1. Time-Resolved Frequency Comb Spectroscopy of Transient Free Radicals in the Mid-IR Bryce J Bjork, Adam J. Fleisher, Bryan Changala, Thinh Quoc Bui, Kevin Cossel, Mitchio Okumura, Jun Ye ISMS, June 16, 2014 JILA, NIST and University of Colorado at Boulder

2. Introduction Transient Radical Chemistry – The OH+CO Reaction and the HOCO Radical Our Mid-IR Frequency Comb Spectrometer – Time-Resolved Comb Spectroscopy DOCO Radical Chemistry – Experiment – Results

3. Transient Radical Chemistry Smith, I. & Zellner, R. Rate Measurements of Reactions of OH by Resonance Absorption. (1973). Atmospheric Chemistry: Recycles OH to HO 2 in the atmosphere. Combustion Chemistry: Primary route for conversion of CO to CO 2. Major fraction of heat released. not linear… (non- Arrhenius) trans- and cis-HOCO Intermediates Francisco, J. S., Muckerman, J. T. & Yu, H.-G. HOCO radical chemistry. Acc. Chem. Res. 43, 1519–26 (2010).

4. Optical Frequency Combs can help! Transient Radical Chemistry Radicals are difficult to study! Produced in small concentrationsRequires high sensitivity Short LifetimesRequires high time resolution Many chemicals participate in reactionRequires broad bandwidth

5. Time (log scale) Wavenumber grating Mid-IR Camera Mid-IR Comb Spectroscopy 1.Mid-IR Frequency Comb Source 2.Optical Enhancement Cavity 3.Spatially Dispersive VIPA Spectrometer (1) (2) (3) VIPA etalon

6. The Mid-IR Comb Source 1/136 MHz  o  +  oo f Fourier Transform Centered at 3.7 μm Bandwidth ~ 300 nm 1. Mid-IR Frequency Comb Source 10 W Comb at 1 μm Synchronously Pumped OPO Mid-Infrared Radiation tunable between 3-5μm (1) (2) (1) (2)

7. DOCO Band The Interaction Cell M1M2 N 2 purge 193 nm Photolysis Beam Chemical Interaction Region 2. Optical Enhancement Cavity The chemical reaction: 193 nm + Acrylic Acid-d1 DOCOVinyl Radical Deuterated to avoid water lines…

8. VIPA Detection 3. Spatially Dispersive VIPA Spectrometer N 2 reference0.2% N 2 O in N 2 at 40 torr Cavity finesse ~1000 InSb Camera Lots of Temporal Information Ref time Sig 1 Sig 2 Sig 3 Excimer Pulse Camera Integration Window 4 ms Looking for 100 us signal

9. DOCO Experiment Results trans-DOCO Simulation HDO Simulation D 2 O Simulation

10. DOCO Experiment Results D 2 O, HDO, C 2 HD Long Timescale Dynamics trans-DOCO at Short Timescales

11. DOCO Experiment Results Diffusion Acrylic Acid Depletion Long Timescale Dynamics 193 nm + Acrylic Acid-d1 propynal (?) HDO 193 nm + Acrylic Acid-d1 formic acid (?)C 2 HD Isotope Exchange D2OD2O HOD Short Timescale Dynamics C 2 HD and HDO unexpected! They appear immediately following the excimer pulse. Therefore, they are possibly formed from unimolecular dissociation of acrylic acid. Fleisher, A. J. et al. Mid-Infrared Time-Resolved Frequency Comb Spectroscopy of Transient Free Radicals. J. Phys. Chem. (2014).

12. Aleksandra Foltynowicz, Piotr Maslowski, Florian Adler, Oliver Heckl JILA|NIST and CU Lora Nugent-Glandorf, Florian Adler, Tyler Neely, Scott A. Diddams National Institute of Standards and Technology Acknowledgements