A View from the Middle for Chemical Reactions

Studying the photodetachment of a stable anion provides an experimental-theoretical benchmark of the chemical dynamics.

Laser induced photodetachment is used to turn a stable F¯(H2O) molecule into FH2O to study the “half reaction” processes experimentally and theoretically.
Image courtesy of University of California, San Diego
Laser induced photodetachment is used to turn a stable F-(H2O) molecule into FH2O to study the “half reaction” processes experimentally and theoretically.

The Science

Using a unique experimental approach, researchers teased apart the intermediate chemical pathways for a reaction with four atoms, fluorine and water, F + H2O → HF + OH, and identified how energy is distributed among the products. The resulting details combine both experiment and theory pushing the limits, in terms of complexity, of currently understood reactions involving a maximum of three atoms.

The Impact

The agreement reported for FH2O between highly detailed experiments and full dimensional quantum mechanical simulations provide a benchmark for our current understanding of chemical reactions. Studying how this and other complexes behave offers insight into the underlying mechanisms that govern reactions and provides a roadmap to improve molecular potential energy surfaces necessary for modeling more complex chemical reactions such as those related to combustion.


Studying the dynamics of a chemical reaction usually involves preparing the reactants and collecting the products after the reaction. However, when two particles collide the entire reaction can take place within a few picoseconds (10-12 sec) and cannot simply be paused midway. This poses a challenge to understand the transition-state region, or intermediate steps, where chemical bonds are broken and formed. Researchers at the University of California, San Diego and University of New Mexico found a way to initiate the reaction of F + H2O → HF + OH directly at the transition state for the chemical reaction and analyze the final products. To prepare the short-lived reaction intermediates, the particles are glued together with an excess electron, forming a stable molecular anion. The anion, F-(H2O), is hit by a short laser pulse to detach the electron turning the anion into a metastable FH2O complex that predominantly dissociates to F + H2O and HF + OH. Surprisingly not all FH2O particles immediately dissociated with some of the species surviving microseconds - an eternity in the world of chemical reactions. Extensive computer simulations confirmed these meta-stable species, which are held together by their own vibrations, also known as ‘Feshbach resonances’ that can only be explained with quantum mechanics.


Robert Continetti
University of California, San Diego, Department of Chemistry and Biochemistry
(858) 534-5559

Hua Guo
University of New Mexico, Department of Chemistry and Chemical Biology
(505) 277-1716


DOE Office of Science, Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences Grant DE-FG03-98ER14879 to R.E.C. and DE-FG02-05ER15694 to H.G.

German Academic Exchange Service DAAD (postdoctoral research fellowship to R.O.)

National Natural Science Foundation of China (21303110) (partial support to J.M.)


Otto, R., J. Ma, A.W. Ray, J.S. Daluz, J. Li, H. Guo, R.E. Continetti, “Imaging Dynamics on the F + H2O → HF + OH Potential Energy Surfaces from Wells to Barriers.” Science, 343, 396-399 (2014). [DOI: 10.1126/science.1247424]

Related Links

Continetti Laboratory website

Guo Laboratory website

University of California, San Diego Press Release (third story on page)

University of New Mexico Press Release

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Program: BES , CSGB

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