Professor of Chemistry
Deputy Editor, Journal of Physical Chemistry A
Ph.D. University of Wisconsin–Madison, 1992
(Theoretical Physical Chemistry)
Research in the McCoy group focuses on two interrelated areas of investigation. The first involves the development of theoretical and computational approaches that allow us to investigate molecules and complexes that undergo large amplitude vibrational motions even at low-levels of excitation. These are processes that are important in a variety of contexts, including systems of interest in astrochemistry, atmospheric chemistry, and in combustion processes. They also allow us probe more fundamental phenomena, such as hydrogen bonding or long-range charge transfer. These represent systems for which standard tools are insufficient, making them particularly interesting from a theoretical perspective. In choosing problems to study, we focus on systems that have been studied or are currently being studied by our experimental collaborators, or are potential targets for future experimental investigation.
One method on which we have focused much of our attention is Diffusion Monte Carlo. While this approach is more commonly used in electronic structure calculations, it is very well suited for studies of vibrational dynamics. We recently extended its application to studies of rotations as well as to couplings of rotations and torsions in H5+ (Figure 1) and CH5+, two molecules of astrochemical interest, and helium delocalization in complexes with NH4+H2O (Figure 2).
Our second area of focus involves conducting detailed studies of specific systems that have been studied experimentally. Recent examples of work in this area include studies of the origins of broadening in the spectrum of hydrogen bonded systems, specifically CaOH+ complexes with water molecules (Figure 3), or energy flow in CH3+CHOO, an important reaction intermediate. These studies often focus on the manifestations of anharmonicity in vibrational spectroscopy.
Interconnections between these two areas of focus are frequently reaffirmed in our research; we often find, in our efforts to elucidate properties of a particular system or process, that we also need to develop the theoretical and computational tools to perform the study.
S. M. Craig, F. S. Menges, C. H. Duong, J. K. Denton, L. R. Madison, A. B. McCoy, M. A. Johnson. Hidden role of intermolecular proton transfer in the anomalously diffuse vibrational spectrum of a trapped hydronium ion. Proc. Nat. Acad. Sci. USA 2017, E4706–E4713.
C. H. Duong, O. Gorlova, N. Yang, P. J. Kelleher, M. A. Johnson, A. B. McCoy, Q. Wu, J. M. Bowman. Disentangling the Complex Vibrational Spectrum of the Protonated Water Trimer, H+(H2O)3, with Two-Color IR-IR Photodissociation of the Bare Ion and Anharmonic VSCF/VCI Theory. J. Phys. Chem. Lett. 2017, 8, 3782–3789.
C. T. Wolke; J. A. Fournier; L. C. Dzugan; M. R. Fagiani; T. T. Odbadrakh; H. Knorke; K. D. Jordan; A. B. McCoy; K. R. Asmis; M. A. Johnson. Spectroscopic snapshots of the proton-transfer mechanism in water. Science 2016, 354, 1131–1135.
Y. Fang; F. Liu; V. P. Barbre; S. J. Klippenstein; A. B. McCoy; M. I. Lester. Communication: Real time observation of unimolecular decay of Criegee intermediates to OH radical products. J. Chem. Phys. 2016, 144 (6), 061102/1–4.
J. E. Ford; A. B. McCoy. Calculating Rovibrationally Excited States of H2D+and HD2+ by Combination of Fixed Node and Multi-State Rotational Diffusion Monte Carlo. Chem. Phys. Lett. 2016, 645, 15–19.
K.-H. Hsu; Y.-H. Huang; Y.-P. Lee; M. Huang; T. A. Miller; A. B. McCoy. Manifestations of Torsion−CH Stretch Coupling in the Infrared Specrum of CH3OO. J. Phys. Chem. A 2016, 120, 4827−4837.
M. L. Marlett; Z. Lin; A. B. McCoy. Rotation/Torsion Coupling in H5+, D5+, H4D+, and HD4+ Using Diffusion Monte Carlo. J. Phys. Chem. A 2015, 119, 9405−9413.
F. Liu; J. M. Beames; A. S. Petit; A. B. McCoy; M. I. Lester. Infrared-driven unimolecular reaction of CH3CHOO Criegee intermediates to OH radical products. Science 2014, 345, 1596–1598.