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Large Intermediates in Hydrazine Decomposition: a Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces

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Large Intermediates in Hydrazine Decomposition: a Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Grinberg Dana, Alon et al. "Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces." Journal of Physical Chemistry A 123, 22 (May 2019): 4679-4692 © 2019 American Chemical Society As Published http://dx.doi.org/10.1021/acs.jpca.9b02217 Publisher American Chemical Society (ACS) Version Author's final manuscript Citable link https://hdl.handle.net/1721.1/124015 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The Journal of Physical Chemistry This document is confidential and is proprietary to the American Chemical Society and its authors. Do not copy or disclose without written permission. If you have received this item in error, notify the sender and delete all copies. Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the N3H5 and N4H6 Potential Energy Surfaces Journal: The Journal of Physical Chemistry Manuscript ID jp-2019-02217p.R1 Manuscript Type: Article Date Submitted by the n/a Author: Complete List of Authors: Grinberg Dana, Alon; Massachusetts Institute of Technology, Chemical Engineering Moore, Kevin; Argonne National Laboratory, Gas Phase Chemical Dynamics Jasper, Ahren; Argonne National Laboratory, Gas Phase Chemical Dynamics Green, William; Massachusetts Institute of Technology, Chemical Engineering ACS Paragon Plus Environment Page 1 of 60 The Journal of Physical Chemistry 1 2 3 4 5 Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the 6 7 N3H5 and N4H6 Potential Energy Surfaces 8 9 1 2 2 1 10 Alon Grinberg Dana , Kevin B. Moore III, Ahren W. Jasper, William H. Green * 11 12 13 1 Department of Chemical Engineering, Massachusetts Institute of Technology, 14 15 Cambridge, MA 02139, United States 16 17 2 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 18 60439, United States 19 20 * Corresponding author. Email: [email protected]; Fax: +1-617-324-0066; Tel: +1-617-253-4580 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 1 59 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 2 of 60 1 2 3 4 Abstract 5 6 7 Large complex formation involved in the thermal decomposition of hydrazine (N2H4) is studied 8 9 10 using transition state theory based theoretical kinetics. A comprehensive analysis of the N3H5 and 11 12 N4H6 potential energy surfaces was performed at the CCSD(T)-F12a/aug-cc-pVTZ//B97x-D3/6- 13 14 15 311++G(3df,3pd) level of theory, and pressure-dependent rate coefficients were determined. 16 17 There are no low-barrier unimolecular decomposition pathways for triazane (n-N3H5), and its 18 19 formation becomes more significant as the pressure increases; it is the primary product of N H 20 2 3 21 22 + NH2 below 550, 800, 1150, and 1600 K at 0.1, 1, 10, and 100 bar, respectively. The N4H6 surface 23 24 has two important entry channels, N H + H NN and N H + N H , each with different primary 25 2 4 2 2 3 2 3 26 27 products. Interestingly, N2H4 + H2NN primarily form N2H3 + N2H3, while disproportionation of N2H3 28 29 + N3H3 predominantly leads to the other N2H2 isomer, HNNH. Stabilized tetrazane (n-N4H6) 30 31 32 formation from N2H3 + N2H3 becomes significant only at relatively high pressures and low 33 34 temperatures due to fall-off back into N2H3 + N2H3. Pressure-dependent rate coefficients for all 35 36 37 considered reactions as well as thermodynamic properties of triazane and tetrazane, which 38 39 should be considered for kinetic modeling of chemical processes involving nitrogen- and 40 41 hydrogen-containing species, are reported. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 2 59 60 ACS Paragon Plus Environment Page 3 of 60 The Journal of Physical Chemistry 1 2 3 4 1. Introduction 5 6 7 Hydrazine (N2H4), the main component of diamine-based rocket fuels, is an excellent 8 9 10 propellant: using oxygen as the oxidizer, it is only second to hydrogen in terms of the specific 11 12 impulse (thrust developed per fuel mass per unit time) it generates.1 Its decomposition could 13 14 2–4 15 lead to auto-ignition and detonation, and it is sometimes used as a monopropellant, usually 16 17 by decomposing over a catalyst.1 Hydrazine and hydrazine-based fuels such as monomethyl 18 19 hydrazine are more commonly used as bipropellants with N O as the oxidizer. Hydrazine is used 20 2 5 21 22 in thruster engines for attitude and in-orbit control of satellites and spacecraft,1 where it is being 23 24 stored and utilized at a maximal pressure of about 25 bar.5–7 25 26 27 No detailed kinetic models for hydrazine-based fuels combustion in N2O5 exist in the current 28 29 literature; a step towards this goal is understanding hydrazine decomposition better. Detailed 30 31 8 32 kinetic models for hydrazine decomposition were previously suggested by Halat-Augier et al. as 33 9 10,11 11 34 well as by Konnov and De Ruyck. More recently, however, computations of the N2H2, N2H3, 35 36 10–12 37 and N2H4 potential energy surfaces determined updated kinetics. Interestingly, none of the 38 39 previous works on hydrazine decomposition has considered species containing more than two 40 41 nitrogen atoms. In the absence of an oxidizer, a monopropellant's decomposition could be 42 43 44 thought of as an extreme case of fuel-rich combustion, a chemistry region in which fuel-radical 45 46 recombination reactions often play a significant role. At low pressures, chemically-activated 47 48 49 isomerization and decompositions are often important. As the working pressure increases, 50 51 radical recombination reactions, leading to formation of relatively large complexes, become 52 53 54 more significant due to collisional stabilization. 55 56 57 58 3 59 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 4 of 60 1 2 3 Unlike carbon, nitrogen does not normally form the major elemental backbone of large 4 5 6 molecules. For example, an experimental study of tetrazene (linear unsaturated N4H4) 7 8 determined that its thermolysis in the solid phase begins at room temperature, while in the gas 9 10 13 11 phase it is metastable. Moreover, cyclic nitrogenous rings, and specifically tetrazetidine (cyclic 12 14–16 13 N4H4), were determined to have relatively high ring strain energies. However, a theoretical 14 15 17 16 study of triazane (N3H5) concluded that it is kinetically stable. Tetrazane (saturated N4H6) was 17 18 also studied theoretically, and its most stable stereoisomer was determined,18 yet its overall 19 20 kinetic stability was not assessed. A sub-atmospheric room temperature experimental 21 22 23 observation of N2H3 self-reaction concluded that the disproportionation reaction yielding N2H4 + 24 25 N2H2 is approximately four times faster than a recombination reaction yielding tetrazane, unlike 26 27 19 28 the tendency of the analogous hydrocarbon radical, C2H5. Yet the behavior of the N2H3 + N2H3 29 30 system at high temperatures and different pressure, and specifically the importance of well- 31 32 33 skipping chemically-activated reactions, has not been reported in the literature. 34 35 In the present contribution, we examine the hypothesis that abundant radicals in 36 37 38 decomposing hydrazine might form relatively large complexes such as triazane and tetrazane, 39 40 becoming more significant as the pressure increases. We therefore explore the NH2 + N2H3 and 41 42 N H + N H reactions which lead to pressure-dependent kinetic networks on the N H and N H 43 2 3 2 3 3 5 4 6 44 45 potential energy surfaces, respectively. Specifically, collisional-stabilized formation of the 46 47 complexes along with well-skipping reactions are considered, and pressure-dependent rate 48 49 50 coefficients are determined. 51 52 53 54 55 56 57 58 4 59 60 ACS Paragon Plus Environment Page 5 of 60 The Journal of Physical Chemistry 1 2 3 4 2. Theoretical methods 5 6 7 2.1. Characterizing the Potential Energy Surface 8 9 10 Geometric structures and vibrational frequencies for all wells and saddle points considered 11 12 here were obtained using density functional theory employing the B97x-D3 functional20 and 13 14 21 22 15 the 6-311++G(3df,3pd) basis set. The growing string method (GSM) was used to provide initial 16 17 guesses for some of the transition state geometries. Intrinsic reaction coordinate (IRC) 18 19 calculations23 were used to verify all transition state configurations by tracking the minimum 20 21 22 energy paths leading to adjacent local minima. 23 24 Higher level single-point energies were obtained by employing the explicitly correlated 25 26 24,25 27 coupled-cluster CCSD(T)-F12a method and using an augmented Dunning’s correlation 28 29 consistent, polarized valence triple- (aug-cc-pVTZ) basis set.26 Zero-point energy (ZPE) 30 31 32 corrections, incorporated into the final energies reported here, were evaluated at the B97x- 33 34 D3/6-311++G(3df,3pd) level and scaled by a recommended factor of 0.97027 to account for their 35 36 10 37 average overestimation, due in part to anharmonicity.
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