Chemistry at the Space-Time Limit (CaSTL) is a Center for Chemical Innovation (CCI) at UCI, which is funded through the National Science Foundation. The center is dedicated to real-time measurements with atomistic resolution to probe the inner workings of molecules. Videography of elementary events in chemistry and photophysics is the aim. Among the targeted processes are: the oxidation and reduction of a single molecule, making and breaking of chemical bonds, charge transfer/transport, heterogeneous catalysis and chemistry on the nanoscale. The capability to follow individual chemical events with atomistic resolution would usher a new perspective and mode of inquiry into molecular science and engineering. Indeed, for the purposes of instructing chemistry, it is hard to imagine a more incisive tool than the time-lapsed images of molecules undergoing chemical change, or responding to various external perturbations.
Our collaborative efforts focus on the creation of novel and far-reaching measurement and computational technologies that are currently being developed. The combined physical measurements and quantum mechanical simulations will be used to provide a real-space, real-time picture of chemical processes at the most fundamental level. In effect, time-lapsed sequences of chemical events will be imaged one bond-at-a-time. Such a development would fundamentally change the modes of scientific inquiry of not only scientists, but also the public at large. Our immediate research goals are to develop the measurement and theoretical apparatus to access the inner workings of complex molecules – individual bonds, interactions among delocalized vibrations, electronically excited states and charge distributions. Observing the making and breaking of a single bond in real-time establishes the ultimate space-time resolution of relevance to chemistry. The attainment of the requisite joint 0.1 nm - 10 fs scale of resolution is technically within reach, requiring the combination of ultrafast nonlinear spectroscopy with scanning probe microscopy (SPM) and developing the necessary theoretical and computational techniques for modeling the response of complex molecules. Rather than viewing the molecule as a single entity, it may be dissected into a collection of parts, each of which may interact differently with its environment, or may respond differently to external perturbations.
The field of ultra-fast nonlinear spectroscopy is well established and has advanced to the limit where molecular processes can be followed at the light cycle limit in time (10-15s in the visible, 10-16s in the X-ray range). Also, time-independent scanning tunneling microscopy (STM) measurements have been demonstrated with sub-atomic resolution. The execution of either of these feats separately requires demanding state-of-the-art skills. Combining the two is a formidable challenge that requires the manipulation of multiple ultrashort laser pulses in the tip area of a scanning probe that operates with atomic resolution. Moreover, the design and interpretation of such measurements requires an arsenal of nonequilibrium electronic structure and dynamics algorithms and codes for current-carrying states. The scope of this effort requires the assembly of expertise in the areas of time-resolved nonlinear molecular spectroscopy, theoretical quantum chemistry of open systems, and scanned probe characterization of single molecules.
We are developing these new tools to probe the dynamics of fundamental processes, such as: electron transport, intramolecular and intermolecular bonding, coupling to the environment, surface and aggregation effects, solvation, electron-photon coupling, energy transfer, and the relaxation dynamics of excitations. The knowledge gained from more traditional chemistry research about any of these processes can be expected to profoundly expand through real-time observations with atomistic resolution.