Theoretical investigation on unimolecular decomposition network of n-propylamine with advanced kinetic methods

Abstract

Unimolecular decomposition network of $n$-propylamine (NPA) is theoretically investigated. Twenty intramolecular H-shift/H${}_2$ elimination reactions and three bond dissociation reactions are identified, including some new reactions producing singlet species. Among these reactions, only one intramolecular H-shift reaction that yields C${}_3$H${}_6$ + NH${}_3$ and three bond dissociation reactions are dominant. The M06-2X/jun-cc-pVTZ and M06-L/jun-cc-pVTZ methods are adopted for kinetic calculations given their well-balanced accuracy and computational costs. The reaction-path variational transition state theory and variable reaction coordinate variational transition state theory are applied to determine the high-pressure limit rate constants of the intramolecular H-shift reaction and bond dissociation reactions, respectively, and the multi-structure torsional anharmonicity and small-curvature tunneling correction are considered. The pressure-dependent rate constants are also determined using the system-specific quantum Rice–Ramsperger–Kassel theory at 700–2000 K and 0.001–100 atm. The C${}_{\alpha }$–C${}_{\beta }$ bond dissociation reaction that produces CH${}_3$CH${}_2$ and CH${}_2$NH${}_2$ radicals is the most important with a branching ratio larger than 0.85 over the investigated temperature range. Our calculated rate constants agree well with the literature data and effectively capture the effect of pressure on the rate constants within the uncertainty in energy determination. With our calculations, a literature combustion model is updated and performs better in predicting the speciation data during the NPA pyrolysis and ignition delay times of NPA.

Novelty and Significance statement

This work theoretically investigates the unimolecular decomposition network of $n$-propylamine (NPA) by using the advanced reaction-path variational transition state theory and the variable reaction coordinate variational transition state theory for reactions with tight and loose transition states, respectively, with the consideration of multi-structure torsional anharmonicity and small-curvature tunneling correction. Some novel unimolecular decomposition reactions producing singlet species are reported. The pressure-dependent rate constants are determined using the system-specific quantum Rice–Ramsperger–Kassel theory at 700–2000 K and 0.001–100 atm. The C${}_{\alpha }$–C${}_{\beta }$ bond dissociation reaction that produces CH${}_3$CH${}_2$ and CH${}_2$NH${}_2$ radicals is predominant. Based on our calculations, a literature combustion model is updated, exhibiting a better performance in predicting the speciation data during the NPA pyrolysis and ignition delay times of NPA.