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

Abstract

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.

Thermochemical and Kinetics of CH3SH + H Reactions: The Sensitivity of Coupling the Low and High-Level Methodologies

“…In previous works, we have employed the dual-level methodology to calculate accurately the properties of several chemical reactions. ,,− In this work, with the experience gained from previous research, a rigorous analysis was carried out regarding the coupling of the low and high-level methods, in particular when calculating the thermochemical properties, and subsequent rate constant calculations. We have analyzed in which conditions this coupling can generate artificial tunneling and variational effects in the calculated rate constants.…”

Effects of multidimensional tunneling in the kinetics of hydrogen abstraction reactions of O (3P) with CH3OCHO

“…An important question arises when single‐reference density wave functional methods are used in electronic structure calculations of reaction paths concerning the multireference character of the studied species. The importance of the non‐dynamical correlation effects in the electronic wave function have been successfully estimated by using the T 1 diagnostic . In this study, the values of T 1 computed with the CCSD/aug‐cc‐pVTZ method and employing the M06‐2X/aug‐cc‐pVTZ geometries are given in Table .…”

Atmospheric Reaction of Hydrazine Plus Hydroxyl Radical. I. Reliable Pathways

“…To estimate the barrier heights of the title reaction more precisely, a dual-level methodology was used similar to previous reactions of hydrazine with atomic oxygen simulated in the atmospheric conditions [40][41][42] . Thus, the CCS(T)/CBS//MP2/aTZ level was chosen.…”