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Our group studies the dynamics of molecules with significant amounts of vibrational energy. The flow of vibrational energy in a molecule, a process known as intramolecular vibrational energy redistribution (IVR), lies at the heart of chemical reactivity. We study the kinetics of energy flow in isolated molecules and molecules in solution. A major emphasis of our work is understanding the spectroscopy of molecules as the IVR process, as well as chemical reaction, occurs. In particular, we are interested in how coherent excitation of highly excited molecules can be used to influence reaction products.

Our group has two main experimental areas: 1) frequency-domain: development of a new broadband Fourier transform microwave (FTMW) spectrometer and its applications to the field of dynamic rotational spectroscopy (DRS) and 2) time-domain: ultrafast transient absorption infrared spectroscopy in gas and solution.
Frequency Domain Experiments
FTMW Chamber Pic

We have recently developed an 11 GHz broadband Fourier transform microwave (FTMW) spectrometer. This spectrometer increases the bandwidth of the current state-of-the-art FTMW spectrometer by a factor of approximately 5000. Among its advantages are it has decreased the necessary data collection time for microwave measurements, has accurate intensity information, and allows all areas of the MW spectrum to see the same IR laser pulses in our IR-MW double resonance and IR-MW-MW triple resonance experiments.

Our lab has also developed a new type of molecular spectroscopy called dynamic rotational spectroscopy to study isomerization reactions of isolated molecules. We utilize IR and MW frequency-domain spectroscopy techniques to obtain the rotational spectrum of a single quantum state of a highly excited molecule. Application of this technique to conformational isomerization reactions has shown that this class of reactions violates the predictions of quantum transition state theory.

Time Domain Experiments
The second area of research in our group investigates the vibrational dynamics of room temperature molecules in gas phase and dilute solution. Using our molecular-beam spectroscopy techniques we can quantitatively measure energy flow rates for the isolated molecule. Our goal for solution phase studies is to understand how solvent molecules modify the dynamics and reactivity of the isolated molecule. This work is performed in the Ultrafast Laser Facility that is part of the university's SELIM program. We have an impressive array of laser tools available for this work including a two-color femtosecond laser system, a two-color picosecond laser system, and a 32-element infrared array detector for multichannel detection. Our first studies have shown that the basic features of isolated molecule IVR dynamics are preserved in solution. In particular, we have found that a new relaxation channel opens for large molecules that correlates with the onset of fast IVR in the isolated system. From this work, we can identify a time window where the molecule in solution retains the energy deposited by the laser (i.e. before interaction with the solvent causes conversion of the internal energy to heat). Knowing this time scale gives us a window of opportunity to study the spectroscopy and kinetics of the vibrationally hot molecule. Examples of our recent work in this area, as well as descriptions of projects planned for the near future, can be found in the time domain section of this website.

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