Two key aspects of the photochemistry at conical intersections define our experimental efforts: First, the timescales of these reactions are approximately 100 femtoseconds (1/10 trillionth of a second), and such a fast timescale demands ultrafast laser pulses to “watch” the reaction in the time domain. Second, near the conical intersection singularity, the electronic and nuclear modes couple very strongly; we have developed a new two dimensional, fifth order spectroscopy that is uniquely sensitive to these electronic-vibrational couplings. Using this ultrafast, 2D spectroscopy, we seek to identify which vibrational modes of the system control the reactivity and how the excited state approaches, navigates, and ultimately traverses the conical intersection to produce reaction products.
The experimental apparatus will use a diffractive optics based two dimensional optical spectroscopy system to carefully control both linear electronic and resonant raman interactions with the system. Leveraging rephasing pathways to eliminate inhomogeneity in the spectrum and spectral interferometry to resolve the full electric field, we can then map the evolution of the excited state toward the conical intersection. |
