Water Clusters in Gas Phases Studied by Liquid Ionization Mass Spectrometry

Abstract

Studies of water clusters under atmospheric pressure are very important. In previous methods, however, clusters existing in vacuum at low temperature have been measured. Therefore, the size distributions of observed cluster ions are likely di#erent from those existing at normal conditions. Liquid ionization (LPI) mass spectrometry we have developed provides information about hydrogen-bonded clusters in a gas phase and also at the liquid surface at ambient temperature under atmospheric pressure. Thus, LPI-MS was applied to study water clusters in gas phases. The results indicated that the sizes of water clusters in vapor increased with the temperature of liquid water and those in the air increased with the relative humidity, while they decreased with increasing the temperature of the gas phase. In general, the size distribution of water clusters shows one smooth envelope, except for a few magic numbered clusters. Adiabatic condensation is negligible to occur in this method and thus, LPI mass spectra give useful information about clusters in gas phases under the normal conditions.

Terahertz vibrational properties of water nanoclusters relevant to biology

“…1 may contribute significantly to the observed strong THz emission from water vapour under optical stimulation. Experiment and theory agree that not only can such water clusters be produced but they also occur optimally in certain numbers (so-called magic numbers) and configurations of water molecules [3,[8][9][10]. Prominent among the magic-number water clusters that have been identified are ones having the "buckyball-like" pentagonal dodecahedral structure [9,10] shown in Fig.…”

Observations of different core water cluster ions Y−(H2O)n (Y = O2, HOx, NOx, COx) and magic number in atmospheric pressure negative corona discharge mass spectrometry

“…Measurement of the ion peak intensities allows the determination of quantitative data such as equilibrium constants, heats and enthalpy for individual hydration steps. Mass spectrometric analysis of positive ion water clusters H 3 O + (H 2 O) n has been performed under various experimental conditions such as field emission ionization in water vapor, [6,7] a free jet expansion of water vapor with electron impact, [8,9] liquid ionization, [10] electrospray, [11] discharge ionization, [12] ion bombardment of ice surfaces [13] and near-threshold vacuum-UV photoionization of neutral clusters. [14] The resulting mass spectra consisting of the dominant water cluster ions H 3 O + (H 2 O) n have some common…”

Cluster Composition Distributions of Pure Ethanol: Influence of Water and Ion–Molecule Reactions Revealed by Liquid-Ionization Tandem Mass Spectrometry

“…We have developed a soft ionization method, termed liquid-ionization mass spectrometry for analysing nonvolatile organic compounds, [21][22][23] (referred to as LPI since 1998 22) ), in which a liquid sample is ionized by collision with excited argon atoms (Ar * ) under atmospheric pressure at ambient temperature (23-25°C). The method (LPI-MS) has been also applied to studies of clusters, such as water, 24) carboxylic acid-water mixtures, 25) and reaction products formed in formaline with a small amount of methanol. 26) The distribution of cluster sizes of water in the air has been measured at ambient temperature and found that the size distributions were related to the humidity, 24) suggesting that neutral clusters of water exist in the air.…”

“…The method (LPI-MS) has been also applied to studies of clusters, such as water, 24) carboxylic acid-water mixtures, 25) and reaction products formed in formaline with a small amount of methanol. 26) The distribution of cluster sizes of water in the air has been measured at ambient temperature and found that the size distributions were related to the humidity, 24) suggesting that neutral clusters of water exist in the air. Alcohol aqueous solutions (20%v/v, methanol and ethanol) have been measured by LPI-MS. 27) The molar ratios of alcohol to water calculated from LPI mass spectra have been agreed with the alcohol concentration of the solution, although the flow rate of a sample solution (F s ) and the voltage applied to the needle (V E ) should be controlled.…”

“…27) It has been clear that the position of the needle tip respect to the pinhole is the most critical parameter for obtaining mass spectra showing the cluster compositions at the liquid surface, because the cluster compositions vary very quickly due to evaporation, sample ions produced at the needle tip, and these ions should go through the pinhole up to the detector. The envelope of ion source used previously was a glass cylinder, [21][22][23][24][25][26][27] so that the image around the needle tip was distorted. In this paper, a glass block was used as the ion source and it is now possible to adjust precisely the position of the needle tip.…”