(189h) Binding Rates of Polyaromatic Hydrocarbons during Soot Formation: Insights from Reactive Molecular Dynamics

In gas-phase synthesis of soot nanoparticles, polyaromatic hydrocarbons (PAHs) form and grow by collisions at high temperatures. While a hard sphere equation is frequently used to predict the sticking rate coefficient, this equation neglects the influences of potential interactions and internal energy of the colliding entities.

Here, a collision rate theory-Molecular Dynamics simulation approach is used to calculate sticking probabilities and dimerization rate coefficients of PAH molecules. The probability of dimerization depends upon the relative velocity between the two colliding PAH clusters and their initial impact parameter and orientation. For all PAH molecules investigated here (naphthalene, pyrene, pentacene and coronene) there is a well-defined region of relative velocities and impact parameters where sticking is highly probable, while outside this region probability drops to zero. The dimerization rate of such PAH molecules is determined by quantifying their binding probability at various process temperatures. Integration over all impact parameters and velocities for collisions (in accordance with the Maxwell Boltzmann distribution) yields the dimerization rate coefficient for a given PAH structure. Criteria for successful dimerization events are proposed based on their collision time.

The accurate binding rates obtained by the presented method can be applied in developing rate equations to predict material formation and growth rates in vapor phase systems.