
Chemists Confirm the Existence of New Type of Bond - denzil_correa
http://www.scientificamerican.com/article/chemists-confirm-the-existence-of-new-type-of-bond/
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quarterwave
Why is the muonic hydrogen required?

From the Bohr formula the Rydberg energy of the muonic hydrogen would be some
200 times larger than regular hydrogen. Anyone know how that plays a role?

It can't be sqrt(spring/mass) for vibration since the proton is anyway already
some 2000x heavier than the electron. Unless spring somehow depended on the
Rydberg energy, which is possible since the P.E-K.E would depend on mass via
the K.E.

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alhw
The decrease in potential energy upon vdW bond formation in reactions with
typical hydrogen isotopes dominates the negligible gains in vibrational zero-
point energy from reactants to products. With the muonic hydrogen
substitution, the authors claim instead that the driving force for "bond
formation" results from a decrease in zero-point energy which compensates for
the expected losses in potential energy.

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gus_massa
I have a few published articles in quantum chemistry, and I barely can
understand your explanation. It feels right, but I think I need to take 30
minutes to try to understand the details. Can you explain this like I'm a
graduate student with only 3 years in the university, please?

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alhw
The authors of the article in topic provide a more coherent explanation than I
could ever articulate:

>> Conventionally, the formation of chemical bonds is due to a decrease in
potential energy (PE), often accompanied by small increases in vibrational
zero point energy (ZPE). In principle, this basic mechanism can be completely
reversed, wherein chemical bonds may even be formed by an increase in PE if
there is a sufficiently compensating decrease in vibrational ZPE, giving rise
to what has been coined “vibrational bonding” of molecules stabilized at
saddle-point barriers on a potential energy surface (PES), far away from
potential minima.

~~~
gus_massa
Thanks. But I think your previous comment has an interesting point about why
muons are different than electrons. I'm not sure because I hadn't made the
calculations, so any confirmation or refutation is welcome. Let's try:

When two normal molecules, with electrons, are close, they can form different
kind of bonds. The weakest bond is the "van der Waals" bond. It's caused
because the electrons of the molecules change their position slightly due to
the presence of the other molecule.

In this experiment they only replace the electron of a hydrogen atom by a
muon. The muons have much more mass than the electrons, so the radius of the
orbit is much smaller. (They are quantum particles, so they don't have orbits,
but please forgive this technical detail.) As the orbits are smaller, the
displacement caused by the other molecule is smaller, so the van der Walls
force is smaller.

In the normal (electron) case the van der Walls force cause the formation of
the intermediate molecule. In this case (muon) the van der Waals forcé is so
weak that other effects are more important.

[I left out the part about zero point energy. It's also interesting but this
explanation is becoming larger than the article :) .]

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sp332
It's the proton that is replaced, not the electron.

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gus_massa
Ups! :( You are right and now I'm confused.

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slapresta
> chemists experimenting at a nuclear accelerator in Vancouver observed that a
> reaction between bromine and muonium—a hydrogen isotope—slowed down when
> they increased the temperature

Isn't saying muonium is "a hydrogen isotope" sort of like saying a car is "a
horse isotope"?

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oasisbob
Sounds like more of a pseudo-isotope?

I thought proton equivalency was the fundamental definition of an isotope,
though perhaps that's just a lie you feed chemistry undergrads.

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saalweachter
The antimuon is "proton-like" for a lot of purposes: it has a +1 charge and
it's much heavier than an electron. So you've got a heavy bit with +1 charge
and an electron orbiting it, you call it hydrogen.

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tjradcliffe
It would have been very nice had the article said that, and described what
"muonium" is. I took it to be a proton plus a muon, not an anti-muon plus an
electron.

To describe it as "a hydrogen isotope" is just about the optimal mix of
uninformative and misleading!

~~~
logfromblammo
It's probably as close as you can get to accuracy while still keeping those
who passed their high school chemistry classes in your audience.

For the purposes of explanation, the antimuon-electron pair is chemically
similar enough to a proton-electron pair to call it an isotope. It has a +1
massive center, with a probability distribution for a less-massive -1 charge
cloud.

Deuterium and tritium, two true isotopes of hydrogen, increase the mass of the
center by adding neutrons. An antimuon is, I think, about 10% the mass of a
proton. So muonium would act a lot like extra-light hydrogen for the instant
before it decays.

It would have been clearer to call it an "exotic atom, chemically similar to
hydrogen", though. That wouldn't conflict with the common definition of
isotope as an atom with the same number of protons as the reference atom, but
with a different number of neutrons.

I'm actually not aware of any exotic atoms that are _not_ chemically similar
to hydrogen or antihydrogen, as getting an exotic helium-like atom would
require forming a +2 exotic center and making two -1 charges interact with it
before it decays. That is likely beyond our current capabilities.

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coldcode
"With a Fleming working on a bond, you could say the atomic interaction is
shaken, not stirred." What a great lol to start the day with.

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FrankenPC
(With a Fleming working on a bond, you could say the atomic interaction is
shaken, not stirred.)

Ha!

So, does that mean the idiotic idea behind that magic material from The Core
called Unobtanium might actually be real?

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nsphere
This is charge shift bonding. I did several computational research projects on
this in undergrad. It's nice to finally see this reaching the media.

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mikexstudios
Link to paper:
[http://dx.doi.org/10.1002/anie.201408211](http://dx.doi.org/10.1002/anie.201408211)

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Qwertious
Given that I have absolutely no real understanding of chemistry, what
implications does this have?

