Our lab is developing new ultrafast vibrational techniques to study both the nuclear geometry changes during ultrafast photochemical and photobiological reactions and the vibrational coupling that allows energy flow in small molecules. Our primary tool for these studies is a laser spectroscopy technique called femtosecond stimulated Raman spectroscopy, or FSRS, that allows the collection of high-resolution vibrational spectra with time-resolution better than 100 fs (see Figures 1 and 2 below). We will be developing a state-of-the-art ultrafast laser lab to determine structural changes during charge-transfer dynamics and the extremely short-lived electronic excited states of DNA (Figure 3). Additionally, our lab will be studying vibrational coupling by using FSRS to impulsively drive molecular vibrations and then observing the movement of the vibrational excitation through the molecule (Figure 4). Construction of the McCamant lab in the basement of Hutchinson was begun in June 2006 and will be completed by the end of the summer to facilitate the arrival of a massive new optical table and a femtosecond titanium:sapphire laser system.

Figure 1. The laser pulses, energy diagrams and detected spectrum relevant to femtosecond stimulated Raman spectroscopy.

Figure 2. Schematic of the optical setup to perform a simple FSRS experiment.

Figure 3. Electronic states involved in the photophysical relaxation of nucleic acids. Shown are the ground-state thymidine dinucleotide, T2, and the two primary photoproducts: the T<>T thymidine cyclobutane dimer, and the T[6-4]T cross-linked dimer. Conical intersections are indicated by “CI”. Adapted from Crespo-Hernandez et al., Chem. Rev. 2004, 104, 1977-2019.

Figure 4. Schematic of multidimensional FSRS experiment on all-trans retinal. Vibrational coupling between a low-frequency backbone torsion and a high-frequency C=-C stretch is monitored by first impulsively driving the torsion into coherence and then monitoring the time-dependent frequency changes in the stretc