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Probing solvation and reactivity in ionized polycyclic aromatic hydrocarbon–water clusters with photoionization mass spectrometry and electronic structure calculations

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Abstract

Polycyclic aromatic hydrocarbons (PAHs) may comprise up to 20% of the carbon budget in our galaxy and most PAHs condense onto water-rich icy grain mantles. Benzene–water clusters have been invoked as model systems for studying the photo-processing of water ice mantles containing PAHs. However, there is a paucity of information on larger aromatics, where the extended π cloud could affect photo-processing. In this study, tunable vacuum ultraviolet (VUV) photoionization of naphthalene–water clusters Nx(H2O)y (N denotes naphthalene) is performed using synchrotron radiation and analyzed by reflectron time-of-flight mass spectrometry. Naphthalene clusters up to x = 4 are generated as are naphthalene–water clusters up to y = 25. At low photon energy (<11 eV), the naphthalene moiety is ionized and there is no proton transfer from N+ to the water sub-cluster, which is very different from the benzene–water system. Protonated products, N[(H2O)xH]+ and OH radical addition product (NOH)[(H2O)xH]+ are generated above 11 eV, suggesting that water sub-clusters dominate the dynamics at high photon energies. Ab initio calculations are performed to decipher the experimental results. Energetics of the neutral structures N(H2O)1–4 and their photoionized counterparts are calculated, including ionization on the N moiety as well as on the water sub-cluster. Energy decomposition analysis (EDA) is performed to understand trends in the binding between the naphthalene and the water sub-cluster in the ionized species.

Graphical abstract: Probing solvation and reactivity in ionized polycyclic aromatic hydrocarbon–water clusters with photoionization mass spectrometry and electronic structure calculations

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Publication details

The article was received on 05 Dec 2018, accepted on 22 Jan 2019 and first published on 22 Jan 2019


Article type: Paper
DOI: 10.1039/C8FD00229K
Faraday Discuss., 2019, Advance Article

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    Probing solvation and reactivity in ionized polycyclic aromatic hydrocarbon–water clusters with photoionization mass spectrometry and electronic structure calculations

    B. Xu, T. Stein, U. Ablikim, L. Jiang, J. Hendrix, M. Head-Gordon and M. Ahmed, Faraday Discuss., 2019, Advance Article , DOI: 10.1039/C8FD00229K

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