The Butterfly Molecule

Jonathan James

If you cast your mind back to chemistry class at school, you’ll probably remember learning about various types of atomic bonds. Typically, we think about the way atoms bind to one another in a couple of ways – ionic bonding, where oppositely charged ions are held together by electrostatic interactions, and covalent bonding, in which electrons are shared between atoms. For a long time, these looked like the only types of bonding that could exist under our current understanding of how atoms bind one another, but a recent discovery has unveiled a whole new type of bonding that seems to defy our understanding of chemistry.

Let’s quickly recap what we know about atoms. In the traditional model, atoms are made up of a positively charged nucleus, made up of protons (which give it its positive charge), and neutrons. This nucleus is tiny, and the clear majority of the atom’s size is empty space. Surrounding the nucleus are negatively charged electrons, which orbit in ‘shells’, a bit like planets around the sun (but not really… That could be an article all by itself!) Typically, atoms take up a volume so small, that you could fit 200,000,000,000,000,000 of them inside the dot on this exclamation point!

Recently, however, scientists have been able to confirm a theory that they’ve had since 2002. The existence of ‘Rydberg molecules.’ Affectionately referred to as ‘Butterfly molecules’ because of the butterfly like distribution of the orbiting electrons, Rydberg molecules are enormous. In fact, at a millionth of a meter across (huge for an atom!), they are about the same size as an entire E. coli bacterium. Their electrons are anywhere from 100-1000 times further away from the nucleus than they should be. At these distances, the electrons become ‘super electronically excited’, which allows them to act like a lasso, grabbing nearby atoms and forming weak interactions with them.

The researchers created the molecules by super cooling Rubidium gas to a just above absolute zero, before exciting them into their Rydberg state using lasers. They then kept the atoms under observation, looking for changes in the frequency of light that they would absorb, as this would show that a bond had been formed. Eventually they discovered that they had indeed triggered the formation of these butterfly molecules.

But why should you be excited about this discovery? After all, it’s just another type of dull chemical bond that kids will be forced to learn about, right? Actually, there is a lot of excitement around Rydberg molecules and how they might be used in nanotechnology and small scale electronics to make them much more efficient. There are even hopes that they might be used in quantum computing, pushing technology even more into the future!

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