Slamming molecules opens new reaction paths
The outcome can be largely demarcated by the kinetic energy of the molecule approaching the surface. Low-energy collision (0.5 – 5 eV) changes the three-dimensional structure (i.e. conformation) of incident molecule, while high-energy collision (5 – 50 eV) can initiate a mechanochemical reaction.
We demonstrate the utility of low-energy collisions by colliding a carbohydrate molecule with a surface to explore its ground and excited conformational states. The carbohydrate molecule used as an example here is a short chain of cellulose, the main structural molecule in plants, which are prepared by chemists at the Max Planck Institute of Colloids and Interfaces. Knowing the range of conformational states that a biomolecule can adopt is important in drug-discovery since the most bioactive conformation of a molecule is not necessarily the most stable or the most abundant one.
High-energy collisions, in contrast, are found to induce selective chemical reactions due to the compression of an incident molecule when it arrives at the surface. Experiments and calculations in collaboration with Dr. Stephan Rauschenbach at the University of Oxford reveal that the molecular compression causing the reaction originates from the fast-approaching molecule being brought to sudden halt when it encounters the surface. The reaction products generated from these high-energy collisions are those that cannot be obtained by conventional thermal chemistry, thereby opening new opportunities to synthesize new molecules on surfaces.