Dr. G. Barratt Park

Principal Research Interests

• Velocity-resolved kinetics of reactions at surfaces
• Chirped-pulse microwave spectroscopy of complex cluster mixtures

Velocity-resolved kinetics of reactions at surfaces: Catalysis is one of the most important technologies for sustainable living in the 21st century. It is involved in the production of 80% of manufactured goods, it is responsible for 40% of the nitrogen atoms found in food worldwide, and it is crucial for curbing the emission of pollutants and greenhouse gases. However, despite its importance to our society, a predictive understanding of heterogeneous catalysis remains elusive, and the development of new catalysts remains largely a trial-and-error endeavor.

State-of-the-art ion imaging techniques used in conjunction with molecular beam and ultrahigh vacuum (UHV) surface science methods allows the kinetics of reactions at surfaces to be studies with unprecedented accuracy, elucidating the site-specific kinetics of elementary reaction steps. Detailed measurements of the rates of the most important elementary reactions will allow large-scale surface-catalyzed reaction systems to be understood from first principles, opening the possibility of a bottom-up approach to the design of heterogeneous catalysts.

Chirped-pulse microwave spectroscopy: Rotational spectroscopy in the microwave region is the most precise method for determining the three-dimensional structure of a molecule or cluster. The chirped-pulse technique revolutionized microwave spectroscopy in the last decade because it dramatically increases the rate at which broadband spectra can be acquired. Because the technique is coherent and frequency-flexible, it opens the door to a smorgasbord of unexplored possibilities based on automated pulse sequences, analogous to methods that have reached maturity after decades of development by the NMR community.

Compared with most other forms of spectroscopy, gas-phase microwave experiments provide far superior ability to resolve spectral lines arising from different chemical species. A chemical species can therefore be easily and unambiguously resolved and identified, even in complex mixtures containing 100s or 1000s of components, making the technique ideally suited to the study of clusters. The challenge lies in assigning the frighteningly complicated pattern of lines that result. My research will address this issue by applying highly sensitive multiple-resonance techniques to provide automated assignments. Research targets include micro-solvated molecules in water clusters, whose study elucidates the fundamental mechanism of aqueous solvation. For example, the world's "tiniest drop of acid" (the (H₂O)₄·HCl cluster) could serve as a model for understanding zwitterion formation during hydrohalic acid dissociation.

Representative Publications

1. J. Quan, Y. Chang Z. Li, Y. Zhao, Z. Luo, Y. Wu, S. Zhang, Z. Chen, J. Yang, K. Yuan, X. Yang, B. C. Krüger, D. Schwarzer, A. M. Wodtke, G. B. Park. “A free electron laser-based 1+1′ Resonance-Enhanced Multiphoton Ionization scheme for rotationally resolved detection of OH radicals with correct relative intensities” J. Mol. Spectrosc. 380, 111509, (2021).
2. A. Kastner, G. Koumarianou, P. Glodic, P. C. Samartzis, N. Ladda, S. T. Ranecky, T. Ring, S. Vasudevan, C. Witte, H. Braun, H.-G. Lee, A. Senftleben, R. Berger, G. B. Park, T. Schäfer, T. Baumert. “High-resolution resonance-enhanced multiphoton photoelectron circular dichroism” Phys. Chem. Chem. Phys. 22, 7404, (2020).
3. K. Prozument, J. H. Baraban, P. B. Changala, G. B. Park, R. G. Shaver, J. S. Muenter, S. J. Klippenstein, V. Y. Chernyak, R. W. Field. “Photodissociation transition states characterized by chirped pulse millimeter wave spectroscopy” Proc. Natl. Acad. Sci. USA. 117, 146, (2020).
4. G. B. Park, T. N. Kitsopoulos, D. Borodin, K. Golibrzuch, J. Neugebohren, D. J. Auerbach, C. T. Campbell, A. M. Wodtke. “The kinetics of elementary thermal reactions in heterogeneous catalysis” Nat. Rev. Chem. 3, 723, (2019).
5. G. B. Park, B. C. Krüger, D. Borodin, T. N. Kitsopoulos, A. M. Wodtke. “Fundamental mechanisms for molecular energy conversion and chemical reactions at surfaces” Rep. Prog. Phys. 82, 096401, (2019).
6. B. C. Krüger, T. Schäfer, A. M. Wodtke, G. B. Park. “Quantum-state resolved lifetime of triplet (ã ³A₂) formaldehyde” J. Mol. Spectrosc. 362, 61, (2019) Special Issue in Honor of Anthony Merer.
7. R. J. V. Wagner, B. C. Krüger, G. B. Park, M. Wallrabe, A. M. Wodtke, T. Schäfer. “Electron transfer mediates vibrational relaxation of CO in collisions with Ag(111)” Phys. Chem. Chem. Phys. 21, 1650, (2018).
8. R. J. V. Wagner, N. Henning, B. C. Krüger, G. B. Park, J. Altschäffel, A. Kandratsenka, A. M. Wodtke, T. Schäfer. “Vibrational relaxation of highly vibrationally excited CO scattered from Au(111): Evidence for CO− formation” J. Phys. Chem. Lett. 8, 4887, (2017).
9. G. B. Park, B. C. Krüger, S. Meyer, A. M. Wodtke, T. Schäfer. “An axis-specific rotational rainbow in the direct scatter of formaldehyde from Au(111) and its influence on trapping probability” Phys. Chem. Chem. Phys. 19, 19904 ,(2017).
10. B. C. Krüger, G. B. Park, S. Meyer, R. J. V. Wagner, A. M. Wodtke, T. Schäfer. “Trapping-desorption and direct scattering of formaldehyde at Au(111)” Phys. Chem. Chem. Phys.19, 19896, (2017).
11. A. Kastner, T. Ring, B. C. Krüger, G. B. Park, T. Schäfer, A. Senftleben, T. Baumert. “Intermediate state dependence of the photoelectron circular dichroism of fenchone observed via femtosecond resonance-enhanced multi-photon ionization.” J. Chem. Phys. 147, 013926, (2017).
12. G. B. Park, B. C. Krüger, S. Meyer, A. M. Wodtke, T. Schäfer. “A 1+1′ resonance-enhanced multiphoton ionization scheme for rotationally state-selective detection of formaldehyde via the à ¹A₂ ← X̃ ¹A₁ transition.” Phys. Chem. Chem. Phys. 18, 22355–22363, (2016).
13. G. B. Park, R. W. Field. “Perspective: The first ten years of broadband chirped pulse microwave spectroscopy.” J. Chem. Phys. 144, 200901, (2016).
14. G. B. Park, B. C. Krüger, S. Meyer, D. Schwarzer, T. Schäfer. “The ν₆ fundamental frequency of the à state of formaldehyde and Coriolis perturbations in the 3ν₄ level.” J. Chem. Phys. 144, 194308 (2016).
15. G. B. Park, J. Jiang, C. A. Saladrigas, R. W. Field. “Observation of b₂ symmetry vibrational levels of the SO₂ C̃ ¹B₂ state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants.” J. Chem. Phys. 144, 144311, (2016).
16. J. Jiang, G. B. Park, R. W. Field. “The rotation-vibration structure of the SO₂ C̃ ¹B₂ state explained by a new internal coordinate force field.” J. Chem. Phys. 144, 144312, (2016).
17. G. B. Park, J. Jiang, R. W. Field. “The origin of unequal bond lengths in the C̃ ¹B₂ state of SO₂: Signatures of high-lying potential energy surface crossings in the low-lying vibrational structure.” J. Chem. Phys. 144, 144313, (2016).
18. A. H. Steeves, G. B. Park, H. A. Bechtel, J. H. Baraban, R. W. Field. “Communication: Observation of local-bender eigenstates in acetylene.” J. Chem. Phys. 143, 071101, (2015).
19. G. B. Park, C. C. Womack, A. R. Whitehill, J. Jiang, S. Ono, R. W. Field. “Millimeter-wave optical double resonance schemes for rapid assignment of perturbed spectra, with applications to the C̃ ¹B₂ state of SO₂.” J. Chem. Phys. 142, 144201, (2015).
20. G. B. Park, R. W. Field. “Edge effects in chirped-pulse Fourier transform microwave spectra.” J. Mol. Spectrosc. 312, 54, (2015).
21. G. B. Park, J. H. Baraban, A. H. Steeves, R. W. Field “Simplified Cartesian basis model for intrapolyad emission intensities in the bent-to-linear electronic transition of acetylene.” J. Phys. Chem. A 119, 857, (2015).
22. J. M. Oldham, C. Abeysekera, B. Joalland, L. N. Zack, K. Prozument, I. Sims, G. B. Park, R. W. Field, A. G. Suits “A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer: I. The low-temperature flow system.” J. Chem. Phys. 141, 1545202, (2014).
23. C. Abeysekera, L. N. Zack, G. B. Park, B. Joalland, J. M. Oldham, K. Prozument, N. M. Ariyasingha, I. R. Sims, R. W. Field, A. G. Suits. “A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer: II. Performance and applications for reaction dynamics.” J. Chem. Phys. 141, 214203, (2014).
24. G. B. Park. “Full dimensional Franck-Condon factors for the acetylene à ¹A_u — X̃ ¹Σ_g⁺ transition. I. Method for calculating polyatomic linear—bent vibrational intensity factors and evaluation of calculated intensities for the gerade vibrational modes in acetylene.” J. Chem. Phys. 141, 134304, (2014).
25. G. B. Park, J. H. Baraban, R. W. Field. “Full dimensional Franck-Condon factors for the acetylene à ¹A_u — X̃ ¹Σ_g⁺ transition. II. Vibrational overlap factors for levels involving excitation in ungerade modes.” J. Chem Phys. 141, 134305, (2014).
26. K. Prozument, G. B. Park, R. G. Shaver, A. K. Vasiliou, J. M. Oldham, D. E. David, J. S. Muenter, J. F. Stanton, A. G. Suits, G. B Ellison, R. W. Field. “Chirped-pulse millimeter-wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions.” Phys. Chem. Chem. Phys. 16, 15739, (2014).
27. J. Jiang, J. H. Baraban, G. B. Park, M. L. Clark, R. W. Field. “Laser-Induced Fluorescence Study of the S₁ State of Doubly-Substituted ¹³C Acetylene and Harmonic Force Field Determination.” J. Phys. Chem. A 117, 13696, (2013).
28. K. Prozument, R. G. Shaver, M. A. Ciuba, J. S. Muenter, G. B. Park, J. F. Stanton, H. Guo, B. M. Wong, D. S. Perry, R. W. Field. “A new approach toward transition state spectroscopy.” Faraday Discuss. 163, 33, (2013).
29. K. Prozument, A. P. Colombo, Y. Zhou, G. B. Park, V. S. Petrovic, S. L. Coy, R. W. Field. “Chirped-Pulse Millimeter-Wave Spectroscopy of Rydberg-Rydberg Transitions.” Phys. Rev. Lett. 107, 143001, (2011).
30. G. B. Park, A. H. Steeves, K. Kuyanov-Prozument, J. L. Neill, R. W. Field. “Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70-102 GHz region.” J. Chem. Phys. 135, 024202, (2011).
31. G. B. Park, D. M. Brown, M. D. Schuh. “Binary and Ternary Complexes Containing α-Cyclodextrin and Bromonaphthalene Derivatives: A Note of Caution in Interpreting UV Absorption Spectral Data.” J. Phys. Chem. B 110, 22510-22516, (2006).