Mixed (HNO3)m(H2O)n clusters generated in supersonic expansion of nitric acid vapor are investigated in two different experiments, (1) time-of-flight mass spectrometry after electron ionization and (2) Na doping and photoionization. This combination of complementary methods reveals that only clusters containing at least one acid molecule are generated, that is, the acid molecule serves as the nucleation center in the expansion. The experiments also suggest that at least four water molecules are needed for HNO3 acidic dissociation. The clusters are undoubtedly generated, as proved by electron ionization; however, they are not detected by the Na doping due to a fast charge-transfer reaction between the Na atom and HNO3. This points to limitations of the Na doping recently advocated as a general method for atmospheric aerosol detection. On the other hand, the combination of the two methods introduces a tool for detecting molecules with sizable electron affinity in clusters.

†J Heyrovský Institute of Physical Chemistry v v i Academy of Sciences of the Czech Republic Dolejškova 3 182 23 Prague 8 Czech Republic

‡Institut für Physikalische Chemie Universität Göttingen Tammannstrasse 6 D 37077 Göttingen Germany

References provided by Crossref.org

Metastable Evaporation of Molecules from Water Clusters

Bridging Gaps between Clusters in Molecular-Beam Experiments and Aerosol Nanoclusters

Stabilization of benzene radical anion in ammonia clusters

Communication: Charge transfer dominates over proton transfer in the reaction of nitric acid with gas-phase hydrated electrons

Electron-triggered chemistry in HNO3/H2O complexes

Atmospheric processes on ice nanoparticles in molecular beams