Mapping Atomic Motions with Ultrabright Electrons: Realization of the Chemists’ Gedanken Experiment
One of the grand challenges in science is to watch atomic motions on the primary timescales of structural transitions, i.e. to watch atoms move in real time. This prospect would provide a direct observation of the very essence of chemistry and the central unifying concept of transition states that links chemistry to biology. This experiment has been referred to as “making the molecular movie”. Due to the extraordinary requirements for simultaneous spatial and temporal resolution, it was thought to be an impossible quest and has been previously discussed in the context of the purest form of a gedanken experiment. With the recent development of ultrabright electron sources capable of literally lighting up atomic motions, this experiment has been realized (Siwick et al. Science 2003). The first studies focused on relatively simple systems. Further advances in source brightness have opened up even complex organic systems and solution phase reaction dynamics to atomic inspection. Recent studies of formally a photoinduced charge transfer process in charge ordered organic systems has directly observed the most strongly coupled modes that stabilize the charge separated state (Gao et al Nature 2013). It was discovered that this nominally 280 dimensional problem distilled down to projections along a few principle reaction coordinates. Similar reduction in dimensionality has also been observed for ring closing reactions in organic systems (Jean-Ruel et al JPC B 2013). ). Even more dramatic reduction in complexity has been observed for the material, Me4P[Pt(dmit)2]2, which exhibits a photo-induced metal to metal electron transfer process for unit cells on par with proteins. This study represents the first all atom resolved structural dynamics with sub-Å and 100 fs timescale resolution. We are tuned to seeing correlations. At this resolution, without any detailed analysis, the large-amplitude modes can be identified by eye from the molecular movie. The structural transition clearly involves a dimer expansion and a librational mode that stabilizes the charge transfer. This phenomenon appears to be general and arises from the very strong anharmonicity of the many body potential in the barrier crossing region. The far from equilibrium motions that sample the barrier crossing region are strongly coupled, which in turn leads to more localized motions. In this respect, one of the marvels of chemistry, and biology by extension, is that despite the enormous number of possible nuclear configurations, chemical processes reduce to a relatively small number of key reaction modes. We now are beginning to see the underlying physics for the generalized reaction mechanisms that have been empirically discovered over time. The “magic of chemistry” is this enormous reduction in dimensionality in the barrier crossing region that ultimately makes chemical concepts transferrable. With the new ability to see the far from equilibrium nuclear motions driving chemistry, it will ultimately be possible to characterize reaction mechanisms in terms of reaction modes, or reaction power spectra, to give a dynamical structural basis for controlling barriers – and optimally directing chemical processes.
These developments will be discussed in the context of developing the necessary technology to directly observe the structure-function correlation in biomolecules ¾ to give the most fundamental (atomic) basis for understanding biological systems at the molecular level.
R. J. Dwayne Miller
The Max Planck Institute for the Structure and Dynamics of Matter
The Hamburg Centre for Ultrafast Imaging and, Departments of Chemistry and Physics
University of Toronto
R. J. Dwayne Miller has published over 200 research articles, one book, and several reviews. He has pioneered the development of both coherent multidimensional spectroscopy methods, associated ultrafast laser technology, and introduced the concept of using ultrabright electron sources to probe structural dynamics. The electron sources developed by his group are sufficiently bright to literally light up atomic motions in real time. He and his group were the first to capture atomic motions during the defining moments of chemistry – to directly observe the very essence of chemistry. This work accomplished one of the dream experiments in science, to bring the chemists’ collective gedanken experiment of chemistry to direct observation.
R. J. Dwayne Miller has trained more than 60 PhD/Postdoctoral students, with former students currently holding faculty or senior scientist positions at Yale, Michigan (2), Kaiserslautern, NIST, Lawrence Livermore National Labs, Fritz Haber Institute, McGill, U Waterloo, U Tokyo, Tokyo Tech, Harvard, U Toronto, as representative examples. His group has also started up 6 companies.
His research accomplishments have been recognized with an A.P. Sloan Fellowship, Camille and Henry Dreyfus Teacher-Scholar Award, Guggenheim Fellowship, Presidential Young Investigator Award (USA), Polanyi Award, Rutherford Medal in Chemistry, the Chemical Institute of Canada (CIC) Medal, and numerous named lectureships. He was inducted as a Fellow of the Royal Society of Canada, Fellow of the CIC, Fellow of the Optical Society of America, and distinguished University Professor at the University of Toronto. He recently received the E. Bright Wilson Award in Spectroscopy, conferred by the American Chemical Society (2015) and the Centennary Prize from the Royal Society of Chemistry (2016). He will be inducted as a Fellow of the Royal Society of Chemistry in November 2016. He is also a strong advocate for science promotion earning the McNeil Medal from the Royal Society of Canada (2011) for founding Science Rendezvous, which is the largest celebration of science (geographically at least) with over 300 events all across Canada with new initiatives in the North, aimed to make science accessible to the general public with over 200,000 attendees annually made possible by 5000 volunteers/researchers.
Tracing his career to this point, R. J. Dwayne Miller began his academic career at the University of Rochester direct from PhD (Stanford,1983), then moved to the University of Toronto (1995) where he still holds a partial appointment, then to the University of Hamburg (2010) and on January 1, 2014, he officially took up the position as co-Founding Director of the newly created Max Planck Institute for the Structure and Dynamics of Matter in Hamburg. He also led the Excellent Research Initiative that led to the creation of the Hamburg Centre for Ultrafast Imaging and is the founding co-Director of the Canadian Institute for Advanced Research Program in the Molecular Architecture of Life.