Molecular Physics – Controlled Molecule Imaging

The independent research group of Controlled Molecule Imaging, headed by Jochen Küpper within the Coherent Imaging Division of the Center for Free Electron Laser Science, develops innovative methods to obtain full control over large molecules and to apply these methods and the created controlled samples in fundamental physics and chemistry studies. The European Research Council (ERC) will support the "Controlling the Motion of Complex Molecules and Particles" (COMOTION) project granting two million euros to further the research on control of complex molecules.

Understanding and controlling chemical reaction dynamics defines a challenging scientific area where in the last decades different instruments have been developed to determine which specific motions, amid the myriad of possibilities, lead a system to the product of the reaction. This marks the miracle of chemical systems: there are usually only a few modes that direct the process by virtue of the exponential dependence on energetics hidden within a complex potential energy landscape. For all but a few simple molecules, we have poorly resolved “maps” of these potential energy surfaces to guide us; yet chemists harness the power of stored chemical potential routinely without full knowledge of the process.

We will advance new means of following chemical reaction dynamics to refine our maps of the forces at play with the goal of implementing electromagnetic-field-based control methodologies. We develop methods to create clean samples of individual species, based on the spatial separation of molecular quantum states, structural isomers, and cluster sizes. These clean samples are further controlled to fix the molecules in space, i.e., align and orient them. These controlled ensembles are ideal samples for the investigation of molecular structure and dynamics in novel imaging experiment, such as electron and X-ray diffraction, ion and photoelectron imaging, a.s.f.

Research Highlights

X-Ray Diffraction from Isolated and Strongly Aligned Gas-Phase Molecules

How do you watch some of the smallest structures on earth, comprised of just a handful of atoms? You need the most powerful microscope, built using an x-ray laser of unprecedented power and brightness as well as molecules precisely fixed in space. At the Linac Coherent Light Source, an x-ray laser in California, it is possible to generate x-ray flashes that are as powerful as focusing all the sunlight hitting the earth into a micrometer spot, but just for a tenth of a millionth of a millionth of a second. This x-ray light is used to illuminate a group of isolated single molecules, and the exposure time to the flash of x-rays is so short that molecular motions are frozen. The molecules have been sorted and are aligned along an axis, using yet another powerful laser beam. The resulting sharp image, generated by x-ray diffraction, allows us to peer at the atoms in the molecules.

Project: Gas-phase diffraction

Disentangling the structure-function relationship through conformer-specific reactivity studies

We have investigated the structure-function relationship of conformer-selected complex molecules. In collaboration with the Willitsch group in Basel we have performed a pioneering benchmark experiment to investigate structure-dependent chemical reactivities. We have determined the conformer-specific rate constants for the reactions of cis- and trans-3-aminophenol with Ca+ ions localized in a so called Coulomb Crystal.

Project: conformer-selected reactions

Press coverage

Pure quantum state samples of complex molecules

Exploiting the distinct effective dipole moments of molecular eigenstates we have created samples of molecules in individual quantum states. Using the electric deflector, we have created a pure sample of OCS molecules all in the absolute ground state. Moreover, in our second generation alternating gradient focuser we have created almost pure ground-state samples of benzonitrile (C6H5N). Some contamination from a J=2 state resulted from the accidental degeneracy of the effective dipole moment of this specific state.

Project: Controlled Molecules

Imaging the electronic structure of complex molecules

The quantum-state-selected polar ensembles produces by our methods allow unprecedented degrees of alignment and orientation. Such state- and conformer selected oriented ensembles are ideal samples for the recording of pictures and movies of molecules in action. We prepare and perform experiments along these lines, e. g., for diffractive imaging studies of gas-phase molecules, for high-harmonic generation and tomographic imaging of the molecules electronic structure, for molecular-frame photoelectron angular-distribution studies, for reactive scattering, and many other experiments in chemistry and physics.

Project: Photoelectron imaging

Lotte Holmegaard, Jonas L. Hansen, Line Kalhøj, Sofie Louise Kragh, Henrik Stapelfeldt, Frank Filsinger, Jochen Küpper, Gerard Meijer, Darko Dimitrovski, Mahmoud Abu-samha, Christian P. J. Martiny, and Lars Bojer Madsen
Photoelectron angular distributions from strong-field ionization of oriented molecules
Nat. Phys. 6, 428 (2010)

Fixing molecules in space

Quantum-state selected cold samples enables strong laser alignment and mixed-field orientation. We have demonstrated the one- and three-dimensional mixed-field orientation of prototypical large molecules. Subsequently, we have disentangled the non-adiabatic effects in the long-pulse mixed-field orientation of OCS.

Project: Controlled Molecules

Iftach Nevo, Lotte Holmegaard, Jens H. Nielsen, Jonas L. Hansen, Henrik Stapelfeldt, Frank Filsinger, Gerard Meijer, and Jochen Küpper
Laser-induced 3D alignment and orientation of quantum-state-selected molecules
Phys. Chem. Chem. Phys., 11, (2009) 9912-9918, selected as hot article
Lotte Holmegaard, Jens H. Nielsen, Iftach Nevo, Henrik Stapelfeldt, Frank Filsinger, Jochen Küpper, and Gerard Meijer
Laser-Induced Alignment and Orientation of Quantum-State-Selected Large Molecules
Phys. Rev. Lett. 102 (2009), 023001

Conformer separation

We apply electric fields to manipulate the translations and rotations of large molecules. This ranges from dc electric fields in the electric equivalent of the Stern Gerlach deflector over switched electric fields in AC guides to linear decelerators for neutral molecules. These are the demonstrations of the the neutral molecule equivalents of the charged particle bender, focuser and linear accelerator (LINAC), respectively. We have independently demonstrated conformer (structural isomer) selection of cis- and trans-3-aminophenol using the focuser and the deflector.

Project: Controlled Molecules

Frank Filsinger, Jochen Küpper, Gerard Meijer, Jonas L. Hansen, Jochen Maurer, Jens H. Nielsen, Lotte Holmegaard, Henrik Stapelfeldt
Pure Samples of Individual Conformers: the Separation of Stereo-Isomers of Complex Molecules using Electric Fields
Angew. Chem. Int. Ed. 48, 6900 (2009), selected as Very Important Paper

Frank Filsinger, Undine Erlekam, Gert von Helden, Jochen Küpper, and Gerard Meijer:
Selector for structural isomers of neutral molecules
Phys. Rev. Lett. 100, 133003 (2008)

Nature News&Views by A. Stolow, Nature 461, 1063 (2009)
Nature Chemistry News&Views by T. S. Zwier, Nat. Chem. 1, 687 (2009)
Physics Today Search and Discovery by J. Miller, Phys. Today 61(6), 17 (2008)
Press coverage


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Jochen Küpper
The first experimental X-ray diffraction results from quantum-state selected and laser-aligned gas-phase ensembles at the X-ray Free-Electron Laser LCLS is published. [More]
The European Research Council (ERC) grant will support our research on control of complex molecules. [More]
Our work on measuring various reaction rates of different forms from the same compound is out. [More]
17. December 2013
European Research Council grants 14 million euros for novel research

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