Research Interests

My group’s research focuses on two interrelated areas of investigation. The first involves the development of theoretical and computational approaches for studying energy flow in chemical systems. We generally focus on systems that have been studied or are currently being studied by our experimental collaborators, or that are potential targets for future experimental investigation. The second involves detailed studies of the targeted systems. These two focuses are clearly interconnected, and often in an effort to elucidate properties of a particular system or process, we find that we need to develop the theoretical and computational tools needed to perform the study.  

More specifically, our research involves studies of energy flow, as probed through spectroscopy and dynamics studies, of molecules, molecular ions, and complexes comprised of small molecules or ions and one or several solvating molecules. These gas phase systems are of interest for several reasons. First, as indicated above, they are systems for which we can make direct connections with experimental studies that are being undertaken by our current and potential future collaborators. A second source of our interest in these small systems comes from the fact that their size makes them amenable to very detailed experimental and theoretical studies. In this way they provide a laboratory through which we can probe fundamental physical phenomena. They also allow us to ask detailed questions relating to atmospheric and combustion chemistry.  

From a purely theoretical prospective, these processes and systems are of particular interest to us because the experimental findings could not be fully interpreted using the computational chemistry tools that are readily available to the chemistry community – specifically running an electronic structure calculation using a commercially available computer program with the appropriate inputs for calculating the vibrational spectrum. As a result, a central goal of my research program has been and continues to be in generating the tools needed to elucidate the experimental signatures of large-amplitude motions.

 

Recent examples

Vibrational Coupling

Studies of the vibrational couplings of the methyl peroxy radical (CH3OO) reveal how the coupling of the torsional and rotational motion with the CH vibrations manifest in the spectral region of the CH stretch fundamentals.

Further Reading:

  1.  Hsu, K.-H.; Huang, Y.-H.; Lee, Y.-P.; Huang, M.; Miller, T. A.; McCoy, A. B. Manifestations of Torsion-CH Stretch Coupling in the Infrared Spectrum of CH3OO. J. Phys. Chem. A 2016, 120, 4827− 4837.
  2. Huang, M.; Miller, T. A.; McCoy, A. B.; Hsu, K.-H.; Huang, Y.-H.; Lee, Y.-P. Modeling the CH Stretch/Torsion/Rotation Couplings in Methyl Peroxy (CH3OO). J. Phys. Chem. A 2017121, 4827− 4837. (Source of image)

 

Electron transfer

A study that probed solvent-induced long-range electron transfer in IBr-·CO2, a general phenomena, but one which could be more deeply investigated through studies of this five atom system.

Further Reading:

  1. Leonid Sheps, Elisa M. Miller, Samantha Horvath, Matthew A. Thompson, Robert Parson, Anne B. McCoy, and W. Carl Lineberger, “Solvent-mediated electron hopping: long-range charge transfer in IBr(CO2),” Science, 328, 220-224 (2010)

 

Hydrogen Bonding and Proton Transfer

A series of studies that focused on connection between hydrogen bond strength, proton transfer and vibrational spectroscopy of the fluoride-water complex and protonated water clusters.

Further Reading:

  1. Samantha Horvath, Anne B. McCoy, Joseph R. Roscioli and Mark A. Johnson, “Vibrationally induced proton transfer in F–.H2O and F–.D2O” Phys. Chem. A 112, 12337-44 (2008). (Source of image)
  2. Conrad T. Wolke, Joseph A. Fournier, Laura C. Dzugan, Matias R. Fagiani, Tuguldur T. Odbadrakh, Harald Knorke, Anne B. McCoy, Kenneth D. Jordan, Knut R. Asmis and Mark A. Johnson, “Spectroscopic snapshots of the proton transfer mechanism in water: Vibrational spectra of frozen protonated water clusters reveal the cooperative structural deformations at the heart of the intermolecular proton transfer event,” Science 354, 1131-1135 (2016).
  3. Chinh H. Duong, Olga Gorlova, Nan Yang, Patrick J. Kelleher, Mark A. Johnson, Anne B. McCoy, Qu Wu and Joel 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. 8, 3782-3789 (2017).

 

Diffusion Monte Carlo

Developments of and extensions to Diffusion Monte Carlo approaches for studying molecular vibrations and rotations.  Molecules of interest have included H5+, CH5+, and protonated and deprotonated water clusters.

Further Reading: 

  1. Jason E. Ford and Anne 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, 645, 15-19 (2016).
  2. Andrew S. Petit, Jason E. Ford and Anne B. McCoy, “Simultaneous Evaluation of Multiple Rotationally Excited States of H3+, H3O+ and CH5+ Using Diffusion Monte Carlo,” J. Phys. Chem. A, 118, 7206-7220 (2014) [K. D. Jordan Festschrift]
  3. Zhou Lin and Anne B. McCoy, “Investigation of the Structure and Spectroscopy of H5+ Using Diffusion Monte Carlo,” J. Phys. Chem. A, 117, 11725-11736 (2013) [Wittig Festschrift]. (Source of image)

 

On-going investigations:

  • Developing the tools necessary to evaluate anharmonic vibrational frequencies “on the fly” using electronic structure theory.
  • Developing quantum/classical approaches to further elucidate the mechanisms of long-range electron transfer.
  • Investigations of the connections between vibrational spectra and molecular vibrations in systems that undergo large amplitude motions, in particular, in ion-water complexes. This work focuses on systems that are important to atmospheric processes.
  • Further developments in Quantum Monte Carlo approaches and their applications