Creating controlled samples of complex molecules for molecular dynamics studies

Conformer selection of neutral molecules

Even at the low temperatures in cold supersonic jets, large molecules typically exhibit multiple conformers (structural isomers). In some cases, this presence of many conformers does not pose a problem. A variety of (spectroscopic) experiments can still be conducted, because most often the conformers can be detected individually. For some experiments, e. g., scattering experiments and X-ray or electron diffraction imaging, however, it is highly desirable to have only one single conformer present in the beam.
While the different conformers of large molecules (i. e., 3-aminophenol, tryptophan) have the same mass and similar rotational constants, they often have widely varying dipole moments. Exploiting dynamic focusing in strong inhomogeneous ac electric fields, these dipole moment differences can be used to separate the individual conformers in an m/µ-selector, similar to an m/q-selector for charged particles.

  • 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 (2009), 6900

Alignment and orientation with laser fields

The state selection achieved using strong inhomogeneous electric fields can be exploited for improved laser alignment and mixed field orientation experiments.

  • 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

We are currently setting up an experiment to study the dynamics of rearrangement processes in small organic molecules. The molecules are quantum state selected by an electric deflector and fixed in space via strong laser pulses

Jens H. Nielsen, Paw Simesen, Christer Z. Bisgaard, Henrik Stapelfeldt, Frank Filsinger,
Bretislav Friedrich, Gerard Meijer, and Jochen Küpper

Stark-selected beam of ground-state OCS molecules characterized by revivals of impulsive alignment

Phys. Chem. Chem. Phys.
13, 18971–18975 (2011)
in themed issue on Physics and Chemistry of Cold Molecules

Stephan Putzke, Frank Filsinger, Henrik Haak, Jochen Küpper, Gerard Meijer
Rotational-state-specific guiding of large molecules
Phys. Chem. Chem. Phys. 13, 18962–18970 (2011) in themed issue on Physics and Chemistry of Cold Molecules