Abstract
The time-dependent kinetics of formation and evolution of nanosize atomic clusters is investigated and illustrated with the nucleation dynamics of ion-seed ${\mathrm{Ar}}_{n}{\mathrm{H}}^{+}$ particles. The rates of growth and degradation of Ar-atomic shells around the seed ion are inferred from molecular dynamics (MD) simulations. Simulations of cluster formation have been performed with accurate quantum-mechanical binary interaction potentials. Both the nonequilibrium and equilibrium growth of ${\mathrm{Ar}}_{n}{\mathrm{H}}^{+}$ are investigated at different temperature and densities of the atomic gas and seed ions. Formation of ${\mathrm{Ar}}_{n\ensuremath{\le}40}$ shells is the main mechanism which regulates the kinetics of nanocluster growth and the diffusive fluctuations of the cluster size distribution. The time evolution of the cluster intrinsic energy and cluster size distributions are analyzed at the nonthermal, quasiequilibrium, and thermal equilibrium stages of ${\mathrm{Ar}}_{n}{\mathrm{H}}^{+}$ formation. We have determined the self-consistent model parameters for the temporal fluctuations of the cluster size and found coefficients of the diffusive growth mechanism describing the equilibrium distribution of nanoclusters. Nucleation of haze and nanodust particles in astrophysical and atmospheric ionized gases is discussed.
Highlights
The nature and characteristics of phase transitions in atomic and molecular systems strongly depend on the interparticle interactions
In the first nonequilibrium stage, the strong ion field removes the barriers to nucleation; the probability to capture a gas atom into the deeply cluster-bound states (1T and 2T) is significantly higher than the probability for all detachment processes
When a gas atom is captured into inner shells, a local release of high kinetic energies occurs
Summary
The nature and characteristics of phase transitions in atomic and molecular systems strongly depend on the interparticle interactions These binary interactions determine how rapidly new phases form and regulate a nucleation of solid or liquid particles from gas and liquid phases. The MD simulations, performed with accurate potentials of interparticle interaction, can successfully describe both nonequilibrium and equilibrium processes of nucleation of nanosize clusters. The formation and growth of nanosize ArnH+ clusters is initiated by ionization of H atoms in the Ar and H gas mixture and is simulated with the use of the Large-scale. The accurate binary potentials of the Ar-Ar and Ar-H+ interactions have already been used in our investigations of nucleation and growth of ArnHm+ solid or liquid particles, where large size clusters include many protons [40]. The repulsion and attraction energies of the Ar-Ar and Ar-H+ interactions are approximately equalized at ∼2.5 Å
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