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Vibrational predissociation spectroscopy of the CO2 reduction intermediate HCO2¯
Helen K. Gerardi1, Andrew F. DeBlase1, Xiaoge Su2, Kenneth D. Jordan2, Anne B. McCoy3, and Mark A. Johnson1 1Sterling Chemistry Laboratory, Yale University, P.O. Box , New Haven, CT 06520, 2Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, 3Department of Chemistry, The Ohio State University, Columbus, OH 43210 66th International Symposium on Molecular Spectroscopy The Ohio State University 6/23/2011
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Conversion of CO2 to Fuels
Products catalyst CO2 Introduction | Section 1 | Section 2 | Section 3 | Section 4
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Reduction of CO2 Yields HCO2¯ Intermediate
Reaction Intermediate h ZnO2/H2 CO2 Introduction | Section 1 | Section 2 | Section 3 | Section 4 Yoshida and coworkers, J. Chem. Soc., Faraday Trans., 1998 Reaction Intermediate Innocent et. al, J Appl Electrochem, 2009
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Brief History of Vibrational Spectra of HCO2¯
Forney, Jacox, Thompson, J. Chem. Phys, 2003 Kidd and Mantsch, Journal of Molecular Spectroscopy, 1981 Na+HCO2¯ HCO2¯ COa COs CH OCOb Introduction | Section 1 | Section 2 | Section 3 | Section 4 3600 4000 3200 2800 2400 1200 800 400 2000 1600 Wavenumbers (cm-1) Why is CH so responsive to environment?
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Experimental Method: Vibrational Predissociation Spectroscopy
Supersonic Expansion Ar / HCOOH hν Reflectron Detector Introduction | Section 1 | Section 2 | Section 3 | Section 4 Mass Gate Ion Optics Reflectron (secondary mass separation) 1 keV Electron Gun
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Gas-phase Structure of Isolated Formate Ion
HCO2¯ MP2/aug-cc-pVTZ Calc. Intensity ωCH ωCOs ωCOa Introduction | Section 1 | Section 2 | Section 3 | Section 4 250 cm-1 HCO2¯ νCOa Ar Prediss. Yield νCH νCOs 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 Photon Energy (cm-1)
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Gas-phase Structure of Isolated Formate Ion
HCO2¯ MP2/aug-cc-pVTZ ωCOa Calc. Intensity ωCH ~250 cm-1 ωCOs νCOa νCOs + νCOa 2νCHb νCOs νCH HCO2¯ Ar Prediss. Yield Introduction | Section 1 | Section 2 | Section 3 | Summary DCO2¯ MP2/aug-cc-pVTZ DCO2¯ Ar Prediss. Yield Photon Energy (cm-1) 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 ωCD ωCOs ωCOa Calc. Intensity Photon Energy (cm-1) 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 2νCHb 2νOOP νCOs + νCOa νCD νCOa νCOs Botschwina and coworkers, PCCP, 2004
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Origin of Weaker Features in Formate IR Spectra
νCOa νCOs HCO2¯ Fermi Fermi Introduction | Section 1 | Section 2 | Section 3 | Summary Ar Prediss. Yield DCO2¯ Photon Energy (cm-1) 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200
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Why so low?...Origin of low-frequency C-H stretch
45000 40000 O C H 35000 C O H¯ 30000 25000 V(rCH) (cm-1) Introduction | Section 1 | Section 2 | Section 3 | Summary 20000 15000 θOCO fixed = 130° θOCO fixed = 180° 10000 5000 RMP2 -5000 0.5 1.0 1.5 2.0 2.5 3.0 3.5 rCH (Å) *PES scans (RMP2 aug-cc-pVTZ) from Anne B. McCoy– The Ohio State University
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Dissociation Dynamics
θOCO () 80 100 120 140 160 180 200 rCH (Å) 1.0 1.5 2.0 2.5 3.0 10,000 cm-1 20,000 cm-1 30,000 cm-1 40,000 cm-1 50,000 cm-1 60,000 cm-1 H +CO 2 HCO Introduction | Section 1 | Section 2 | Section 3 | Summary *2D plot from RMP2 calculations by Anne B. McCoy
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Electrostatic Potentials Depict Charge Migration
rCH 2.5 Å rCH 1.9 Å 2 Å 1.8 Å rCH Introduction | Section 1 | Section 2 | Section 3 | Summary 1.7 Å 1.5 Å 1.6 Å 1 Å
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Response of C-H stretch frequency with solvation
D HCO2¯·HCOOH 2632 Na+HCO2¯ 2553 HCO2¯·H2O Introduction | Section 1 | Section 2 | Section 3 | Summary Predissociation Yield 2465 HCO2¯·Ar2 Photon Energy (cm-1) 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 2449 HCO2¯·Ar
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Response of C-H stretch frequency with solvation
50000 40000 Na+HCO2¯ 30000 V(rCH) (cm-1) HCO2¯· H2O Introduction | Section 1 | Section 2 | Section 3 | Summary 20000 relaxed 10000 0.5 1.0 1.5 2.0 2.5 3.0 3.5 rCH (Å) *PES scans (RMP2 aug-cc-pVTZ) from Anne B. McCoy– The Ohio State University
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Summary The vibrational spectrum of isolated HCO2¯ is reported for the first time with both experimental transition energies and intensities Weaker features are described through Fermi resonances between both CH/D bends (out-of-plane and in-plane) and the CH/D stretch as well as a combination band involving the symmetric and asymmetric CO stretches The unexpectedly low frequency of the CH stretch in the formate ion is due to preferential dissociation to lower energy asymptote – production of neutral CO2 and hydride (H¯) for isolated formate. The solvent response of the CH stretching frequency toward higher energy is linked to charge retention on the CO2 component for longer C-H distances.
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Acknowledgments rCH z Mark A. Johnson Anne B. McCoy Kenneth D. Jordan
Andrew DeBlase Christopher Leavitt Rachael Relph Etienne Garand Kristin Breen Mike Kamrath Arron Wolk Gary Weddle I’d like to thank my advisor Mark Johnson and the entire Johnson lab. In particular, Andrew DeBlase who worked closely on this project with me. I also want to thank our theoretical collaborators Anne McCoy and Ken Jordan. And a big thanks of course to the organizations that funded this research. Anne B. McCoy Kenneth D. Jordan Department of Energy National Science Foundation
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