The prospects for making sense of dynamics in liquids have improved dramatically in the recent years. With the advent of ultrafast lasers has come the ability to look at times short enough that the painful complications have barely begun to set in. Our own work has been focused on developing a theoretical understanding of this ultrafast dynamics. In particular, we are hoping to discern the molecular mechanisms of events such as solvation and vibrational relaxation -- the elementary steps that determine the course of chemical reactions in liquids.

Motion in liquids is an intrinsically complicated business. One might not say the same of gases, which are easily thought of in terms of sharp, well-defined collisions between molecules, or of crystalline solids, where the periodicity of the crystal lattice makes the dynamics almost as simple as that seen in gases. Molecules in liquids, by contrast, are constantly disordered and in a perpetual state of collision, making it difficult to understand processes such as chemical reactions in liquids.

What we have been engaged in over the last several years is a theoretical effort to get at the most elementary, short-time, events in liquid dynamics. We have discovered that it is possible to compute what one might call the instantaneous normal modes of a liquid, and that these modes can serve as a powerful entry into the elementary events in liquids. Partitioning these modes into components arising from nearby and distant solvents and from solvent translation and libration, for example, has made it clear that the ultrafast solvation is accomplished most easily in polar solvents by reorienting selected, neighboring, solvent molecules. Moreover, analyzing the important modes for each instantaneous configuration of the liquid has revealed that a sizeable fraction of the prompt dynamics in both nonpolar solvation and vibrational population relaxation arises from a relatively small number of modes -- and that the main function of most of these is to move just a single solvent molecule at a time. It seems, then, that the complexities of liquid dynamics do indeed begin to disappear at short times. Our group is actively engaged in pursuing the spectroscopic consequences of these findings.

In parallel with this effort, we have begun to look at a variety of nonlinear ultrafast spectroscopies to see if having an insight into the organization of liquid motion helps us understand the molecular lessons of these new spectroscopies. Optical-Kerr-effect spectroscopy of liquids can, in principle, measure the very intermolecular vibrations that we have been studying, and two-dimensional ("fifth-order") Raman spectroscopy even has the potential to look directly at the coherence of these vibrations. But can we tease out of these spectra any of the genuinely microscopic information that we want? We are working with these and other kinds of novel spectroscopies trying to ascertain what each kind of measurement reveals about liquid dynamics.

National Science Foundation, Exploring the Connections between the Nonlinear Spectroscopy and the Potential Energy Landscapes of Liquids ; $435,000; 5/1/13-4/30/16

National Science Foundation: Exploring the Ultrafast Dynamics of Liquids Through the Next Generation of Solvation Spectroscopies ; $420,000; 8/1/08 - 7/31/12

National Science Foundation: Anharmonicities and Nonlinearities in the Ultrafast Dynamics of Liquids ; $420,000; 8/1/05 - 7/31/08

X. Sun, B. M. Ladanyi, and R. M. Stratt, J. Phys. Chem. B 119, 9129 (2015).  The effects of electronic-state-dependent solute polarizability: Application to solute-pump/solvent-probe spectra. (2014 American Chemical Society Editors' Choice article.)

L. Frechette, D. Jacobson, and R. M. Stratt, J. Chem. Phys. 141, 209902 (2014).  Erratum: "The inherent dynamics of a molecular liquid: Geodesic pathways through the potential energy landscape of a liquid of linear molecules. [J. Chem. Phys. 140, 174503 (2014)] "

Q. Ma and R. M. Stratt, Phys. Rev. E 90, 042314 (2014).  The potential energy landscape and inherent dynamics of a hard-sphere fluid.

D. Jacobson and R. M. Stratt, J. Chem. Phys. 140, 174503 (2014). The inherent dynamics of a molecular liquid: Geodesic pathways through the potential energy landscape of a liquid of linear molecules.

X. Sun and R. M. Stratt, J. Chem. Phys. 139, 044506 (2013). How a solute-pump/solvent-probe spectroscopy can reveal structural dynamics: Polarizability response spectra as a two-dimensional solvation spectroscopy.

X. Sun and R. M. Stratt, Phys. Chem. Chem. Phys. 14, 6320 (2012). The molecular underpinnings of a solute-pump/solvent-probe spectroscopy: The theory of polarizability response spectra and an application to preferential solvation.

C. N. Nguyen, J. I. Isaacson, K. B. Shimmyo, A. Chen, and R. M. Stratt, J. Chem. Phys. 136, 184504 (2012). How dominant is the most efficient pathway through the potential energy landscape of a slowly diffusing disordered system?

B. Zhang and R. M. Stratt, J. Chem. Phys. 137, 024506 (2012). Vibrational energy relaxation of large-amplitude vibrations in liquids.

X. Liang, M. G. Levy, S. Deb, J. D. Geiser, R. M. Stratt, and P. M. Weber, J. Mol. Struct. 978, 250 (2010). Electron diffraction with bound electrons: The structure sensitivity of Rydberg fingerprint spectroscopy.

C. N. Nguyen and R. M. Stratt, J. Chem. Phys. 133, 124503 (2010). Preferential solvation dynamics in liquids: How geodesic pathways through the potential energy landscape reveal mechanistic details about solute relaxation in liquids. (2010 Editors' Choice paper)

G. Tao and R. M. Stratt, J. Phys. Chem. B 112, 369 (2008). The anomalously slow solvent structural relaxation accompanying high-energy rotational relaxation.

R. M. Stratt, Science 321, 1789 (2008). Nonlinear thinking about molecular energy transfer.

C. Wang and R. M. Stratt, J. Chem. Phys. 127, 224503 (2007). Global perspectives on the energy landscapes of liquids, supercooled liquids, and glassy systems: The potential energy landscape ensemble.

C. Wang and R. M. Stratt, J. Chem. Phys. 127, 224504 (2007). Global perspectives on the energy landscapes of liquids, supercooled liqids, and glassy systems: Geodesic pathways through the potential energy landscape.

A. C. Moskun, A. E. Jailaubekov, S. E. Bradforth, G. Tao, and R. M. Stratt. Science 311, 1907 (2006). Rotational coherence and a sudden breakdown in linear response seen in room-temperature liquids.

G. Tao and R. M. Stratt, J. Phys. Chem. B 110, 976 (2006). Why does the intermolecular dynamics of liquid biphenyl so closely resemble that of liquid benzene? Molecular dynamics simulation of the optical-Kerr-effect spectra.

G. Tao and R. M. Stratt, J. Chem. Phys. 125, 114501 (2006). The molecular origins of nonlinear response in solute energy relaxation: The example of high-energy rotational relaxation

A. Ma and R. M. Stratt, J. Chem. Phys. 121, 11217 (2004). Multiphonon vibrational relaxation in liquids: Should it lead to an exponential-gap law?

Polly B. Graham, Kira JM Matus, and Richard M. Stratt, J. Chem. Phys. 121, 5348 (2004). The workings of a molecular thermometer: The vibrational excitation of carbon tetrachloride by a solvent.

S. Ryu, R. M. Stratt, K. K. Baeck, and P. M. Weber, J. Phys. Chem. A 108, 1189 (2004). Electron diffraction of molecules in specific quantum states: A theoretical study of vibronically excited s-tetrazine.

P. M. Weber, R. C. Dudek, S. Ryu, and R. M. Stratt, Experimental and theoretical studies of pump-probe electron diffraction: time-dependent and state-specific signatures in small cyclic molecules, in FEMTOCHEMISTRY and FEMTOBIOLOGY: Ultrafast Events in Molecular Science, edited by M. M. Martin and J. T. Hynes (Elsevier, Amsterdam, 2004).

S. Ryu and R. M. Stratt, J. Phys. Chem. B 108, 6782 (2004). A case study in the molecular interpretation of optical Kerr effect spectra: Instantaneous-normal-mode analysis of the OKE spectrum of liquid benzene.

A. Ma and R. M. Stratt, J. Chem. Phys. 119, 8500 (2003). Selecting the information content of two-dimensional Raman spectra in liquids.

A. Ma and R. M. Stratt, J. Chem. Phys. 119, 6709 (2003). Multiphonon vibrational relaxation in liquids: An exploration of the idea and of the problems it causes for molecular dynamics algorithms.

S. Ryu, R. M. Stratt, and P. M. Weber, J. Phys. Chem. A 107, 6622 (2003). Diffraction signals of aligned molecules in the gas phase: Tetrazine in intense laser fields.

Ao Ma and R. M. Stratt, Bull. Kor. Chem. Soc. 24, 1126 (2003) (special issue on Multidimensional Vibrational Spectroscopy). What do we learn from two-dimensional Raman spectra by varying the polarization conditions?

Y. Deng, B. M. Ladanyi, and R. M. Stratt, J. Chem. Phys. 117, 10752 (2002). High-frequency vibrational energy relaxation in liquids: The foundations of instantaneous-pair theory and some generalizations.

Ao Ma and R. M. Stratt, J. Chem. Phys. 116, 4972 (2002). The molecular origins of the two-dimensional Raman spectrum of an atomic liquid. II. Instantaneous-normal-mode theory.

Ao Ma and R. M. Stratt, J. Chem. Phys. 116, 4962 (2002). The molecular origins of the two-dimensional Raman spectrum of an atomic liquid. I. Molecular dynamics simulation.

Y. Deng and R. M. Stratt, J. Chem. Phys. 117, 1735 (2002). Vibrational energy relaxation of polyatomic molecules in liquids: The solvent's perspective.

R. M. Stratt, The Molecular Mechanisms Behind the Vibrational Population Relaxation of Small Molecules in Liquids, in Ultrafast Infrared and Raman Spectroscopy, edited by M. D. Fayer (Marcel Dekker, New York, 2001).

J. Jang and R. M. Stratt, J. Chem. Phys. 113, 11212 (2000). Dephasing of Individual Rotational States in Liquids.

J. Jang and R. M. Stratt, J. Chem. Phys. 113, 5901 (2000). Rotational Energy Relaxationof Individual Rotational States in Liquids.

Ao Ma and R. M. Stratt, Phys. Rev. Lett. 84, 1004 (2000). The Fifth-Order Raman Spectrum of an Atomic Liquid: Simulation and Instantaneous-Normal-Mode Calculation.

J. Jang and R. M. Stratt, J. Chem. Phys. 112, 7538 (2000). The short-time dynamics of molecular reorientation in liquids. II. The microscopic mechanism of rotational friction.

J. Jang and R. M. Stratt, J. Chem. Phys. 112, 7524 (2000). The short-time dynamics of molecular reorientation in liquids. I. The instantaneous generalized Langevin equation.

S. Ryu, P. M. Weber, and R. M. Stratt, J. Chem. Phys. 112, 1260 (2000). The diffraction signatures of individual vibrational modes in polyatomic molecules.

National Science Foundation Postdoctoral Fellowship 1980
Alfred P. Sloan Foundation Fellow, 1985-1989
Fulbright Scholar, 1991-1992
Elected Fellow of the American Physical Society, 1997
Harrison S. Kravis University Professor 1999-2000
Newport Rogers Professor in Chemistry, 2004-
Philip J. Bray Award for Excellence in Teaching in the Physical Sciences, 2010
Elected Fellow of the American Chemical Society, 2013

American Chemical Society's Joel Henry Hildebrand Award in the Theoretical and Experimental Chemistry of Liquids, 2022

Awards to research group:

Materials Research Society Student Award - 1985 (V. Dobrosavljevic)
American Physical Society Apker Award - 1990 (S. Simon)

American Chemical Society
Chair, Theoretical Subdivision, 1998-1999
Chair, Physical Chemistry Division, 2001-2002

American Physical Society

Courses taught include introductory chemistry and a range of undergraduate and graduate physical chemistry courses.

We are also always interested in having undergraduate students working with our research group.