Seeking the origins of the molecule that made the universe

The vastness of the universe holds countless mysteries, from the birth of galaxies to the intricate chemistry of interstellar space. Among the many molecular players shaping the cosmos, one stands out for its fundamental role in star formation and chemical evolution – trihydrogen, or H₃⁺.

Often called “the molecule that made the universe,” it plays a crucial role in interstellar chemistry, fueling reactions that contribute to the formation of stars and planets.

H₃⁺ is found across the universe, in everything from glowing nebulae to gas giants like Jupiter and Saturn. Scientists have long understood its primary formation mechanism: when molecular hydrogen (H₂) collides with its ionized form (H₂⁺), H₃⁺ is created.

Yet, researchers remain eager to explore alternative pathways leading to the formation of H₃⁺ and to get an estimate of its full abundance across the cosmos.

A recent study from Michigan State University (MSU) has shed new light on this puzzle. Led by researchers Piotr Piecuch and Marcos Dantus, the study provides insights into how H₃⁺ forms in compounds known as methyl halogens and pseudohalogens.

The findings build upon previous discoveries and open new avenues in astrochemistry.

New pathways to H₃⁺ formation

Until recently, scientists assumed that H₃⁺ primarily formed through well-known ionization reactions in space. However, the MSU team challenged this notion by investigating alternative sources.

Their earlier work revealed that H₃⁺ could emerge from a process known as the “roaming mechanism” in doubly ionized organic molecules.

Double ionization occurs when a molecule loses two electrons due to intense energy exposure, such as from cosmic rays or high-powered lasers. Traditionally, a doubly ionized molecule was expected to fragment violently due to repulsion between the two positive charges.

Instead, the researchers observed an unusual effect. The molecule did not break apart immediately. Instead, a neutral hydrogen molecule (H₂) formed within the structure, roamed around, and eventually captured an extra proton, leading to the creation of H₃⁺.

The study provided a fresh perspective on how H₃⁺ could arise in environments beyond the standard hydrogen ionization pathway. Building on this work, the team turned their attention to halogenated compounds, seeking to determine whether similar processes could occur in these substances.

Methyl halogens and pseudohalogens

Methyl halogens and pseudohalogens are compounds that contain carbon, hydrogen, and halogen elements, such as fluorine, chlorine, or bromine.

These molecules exist in space and play a role in various chemical reactions. The MSU researchers suspected that H₃⁺ might form within these compounds through double ionization and the roaming mechanism.

By using ultrafast laser spectroscopy and advanced computational modeling, the team observed the formation process in unprecedented detail. Their experiments confirmed that H₃⁺ could emerge from several methyl halogens and pseudohalogens, which provided new evidence of this alternative formation pathway.

Understanding these reactions is significant because it suggests that H₃⁺ may originate from a broader range of molecular sources than previously thought. If these mechanisms occur frequently in space, they could contribute significantly to the overall abundance of H₃⁺ in the universe.

Significance of H₃⁺ in astrochemistry

“H₃⁺ is a small molecule that might not be as important to us on Earth as water or proteins, but it’s a molecule we truly want to understand in terms of its abundance in the universe, how it is produced, and how fast its chemical reactions are,” explained Piecuch.

“With our findings, we can communicate with others who are looking for sources of H₃⁺ and the molecules that can form it.”

The importance of H₃⁺ extends beyond its formation. It acts as a key reactant in many interstellar chemical reactions, and plays a pivotal role in forming more complex organic molecules. These molecules, in turn, contribute to the chemistry that eventually leads to the building blocks of life.

Behavior of doubly ionized molecules

Being “the molecule that made the universe” comes with significant expectations. Scientists have long recognized the essential role of H₃⁺, but the unexpected discovery of the roaming mechanism has reshaped how they think about molecular behavior under extreme conditions.

“H₃⁺ is essential for astrochemistry, from the birth of stars to the formation of many organic molecules,” said Dantus.

The team’s previous work had already suggested that doubly ionized molecules do not always explode apart as conventional wisdom predicted.

Instead, their experiments revealed that neutral hydrogen molecules can linger within the ionized structure, searching for a way to interact. The roaming H₂ then captures an additional proton, forming H₃⁺.

“We demonstrated that the hydrogen didn’t simply fly away, but it stuck around, sometimes for quite a long time,” Dantus added. “This was highly unusual.”

Piecuch compared this roaming effect to the expected Coulomb explosion, where two positive charges within a small molecule repel each other with great force. Instead, the study showed a more intricate and delicate process where charged and neutral components interact in unexpected ways.

Searching for new H₃⁺ sources

The researchers did not stop at merely identifying compounds that produce H₃⁺. Equally important was recognizing which compounds failed to generate H₃⁺ under similar conditions.

By comparing successful and unsuccessful cases, they developed a set of predictive factors that could help identify other molecules capable of forming H₃⁺.

Turning their attention to halogens and pseudohalogens, Piecuch, Dantus, and their colleagues confirmed several more molecules that form H₃⁺ through double ionization. Just as crucially, they also identified those that do not.

To illustrate their findings, the researchers worked with Professor Benjamin Levine at Stony Brook University to create computer simulations of these reactions. The resulting animations, included in the study’s supplementary material, provide a visual representation of H₃⁺ formation in real-time.

Advanced techniques in chemistry

These discoveries were made possible through a combination of ultrafast laser spectroscopy and computational chemistry.

The ability to measure reactions occurring on femtosecond timescales – one quadrillionth of a second -allowed the researchers to capture molecular movements that would otherwise remain invisible.

Piecuch emphasized the importance of combining experimental and theoretical approaches.

“What was quite special about this project – to bring it to fruition – was the use of state-of-the-art techniques from each side, including high-level theory and experimentation,” he said.

By leveraging these tools, the researchers uncovered fundamental insights into how molecular ions behave – knowledge that could influence multiple fields of chemistry and physics in the future.

Understanding cosmic chemistry

The findings have broad implications for astrochemistry. By establishing a set of governing factors for H₃⁺ formation, they provide a framework for future research. This knowledge can guide scientists in identifying other organic compounds that might contribute to H₃⁺ production.

“Hydrogen is the most common element in the universe, so H₂ meeting H₂⁺ is still the key,” Dantus explained. “However, there are so many organic molecules in these diffuse molecular clouds that it’s possible a lot of H₃⁺ is still being formed by the processes we’ve studied.”

“Even if there are only a few percent more H₃⁺ molecules in the universe because of the small organic compounds we and others have studied, the models that scientists use to study processes such as star formation may have to be revisited,” Piecuch concluded.

As researchers continue to explore the origins and behavior of H₃⁺, they push the boundaries of what is known about the molecules that shape the universe. With each discovery, scientists come closer to understanding the fundamental chemistry that governs the cosmos.

The study is published in the journal Nature Communications.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–