Towards ultrafast dynamics in controlled molecules

Time-resolved photoelectron imaging (TR-PEI) has established itself as a powerful tool for studying ultrafast dynamics in the gas-phase, in particular excited-state non-adiabatic dynamics. Recent developments in ultrafast VUV sources, such as high-harmonic generation, now enable us to remove previous restrictions on the available ‘observation window’. This allows one to follow the entire reaction coordinate, from reactants through intermediates to products, in a single experiment and with ultrafast time resolution.1

The other key element to these experiments – the molecular beam of sample molecules – has received considerably less attention. However, with experiments moving to ever more complex systems this becomes increasingly important, as even under the rotationally-cold conditions of a supersonic expansion (bio)molecules often populate many different conformational states. I will show how strong electrostatic fields can be used to control neutral polar molecules and create ‘pure’ gas-phase samples.2 For small molecular systems, e.g. water, this allows the creation of single quantum-state samples,3 whilst for much larger samples such as peptides it enables the separation of different conformations (folding states).4 Combining these approaches – TRPEI and Stark control – will allow the investigation of the structure-function relationship on the level of single conformeric structures.

1 A.D. Smith et al., Phys. Rev. Lett. 120, 183003 (2018).
2 Y.-P. Chang, D.A. Horke, S. Trippel, and J. Küpper, Int. Rev. Phys. Chem. 34, 557 (2015).
3 D.A. Horke et al., Angew. Chem. Int. Ed. 53, 11965 (2014).
4 N. Teschmit, D. Horke, and J. Küpper, Angew. Chem. Int. Ed. 57, 13775 (2018).