New method of energymass dispersion applied to mass spectral data from positively charged water vapor clusters
A new method is presented by which energymass, volumemass, and enthalpymass dispersion curves may be determined for charged water vapor clusters. This method involves two closely spaced partial pressures at a fixed temperature. The method is exemplified by using mass spectral data from positively charged water vapor clusters (H+(H2O)M) where 6 ≤ M ≤ 45. A ΔGmass dispersion was also determined using the ΔHmass dispersion for comparison. ΔG displays an enormous minimum, which is of signal importance because it indicates that a size of maximum stability (SMS) exists. The SMS corresponds to M = 13 for pressures between 0.056 and 0.151 bar (1 bar = 100 kPa) at 373.15 K, and to M = 32±1 for pressures between 0.473 and 0.556 bar at 372.15 K. The free energy corresponding to M = 45 occurs far above that corresponding to the SMS. The resultant instability leads to condensation for pressures above 0.556 bar at 372.15 K.Key words: clusters, mass spectrometry, thermodynamics, water vapour.