“Third-Body” collision efficiencies for combustion modeling: Hydrocarbons in atomic and diatomic baths

• Published in: Proceedings of the Combustion Institute 2015-01, Vol.35 (1), p.197-204
• Main Authors: Jasper, Ahren W., Oana, C. Melania, Miller, James A.
• Format: Article
• Language: English
• Subjects: Angular momentum; Bath gas efficiencies; Carbon; Classical trajectory simulations; Collision dynamics; Combustion; Dynamical systems; Dynamics; Energy transfer; Hydrocarbons; Mathematical models; Trajectories; Unimolecular kinetics; Weak collider
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/j.proci.2014.05.105

The collisional energy transfer dynamics relevant to the unimolecular kinetics of linear, branched, and cyclic hydrocarbons, including both radicals and saturated and unsaturated molecules, in atomic and diatomic baths is studied via classical trajectories. A set of full-dimensional potential energy surfaces (PESs) suitable for efficient trajectory simulations involving large hydrocarbons (CxHy) colliding with any of seven baths (M=He, Ne, Ar, Kr, H2, N2, O2) is validated against direct dynamics calculations for two small systems. The PESs are then used to calculate Lennard-Jones collision parameters, and a general rule for calculating these parameters based only on the number of carbon atoms and the bath gas is obtained. Next, the PESs are used to calculate low-order moments of the collisional energy transfer function relevant to low-pressure-limit unimolecular kinetics for a total of 266 systems (38 unimolecular reactants in 7 baths), with a focus on the average angular momentum and total energy transferred in deactivating collisions. These moments are used to quantify the relative rotational and total collision efficiencies of the 7 baths for the various hydrocarbon reactants. Trends in the collision efficiencies with respect to the chemical structures of the hydrocarbon reactants are discussed.