By Arturo RobertazziAbout-Science, My-Stories

Quantum Nanoreactor Simulations of The Early Universe: The Dawn of Interstellar Chemistry

Alright quantum friends, today we’re going to talk about some seriously mind-boggling stuff: Quantum nanoreactor simulations of the first molecules of the universe. Yeah, you heard me right. We will dig into the chemical processes of the primordial soup, from which everything originated, stars, planets and our very own existence. Have patience, I promise we will get to the core of it, but first, let’s answer one essential question:

When did Chemistry begin?

Well, everything started with the Big Bang, right? While there may be some scientific-philosophical debate surrounding the validity and limitations of the theory, let’s assume for our purposes that the Big Bang is simply the origin of spacetime, stars, and all the stuff the universe is made of.

So here’s the deal: about 380.000 years after the Big Bang, the hot soup of protons, electrons, photons, and all sort of other particles that was our universe began to cool down. And when it hit around 4.000 kelvin, the ions of light elements started to recombine. This set off a chain reaction that eventually led to the formation of more complex molecules and structures, which, after billions of years, gave rise to life as we know it.

Let’s skip the wildly cool fact that at this point the universe became transparent and that we can still see the primordial light in the cosmic background radiation. Let’s also skip the birth of spacetime, the arrow of time, the past hypothesis, and the scientific discussion about the entropic state of the early universe.

Instead, let’s think chemistry.

The Jewel Bug Nebula (NGC 7027) is situated in the Cygnus constellation, about 3.000 light-years away from us. Credits: SciTech Daily

The Dawn of Interstellar Chemistry

What started this whole chemical shebang that we call nature?

Well, it was a small positively charged molecule, the helium hydride ion, aka HeH+. And let me tell you, creating this molecule is no small feat. Helium is a little greedy noble atom and notoriously difficult to combine with other elements. However, the conditions of the early universe were harsh enough for it to look desperately for companions. While this naturally happened after the Big Bang, it took us humans about 14 Billion years to force helium (in 1925) to interact with hydrogen and make HeH+ in the lab.

Later, in the ’70s, quantum chemistry calculations fed the hypothesis that local astrophysical plasmas, like for example a nebula, might just be the perfect environment for the formation of our primordial molecule. It was an exciting prospect, but the observations at the time were – how shall I put it? – about as hazy as a blurry mirage.

Fast forward four decades later, to 2019, and astronomers finally observed helium hydride ions in the planetary nebula NGC 7027, or as cosmic friends call it: the Jewel Bug Nebula.

So what’s the big deal, you ask?

Well, for starters, the story of this discovery is an epic tale of its own as it gives us a glimpse into the chemical processes that occurred in the early universe. But here’s the really exciting part. HeH+ may actually be the precursor of the first interstellar acid, H3+: the cosmic chemical initiator of the stuff that makes up trees and walls, air, and even you.

Pretty neat, right?

Ab Initio Nanoreactor Simulations - H3+, The Cosmic Chemical Initiator
Cartoonized molecular structure of H3+

Meet H3+, The Cosmic Chemical Initiator

H3+ is the second most abundantly produced interstellar molecule after H2 and is all over the place, in both dense and diffuse gas clouds. But it’s also very reactive as it can act as a universal proton donor to molecules containing oxygen, nitrogen and other elements, thus triggering all sorts of ion-molecule reactions. This can lead to the formation of some pretty complex species that are key to making all the good stuff that we see here, there, and everywhere.

Cosmic chemical tree - Ab Initio Nanoreactor Simulations

When H3+ protonates atoms and molecules, it totally amps them up and gets them super active, which kicks off a whole chain of reactions. You can imagine H3+ as the root of the cosmic chemical tree (figure on the left adapted from McCall 2001). Without the proton exchange via H3+, the formation of interstellar molecules would take way longer. And when you’re trying to cool down gas that’s condensing because of gravity, timing is everything.

So yeah, H3+ is the cosmic chemical initiator. But, there’s still a lot we don’t know for sure:

  • How did He and H protons collide in a positively charged atmosphere?
  • What kind of chemical reactions went down at the beginning of the Universe?
  • Was HeH+ the first molecule? And if so, how did H3+ form?

To shed light on these big questions, Dash & Co. dropped a new study based on a fancy technique: They performed quantum nanoreactor simulations of the first chemical reactions at the beginning of the universe.

Example of nanoreactor simulations in QuantistryLab

Wait what, quantum nanoreactor simulations of the early universe?

Well done, you made it so far. Now, let’s talk about some cool quantum chemistry.

Discovering new compounds and understanding how they behave is a huge part of chemistry. And while experimental research is vital, theory and computation have become just as critical when it comes to understanding chemical processes and reactions at a deeper level.

Meet the quantum nanoreactor. With this computational device, quantum chemists can conduct unguided first-principles molecular dynamics simulations of chemical reactions – that means, simulations without preconceived ideas about what will happen.

Picture this: you throw all sort of atoms and molecules into a “virtual” reactor and, by solving quantum mechanics-based equations, you can follow the dynamics of the system, observe reactions occurring, and products being formed. All without stepping foot in the lab. With this amazing tool, you can uncover new pathways, molecules, and mechanisms that may have otherwise gone unnoticed.

Now, imagine applying this simulation approach to the early universe. It is like taking a trip with a time machine back to 380.000 years after the Big Bang. And that is exactly what Dash & Co. did.

They recreated the conditions of the early universe by running quantum nanoreactor simulations on systems containing helium and hydrogen atoms and ions. They set up their models varying key conditions like temperature, overall positive charge, and the ratio of hydrogen to helium. Then they popped some corn, cracked a couple of beers, and observed how the systems evolved, chemical species collided, and reactions occurred.

Here’s the movie trailer:

Ab initio nanoreactor simulation of 15 H (white) and 15 He atoms (peach), with an overall positive charge of 20. The animation shows He chains forming. Video from Dash et al. 2021

Quantum nanoreactor simulations of the primordial chemical soup

So, what do we actually learn from these quantum chemistry simulations? Brace yourself, because it’s pretty epic:

  1. HeH+ was the first molecule to form within 15 femtoseconds in every simulation – in agreement with previous findings.
  2. The overall positive charge was key to the formation of H3+. While no intermediates or H3+ were observed throughout neutral simulations, the formation rate of H3+ increased with the overall positive charge of the system.
  3. Up to a positive charge of +6, H3+ was the only end product. Beyond that, also H+ and HeH+ formed, balancing out the total charge of the system.
  4. The formation of short-lived species was also observed, such as He2H+, He3H+, and He22+, confirming the existence of previously suggested mono-cationic He ion clusters.
  5. These secondary species needed a longer time to form (0.1 picoseconds) and survived for only 5-10 femtoseconds before dissociating and participating to the formation of H3+.
  6. Two pathways with similar thermodynamics led to the formation of H3+
    • One involving H2 snatching a proton from HeH+;
    • A second pathway, in which the proton is stolen from a mono-cationic dihydrogen molecule.
  7. And finally the most intriguing finding: H3+ and H2 were the only stable hydrogen forms left in the simulated reaction mixture, in agreement with what we know about our universe.
Thermodynamics of H3+ formation. - Ab Initio Nanoreactor Simulations
Thermodynamics of H3+ formation. Adapted from Dash et al. 2021

Quantum nanoreactor simulations: a journey back in time

Imagine if you could hop in a time machine and go back to 380.000 years after the Big Bang. What would you see? You’d be greeted with a frantic jumble of protons colliding into each other. After a mere 15 femtoseconds (that’s 0.000000000015 seconds!), you’d witness something truly remarkable – the formation of the first molecule, HeH+, amidst a frenzied cluster of helium and hydrogen protons. As things gradually settle down, a species emerges: H3+, the cosmic chemical initiator.

Chemistry is born.

Of course, the reality is far more Intricate. It always is. Nature loves to throw surprises at us. But that’s why the approach of Dash & Co. is so illuminating. They applied the spherical cow method to chemistry, developing simplified models that help us understand complex systems bottom-up – from atoms and electrons to the origin of chemical processes, which ultimately lead to life and the emerging phenomena we experience every day.

A final Personal Touch

Writing on From Atoms to Words has been a constant joy for me. But amidst all the fun, I’ve also rediscovered the beauty of (quantum) chemical simulations – from the early days when human computers would painstakingly solve the Schrödinger equation by hand, to the fascinating world of astrochemistry and the building blocks of life itself, to the dazzling possibilities of a future where computational chemistry grasps more and more that wonderful emerging complexity.

And today we have learned that simulations based on quantum chemistry can also shed light on the early universe and the formation of the first molecules 380.000 years after the Big Bang.

Yes, I’m having fun. I hope you are too.

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From Quantum Chemistry To Stories

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A collection of my thoughts and musings on science, writing, and the intersection of the two.

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Arturo Robertazzi - Me, my room. My books.