KubarychGroup

 

Timing Energy Flow

 

Energy is the currency of chemical transformations. At equilibrium, energy is largely thought of as being randomly distributed among all possible degrees of freedom. Away from equilibrium, however, we lose many of the powerful universal theories and we must rely on experiment, simulation and modeling. Fortunately infrared transitions often have structural specificity making them excellent local probes of non-equilibrium energy flow and structural fluctuations.

 

Energy Transfer

Chemical energy is transduced into mechanical motion. Many proteins, for example, make amazingly efficient use of small energy changes of the order of one bond to arrive at new conformations involving the coordinated motion of thousands of atoms.

Using cleverly selected vibrational probes it is now possible to track the fundamental energy transduction processes with the spatial precision of a single bond and ultrafast time resolution.

ωdetect

ωexcite

Intramolecular Vibrational Redistribution

In molecules, there is also an additional consideration: proximity. Vibrational energy transfer (or electronic for that matter) will only occur if there is good spatial overlap between the initial and final states. For this reason, intramolecular vibrational redistribution can be either lightning quick or insignificant depending on spatial and energy matching.

The probability that a system initially prepared in one state will end up in some other state within a continuum of nearby energy levels is well-known to be sharply peaked right where the energy gap ΔEif is zero between the initial and final states. The transition probability is given by “Fermi’s Golden Rule.”