Molecular vibrations are excellent experimental probes of the molecular-scale environment. Mapping spectral features onto a molecular picture presents a significant challenge. This requires new theoretical approaches to reveal the molecular fingerprints of spectral features and to shed light on the collective motions involved in association/dissociation reactions to make contact experiments that can probe these processes on the nm and sub-nm length and ps time scale. I will discuss in three cases to highlight recent advances in studying ion-pairing in bulk and at interfaces using ab initiodensity functional theory approaches. The first example of the spectroscopy of N-methylacetamide (NMA) suggests the breakdown of an electrostatic based frequency map approach for cation binding with NMA. Additionally, it highlights the need to better formulate the relationship between averaged frequencies over a short time interval and instantaneous frequencies of a well-defined configuration.a)The second example of the SCN-system demonstrates how large-scale DFT-MD can be used to disentangle the information from multiple different spectroscopic techniques. It showcases a system size where it is not practical to obtain instantaneous frequencies using normal modes techniques across a useful ensemble of configurations.a)The third example demonstrates the sensitivity of a coupled oscillator to its local environment. The system is an ion binding to a carboxylic acid, studied in both the gas and condensed phase.b)

Vibrational signatures of ion pairing in bulk and at interfaces with ab initio DFT

2019 Spring National Meeting

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