Activation energies for evaporation from protonated and deprotonatedwater clusters from mass spectra

摘要

Experimental mass abundance spectra are used to extract evaporative activation energies(dissociation energies) for protonated water clusters, (H_2O)NH~+, and deprotonated water clusters,(H_2O)NOH~-,in the size range up to hundred molecules. The inversion is achieved by application ofthe shell correction method adapted from nuclear physics to the abundance spectra. The well knownabundance anomaly for protonated clusters which occurs for N=20-22 is found to have thecharacteristic behavior of a shell closing, whereas other apparent magic numbers are only prominentpeaks in the abundance spectra because of the instability of the evaporative precursor. For thedeprotonated clusters, we find a similar shell closing for N=55-56.