Physicists captured individual atoms and observed them merge into a molecule

Interesting discussion on reddit:

> It appears you need the energy from 3 in order for the 2 to make a bond.

> It's the other way around. Two atoms alone will release a bunch of energy when they form a molecule; exactly enough energy to rip the molecule back apart. That energy has to go somewhere, and where it goes is the third atom.

For those wondering about why the article says "Two atoms alone can’t form a molecule, it takes at least three to do chemistry", here's another explanation from the reddit thread [0]

> Each atom has some amount of energy associated with it. If you just bring two atoms together, the total energy is simply the sum of their individual energies. This state is typically referred to as an excited state. However, the stable bonded form of the two atoms actually has a lower energy. So to go from two separate atoms to two bonded atoms, the atoms have to first collide and form the excited state and then lose some amount of energy to go to the stable state. If they don’t lose that energy, then they can and will break apart again. One way to lose that energy is via collision with the third atom.

> In normal systems where you have tons of atoms flying around, collisions happen very frequently, so you can typically assume that the stabilization will happen immediately following the reaction. This is why the idea that stabilization is an important step in a chemical reaction is typically not covered in intro chemistry. However, it’s not uncommon to have conditions where that assumption does not hold. This then gets into the concept of pressure dependent reaction kinetics, which studies the effect of having slow stabilization.

[0] https://www.reddit.com/r/science/comments/f7mqwl/physicists_...

Yep, this is spot on.

In other atomic physics experiments it's a problem - three-body collisions are able to dump energy into one of the three atoms and that atom has enough energy to escape the trap. These are "three-body losses".

Whereas with two-body collisions, neither atom can be going any faster afterwards than the fastest one was before the collision. So they remain trapped.

Since the three-body collision rate is proportional to the cube of the density of atoms, and the two-body collision rate only to the square of density (for obvious reasons), this phenomenon limits the density of atomic clouds we can do experiments with. If we increase the density to the point where three-body collisions are significant, we rapidly lose atoms.

Couldn’t they poot off a photon?

We still don’t know exactly how catalysts work, because they operate at high temperature and pressure, so it is very hard to study.