Nonequilibrium Soot Nucleation Precursors: Energy Partition in Bimolecular Collisional Dynamics of Coronene Monomers

Classical MD simulations of the bimolecular collision dynamics of coronene monomers were carried out at typical combustion conditions (1500 K, 1 atm). Statistical analysis of over 49,000 collisional trajectories reveals a biexponential decay kinetics with a characteristic metastable dimerization of collisional complexes. By employing a time-dependent energy decomposition framework, we demonstrate that metastable dimerization is characterized by a decoupled and translationally cold center-of-mass separation (COMS) coordinate while the intramonomer vibrational degrees of freedom are thermally excited. The stabilization of these nonequilibrium complexes is driven by the magnitude of the inelastic absorption of the collision impact energy into low-frequency intramonomer vibrational modes and by the weak character of the intermonomer physical interactions. These findings provide critical mechanistic insights into the nonequilibrium precursors essential for accelerating chemical cross-linking of PAH monomers during soot nucleation.