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Main Title: Microsolvation of H2O+, H3O+, and CH3OH2+ by He in a cryogenic ion trap: structure of solvation shells
Author(s): Müller, David
Dopfer, Otto
Type: Article
Abstract: Due to the weak interactions of He atoms with neutral molecules and ions, the preparation of size-selected clusters for the spectroscopic characterization of their structures, energies, and large amplitude motions is a challenging task. Herein, we generate H2O+Hen (n ≤ 9) and H3O+Hen (n ≤ 5) clusters by stepwise addition of He atoms to mass-selected ions stored in a cryogenic 22-pole ion trap held at 5 K. The population of the clusters as a function of n provides insight into the structure of the first He solvation shell around these ions given by the anisotropy of the cation–He interaction potential. To rationalize the observed cluster size distributions, the structural, energetic, and vibrational properties of the clusters are characterized by ab initio calculations up to the CCSD(T)/aug-cc-pVTZ level. The cluster growth around both the open-shell H2O+ and closed-shell H3O+ ions begins by forming nearly linear and equivalent OH⋯He hydrogen bonds (H-bonds) leading to symmetric structures. The strength of these H-bonds decreases slightly with n due to noncooperative three-body induction forces and is weaker for H3O+ than for H2O+ due to both enhanced charge delocalization and reduced acidity of the OH protons. After filling all available H-bonded sites, addition of further He ligands around H2O+ (n = 3–4) occurs at the electrophilic singly occupied 2pz orbital of O leading to O⋯He p-bonds stabilized by induction and small charge transfer from H2O+ to He. As this orbital is filled for H3O+, He atoms occupy in the n = 4–6 clusters positions between the H-bonded He atoms, leading to a slightly distorted regular hexagon ring for n = 6. Comparison between H3O+Hen and CH3OH2+Hen illustrates that CH3 substitution substantially reduces the acidity of the OH protons, so that only clusters up to n = 2 can be observed. The structure of the solvation sub-shells is visible in both the binding energies and the predicted vibrational OH stretch and bend frequencies.
Subject(s): cryogenic ion trap
solvation shells
size-selected clusters
Issue Date: 20-Apr-2022
Date Available: 12-Aug-2022
Language Code: en
DDC Class: 530 Physik
Journal Title: Physical Chemistry, Chemical Physics
Publisher: Royal Society of Chemistry
Volume: 24
Issue: 18
Publisher DOI: 10.1039/D2CP01192A
Page Start: 11222
Page End: 11233
EISSN: 1463-9084
ISSN: 1463-9076
TU Affiliation(s): Fak. 2 Mathematik und Naturwissenschaften » Inst. Optik und Atomare Physik » FG Lasermolekülspektroskopie und Umweltphysik
Appears in Collections:Technische Universität Berlin » Publications

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