina; Ferrão, Luiz F. A.; Carvalho, Edson Firmino Viana de; Roberto‐Neto, Orlando; Machado, Francisco B. C.; Truhlar, Donald G.

doi:10.1063/1.4707734

Cited by 27 publications

(7 citation statements)

References 78 publications

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“…Troya and O’Neil reported theoretical reaction-dynamics properties for the N 2 H 4 + O reaction, such as the cross sections and product-energy distributions. On the basis of the experience gained in previous investigations of our group studying the hydrazine properties , and its reaction with hydrogen and nitrogen, − the reaction with atomic oxygen has been studied by us in detail as well, reporting thermochemical properties and rate constants based on two reaction paths for the hydrogen abstraction by oxygen and achieving good agreement with the previous experimental results, ,, in particular lying within the estimated error determined by Shane and Brennen . In qualitative agreement with Gehring et al, , our calculated rate constants showed a positive dependence on the temperature.…”

Section: Introductionsupporting

confidence: 89%

Thermochemical and Kinetics of Hydrazine Dehydrogenation by an Oxygen Atom in Hydrazine-Rich Systems: A Dimer Model

et al. 2015

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The kinetics of the reaction of N2H4 with oxygen depends sensitively on the initial conditions used. In oxygen-rich systems, the rate constant shows a conventional positive temperature dependence, while in hydrazine-rich setups the dependence is negative in certain temperature ranges. In this study, a theoretical model is presented that adequately reproduces the experimental results trend and values for hydrazine-rich environment, consisting of the hydrogen abstraction from the hydrazine (N2H4) dimer by an oxygen atom. The thermochemical properties of the reaction were computed using two quantum chemical approaches, the coupled cluster theory with single, double, and noniterative triple excitations (CCSD(T)) and the M06-2X DFT approach with the aug-cc-pVTZ and the maug-cc-pVTZ basis sets, respectively. The kinetic data were calculated with the improved canonical variational theory (ICVT) using a dual-level methodology to build the reaction path. The tunneling effects were considered by means of the small curvature tunneling (SCT) approximation. Potential wells on both sides of the reaction ((N2H4)2 + O → N2H4···N2H3 + OH) were determined. A reaction path with a negative activation energy was found leading, in the temperature range of 250-423 K, to a negative dependence of the rate constant on the temperature, which is in good agreement with the experimental measurements. Therefore, the consideration of the hydrazine dimer model provides significantly improved agreement with the experimental data and should be included in the mechanism of the global N2H4 combustion process, as it can be particularly important in hydrazine-rich systems.

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Section: Introductionsupporting

confidence: 89%

Thermochemical and Kinetics of Hydrazine Dehydrogenation by an Oxygen Atom in Hydrazine-Rich Systems: A Dimer Model

et al. 2015

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“…An additional noteworthy feature is that the observed major product 4c , resulting from the transformation of 3c , actually is separated from the precursor by a higher computed energy barrier than the minor product 3 A 2 - 2c . This contradicts the rules inferred from classical TST and cannot be explained in terms of a thermal over-the-barrier process, but only by considering the occurrence of heavy-atom QMT dominated by tunneling control . ,, …”

Section: Resultsmentioning

confidence: 69%

Competitive Nitrogen versus Carbon Tunneling

et al. 2019

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Quantum mechanical tunneling (QMT) of heavy atoms like carbon or nitrogen has been considered very unlikely for the longest time, but recent evidence suggests that heavy-atom QMT does occur more frequently than typically assumed. Here we demonstrate that carbon vs nitrogen heavyatom QMT can even be competitive leading to two different products originating from the same starting material. Aminosubstituted benzazirine was generated in solid argon (3−18 K) and found to decay spontaneously in the dark, with a half-life of 210 min, to p-aminophenylnitrene and amino-substituted ketenimine. The reaction rate is independent of the cryogenic temperature, in contradiction to the rules inferred from classical transition state theory. Quantum chemical computations confirm the existence of two competitive carbon vs nitrogen QMT reaction pathways. This discovery emphasizes the quantum nature of atoms and molecules, thereby enabling a much higher level of control and a deeper understanding of the factors that govern chemical reactivity.

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“…The model includes 38 species and 265 elementary reactions. It was constructed based on previous models; i.e., the H 2 subset was adopted from Hashemi et al, and the ammonia subset was mainly adopted from the Shrestha mechanism, replacing the rate constants of reactions NH 2 + H = NH + H 2 , N 2 H 2 + H = NNH + H 2 , and N 2 H 2 + M = NNH + H + M with more recent values. ,, The authors demonstrated the good performance of this mechanism for predicting the laminar burning velocity of ammonia mixtures under 0.1, 0.2, and 0.5 MPa. The mechanism also shows satisfactory performance for the ignition delay times measured in a shock tube (high temperatures and low to high pressures) by Mathieu and Petersen …”

Section: Combustionmentioning

confidence: 99%

Review on Ammonia as a Potential Fuel: From Synthesis to Economics

et al. 2021

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Ammonia, a molecule that is gaining more interest as a fueling vector, has been considered as a candidate to power transport, produce energy, and support heating applications for decades. However, the particular characteristics of the molecule always made it a chemical with low, if any, benefit once compared to conventional fossil fuels. Still, the current need to decarbonize our economy makes the search of new methods crucial to use chemicals, such as ammonia, that can be produced and employed without incurring in the emission of carbon oxides. Therefore, current efforts in this field are leading scientists, industries, and governments to seriously invest efforts in the development of holistic solutions capable of making ammonia a viable fuel for the transition toward a clean future. On that basis, this review has approached the subject gathering inputs from scientists actively working on the topic. The review starts from the importance of ammonia as an energy vector, moving through all of the steps in the production, distribution, utilization, safety, legal considerations, and economic aspects of the use of such a molecule to support the future energy mix. Fundamentals of combustion and practical cases for the recovery of energy of ammonia are also addressed, thus providing a complete view of what potentially could become a vector of crucial importance to the mitigation of carbon emissions. Different from other works, this review seeks to provide a holistic perspective of ammonia as a chemical that presents benefits and constraints for storing energy from sustainable sources. State-of-the-art knowledge provided by academics actively engaged with the topic at various fronts also enables a clear vision of the progress in each of the branches of ammonia as an energy carrier. Further, the fundamental boundaries of the use of the molecule are expanded to real technical issues for all potential technologies capable of using it for energy purposes, legal barriers that will be faced to achieve its deployment, safety and environmental considerations that impose a critical aspect for acceptance and wellbeing, and economic implications for the use of ammonia across all aspects approached for the production and implementation of this chemical as a fueling source. Herein, this work sets the principles, research, practicalities, and future views of a transition toward a future where ammonia will be a major energy player.

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A product branching ratio controlled by vibrational adiabaticity and variational effects: Kinetics of the H + trans-N2H2 reactions

Cited by 27 publications

References 78 publications

Thermochemical and Kinetics of Hydrazine Dehydrogenation by an Oxygen Atom in Hydrazine-Rich Systems: A Dimer Model

Thermochemical and Kinetics of Hydrazine Dehydrogenation by an Oxygen Atom in Hydrazine-Rich Systems: A Dimer Model

Competitive Nitrogen versus Carbon Tunneling

Review on Ammonia as a Potential Fuel: From Synthesis to Economics

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