Adsorption of NxOy-based molecules on large water clusters: An experimental and theoretical study

The sticking efficiencies for a range of NxOy species (NO, NO2, N2O, N2O5 and HNO3) onto large water clusters have been studied using a supersonic molecular beam expansion to generate water clusters containing 50-450 water molecules. NO, NO2, and N2O are found to stick with very low efficiencies relative to the organic species studied previously. This is in accord with studies for the corresponding species performed on cooled water ice films. In contrast, N2O5 is efficiently converted to nitric acid by a heterogeneous surface reaction with the water cluster. Quantum mechanical-molecular dynamics calculations of the energies for the interaction of NO, NO2 and N2O with a water molecule and a small water cluster, (H2O)(10), have beef performed. These show that the NOx molecule prefers to be bended to the surface of the cluster and that it boils off the cluster at 140 K.