How H2 becomes ‘molecule that made the universe’

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High-speed lasers are helping to shine a spotlight on the unusual chemistry of the molecule that made the universe, Trihydrogen, or H3+.

H3+ is prevalent in the universe, the Milky Way, gas giants, and the Earth’s ionosphere. The lab of Marcos Dantus, a professor in chemistry and physics at Michigan State University, is also creating and studying it. The researchers are using ultrafast lasers—and technology Dantus invented—to begin to understand the chemistry of this iconic molecule.

The new research appears in Nature Communications and the Journal of Chemical Physics.

“Observing how roaming H2 molecules evolve to H3+ is nothing short of astounding,” Dantus says. “We first documented this process using methanol; now we’ve been able to expand and duplicate this process in a number of molecules and identified a number of new pathways.”

The small picture

Astrochemists see the big picture, observing H3+ and defining it through an interstellar perspective. It’s created so fast—in less time than it takes a bullet to cross an atom—that it’s extremely difficult to figure out how three chemical bonds break and three new ones form in such a short timescale.

That’s when chemists using femtosecond lasers come into play. Rather than study the stars using a telescope, Dantus’ team literally looks at the small picture. The researchers view the entire procedure at the molecular level and measured it in femtoseconds—1 millionth of 1 billionth of a second. The process the team views takes between 100 and 240 femtoseconds. Dantus knows this because the clock starts when he fires the first laser pulse. The laser pulse then “sees” what’s happening.

The two-laser technique revealed the hydrogen transfer, as well as the hydrogen-roaming chemistry, that’s responsible for H3+ formation. Roaming mechanisms briefly generate a neutral molecule (H2) that stays in the vicinity and extracts a third hydrogen molecule to form H3+. And it turns out there’s more than one way it can happen. In one experiment involving ethanol, the team revealed six potential pathways, confirming four of them.

Since laser pulses are comparable to sound waves, Dantus’ team discovered a “tune” that enhances H3+ formation and one that discourages formation. When converting these “shaped” pulses to a slide whistle, successful formation happens when the note starts flats, rises slightly and finishes with a downward, deeper dive. The song is music to the ears of chemists who can envision many potential applications for this breakthrough.

The chemistry of life

“These chemical reactions are the building blocks of life in the universe,” Dantus says.

“The prevalence of roaming hydrogen molecules in high-energy chemical reactions involving organic molecules and organic ions is relevant not only for materials irradiated with lasers, but also materials and tissues irradiated with x-rays, high energy electrons, positrons, and more.”

This study reveals chemistry that is relevant in terms of the universe’s formation of water and organic molecules. The secrets it could unlock, from astrochemical to medical, are endless, he adds.

Researchers from Kansas State University also contributed to the Nature Communications study. The Department of Energy and the National Science Foundation funded the work.

Source: Michigan State University