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 quantum states, conformers (structural isomers), and clusters. In some cases, this presence of different systems does not pose a problem. For some experiments, e. g., scattering experiments and X-ray or electron diffraction imaging, however, it is highly desirable to have only one single system present in the beam. While the different conformers of large molecules have the same mass and similar rotational constants, they often have widely varying dipole moments. We use strong inhomogeneous electric fields to spatially separate our systems present in the molecular beam according to individual quantum states, shapes, and structures. This allows performing experiments on well-defined and pure samples. Examples are the separation of indole-water and pyrrole-water from all other species of the molecular beam. For small molecules like OCS, we can separate the absolute rovibrational ground state. Different conformers like those of 3-chlorophenol, 3-aminophenol, and 3-fluorophenol, can be separated and studied individually.

Publications

Fixing molecules in space - Alignment and Orientation

To study the dynamics like half collisions, internal rotations, or the ring-opening of small model systems it is very often desirable to do investigations in the molecular frame. We, therefore, align or orient molecules in the gas phase making use of laser alignment and mixed field orientation. We develop new methods to strongly orient and align molecules in field-free space using shaped picosecond pulses.

Methods

• Alignment and orientation at high repetition rates using Ti:Sa based laser systems
• Optimizing field-free alignment and orientation using shaped laser pulses
• Alignment at arbitrary repetition rates

Publications