  Kinetics of collision-sticking processes between vapor molecules and
molecular clusters of low volatile compounds facilitates the initial steps of
atmospheric clustering. Conventional theoretical models are quite inaccurate
due to the neglection of long-range interactions that essentially govern the
kinetics of these microscopic phenomena. Here, we present a consistent and
generic theoretical model for evaluating collision rates between molecules and
molecular clusters with intermolecular potentials properly incorporated. The
model requires solely the elementary molecule-molecule potential as a-priori
information but predicts collision rates of molecular clusters at arbitrary
sizes, with an accuracy comparable to all-atom molecular dynamics simulations
we performed for sulfuric acid-dimethylamine clusters, a typical example of
acid-base induced clustering. The carefully devised simulations validate the
theoretical model and elucidate the kinetics of the molecular
collision-sticking process. It is found that the vibrational coupling after the
collision between a sulfuric acid molecule and a sulfuric acid cluster can be
occasionally unsuccessful, i.e., no stable bond is formed after the collision.
However, introducing dimethylamine molecules to the sulfuric acid cluster can
notably increase the probability of forming stable bonds and hence stable
product clusters. The results offer fundamental insights into the initial steps
of molecular clustering and will facilitate the development of efficient
kinetic approach-based nucleation models.
