Abstract
Hydrate clusters with atmospheric ions have been of long-standing interest in the field of atmospheric sciences, because of their central role in the formation of tropospheric aerosols. A large number of thermochemical studies of the typical positive-ion hydrate clusters, H3O+(H2O)n, using mass spectrometry have been reported, while there is little thermochemical information concerning negative-ion hydrate clusters. The absence of information is due to lack of ionization methods for the reproducible formation of specific negative atmospheric ions and their hydrates, and resulting difficulties in obtaining reliable mass spectrometry data from negative-ion hydrate clusters. We have recently established an atmospheric pressure DC corona discharge device that includes a specific needle electrode that leads to the regular formation of various atmospheric negative ions Y−. Furthermore, the use of this discharge system coupled to mass spectrometers resulted in the stable formation of large hydrate clusters, Y−(H2O)n, due to adiabatic expansion caused by pressure difference between the ambient discharge area (760 torr) and the vacuum region in the mass spectrometers (≈ 1 torr). Here, we show the resulting mass spectra of large hydrate clusters, Y−(H2O)n, with the negative atmospheric ions, Y−, such as HO−, O2−, HO2−, CO3−, NO3− and NO3−(HNO3)2, which play a central role in atmospheric chemistry. Those reliable mass spectrometry data have provided information about specific cluster sizes having particular thermochemical stability in individual cluster ion series, Y−(H2O)n, which may correspond to first hydrated shell and magic number for Y−(H2O)n. Here, we also describe the detailed mechanism of the formation of negative atmospheric ions, Y−, and their hydrates, Y−(H2O)n, in an atmospheric pressure corona discharge ionization mass spectrometry.
