Solvent Independent Anharmonicity for Carbonyl Oscillators

TitleSolvent Independent Anharmonicity for Carbonyl Oscillators
Publication TypeJournal Article
Year of Publication2017
AuthorsSchneider SH, Kratochvil H.T., Zanni M T., Boxer SG
Secondary TitleJournal of Physical Chemistry B
Date Published02/2017
PublisherJournal of Physical Chemistry B

The physical origins of vibrational frequency shifts have been extensively studied in order to understand non-covalent intermolecular interactions in the condensed phase. In the case of carbonyls, vibrational solvatochromism, MD simulations, and vibrational Stark spectroscopy suggest that the frequency shifts observed in simple solvents arises predominately from the environment’s electric field due to the vibrational Stark effect. This is contrary to many previously invoked descriptions of vibrational frequency shifts, such as bond polarization, whereby the bond’s force constant and/or partial nuclear charges are altered due to the environment, often illustrated in terms of favored resonance structures. Here we test these hypotheses using vibrational solvatochromism as measured using 2D IR to assess the solvent-dependence of the bond anharmonicity. These results indicate that the carbonyl bond’s anharmonicity is independent of solvent as tested using hexanes, DMSO, and D2O and supported by simulated 2D spectra. In support of the linear vibrational Stark effect, these 2D IR measurements are consistent with the assertion that the Stark tuning rate is unperturbed by the electric field generated by both hydrogen and non-hydrogen bonding environments and further extends the general applicability of carbonyl probes for studying intermolecular interactions.