Knowledge of molecular interactions is essential for understanding how nature works and for developing new materials, drugs and technologies that improve our daily lives. Collision experiments are an effective tool for understanding molecular interactions. Radboud University physicists have made groundbreaking discoveries about how molecules with a skewed charge distribution collide and change from high to very low temperatures. These discoveries concern molecular interactions and how quantum mechanical effects are expressed in molecular collisions. They enable the development of new ways to control molecular collisions using external fields. The results of the study have been published in the scientific journal Science. Molecular interactions form the basis of biological and chemical processes in nature. The electrical charge and polarity of molecules are fundamental properties that influence these interactions. Collision experiments allow researchers to collect information about how atoms and molecules interact when they collide, and what forces are generated under different conditions, such as at various temperatures. Pushing the boundaries of collision experiments In an experiment, the physicists studied how molecules behave when they collide with each other. They studied collisions between dipolar molecules, in which the positive and negative charge is not evenly distributed, and discovered how these collisions change at high to very low temperatures. Until now, it was a challenge to study two molecules in a collision experiment in a controlled situation, however, the research team succeeded in measuring and controlling collisions between two different molecules. This allowed them to investigate the collision properties over a huge range of temperatures, from above room temperature to about 0.1 degree above absolute zero. “This is a major experimental breakthrough because until now only one of the colliding molecules could be controlled,” says Bas van de Meerakker, Professor of Spectroscopy of Cold Molecules at the Radboud University Institute for Molecules and Materials (IMM). Interaction without external electric field At higher energies, molecules collide like billiard balls, while at lower energies, their interaction creates ‘U-turns’. Strong effects of the dipolar interaction were observed at very low temperatures. So far, researchers always assumed that these interactions only take place in an external electric field. In the study, the molecules collide without this external field. The experiment showed that the molecules polarise each other during the collision, ‘activating’ their dipole moment. This self-polarisation effect disappears, depending on the collision energy. “By combining experiment and theory, we now have a clear picture of the mechanisms triggering these U-turn trajectories and the mutual polarisation of dipoles,” says theoretical physicist and member of the research team Tijs Karman. The results of the study provide new insights into the interactions between molecules, and open up avenues for innovative ways to control such collisions using external electric fields. This knowledge helps to better understand how molecular interactions work and may lead to the development of new technologies using quantum physics. “We can now study collisions of molecules at high temperatures in the classical world, and also at low temperatures in the world of quantum mechanics.” More information: link to IMM article photo: JUNO KWON via Pixabay Contact information Organizational unit Spectroscopy of Cold Molecules