Trihydrogen, or H3+, is a small but incredibly important molecule that has earned its nickname as “the molecule that made the universe.” Found in everything from the formation of stars to the complex chemistry of gas giants like Jupiter and Saturn, H3+ plays a crucial role in the cosmos, fueling everything from interstellar reactions to the birth of new stars. Though it may not seem as directly important to life on Earth as water or proteins, H3+ is central to our understanding of the chemistry of the universe.
While scientists have a clear picture of how the majority of H3+ is formed, much of its origin and abundance across the universe remain a mystery. Traditionally, it is thought to form when H2, a hydrogen molecule, collides with its ionized counterpart, H2+. But there is an emerging interest in understanding the alternate pathways through which H3+ can form, and this is where new research from Michigan State University (MSU) has made groundbreaking progress.
The Role of H3+ in the Universe
The importance of H3+ cannot be overstated. As one of the most common molecules in the universe, H3+ plays a key role in astrochemistry. Its presence is fundamental to processes such as star formation, the birth of organic molecules, and the chemistry that takes place in molecular clouds. This molecule even helps regulate the chemistry of the interstellar medium, providing the proton that allows other complex molecules to form, which in turn may lead to the creation of life.
Piotr Piecuch and Marcos Dantus, researchers from Michigan State University, have focused on unraveling the formation mechanisms of H3+ and have recently made strides in explaining how it forms in new and unexpected ways. While scientists have long known about its formation from H2 and H2+, these new insights reveal that H3+ can also emerge from other compounds, particularly methyl halogens and pseudohalogens.
The Breakthrough Discovery: Roaming Mechanism in Doubly Ionized Organic Molecules
The breakthrough, published in the journal Nature Communications, builds on MSU’s previous work on doubly ionized organic molecules, a key step in the quest to understand H3+ formation. When molecules are subjected to intense energy, such as from cosmic rays or lasers, they can lose two electrons, resulting in double ionization. When this happens, one might expect the molecule to break apart due to the repulsion of two positive charges—a phenomenon known as the Coulomb explosion. However, the MSU team made an unexpected discovery.
Instead of breaking apart immediately, the doubly ionized molecule exhibited a “roaming mechanism”. In this process, the molecule did not immediately fragment but instead expelled a neutral hydrogen molecule (H2) from its structure. This hydrogen molecule then roamed around the ionized structure, sometimes for a significant period of time, before grabbing a proton from within the molecule, forming H3+ in the process.
This finding was highly unusual and contrary to what scientists traditionally believed would occur in doubly ionized molecules. As Marcos Dantus explained, “It’s not the usual way of thinking about the behavior of doubly ionized molecules,” emphasizing that this roaming mechanism is far more complex than the straightforward Coulomb explosion many researchers assumed.
New Insights into Halogens and Pseudohalogens
With this breakthrough in mind, the team turned their attention to a class of compounds known as methyl halogens and pseudohalogens. These molecules are known for their interactions with halogen atoms like fluorine, chlorine, bromine, and iodine, as well as pseudohalogens like cyanide. The researchers observed the roaming mechanism in these compounds, uncovering more examples of how H3+ can form.
The team’s work helped identify not only the molecules that can form H3+ via the roaming mechanism but also those that cannot. By understanding the factors that govern H3+ formation, the researchers now have a clearer view of the potential for other compounds to yield this crucial molecule. These findings, published in the latest paper, provide a roadmap for scientists searching for H3+ in various organic compounds, both on Earth and throughout the cosmos.
One of the most exciting aspects of this discovery is the ability to apply these formation principles to a wide variety of molecules. This broadens the scope of astrochemical research, allowing researchers to predict which molecules, including many not yet studied, could potentially form H3+ in space.
Tools and Techniques: Pushing the Limits of Science
The research team at MSU employed a combination of ultrafast laser spectroscopy and cutting-edge computational chemistry to explore these mechanisms. The balance between these advanced techniques, brought together by the expertise of both the Piecuch and Dantus groups, was key to the success of the project.
Piotr Piecuch, a University Distinguished Professor and MSU Research Foundation Professor, highlighted the significance of their approach, stating, “What was quite special about this project was the use of state-of-the-art techniques from each side, including high-level theory and experimentation.” This collaboration allowed them to create movies that illustrate the formation of H3+ under different conditions, which can be found in the supplementary materials of the paper.
These state-of-the-art techniques, paired with high-level theoretical models and experimental verification, have propelled the team’s understanding of the formation mechanisms of H3+ forward, yielding a clearer picture of how such processes occur in the universe.
Implications for Future Research
The researchers’ work does more than just explain the roaming mechanism of H3+ in methyl halogens and pseudohalogens; it lays the groundwork for future studies into the molecule’s abundance and formation across the universe.
Marcos Dantus emphasized the importance of hydrogen in the universe, stating, “Hydrogen is the most common element in the universe, so H2 meeting H2+ is still the key.” However, he and his colleagues also believe that organic molecules in the diffuse clouds of interstellar space may be responsible for a surprising amount of H3+ formation. These findings are crucial for astronomers and chemists who want to understand the origins of this vital molecule and its role in star formation and molecular synthesis.
By uncovering these alternative pathways for H3+ production, scientists can better understand its abundance and distribution in various regions of the cosmos. The data could also provide new insights into the chemical reactions that drive the processes involved in star birth and the formation of complex organic molecules.
The Bigger Picture: Revising Models of Star Formation
This discovery has the potential to significantly impact how scientists model and understand key processes in astrochemistry. As Piecuch stated, even if only a few extra percent of H3+ is produced by the mechanisms the team has studied, it could require scientists to revisit and adjust models used to understand processes like star formation.
These alternative pathways of H3+ formation can help shape models that account for the molecule’s presence in a wide range of environments, from molecular clouds in space to the gas giants in our solar system. The discovery adds an important layer of complexity to our understanding of cosmic chemistry, opening new avenues for research into how the universe’s building blocks come together.
Conclusion
The discovery of new sources of H3+ is a vital step forward in our understanding of the chemistry of the cosmos. By uncovering the factors that govern the formation of this molecule in methyl halogens and pseudohalogens, the MSU team has expanded the horizon for researchers studying H3+ and its role in the universe.
This research has far-reaching implications for the study of interstellar chemistry, the formation of stars, and the overall chemical makeup of the universe. It could redefine how we understand the molecular processes that govern the birth of stars, planets, and life itself.
As research continues and more discoveries are made, the enigmatic molecule H3+ will undoubtedly continue to offer new insights into the nature of the universe and the forces that shape it. And as Piecuch and Dantus note, this is just the beginning of the search for H3+—an investigation that could reshape our view of the cosmos.
Reference: Jacob Stamm et al, Factors governing H3+ formation from methyl halogens and pseudohalogens, Nature Communications (2025). DOI: 10.1038/s41467-024-55065-5