Aqueous solutions of chloride, bromide, and iodide salts have been probed by Raman spectroscopy, both off-resonance and on-resonance with the charge-transfer-to-solvent bands.  We focus largely on the water intramolecular bend, which is a normal mode that is typically considered unperturbed as a function of added solutes. In fact, we have found distinct shifts in the bend frequency.  An intriguing aspect is that the direction of the shifts depends upon whether the excitation is resonant or not.  Generally, upshifts in the bend frequency are observed with off-resonance excitation, whereas downshifts are observed when the halides are probed on resonance.  The resonance enhancement in the deep-UV can approach a factor of 10000, and depends on the halide and the excitation wavelength.  These findings are discussed in the context of electric field and charge-transfer effects caused by the halides.

Solvation of halides in water: Insights from a comparison of on- and off-resonance Raman spectroscopy

246th National Meeting (2013)

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