Determining Transition-State Geometries in Liquids Using 2D-IR
James F. Cahoon,
Karma R. Sawyer,*
Jacob P. Schlegel,*
Charles B. Harris
Many properties of chemical reactions are determined by the
transition state connecting reactant and product, yet it is
difficult to directly obtain any information about these short-lived
structures in liquids. We show that two-dimensional infrared
(2D-IR) spectroscopy can provide direct information about transition
states by tracking the transformation of vibrational modes as
a molecule crossed a transition state. We successfully monitored
a simple chemical reaction, the fluxional rearrangement of Fe(CO)
5,
in which the exchange of axial and equatorial CO ligands causes
an exchange of vibrational energy between the normal modes of
the molecule. This energy transfer provides direct evidence
regarding the time scale, transition state, and mechanism of
the reaction.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: cbharris{at}berkeley.edu
