SSCU Seminar
Name: Dr. Krupa Ramasesha
Affiliation: Principal Investigator, Sandia National Laboratories, Livermore, California, USA
Title: Molecular Control of Ultrafast Energy Redistribution in Complex Materials
Date & Time: Thursday, 19th November 2026 at 11:30 a.m.
Venue: A-104 Lecture Hall, First Floor, Chemical Sciences Building
Abstract:
Photoexcitation drives molecular materials and molecule–metal interfaces away from equilibrium, launching ultrafast energy flow that determines the onset of chemistry. In this seminar, I will discuss how broadband ultrafast spectroscopy, combined with electronic structure theory, reveals early-time mechanisms of energy redistribution in energetic molecular solids and at functionalized metal surfaces.
I will begin with energetic materials, where a central question is how vibrational energy transfer between molecular vibrations and lattice phonons contributes to shock-driven reaction initiation. Broadband infrared spectroscopy under static compression reveals mode-selective, multistage vibrational energy transfer that remains incomplete out to hundreds of picoseconds and is strongly modulated by intermolecular interactions, pressure, and polymorphic phase. I will then turn to interfacial dynamics in self-assembled monolayers of 4-mercaptobenzoic acid on gold. Following interband excitation of Au nano-islands, ultrafast UV-visible transient absorption spectroscopy shows that molecular adsorption substantially prolongs electron–phonon and phonon–phonon relaxation. First-principles calculations suggest that coupling between Au acoustic phonons and molecular vibrations slows energy dissipation at the metal–molecule interface.
Together, these studies examine how nonequilibrium energy flow is shaped by molecular structure, intermolecular coupling, and local environment. By resolving these early-time pathways, this work provides molecular-level insight into how complex materials dissipate and redirect energy flow following impulsive excitation.
Biographical Sketch:
Dr. Krupa Ramasesha is a principal investigator at Sandia National Laboratories in Livermore, California, where she leads a research program on ultrafast dynamics in gas-phase, condensed-phase, and interfacial systems. The work in the Ramasesha group spans gas-phase photophysics and photochemistry, charge and energy transfer across plasmonic metal–molecule interfaces, and electronic and vibrational dynamics in molecular solids, including energetic materials and organic semiconductors. The group uses a suite of ultrafast methods, including table-top soft X-ray spectroscopy, ultrafast electron diffraction at SLAC MeV-UED, and broadband infrared and UV-visible transient absorption spectroscopy, with interpretation supported by collaborations with theorists.
Dr. Ramasesha received her B.S. in Chemistry from the University of Wisconsin–Madison, where she studied solution-phase photoisomerization and bimolecular reaction dynamics. She earned her Ph.D. at the Massachusetts Institute of Technology, investigating hydrogen-bonding and proton-transfer dynamics with ultrafast broadband multidimensional infrared spectroscopy. She then conducted postdoctoral research at the University of California, Berkeley, studying electron dynamics in semiconductors using attosecond soft X-ray spectroscopy, and at Sandia National Laboratories, investigating chemical reaction kinetics with synchrotron-based multiplexed photoionization mass spectrometry.
Her honors include the Fulbright U.S. Scholar Award/Fulbright-NAWI Graz Visiting Professorship, the U.S. Department of Energy Early Career Award, the Journal of Physical Chemistry/American Chemical Society Physical Chemistry Division Lectureship, and the MIT Presidential Fellowship. She serves on the Editorial Advisory Boards of the Journal of Chemical Physics and the Journal of Physical Chemistry A/B/C, the User Committee of the NSF National eXtreme Ultrafast Science facility, and the Proposal Review Panel for the Linac Coherent Light Source at Stanford.