The dynamics of borohydride dihydrogen bonding in water and dissolved in an ionic liquid are examined using 2D-IR vibrational echo and pump-probe spectroscopy, using the B-H stretch as a probe. Due to the low electronegativity of boron and the sharing of a negative charge, the hydrogens of borohydride are partially negatively charged leading them to form hydrogen bonds with the hydrogens of water. It is found that the rotational anisotropy and the spectral diffusion of the ion in solution both undergo a rapid decay from a changing superposition of the excited stretch due to the symmetry of the molecule; but after this initial decay the spectral diffusion exhibits the same time constants observed by the OD stretch of HOD in water. Through 2D-IR, various cross peaks in the spectrum are observed and examined which arise from a Fermi resonance with a neighboring overtone and combination band. Isolating the borohydride in the ionic liquid allows all of the cross peaks in the spectrum to be resolved, which further inform the interpretation of the borohydride in water data.

Dynamics of dihydrogen bonding:  Spectral diffusion of borohydride in water

248th National Meeting (2014)

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