Understanding and Representing the Distinct Kinetics Induced by Reactive Collisions of Rovibrationally Excited Ephemeral Complexes across Reactive Collider Mole Fractions and Pressures

Rovibrationally excited ephemeral
complexes AB**, formed
from the association of two molecules A + B, are generally considered
to undergo collisions only with an inert bath gas M that transfer
energyinducing termolecular association reactions A + B (+M)
→ AB (+M). Recent studies have demonstrated that reactive collisions
of AB** with a third molecule Cinducing chemically
termolecular reactions A + B + C → productscan also
be significant in combustion and planetary atmospheres. Previous studies
on systems with reactive collisions have primarily focused on limited
ranges of reactive collider mole fraction, XC, and pressure, P, specific to the chosen
application. Yet, it remains to be established how such systems, and
the rate constants of their emergent phenomenological reactions, behave
over the wide XC and P ranges of potential interesta gap in the present understanding
that has impeded the development of broadly applicable rate laws and
general treatment of such systems in kinetic modeling. Here, we present
results from master equation calculations for HO2** formed from H + O2 and its reactions with H to advance understanding and explore representations
of systems with reactive colliders across wide ranges of XC and P. With regard to understanding,
we demonstrate that reactive collisions can both (1) increase the
overall rate of conversion of reactants to products and (2) alter
the branching ratio among final products. With regard to representations
in kinetic models, we find that rate constants of all emergent phenomenological
reactionstermolecular association A + B (+M), chemically termolecular
A + B + C, and bimolecular AB + Cexhibit a rich XC and P dependence. We also present analyses
to explore the existence of a unique phenomenological representation
(or lack thereof) and assess ways for the distinct effects of reactive
collisions to be represented in kinetic models.