Society for Science & the Public, which publishes Science News, uses cookies to personalize your experience and improve our services. For more information on how we use cookies on our websites, visit our Cookie Policy</s>As the element that makes up 75 percent of all the mass in the Universe, and more than 90 percent of all the atoms, we’re all pretty well acquainted with hydrogen.

But the simplest and most abundant element in the Universe still has some tricks up its sleeve, because physicists have just created a never-before-seen form of hydrogen - negatively charged hydrogen clusters.

To understand what negatively charged hydrogen clusters are, you first have to wrap your head around their far more common counterparts - positively charged hydrogen clusters.

Positively charged hydrogen clusters are pretty much exactly what they sound like - positively charged clusters of a few or many hydrogen molecules.

Known simply as hydrogen ion clusters, they form at very low temperatures, and can contain as many as 100 individual atoms.

Physicists confirmed the existence of hydrogen ion clusters some 40 years ago, and while a negative counterpart to these clusters boasting large numbers of atoms were theorised, no one could figure out how to create one.

But that didn't stop a team of physicists led by Michael Renzler from the University of Innsbruck in Austria from giving it a shot.

First, they injected cold liquid helium droplets with hydrogen (H2) molecules. This caused the mixture to form clusters with a neutral charge.

Next, they exposed these H2-infused droplets to an electron beam, and that caused some of the hydrogen molecules to ionise, and be flung out into the surrounding vacuum as negatively charged hydrogen ions.

Soon, nearby hydrogen molecules started clustering around the negatively charged ions, and the researchers discovered that these newly formed groups could boast a few, or many molecules each.

As is often the case with the most elusive structures in particle physics, these negatively charged hydrogen clusters existed only for an incredibly fleeting moment - several microseconds (1 microsecond = 0.000001 seconds).

But that was enough time for the team to determine their geometric structures.

As Michael Schirber reports for the American Physical Society, the researchers found that the clusters only had odd atom numbers, ranging from n= 5 to n = 129.

The most stable clusters had a central, negatively charged H− ion core sounded by shells that were completely filled up by hydrogen molecules.

"The odd values implied that the clusters were a combination of several H2 molecules and a single H− ion core, held together through an induced dipole attraction," Schirber explains.

The most commonly recorded clusters had the atomic numbers n = 25, n = 65, and n = 89.

These 'magic numbers', as the team calls them, correspond to symmetrical, almost solid arrangements of H2 molecules, such as a 20-sided icosahedron. (You can see one of these formations in the image at the top of the page.)

So why does all this matter? For years now, researchers have suspected that these large hydrogen clusters could form naturally in outer space, either in cold, dense clouds, or the atmospheres of gas planets.

Now that we know that negatively charged hydrogen clusters aren't impossible, and what their most common and stable form could be, it could make it easier to identify them in nature for the time.

And at a time when researchers are questioning if dark matter - the stuff that hypothetically makes up 27 percent of the observable Universe - even exists, we need all the help we can get when it comes to deciphering the smallest constituents of the space around us.

The research has been published in Physical Review Letters.</s>An Environment Ministry survey has found hydrogen sulfide levels above the national criteria in 33 hot springs baths across Japan, it was learned on Monday.

The survey covered 6,434 hot springs baths in the first such detailed research but did not receive reports on 1,996 of them from relevant local authorities. Regular monitoring for the chemical is not mandatory.

The criteria call for keeping hydrogen sulfide levels below 20 parts per million at a level 10 cm above the bathtub and below 10 ppm 70 cm above the bathroom floor.

No readings were reported above 50 ppm, considered the threshold for levels likely to harm health.

The ministry survey is part of work to review structural standards for spa facilities to prevent accidental poisoning.

In October 2014, a man became unconscious at a spa in the town of Ashoro, Hokkaido. Hydrogen sulfide levels there were about 10 times the limit.
Scientists have created a new form of hydrogen at temperature near absolute zero. These anions or clusters are formed by an electron addition to liquid helium nanodroplets doped with molecular hydrogen or deuterium.