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Physicists captured individual atoms and observed them merge into a molecule

123 points by martonlanga 7y ago

martonlanga 7y ago
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.
- ASDfa123 7y ago
  Link? That's a good point if it's true. The article got the explanation all wrong.
- doubleunplussed 7y ago
  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.
JeremyHerrman 7y ago
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_captured_individual_atoms_and_observed/ https://www.reddit.com/r/science/comments/f7mqwl/physicists_...
- sfifs 7y ago
  Interesting. Is this how catalysts work? By bringing the atoms/molecules reacting together and providing a path for taking away the excess energy more easily?
  - staticautomatic 7y ago
    Catalysts work principally by lowering the activation energy of the reaction. https://en.m.wikipedia.org/wiki/Activation_energy https://en.m.wikipedia.org/wiki/Activation_energy They don't necessarily bring atoms or molecules together, per se, but some do.
    - sfifs 7y ago
      Yes but activation energy is still a "system" level concept. It's not the actual atomic level mechanism that results in the reaction.
  - mensetmanusman 7y ago
    We still don’t know exactly how catalysts work, because they operate at high temperature and pressure, so it is very hard to study.
    - Ao7bei3s 7y ago
      That doesn't seem right. Cars have catalysts where the air flows through. Also 2 H2 + O2 -> 2 H2O (+ a characteristic bang :-)) at room temperature and pressure (initially) using a platinum catalyst is shown in school chemistry classes. Just learned on Wikipedia (en/Platinum) that the 2007 Nobel price in Chemistry was awarded for explaining how that works. doi:10.1002/anie.200800480
      - pritovido 7y ago
        Car's catalyst work at high temperatures, not at room temperature. In fact, at room temperature they don't work at all, which is exactly the problem with catalysts, they don't work when you start your car. They need to heat with the hot combustion gases to start working, and that takes a while. This is one of the reasons that laboratory's measurements of particles and gases like nitrogen oxides do not apply to real emissions in cities, because most people in cities will use the cars, for example, diesels in Europe, for very short periods of time, then let the car cool down and use it again to go back less than 10 kilometers away.
iandanforth 7y ago
I love how much of science is "We built a thing to look more closely at things and now we know more!"
basicplus2 7y ago
Pity there are no images of the merge occuring..
wruza 7y ago
Can someone please comment on the picture? What is bottom-righty part, which looks like some device?
nyc_pizzadev 7y ago
Simplified version with graphic: https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.124.073401 https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.124...
panic 7y ago
Here’s an arXiv link if you’re hitting a paywall on the paper itself: https://arxiv.org/abs/2001.05141 https://arxiv.org/abs/2001.05141

123 points by martonlanga 7y ago

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.

ASDfa123 7y ago
Link? That's a good point if it's true. The article got the explanation all wrong.
doubleunplussed 7y ago
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.

JeremyHerrman 7y ago

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_captured_individual_atoms_and_observed/ https://www.reddit.com/r/science/comments/f7mqwl/physicists_...

sfifs 7y ago
Interesting. Is this how catalysts work? By bringing the atoms/molecules reacting together and providing a path for taking away the excess energy more easily?
- staticautomatic 7y ago
  Catalysts work principally by lowering the activation energy of the reaction. https://en.m.wikipedia.org/wiki/Activation_energy https://en.m.wikipedia.org/wiki/Activation_energy They don't necessarily bring atoms or molecules together, per se, but some do.
  - sfifs 7y ago
    Yes but activation energy is still a "system" level concept. It's not the actual atomic level mechanism that results in the reaction.
- mensetmanusman 7y ago
  We still don’t know exactly how catalysts work, because they operate at high temperature and pressure, so it is very hard to study.
  - Ao7bei3s 7y ago
    That doesn't seem right. Cars have catalysts where the air flows through. Also 2 H2 + O2 -> 2 H2O (+ a characteristic bang :-)) at room temperature and pressure (initially) using a platinum catalyst is shown in school chemistry classes. Just learned on Wikipedia (en/Platinum) that the 2007 Nobel price in Chemistry was awarded for explaining how that works. doi:10.1002/anie.200800480
    - pritovido 7y ago
      Car's catalyst work at high temperatures, not at room temperature. In fact, at room temperature they don't work at all, which is exactly the problem with catalysts, they don't work when you start your car. They need to heat with the hot combustion gases to start working, and that takes a while. This is one of the reasons that laboratory's measurements of particles and gases like nitrogen oxides do not apply to real emissions in cities, because most people in cities will use the cars, for example, diesels in Europe, for very short periods of time, then let the car cool down and use it again to go back less than 10 kilometers away.

iandanforth 7y ago

I love how much of science is "We built a thing to look more closely at things and now we know more!"

basicplus2 7y ago

Pity there are no images of the merge occuring..

wruza 7y ago

Can someone please comment on the picture? What is bottom-righty part, which looks like some device?

nyc_pizzadev 7y ago

Simplified version with graphic: https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.124.073401 https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.124...

panic 7y ago

Here’s an arXiv link if you’re hitting a paywall on the paper itself: https://arxiv.org/abs/2001.05141 https://arxiv.org/abs/2001.05141