A Computational and Experimental View of Hydrogen Bonding in Glycerol Water Clusters

Abstract

Polyol–water clusters provide a template to probe ionization and solvation processes of paramount interest in atmospheric and interstellar chemistry. We generate glycerol water clusters in a continuous supersonic jet expansion and interrogate the neutral species with synchrotron-based tunable vacuum ultraviolet photoionization mass spectrometry. A series of glycerol fragments (m/z 44, 61, 62, and 74) clustered with water are observed. A judicious combination of backing pressure, nozzle temperature, and water vapor pressure allows for tuning the mol % of glycerol. The recorded appearance energies of the water cluster series m/z 62 and 74 are similar to that observed in pure glycerol, while the m/z 61 series shows a dependence on cluster composition. Furthermore, this series also tracks the water concentration of the beam. Theoretical calculations on neutral and ionized clusters visualize the hydrogen bond network in these water clusters and provide an assessment of the number of glycerol–glycerol, glycerol–water, and water–water hydrogen bonds in the cluster, as well as their interaction energies. This method of bond counting and interaction energy assessment explains the changes in the mass spectrum as a function of mol % and offers a glimpse of the disruption of the hydrogen bond network in glycerol–water clusters. The calculations also reveal interesting barrierless chemical processes in photoionized glycerol water clusters that are either activated or do not occur without the presence of water. Examples include spontaneous intramolecular proton transfer within glycerol to form a distonic ion, nonactivated breaking of a C–C bond, and spontaneous proton transfer from glycerol to water. These results appear relevant to radiation-induced chemical processing of alcohol–water ices in the interstellar medium.

Magic Numbers in Formic Acid Water Clusters Revealed by VUV Photoionization Mass Spectrometry and Density Functional Calculations

“…This approach, previously used in studying proton transfer in acetaldehyde water clusters 37 and naphthalene water clusters, 38 also contributed to identifying magic numbers in water clusters beyond the traditional "21" 39 and the identification of the hydrogen bond networks in diol 40 and polyol water clusters. 41 Mass spectra results demonstrate that upon ionization of mixed FA-water clusters, the resulting clusters are protonated. The stability of magic numbers of different FA-water clusters was observed in the mass spectra, specifically for clusters:…”

A Vacuum Ultraviolet Photoionization Mass Spectrometry and Density Functional Calculation Study of Formic Acid–Water Clusters

“…This approach, previously used in studying proton transfer in acetaldehyde−water clusters 37 and naphthalene water clusters, 38 also contributed to identifying enhanced intensities of a number of protonated water clusters from VUV photoionization 39 and the identification of the hydrogen bond networks in diol 40 and polyol water clusters. 41 Mass spectra results demonstrate that upon ionization of mixed FA-water clusters, the resulting clusters are protonated. Enhanced intensities are observed for masses corresponding to the following clusters: FA 1 W 5 H + , FA 2 W 4 H + , FA 3 W 3 H + , FA 4 W 2 H + , FA 5 W 1 H + , FA 6 W 2 H + .…”

“…The employed methodology includes intensity measurements of various masses at variable photon energies, the appearance energies (AE) of various fragments, and an interpretation of their stability guided by theoretical calculations. This approach, previously used in studying proton transfer in acetaldehyde–water clusters and naphthalene water clusters, also contributed to identifying enhanced intensities of a number of protonated water clusters from VUV photoionization and the identification of the hydrogen bond networks in diol and polyol water clusters …”

Magic Numbers and Stabilities of Photoionized Water Clusters: Computational and Experimental Characterization of the Nanosolvated Hydronium Ion

“…The unquestioned importance of water in biological 1 and atmospheric 2 processes on earth and in astrochemistry 3 drives our quest to study the photon-induced dynamics of hydrogenbonded water clusters at the molecular level. 4 The process through which water clusters form under various conditions is hence critical to understand.…”