Strange quantum event happens once every 10 billion chances

When hydrogen molecules and charged atoms of deuterium collide, they can exchange a proton through a quantum process called tunnelling, but this only happens once in 10 billion collisions.

Quantum tunnelling is an odd effect that allows particles like electrons to travel through barriers in nano-sized devices or protons to move between molecules. The latter is important for chemistry, where a tunnelling proton can change the makeup of molecules even when they don’t have enough energy for a conventional reaction that …