SignificanceGas-to-particle conversion, also known as atmospheric aerosol nucleation, is responsible for about half of the global cloud condensation nuclei. It has been further argued that homogenous ternary nucleation including water is the major pathway for atmospheric aerosol formation. In contrast to earlier results on pure protonated water clusters, the shape of the measured velocity distributions of water molecules evaporated from excited water clusters doped with pyridinium, an abundant anthropogenic ion in the troposphere, shows evidence for out-of-equilibrium evaporation prior to thermalization. Water molecule evaporation is found to be much slower for the doped clusters, indicating in turn how such contaminants facilitate the growth of water clusters and consequently the nucleation processes at the early stages of atmospheric aerosol formation.

In this work, ionization and fragmentation of the prebiotic molecule Hydantoin by electron impact was investigated in our new experimental set-up. Scanning of the incident electron energy make possible the...