“Third‐body” collision parameters for hydrocarbons, alcohols, and hydroperoxides and an effective internal rotor approach for estimating them

Abstract

Collision rate constants and third-body collision efficiencies are calculated for more than 300 alkanes, alcohols, and hydroperoxides, for the bath gases He, Ar, H 2 , and N 2 , and from 300 to 2000 K. The data set includes highly branched species and species with as many as 16 nonhydrogen atoms N, and it is analyzed to develop strategies for estimating collision properties more generally. Simple analytic formulas describing the Lennard-Jones collision parameters and are obtained for each of the three classes of systems as a function of N. Trends in the collision efficiency range parameter = ⟨ΔE d ⟩ are more complicated, and a method is developed and validated for estimating based on the numbers and types of internal rotors and oxygen-containing groups. Specifically, the approach maps the expected value of for a branched alkane, alcohol, or hydroperoxide onto those for the corresponding normal (linear) series via an effective number of nonhydrogen atoms N eff . The prescription for N eff is based on counting internal rotor types and is shown to be insensitive to temperature and fairly insensitive to the identity of the bath gas. Together, these strategies allow for the ready estimation of the collision parameters , , and so long as results for the associated linear series are available. K E Y W O R D Sclassical trajectories, Lennard-Jones parameters, third-body collision efficiencies, unimolecular kinetics, automation Int J Chem Kinet. 2020;52:387-402. wileyonlinelibrary.com/journal/kin

Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory

“…2) is likely a better estimate for a molecule the size of the HPBF adduct with 9 heavy atoms. 7 The majority of the calculations were performed for reaction with normal FA (H 2 -formic acid).…”

Diastereomers and Low-Temperature Oxidation

“…Microcanonical transition state theory with the RRKM/ME code MESS was used to calculate temperature- and pressure-dependent rate coefficients . Collisional energy transfer parameters ⟨Δ E down ⟩, σ, and ε were calculated based on system stoichiometry and the number and types of bonds present following the methodology of Jasper . N 2 was selected as the bath gas to replicate conditions in air-aspirated internal combustion engines.…”

Molecular Collision Diameters and Electronic Polarizabilities: Inherent Relationship and Fast Evaluation

“…Nevertheless, we must admit that until now, there is no generally accepted simple approach for determining the molecular collision diameter theoretically. At present, there are methods for assessing the collision diameter through only the elemental composition of the species, 5,23−26 through both spatial structure and elemental composition, 5,13,14,27 as well as via the analysis of electron density in a molecule. 11,28 Unfortunately, the approaches based on the empirical correlations of σ with atomic composition only, 23−25 which go back to the seminal works of Hirschfelder, 7 for all their simplicity, do not allow for the spatial structure of the molecules and, therefore, are applicable with confidence only for the smallest (di-and triatomic) species.…”

“…11,28 Unfortunately, the approaches based on the empirical correlations of σ with atomic composition only, 23−25 which go back to the seminal works of Hirschfelder, 7 for all their simplicity, do not allow for the spatial structure of the molecules and, therefore, are applicable with confidence only for the smallest (di-and triatomic) species. The search for correlations of σ with the number of nonhydrogen atoms for hydrogen- containing compounds within homologous series also holds some promise; 5,26 however, it lacks generality. The methods for estimating the collision diameter involving the analysis of the equilibrium molecular structure 5,13,14,27 have been developed only recently but have already proven themselves well in various applications.…”