Vibrational Spectroscopy and Dynamics of HN 3 Cassidy Houchins 1, Dan Weidinger 1, Doug Brown 2 and Jeff Owrutsky 1 1 Chemistry Division, Naval Research Laboratory 2 Department of Chemistry, US Naval Academy This work supported by the Office of Naval Research through the Naval Research Laboratory

Outline Introduction –Background and N 3 - –Motivate acid studies Bulk Solvents –Baseline for more complex systems Reverse Micelles –One example of complex environment Conclusions

Introduction Vibrational Energy Relaxation –Depends on environment/phase – solute/solvent interactions simple (gas) condensed (liquid) complex systems (confined, interfaces) Small anions as benchmark probes –Solvation in bulk (e.g. Li et al) VER correlates with frequency VER correlates with H-bonding –Complex environments (e.g. Dahl et al) Confined heterogeneous Ionic liquids HN 3 (Houchins et al) –Do trends extend? –New molecular probe? Ohta, K.; Tominaga, K. Chem. Phys. Lett. 2006, 429, 136. Li, M.; Owrutsky, J.; Sarisky, M.; Culver, J. P.; Yodh, A.; Hochstrasser, R. M. J. Chem. Phys. 1993, 98, Dahl, K.; Sando, G. M.; Fox, D. M.; Sutto, T. E.; Owrutsky, J. C. J. Chem. Phys. 2005, 123, Houchins, C.; Weidinger, D.W.; Owrutsky, J.C. J. Phys. Chem. B (accepted for publication)

FTIR of HN 3 in CH 2 Cl 2 and Toluene v1v1 v2v2 v3v3 v4v4 v5v5 v6v6 Gas * CH 2 Cl Toluene *Moore, C. B.; Rosengren, K. J. Chem. Phys. 1966, 44, *Dows, D. A.; Pimentel, G. C. J. Chem. Phys. 1955, 23, 1258.

FTIR of HN 3 (ν 2 ) and N 3 - (ν 2 ) in Several Solvents Note axes! HN 3 = small solvent shift –Water different from other solvents –Very little variation among FA, CH 2 Cl 2, Toluene, NMF N 3 - = large solvent shift Li, M.; Owrutsky, J.; Sarisky, M.; Culver, J. P.; Yodh, A.; Hochstrasser, R. M. J. Chem. Phys. 1993, 98, Dahl, K.; Sando, G. M.; Fox, D. M.; Sutto, T. E.; Owrutsky, J. C. J. Chem. Phys. 2005, 123,

IR Pump – IR Probe for Vibrational Energy Relaxation Times HN 3 slower than N 3 - HN 3 N3-N3- VER times, T 1 (ps) VER times, T 1 (ps) H2OH2O CH 3 OH Formamide NMF Toluene CH 2 Cl Solvent trends extend from N 3 - to HN 3 –VER scales with H-bonding

Major results from bulk studies VER and H-bonding scale Frequency Shift Solvent N3-N3- HN 3 Small range of δν Transient Abs. Time N3-N3- HN 3 HN 3 generally slower than N 3 - K 1 = 1/T 1 Solvent N3-N3- HN 3 HN 3 results promising… How about more complex environments?

Reverse Micelles (RMs): Surfactant stabilized water-in-oil dispersions Water nanodroplets: –monodisperse & controllable size –radii increase with  =[water]/[surfactant] few to tens of nm Motivation: –model interfacial system: biomimetic –nanoparticle synthesis –water confinement effects Spectroscopy of RMs: –Standard characterization (TRFQ, IR of water): NP RMs –IR of ions in RMs Static IR – New diagnostic for RMs Ultrafast – New venue for solute vibrational dynamics IR Spectroscopy of Solutes in Reverse Micelles

FTIR of HN 3 (ν 2 ) and N 3 - (ν 1 ) in Reverse Micelles Peaks shift in RMs of both surfactants…different from N 3 - Shoulders in AOT and NP suggests segregation HN 3 peaks sensitive to –Confinement –Interface

VER of HN 3 in RMs VER longer than in bulk…different from N 3 - –2.3 ps bulk vs. ~6 ps in AOT for all w 0 studied –2.3 ps bulk vs. ~7 ps in NP for all w 0 studied HN3 VER not sensitive to size suggests interface But sensitive to surfactant supports interface

Summary and Conclusions VER and Spectra in Bulk Spectroscopically distinct from anion HN 3 slower than N 3 - Small solvent-dependent shift Rate scales with solvent HN 3 a new probe…in RMs VER and spectra shift from bulk for both surfactants HN 3 segregates into distinct regions of RM Interrogates water/surfactant interface Other enviroments Anion exclusion polymers Ionic liquids Acidic solvents

Acknowledgements Coworkers : Jeff Owrutsky Dan Weidinger Doug Brown Mike Pomfret Dan Steinhurst National Research Council Office of Naval Research

IR Pump/Probe Spectroscopy OPADFG monochromator Sample cell polarizer to lock-in amp, computer 120 fs, kHz, Ti:Sapphire Regenerative Amplifier IR detector Two-color ultrafast (200 fs, 5 μJ) IR (~2000 cm -1 ) Broadband IR pump Broadband IR frequency-resolved probe T 1 by excited state (v=1→2) decay and (v=0→1) bleach recovery. Energy Levels V=0 V=1 V=2 Vibrational Energy Relaxation (VER)