Molecular Nobility

I have obtained permission from Haley Gomez to geek out over the internet about something in her talk at this conference today – which is possibly the most exciting thing I’ve ever seen at an astronomy conference! Specifically, none other than a noble gas compound detected in a supernova remnant! I know, right?

Remember kids, "noble" does not mean "inert"!Noble gas compounds, supernova chemistry, supernova remnants generally, and identifying mysterious astronomical spectroscopic lines are already some of my favourite things, but all of those things together? Just fantastic.

Without going into too much detail about the specifics, which are presently being kept under wraps, a certain popular supernova remnant has had a couple of unidentified spectroscopic lines in it for quite some time. However, with a little careful examination, it seems that those lines are in fact due to the Argon Hydride molecule, ArH+. Which would be the first firm detection of a noble gas compound astronomically. Seriously, I knew it was only a matter of time (any long time readers of mine may recall me musing about noble gas compounds before…). I’m going to be eagerly waiting for the paper to be published on this.

Interestingly enough, another talk yesterday said something about evidence for krypton depletion in cold diffuse interstellar environments too. Which makes me wonder…

Yes, supernova remnants can be popular. Most of them have more fans than I do.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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4 Responses to Molecular Nobility

  1. Orion says:

    So, I’m a physicist with a basic idea of how covalent and ionic bonds work in molecules, but it’s not clear to me how this ArH+ is held together. I’ve seen a couple articles on this finding, but so far none have explained how that works.

    • invaderxan says:

      A good question! It seems not many people are talking about the actual mechanics of these molecules…

      Ok, so the type of bonding in a molecule like this is technically known as a dative covalent bond, where both the electrons in the bond come from one of the two atoms involved. Think of it as being partway between an ionic and a covalent bond – highly polar, but the electrons are still shared between the two atoms. It only works because the molecule is charged, and because H+ is tiny. In fact, H+ is basically just a free proton. It’s only attached because it can latch onto a pair of the (plentiful) electrons orbiting the Argon atom.

      As you can imagine, this is a rather tenuous chemical bond. If an electron were to attach to this molecule, it would destroy it and two neutral atoms would drift away from each other. I’d imagine that argon hydride is a powerful gas phase acid. Collisions with other molecules would readily destroy it, giving an Argon atom and the protonated form of whatever molecule were to collide with it. Interestingly, that would seem to imply a relatively efficient formation mechanism in order to maintain a detectable population.

      For more about similar outlandish chemistry, see here and here. Hope that helps! :)

  2. Peter Dawson says:

    evidence for krypton depletion

    One wonders whether Superman has been nosing around up there…

    • invaderxan says:

      Well you know, given the reason why Superman came to Earth in the first place, I’d say Krypton is pretty well depleted.

      (Also, there is actually a hypothetical Krypton oxide, the anion of which would be correctly called kryptonite. Just sayin’…)

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