To understand how atoms combine to form molecules, we need to catch them in action. But to do this, physicists must make the atoms stop long enough for their interactions to be recorded.
This is not an easy task, but it was managed by physicists from the University of Otago.
So far, the best way to understand the intricacies of the various interactions of atoms has been to calculate correlations based on the mean values among a cluster of particles.
This crowdsourced version of atomic technology provides a lot of useful science, but fails to grasp the key details of collision and crushing collisions between individual particles that cause others to scatter and merge.
Even if you manage to capture several atoms in the same space, each collision can cause the atoms to get out of your experiment.
One way to analyze such collisions is to grab isolated atoms with the equivalent of a tiny pair of tweezers, hold them still, and record changes as they come.
Fortunately, such a pair of tweezers exists. Made from specially aligned polarized light, these laser pliers can act as optical traps for tiny objects.
Given the relatively short wavelengths of light, the experimenter has a good chance of catching something as tiny as a single atom. Of course, you first need to cool the atoms to make them easier to capture, and then select them in empty space.
Mikkel Andersen (left) and Marvin Weiland in the physics laboratory.
It sounds easy. But the process requires the right technology and a lot of patience to achieve.
“Our method involves individually capturing and cooling three atoms to about one millionth Kelvin using highly focused laser beams in a hypervacuum (vacuum) chamber the size of a toaster,” says physicist Mikkel F. Andersen.
“We are slowly combining traps containing atoms to produce controlled interactions that we measure.”
In this case, all the atoms were varieties of rubidium that bind to form dirubidium molecules, but just two atoms are not enough to achieve this.
“Two atoms cannot form a molecule; chemistry requires at least three,” says physicist Marvin Weiland.
Modeling how this happens is a real challenge. Clearly, two atoms must get close enough to form a bond, while the third takes away some of that bond energy to leave them bound.
Working out the mathematics of how just two atoms meet to build a molecule is difficult. Taking all actions into account can be a nightmare.
In theory, the recombination of three bodies between atoms should force them to leave the trap, which usually adds another problem for physicists trying to study interactions between multiple atoms.
Using a dedicated camera to observe the changes, the team captured the moment the rubidium particles approached each other and found that the rate of loss was not as high as expected.
In reality, this also means that the molecules did not assemble as quickly as existing models might explain.
Something about limiting atoms and quantum short-range effects may help explain this slowness, but the fact that this is unexpected means that a lot of physics can be explored through this process.
“With development, this technique could provide a way to create and control individual molecules of certain chemicals.”
Further experiments will help refine these models to better explain how groups of atoms work together to meet and bond under different conditions.
In a world of ever-improving technology, it's not hard to imagine the need for processes in which microscopic circuits and advanced drugs are built atom by atom, one compound at a time.
“Our research is trying to pave the way for the ability to build on a very small scale, namely at the atomic scale, and I am very excited to see how our discoveries will affect technological progress in the future,” says Andersen.
This research was published in Physical Review Letters.
Sources: Photo: University of Otago
