Ab initio kinetics for H-atom abstraction from nitroethane

Abstract

Nitroethane (NTH) is nitro-containing energetic fuel for detonation engine. The study of the kinetic mechanism of nitroethane combustion is helpful for the development of models of nitrogen-containing energetic materials and provides theoretical support for CFD simulation of detonation engines. H-atom abstraction reactions play a crucial role as chain initiation processes in the detailed chemical kinetic modeling of NTH combustion. Therefore, high-level quantum chemical calculations were performed to determine the rate coefficients for eighteen abstraction reactions, as well as the thermodynamic properties of the species involved. M06–2X/6–311++G(d, p) level of theory was employed for geometry optimization, vibrational frequency calculation, Intrinsic Reaction Coordinate (IRC) analysis, and dihedral angle scans. The QCISD(T)/cc-pVXZ (X=D and T) MP2/cc-pVXZ (X=D, T and Q) and CCSD(T)/cc-pVXZ (X=T and Q) methods with two complete basis set extrapolations are employed for determining the single-point energy (SPE) for all species. The bond dissociation energies (BDEs) of all C-H, C–C, and C-N bonds in NTH were calculated at QCISD(T)//MP2//M06–2X/6–311++G(d, p) level. Rate constants and thermochemistry were carried out based on transition state theory (TST) and statistic thermodynamic theory using Multiwell software. The Master Equation System Solver (MESS) program suite was employed here to calculate the reaction rate constants for complex-forming reactions for ȮH and O₂ system. The reaction energy barriers and reaction rate constants calculated using two methods—QCISD(T)/cc-pVXZ (with X as D and T) and MP2/cc-pVXZ (with X as D, T, and Q), as well as CCSD(T)/cc-pVXZ (with X as T and Q)—show little difference. All results were then incorporated into the PLUG model, which significantly improved predictions for ignition delay time (IDT) as well as the speciation profile in both premixed flames and flow reactors. Sensitivity and flux analyses were conducted to identify the essential reactions controlling reactivity, revealing that H-atom abstraction by ȮH, Ḣ, CḢ₃, and O₂ are the critical reactions.