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

Link to Full Publication List: Publications

1. J. Quan, R. Yin, Z. Zhao, X. Yang, A. Kandratsenka, D. J. Auerbach, A. M. Wodtke, H. Guo, G. B. Park. “Highly Rotationally Excited N₂ Reveals Transition-State Character in the Thermal Decomposition of N₂O on Pd(110)” J. Am. Chem. Soc., 145, 12044‒12050 (2023).
2. Z. Zhao, Y. Wang, X. Yang, J. Quan, B. C. Krüger, P. Stoicescu, R. Nieman, D. J. Auerbach, A. M. Wodtke, H. Guo, G. B. Park. “Spin-dependent reactivity and spin-flipping dynamics in O atom scattering from Graphite” Nature Chemistry, 15, 1006‒1011 (2023).
3. D. Borodin, N. Hertl, G. B. Park, M. Schwarzer, J. Fingerhut, Y. Wang, J. Zuo, F. Nitz, G. Skoulatakis, A. Kandratsenka, D. J. Auerbach, D. Schwarzer, H. Guo, T. N. Kitsopoulos, A. M. Wodtke. “Quantum effects in thermal reaction rates at metal surfaces” Science, 377, 146, 394–398 (2022).
4. S. T. Ranecky, G. B. Park, P. C. Samartzis, I. C. Giannakidis, D. Schwarzer, A. Senftleben, T. Baumert, T. Schäfer. “Detecting chirality in mixtures using nanosecond photoelectron circular dichroism” Phys. Chem. Chem. Phys. 24, 2758–2761, (2022).
5. 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).
6. 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).
7. 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).
8. 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).
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. G. B. Park, R. W. Field. “Perspective: The first ten years of broadband chirped pulse microwave spectroscopy.” J. Chem. Phys.144, 200901, (2016).
11. 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).
12. 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).
13. 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).
14. 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).
15. 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).