Temperature dependence of magic number and first hydrated shell of various core water cluster ions Y−(H2O)n (Y = O2, HOx, NOx, COx) in atmospheric pressure negative corona discharge mass spectrometry

Abstract

The relationship between orifice temperature and the size distribution in water clusters Y−(H2O)n with various negative atmospheric core ions Y− such as O2−, HO−, HO2−, NO2−, NO3−, NO3−(HNO3)2, CO3− and HCO4− has been investigated using atmospheric pressure negative corona discharge mass spectrometry. Although the cluster distributions shifted in the lower-mass region with increasing orifice temperature due to insufficient cooling during adiabatic expansion, the anomalous discontinuities in ion peak intensity at certain size clusters Y−(H2O)m in the Y−(H2O)n cluster series reproducibly observed at the lowest orifice temperature did not vary with change in temperature. The results obtained suggest that the clusters Y−(H2O)m have particular thermochemical stability compared to other size clusters Y−(H2O)n under arbitrary temperature conditions, and that the Y−(H2O)m would correspond to the magic number or first hydrated shell in the cluster series Y−(H2O)n. The specific stability of Y−(H2O)m was also confirmed by using the ratio of Y−(H2O)n to Y−(H2O)n+1 peak intensity, which is a reliable method to identify the magic numbers in arbitrary cluster distributions obtained by varying the temperature and solvent partial pressure in a reaction chamber.