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Transition from Water Wires to Bifurcated H-Bond Networks in 2-Pyridone·(H 2 O) n , n = 1–4 Clusters

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Siffert Luca, Blaser Susan, Ottiger Philipp, Leutwyler Samuel,
Project Spektroskopie, Photophysik und Photochemie von Molekülclustern in Überschallmolekularstrahlen
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Original article (peer-reviewed)

Journal The Journal of Physical Chemistry A
Volume (Issue) 122(48)
Page(s) 9285 - 9297
Title of proceedings The Journal of Physical Chemistry A
DOI 10.1021/acs.jpca.8b09410

Open Access

URL https://pubs.acs.org/doi/10.1021/acs.jpca.8b09410
Type of Open Access Publisher (Gold Open Access)

Abstract

Mass-selective two-color resonant two-photon ionization (2C-R2PI), UV/UV hole-burning, and infrared (IR) depletion spectra of supersonic jet-cooled 2-pyridone center dot(H2O)(n) clusters with n = 1-4 have been measured to investigate the local hydration patterns around 2-pyridone (2PY) as a function of cluster size. As shown by others, the IR frequencies of the OH and NH stretches of the n = 1, 2 clusters are characteristic of water wires stretching from the NH to the C=O group of 2PY. We identify two isomers (3A and 3B) of the n = 3 cluster in the 2C-R2PI spectrum and separate them by IR/UV and UV/UV hole-burning techniques. Isomer 3A exhibits a three-membered water wire, extending the n = 1, 2 structural motif. Isomer 3B exhibits bifurcated water wires with the first H2O donating to two waters that form H-bonds to the C=O group. This increases the H-bond strength between the NH group of 2PY and the proximal H2O molecule, lowering the NH stretch to similar to 2800 cm(-1) The n = 4 cluster is also bifurcated with two water wires between the bifurcating H2O and the C=O group. The cluster-selective IR spectra are complemented with density-functional calculations using the PW91, B3LYP, B97-D, and M06-2X functionals, where the latter two include long-range dispersive interactions, and with the ab initio correlated SCS-CC2 method. The calculated IR spectra provide firm assignments of the structures of the n = 1-4 cluster structures and allow us to understand the evolution of individual H-bond strengths with increasing cluster size.
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