Spectroscopic evidence for cyclical aggregation and coalescence of molecular aerosol particles.

Developments in understanding the relationship of FTIR spectra of molecular aerosols to the shapes of aerosol particles are exploited to analyze the stages by which such particles mature as a function of time as observed at a series of fixed low temperatures. Based on recent advances from exciton modeling and new molecular-dynamics simulations, two sequential maturation cycles of CO2 particles in He(g) are identified by data obtained between 35 and 100 K. Observation of the stages of these cycles, which include particle aggregation, sintering and ultimately coalescence to a "globular" form, also provides a basis for the concept that the formation of an aerosol from dilute co-mixtures of CO2 and H2O in a carrier gas may lead to nucleation and isolation of primary CO2 particles on aggregates of water-ice particles.