Dynamics at Ice Surfaces using Velocity Map Imaging

• Applicant: Professor Dr. Sven Köhler
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Astrophysics and Astronomy ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545664458

Photodesorption from ices has been suggested as a major desorption process explaining the observations of molecules in the cold interstellar medium. The determination of photodesorption yields from ice analogues has been the subject of many studies in the last decade, however, the mechanisms explaining the desorption are still poorly understood. In this collaborative project, the groups at Sorbonne and at Hannover combine and share their respective expertise to shed new insight onto the photodesorption dynamics of ices. We propose a truly novel experimental approach by using the 3D-velocity map imaging (VMI) method for the analysis of the photodesorption from ices (VMICES: velocity map imaging from ices). Irradiation of condensed CO, N2, NO and H2O ices with photons in the range between 7-14 eV (VUV-laser or synchrotron radiation) will lead to desorption of molecules or fragments for which the velocity and angular distributions will be measured for the first time. This approach will be crucial to explain the photodesorption of many species in space. Covering interest areas such as astrophysics, reaction dynamics, surface science and laser design, the transdisciplinary nature of this proposal is also apparent in the team’s composition, with the French group based in Physics, while the German group consists of chemists based in Mechanical Engineering. The expertise within the two groups in complementary: The Paris group has a highly successful track record of studying photodesorption on ices at temperatures of just a few Kelvin. The Hannover group is one of 5 worldwide to have developed a VMI spectrometer for surface studies, capable of determining the speed of desorbing fragments in 3 dimensions independently, and hence extract angular distributions. It is precisely the capability of measuring angular distributions which, when added to the Paris setup, allows one to make the otherwise challenging distinction between different photodesorption mechanisms from ices. For example, electrostatic repulsion, energetic photochemical channels or momentum transfer channels are all likely to have different angular signatures in their desorption channels, but would otherwise be difficult to disentangle based on the kinetic energy distribution alone. The groups have already collaborated in a previous 2-year French-UK project in which the experimental apparatus has been simulated and designed. Crucially, in this project, the so-called SPICES-VMI setup will be completed, tested, and employed for experiments ranging from photodesorption experiments on ices (some grown on graphene) to desorption of small organic chiral molecules in space using circularly polarized light, which are likely desorbed showing different angular signatures, thus making full use of the VMI capability.

• DFG Programme: Research Grants
• International Connection: France
• Major Instrumentation: Desorption Laser
• Instrumentation Group: 5710 Gas-Laser
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partner: Professor Dr. Jean-Hugues Fillion