Broadband transient absorption spectroscopy allows us to take a UV-Vis of the excited electronic state of a molecule with respect to time. By using non-linear optical parametric amplifiers we are able to tune the wavelength of the pump beam from the UV through the visible regions of the spectrum. This allows for the selective excitation of molecules in a complex system or exciting into different excited states for single molecules. By using the 1 kHz laser we are able to get a time resolution of ~100 fs. The probe beam for this experiment is white light (350-750 nm) which allows for a broad spectrum to be collected at once thus expediting the data collection process. Broadband transient absorption spectroscopy is useful in determining the electronic structure of molecules, detecting reaction intermediates, and monitoring electron transfer.
Single wavelength transient absorption spectroscopy allows us to determine the kinetics of a single process occurring within the system. Kinetic data is particularly useful for determining the rates of processes that occur from the excited states of molecules. By collecting many points at one wavelength, we can obtain better time resolution than with the broadband transient absorption system.
Infrared transient absorption spectroscopy allows us to take an IR spectrum of the excited electronic state of a molecule. This experiment is useful in determining the geometrical changes that occur in the excited states of molecules and is another method for detecting reaction intermediates and products of electron transfer reactions. Many systems have electronic transitions from the excited electronic state that are outside of the detectable region for the broadband transient absorption system. This problem can be solved by using IR transient absorption spectroscopy.
Femtosecond stimulated Raman spectroscopy (FSRS) is a technique that allows us to take a Raman spectrum of the excited electronic state of a molecule. Many times characteristic vibrational transitions of molecules are not IR active modes. Generally these modes are Raman active. Thus using FSRS we are able to detect geometry changes in the excited electronic state of modes that are Raman active.
Time correlated single photon counting (TCSPC) is a technique that allows us to measure the lifetime of the fluorescence of a molecule. This is another technique that allows for the characterization of the excited state properties of molecules as well as characterization of electron transfer reactions.
Nanosecond infrared transient absorption spectroscopy is a technique that allows for the detection of longer lived species and states of molecules. Many times intermediates or products of reactions have a lifetime that is longer than 2-3 ns (the longest time measurable in femtosecond experiments) and it is important to determine how long these species survive.
See the Center for Chemical and Biophysical Dynamics (CCBD) webpage for more information