We are interested in solving atomic structures and chemical reaction mechanisms using a variety of experimental tools, including electron diffraction, optical spectroscopy, and mass spectrometry.
1. Electron diffration
One of our overarching goals is to solve the crystallization problem in crystallography by building a molecular goniometer for electron diffraction. We embed molecules and ions in superfluid helium droplets, so the “dopant” can be cooled to 0.4 K for easy orientation by an external electric field. Using an elliptically polarized laser and an additional pulsed electric field, we can achieve three-dimensional orientation of any macromolecule to a high precision, as high as 1º. The oriented molecules are subjected to high energy electrons for diffraction, and by accumulating single molecule diffraction signals over an extended period of time, high quality diffraction images from one orientation can be obtained. Diffraction patterns from different molecular orientations are obtained by simply changing the polarization property of the orientation laser. These multiple projections of the same diffractive object are sufficient for structure determination. The animation of this project is shown on the landing page.- We are actively recruiting graduate students who are not afraid of big challenges, and has an interest in atomic structures, diffraction, laser physics, and hands-on activities.
2. Coulomb explosion
We are also interested in studies of laser-matter (cluster) interactions, and the resulting Coulomb explosion can be used for structure determination. Laser-matter interaction has long been divided into two regimes, the weak field and the strong field, but in between the two extremes, it has been “no man’s land” because the modeling process is complicated. However, atomic clusters of rare gas atoms, mixed clusters of molecules and rare gas atoms, and neat molecular clusters, are all observed to produce highly charged atomic ions in moderately intense nanosecond laser fields, and the mechanism of which is still quite controversial. In collaboration with theorists, our overarching goal is to develop a comprehensive understanding of laser matter interactions across a wide intensity regime, from moderate to strong fields, and through an extensive time scale, from femtosecond to nanosecond.- This project is in collaboration with theorists and electrical engineers. We are recruiting students who are interested in solving nature’s mysteries.
3. Superfluid helium droplets as microreactors
Superfluid helium droplets are non-interfering but ultracold reactors, and reactions in superfluid helium droplets can also be used to synthesize new molecules or clusters. These reactions can be relevant to astrophysical conditions or nucleation events in the upper atmosphere.- We are recruiting students interested environmental chemistry.
4. Innovation in mass spectrometry
we are working a prototype that combines mass spectrometry and electron diffraction, which can provide structure information of mass selected ionic species.- We are recruiting students who are interested in innovation and entrepreneurship in mass spectrometry and diffraction.