In a feat of modern-day alchemy, atom tinkerers have fooled hydrogen atoms right into accepting a helium atom as one of their own. The camouflaged atom behaves chemically prefer hydrogen, yet has 4 times the massive of typical hydrogen, allowing predictions for just how atomic fixed affects reaction rates to be put to the test.

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A helium atom consists of a cell core containing 2 positively fee protons and two neutrons, encircled by 2 orbiting electrons which lug a negative charge. A hydrogen atom has just one proton and one electron. Donald Fleming of the college of brother Columbia in Vancouver, Canada, and colleagues managed to disguise a helium atom together a hydrogen atom by replacing one of its orbiting electrons v a muon, which is much heavier 보다 an electron.

Because the is therefore heavy, the muon sits 200 times closer to the helium nucleus 보다 the electron the replaces and cancels out one of the nucleus’s positive charges. The continuing to be electron then behaves as if it to be orbiting a nucleus with simply one positive charge, similar to the electron in a hydrogen atom. The difference is that the nucleus is 4.1 times heavier than normal.


Fleming and his colleagues offered this “super-heavy hydrogen”, to check the effects of fixed on chemical reaction rates. A lone hydrogen atom can kind a brand-new hydrogen molecule by stealing among the 2 atoms native a pre-existing hydrogen molecule – yet for the to happen there needs to be sufficient energy accessible to break the link holding the existing molecule together.

Quantum tunnels

According to quantum mechanics, the is not always necessary to climb over this power barrier: instead, particles have the right to “tunnel” with it. Yet the more heavier the corpuscle are, the harder the is to tunnel, for this reason the less generally the partner-swapping reaction take away place.

Two hydrogen isotopes, include one or 2 neutrons and with two or 3 times the massive of typical hydrogen, deserve to be supplied to check this. An even heavier isotope, with three neutrons, exists but decays also quickly. Muonic helium, which has actually the same mass together this isotope, lasts long enough to react through a hydrogen molecule.

Fleming’s team shooting muons created at the TRIUMF accelerator in Vancouver right into a cloud that helium, molecular hydrogen and also ammonia. The helium atoms captured the muons, then pulled hydrogen atoms away from the molecule hydrogen and also bonded v them.

The team compared how lengthy this took through the price of the very same reaction using common hydrogen, and with a reaction price recorded in 1987 as soon as a kind of ultra-light hydrogen, called muonium, to be used. Chemists formed this by instead of the proton in a hydrogen atom v an antimuon, the muon’s positively fee antimatter partner.

‘Very sexy’

As expected, the reaction with the disguised helium was the slowest, adhered to by regular hydrogen, climate the light hydrogen. The prices perfectly matched predictions from quantum mechanically calculations led by Fleming’s teammate Donald Truhlar that the college of Minnesota in Minneapolis.

The means any physics system alters with time can, in theory, be predicted indigenous the quantum claims of that is particles. Many reactions involve much too plenty of particles because that this to be practical, but Truhlar says the hydrogen reaction was just basic enough.

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Millard Alexander of the university of Maryland in university Park calls it “very sexy atom chemistry”.