Associate Professor of Chemistry
Ph.D. Massachusetts Institute of Technology, 2004
The Khalil group aims to understand the ultrafast structural dynamics of light-driven chemical and biological processes in solution. We study how transient molecular configurations on relevant electronic surfaces and their interactions with the surrounding solvent dictate the course of chemical reactions. Our goal is to design experiments that are sensitive to the details of the electronic and atomic structural rearrangements as the reaction of interest evolves over decades in time.
Current problems of interest include: (i) mapping intra and inter-molecular vibrational phase and energy relaxation on excited electronic states during charge transfer processes and photolysis in solution; (ii) deciphering the electronic and structural basis for light-induced molecular changes in coordination compounds in the condensed phase; and (iii) unraveling the complex interactions between natural chromophores and their protein hosts that leads to optical signals being converted to large scale atomic motions. These problems are important both from a basic science perspective and for designing new materials and molecular devices.
To study these problems, we use and develop multidimensional vibrational and electronic spectroscopies along with ultrafast x-ray absorption spectroscopy. Multidimensional spectroscopy probes time-dependent vibrational and electronic couplings and relative orientations between interacting chemical moieties. These observables quantify physical parameters of the chemical system, such as conformational heterogeneity, phase and energy relaxation dynamics and solute-solvent interactions. Ultrafast x-ray absorption spectroscopy is an ideal tool for understanding local time-dependent phenomena accompanying chemical processes in solution as it provides element-specific information about electronic and structural rearrangements with sub-angstrom resolution. The x-ray experiments are performed at the Advanced Light Source located at Lawrence Berkeley National Laboratory.
“Probing the electronic structure of a photoexcited solar cell dye with transient X-ray absorption spectroscopy” Van Kuiken, B.E.; Strader, M.L.; Cho, H.; Lynch, M.S.; Huse, N.; Schoenlein, R.W.; Khalil, M., J. Phys. Chem. Lett. 2012, 3 (12): 1695.
“Probing non-equilibrium vibrational relaxation pathways of highly excited CºN stretching modes following ultrafast back-electron transfer” Lynch, M.S.; Slenkamp, K.; Khalil, M. J. Chem. Phys. 2012, 136 (24): 241101.
“Coherent Fifth-Order Visible–Infrared Spectroscopies: Ultrafast Non-Equilibrium Vibrational Dynamics in Solution” Lynch, M.S.; Slenkamp, K.; Cheng, M.; Khalil, M. J. Phys. Chem. A 2012, 116 (26): 7023.
“Generation of tunable octave-spanning mid-infrared pulses by filamentation in gas media” Cheng, M.; Reynolds, A.; Widgren, H.; Khalil, M. Optics Letters 2012, 37 (11): 1787.
“On the Role of High-Frequency Intramolecular Vibrations in Ultrafast Back-Electron Transfer Reactions” Lynch, M.S.; Van Kuiken, B.E.; Daifuku, S.L.; Khalil, M. J. Phys. Chem. Letters 2011, 2: 2252.
“Probing the Photoinduced Metal-Nitrosyl Linkage Isomerism of Sodium Nitroprusside in Solution Using Transient Infrared Spectroscopy” Lynch, M.S.; Cheng, M.; Van Kuiken, B.E.; Khalil, M. J. Am. Chem. Soc. 2011, 133 (14): 5255.