FTIR spectroscopy of azide and cyanate ion pairs in AOT reverse micelles

PHYS 317

Jeffrey C. Owrutsky, jeff.owrutsky@nrl.navy.mil, Michael B. Pomfret, michael.pomfret.ctr@nrl.navy.mil, David J. Barton, and David A. Kidwell. Chemistry Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375-5342
The formation of ion pairs (IP) in aqueous AOT reverse micelles (RMs) is demonstrated using infrared spectroscopy of azide and cyanate with Li+, Na+, K+ and NH4+ counterions. The anions' antisymmetric stretching bands (near 2000 cm-1) blue shift in LiAOT and NaAOT RMs, but not in KAOT and NH4AOT RMs. The shifts are due to anion/counterion pairing, which is supported by the same trend being observed for producing contact IPs (Li+, Na+, K+) in bulk DMSO. The largest shifts are observed with low water content (wo) and the vibrational frequencies approach those in bulk water as wo increases. Similar results in terms of increased ion pair formation are also observed for the anions in formamide-containing AOT RMs. Ion pair formation is consistent with the reduced polarity and hydrogen bonding of water confined in RM systems. The spectra demonstrate ion specific effects at interfaces.

PHYS Poster Session - Water Mediated Interactions
7:30 PM-10:00 PM, Wednesday, August 20, 2008 Pennsylvania Convention Center -- Hall C, Poster

Division of Physical Chemistry

The 236th ACS National Meeting, Philadelphia, PA, August 17-21, 2008