Molecular collisions
Ammonia is a simple yet important molecule, especially in space. But until now, it was very difficult to study its collisions in detail. To succeed, researchers need to control the molecules extremely well before the collision and measure them very accurately afterwards. “At these low temperatures, molecules don’t behave like we are used to. They follow the strange rules of quantum mechanics”, PhD researcher Stach Kuijpers explains. “By studying their collisions, we can learn more about those quantum effects.”
Sharper images
The team used a special machine, called a Stark decelerator, to control the ammonia molecules before they hit hydrogen molecules. After the collision, they used lasers and cameras to take pictures of what happened. These pictures, called ‘scattering images’, show how the ammonia moves after the collision and give a peek into its quantum behavior.Previous efforts to do this with ammonia didn’t work well. The lasers added too much energy, making the images blurry. But Kuijpers and his team found a new way to detect the ammonia, which led to the first sharp images of how it scatters after a collision.
Quantum effects
By taking pictures at different collision energies, the team saw clear signs of ‘scattering resonances’. This is a special effect that only happens in the quantum world. “It is like the particles briefly stick together during the collision, which significantly increases the chance of a collision, while drastically changing the scattering image”, Kuijpers explains. To better understand these effects, the researchers worked with theorists who made new, advanced computer models. Only these state-of-the-art models matched the experiments, confirming that this method is a powerful way to study how molecules interact.
Ammonia is not only important in space but also useful in experiments on Earth because it has a strong electric dipole moment. This means that ammonia can be influenced by electric fields. “One of our goals is to steer how molecules collide by applying electric fields,” Kuijpers says. “With this new technique, we are one step closer to making this possible”. The results can help scientists explore the quantum world and understand molecular behavior in extreme conditions, with future applications in physics, chemistry, and space science.
