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Mitra S, Denton JK, Kelleher PJ, Johnson MA, Guasco TL, Choi TH, Jordan KD. Water Network Shape-Dependence of Local Interactions with the Microhydrated -NO 2- and -CO 2- Anionic Head Groups by Cold Ion Vibrational Spectroscopy. J Phys Chem A 2022; 126:2471-2479. [PMID: 35418229 DOI: 10.1021/acs.jpca.2c00721] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report the structural evolutions of water networks and solvatochromic response of the CH3NO2- radical anion in the OH and CH stretching regions by analysis of the vibrational spectra displayed by cryogenically cooled CH3NO2-·(H2O)n=1-6 clusters. The OH stretching bands evolve with a surprisingly large discontinuity at n = 6, which features the emergence of an intense, strongly red-shifted band along with a weaker feature that appears in the region assigned to a free OH fundamental. Very similar behavior is displayed by the perdeuterated carboxylate clusters, RCO2-·(H2O)n=5-7 (R = CD3CD2), indicating that this behavior is a general feature in the microhydration of the triatomic anionic domain and not associated with CH oscillators. Electronic structure calculations trace this behavior to the formation of a "book" isomer of the water hexamer that adopts a configuration in which one of the water molecules resides in an acceptor-acceptor-donor (AAD) (A = acceptor, D = donor) H-bonding site. Excitation of the bound OH in the AAD site explores the local network topology best suited to stabilize an incipient -XO2H-OH-(H2O)2 intracluster proton-transfer reaction. These systems thus provide particularly clear examples where the network shape controls the potential energy landscape that governs water network-mediated, intracluster proton transfer. The CH stretching bands of the CH3NO2-·(H2O)n=1-6 clusters also exhibit strong solvatochromic shifts, but in this case, they smoothly blue-shift with increasing hydration with no discontinuity at n = 6. This behavior is analyzed in the context of the solute-ion polarizability response and partial charge transfer to the water networks.
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Affiliation(s)
- Sayoni Mitra
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Joanna K Denton
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Patrick J Kelleher
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Timothy L Guasco
- Department of Chemistry, Millikin University, Decatur, Illinois 62522, United States
| | - Tae Hoon Choi
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Kenneth D Jordan
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
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Huchmala RM, McCoy AB. Exploring the Origins of Spectral Signatures of Strong Hydrogen Bonding in Protonated Water Clusters. J Phys Chem A 2022; 126:1360-1368. [PMID: 35171593 DOI: 10.1021/acs.jpca.1c10036] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effects of anharmonicity on the spectral features of strong ionic hydrogen bonds are explored through reduced dimensional studies of the couplings between the hydrogen bonding OH and the donor-acceptor OO stretching vibrations in protonated water clusters with 2-4 water molecules. Specifically, this study focuses on how the anharmonicities and couplings in these ions are reflected in the vibrational spectra by exploring the intensities of the transitions to states with excitation in both the OH and the OO stretching vibrations and changes in the frequency of the OO stretching vibration when the OH stretching vibration is excited. These questions are addressed through the application of several approximate treatments that are based on an adiabatic separation of the high-frequency OH and low-frequency OO stretching vibrations as well as low-order expansions of the potential and dipole surfaces. While an adiabatic approximation captures most of the trends found in the spectra and from an analysis of the two-dimensional model, a vibrational Franck-Condon approach fails to capture the intensities of these transitions. Of the terms in the expansion of the dipole moment function, those that are proportional to ΔrOH and ΔrOH2 are found to provide the largest contributions to the calculated intensities of the transitions involving excitation of both the OH and the OO stretches. This leads to the conclusion that the intensities of these transitions encode information about the frequency and anharmonicity of the OH stretching vibration and how they are affected by changes in the OO distance. The anharmonicity of the potential also leads to changes in the OO stretching frequency with excitation of the OH stretching vibration. The direction of this change in frequency encodes additional information about the strength of the ionic hydrogen bond.
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Affiliation(s)
- Rachel M Huchmala
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Anne B McCoy
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
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