Real time mapping of methyl iodide dissociation at a conical intersection
Real time mapping of methyl iodide dissociation at a conical intersection lead image
Attosecond core-to-valence ultraviolet absorption spectroscopy is an effective tool to follow the electronic and structural changes that occur in chemical reactions. Direct probing of the valence shell during transitions from specific core orbitals allows for analysis of the bonding configuration and electronic state of the system.
Chang et al sought to clarify wave packet dynamics through a conical intersection encountered during the molecular fragmentation of methyl iodide, or CH3I.
Conical intersections are quite common in nature, including the visional processes in the human eye and the resilience of DNA against radiation damage. Despite their ubiquitous occurrence, molecular dynamics at conical intersections are relatively unexplored due to the ultrafast time resolution required to capture them directly.
“This work represents a key technological benchmark in observing ultrafast conical intersection dynamics,” said co-author Kristina Chang.
Researchers used a combination of femtosecond ultraviolet pump pulses and attosecond extreme ultraviolet probe pulses to map the dissociation of CH3I. Typically, this reaction occurs so quickly (around 10 to 20 femtoseconds) that direct experimental observations are challenging. Using significantly shorter ultraviolet pulses allows for observation of spectral signatures of wave packet bifurcation along distinct valence-excited states.
Chang notes attosecond transient absorption spectroscopy could be used to explore the systematic measurement of dynamics in molecules that vary only slightly in their chemical structure.
“Such an experiment would help to explore the role of chemical structure on the reaction dynamics of molecules,” said Chang.
Source: “Mapping wave packet bifurcation at a conical intersection in CH3I by attosecond XUV transient absorption spectroscopy,” by Kristina F. Chang, Han Wang, Sonia M. Poullain, David Prendergast, Daniel M. Neumark, and Stephen R. Leone. “Journal of Chemical Physics” (2021). The article can be accessed at https://doi.org/10.1063/5.0056299 .
This paper is part of the Special Collection in Honor of Women in Chemical Physics and Physical Chemistry and is dedicated to Eileen Spain for her contributions to undergraduate education in physical chemistry. Learn more about the collection here .
