Helonium Explained: The Real Story of HeH⁺ and the Universe’s First Chemistry

Introduction

The name sounds like an element.

It is not.

HeH⁺ is the helium hydride ion, a positively charged molecular ion made from helium and hydrogen. Its systematic name is hydridohelium(1+). Scientists study it because early-Universe models place this ion near the very start of molecular chemistry.

Its story spans a century.

Laboratory evidence appeared in 1925. Astronomers found it securely in space in 2019. Recent work is still sharpening how fast it reacts and exactly where its main rotational line sits.

Direct Answer: What Is Helonium?

Helonium is another name for the helium hydride ion, HeH⁺. It contains helium and hydrogen, carries a +1 charge, and is a molecular ion rather than a chemical element.

ChEBI lists it as hydridohelium(1+), with the formula HHe, net charge +1, and average mass of about 5.011 Da.

That is the short answer.

Here is the full story.

Quick Facts

Fact	Verified detail
Common scientific name	Helium hydride ion
Formula	HeH⁺ / HHe⁺
Systematic name	Hydridohelium(1+)
Net charge	+1
Main atoms	Hydrogen and helium
ChEBI ID	CHEBI:33688
Average mass	5.011 Da
First laboratory evidence	1925
First secure space detection	2019
Detection site	NGC 7027
Observatory	SOFIA
Instrument	GREAT/upGREAT
Famous space line	149.1 μm
2026 measured frequency	2010.183312(8) GHz
Periodic-table element?	No

The chemical details come directly from ChEBI, while the laboratory and space dates are supported by Physical Review and Nature.

Is HeH⁺ a Chemical Element?

No.

The answer is clear.

A chemical element has an atomic number. Helium is element 2. Hydrogen is element 1.

HeH⁺ is different.

It is a charged molecular species formed from helium and hydrogen. It has no separate atomic number and no position of its own on the periodic table.

ChEBI places hydridohelium(1+) under helium hydrides.

So claims that it is “element 119,” a hidden element, or a newly discovered metal do not match established scientific records.

What Is HeH⁺ Made Of?

It contains helium and hydrogen.

A simple formation reaction is:

He + H⁺ → HeH⁺ + photon

Here, neutral helium joins with a proton.

Energy leaves as a photon.

Chemists call this type of process radiative association. The same reaction is central to models of HeH⁺ formation in the young Universe.

The ion carries a positive charge.

That makes its chemistry very different from ordinary neutral helium gas.

Why Is HeH⁺ Linked to the First Chemistry in the Universe?

The early Universe was extremely hot.

Then it cooled.

As cooling continued, helium ions captured electrons before hydrogen fully recombined. Neutral helium atoms could then meet protons still present in the gas.

Those particles could form HeH⁺.

The 2019 Nature paper states that neutral helium and protons formed what researchers describe as the Universe’s first molecular bond in the helium hydride ion.

This is why the ion often appears in discussions about the start of cosmic chemistry.

There is one detail to keep clear.

Scientists did not directly watch the first HeH⁺ ion form after the Big Bang. Its early history is reconstructed from physics, chemistry, laboratory measurements, astronomical observations, and cosmological models.

Was HeH⁺ the First Molecule?

A precise answer is:

HeH⁺ is widely described as the first molecular ion, and its bond is described as the first molecular bond expected to form in the early Universe.

The 2019 research ties HeH⁺ to that first molecular bond. Nature Astronomy later described its detection as the discovery of the first molecular ion in the Universe.

The wording matters.

HeH⁺ carries an electric charge.

It is not a neutral molecule like H₂.

So “first molecular ion” is often the clearest phrase.

How Did HeH⁺ Help Lead to Molecular Hydrogen?

HeH⁺ can react with hydrogen.

One key reaction is:

HeH⁺ + H → He + H₂⁺

Then H₂⁺ can join other reactions that form neutral molecular hydrogen, H₂.

This gave early cosmic chemistry a path from a very simple helium-hydrogen ion toward molecular hydrogen.

Why does H₂ matter?

Molecules can lose energy through rotational and vibrational radiation. That can help gas cool.

Cooling matters because contracting gas needs to lose heat before dense structures and early stars can form.

So this tiny ion sits near the root of a much larger chemical story.

When Was HeH⁺ First Found in a Laboratory?

The first laboratory evidence dates to 1925.

T. R. Hogness and E. G. Lunn published their paper in Physical Review on July 1, 1925.

They studied ions formed through electron impact.

In helium containing hydrogen, they reported evidence for HeH⁺. They also reported possible evidence for another heavier helium-hydrogen ion.

That happened long before astronomers could confirm the ion in space.

The gap was huge.

Nearly 94 years.

Why Was HeH⁺ So Hard to Find in Space?

Its strongest useful spectral signal is tough to observe from the ground.

A key rotational transition lies near:

149.1 micrometres

That corresponds to a frequency near:

2.010 THz

Earth’s atmosphere absorbs much of the radiation in this part of the spectrum.

There was another issue.

Spectral features from CH sit close to the expected HeH⁺ signal. Astronomers needed enough spectral resolution to separate the features clearly.

SOFIA helped.

The observatory flew high above much of Earth’s water vapour, giving its instruments a clearer view of far-infrared and terahertz radiation.

Its GREAT receiver provided the detail needed.

Where Was HeH⁺ Found in Space?

Astronomers securely detected it in the planetary nebula NGC 7027.

Rolf Güsten and colleagues reported the finding in Nature on April 17, 2019.

They used the GREAT/upGREAT spectrometer aboard the Stratospheric Observatory for Infrared Astronomy, better known as SOFIA.

The team detected the J = 1–0 ground-state rotational transition at 149.1 μm.

This was the first unambiguous detection of the helium hydride ion in interstellar space.

A molecule known in laboratories since 1925 had, at last, been seen beyond Earth.

Why Was NGC 7027 a Good Place to Look?

NGC 7027 contains conditions that favour HeH⁺ chemistry.

The planetary nebula has hot ionized gas, helium, hydrogen, and a very hot central star.

These conditions create regions where the required helium and hydrogen species can meet.

That made NGC 7027 one of the best places to search.

But there is an easy mistake here.

NGC 7027 is not leftover primordial gas from the Big Bang.

It is a much younger astronomical object.

Scientists can still use its chemistry to test reactions that also matter in models of the early Universe.

How Do Scientists Identify HeH⁺ in Space?

They read its spectrum.

Molecules have specific energy states.

When they move between those states, they can emit or absorb radiation at set frequencies.

Think of those frequencies as fingerprints.

HeH⁺ has its own fingerprint.

One of its most famous lines is the J = 1–0 rotational transition near 2.010 THz.

Astronomers compare signals from space with very precise laboratory measurements.

A match can identify the molecule.

That is exactly why better laboratory spectroscopy matters so much.

What Did Scientists Learn About HeH⁺ in 2025?

A 2025 experiment checked how the ion reacts at extremely low temperatures.

Researchers at the Max Planck Institute for Nuclear Physics studied HeH⁺ reacting with deuterium, an isotope of hydrogen.

They stored HeH⁺ ions inside a cryogenic storage ring at temperatures of only a few kelvin.

Then they collided them with neutral deuterium atoms.

Older calculations predicted that the reaction rate would fall strongly at low temperature.

That did not happen.

The measured rate stayed almost constant across the low-energy region tested.

New calculations using a corrected potential-energy surface fit the experiment far better.

The study described the process as a fast, barrierless reaction.

Why Does the 2025 Result Matter?

Reaction rates affect abundance estimates.

If HeH⁺ is destroyed faster, less of it may remain at a given stage of cosmic history.

The 2025 Astronomy & Astrophysics paper specifically suggests a lower abundance of the first molecules at very high redshifts than some older calculations predicted.

This does not erase the ion’s place in early chemistry.

It changes the numbers.

And better numbers mean better models.

What Changed in 2026?

Scientists measured the main rotational transition much more precisely.

A 2026 paper in Physical Chemistry Chemical Physics reported the frequency as:

2010.183312(8) GHz

The researchers used a 4 K, 22-pole ion trap and several action-spectroscopy methods.

The measurement improved the earlier value by about one order of magnitude.

That is useful for astronomers.

A sharper laboratory frequency tells them exactly where to check when searching spectra from space.

The paper was first published on January 27, 2026.

Is HeH⁺ a Strong Acid?

In gas-phase chemistry, it is an extremely strong proton donor.

That needs context.

HeH⁺ can give its proton to many other chemical species very easily because helium has a very low proton affinity.

But do not picture a bottle of liquid acid.

This comparison belongs to gas-phase ion chemistry.

It does not mean scientists handle HeH⁺ like sulfuric acid or another common laboratory liquid.

Can Scientists Make HeH⁺ on Earth?

Yes.

They have done it for about a century.

The 1925 experiment already provided laboratory evidence. Modern researchers can create, trap, cool, and measure the ion with very high precision.

The 2026 spectroscopy study produced HHe⁺ ions using a hydrogen-helium mixture and electron impact.

The ions were then studied inside a cryogenic trap.

So the species is real.

It is measurable.

And scientists can reproduce it.

Does HeH⁺ Have Everyday Uses?

No standard everyday use is established.

Its value is mainly scientific.

Researchers use it to study:

• early-Universe chemistry;
• astrochemical reaction rates;
• molecular spectroscopy;
• ion reactions;
• molecular structure calculations;
• astronomical line searches;
• very low-temperature chemical processes.

It is not sold like helium gas.

It is not a consumer material.

It is also not a normal bulk laboratory chemical stored in bottles.

Helium vs HeH⁺

Feature	Helium	HeH⁺
Type	Chemical element	Molecular ion
Symbol/formula	He	HeH⁺
Atomic number	2	None
Net charge in form shown	0	+1
Contains hydrogen	No	Yes
Periodic-table entry	Yes	No
Main context here	Noble-gas atom	Astrochemistry and spectroscopy

Key Timeline

1925: T. R. Hogness and E. G. Lunn report laboratory evidence for HeH⁺.

Late 1970s: Researchers begin seriously discussing planetary nebulae as possible astronomical sources.

2019: SOFIA detects HeH⁺ in NGC 7027. The finding appears in Nature.

2025: Cryogenic reaction work with deuterium finds a fast low-temperature reaction that conflicts with older rate predictions.

2026: Laboratory spectroscopy refines the fundamental rotational transition to 2010.183312(8) GHz.

Common Claims Checked

Claim	Answer
It is a chemical element	False
It has atomic number 119	False
Its formula is HeH⁺	True
It contains helium and hydrogen	True
Its charge is +1	True
Laboratory evidence dates to 1925	True
Secure space detection came in 2019	True
NGC 7027 was the detection target	True
SOFIA was used for the detection	True
It is tied to early-Universe chemistry	True
Scientists were still studying it in 2026	True

Why Does This Ion Still Matter?

It is small.

The questions are big.

Scientists can use a very simple molecular ion to test reaction models, spectral calculations, and ideas about chemistry before the first stars appeared.

The 2019 detection proved HeH⁺ exists in interstellar space.

The 2025 work changed how researchers may calculate some of its low-temperature reactions.

The 2026 measurement gave astronomers a sharper frequency for future searches.

That keeps the ion useful today.

Final Thought

HeH⁺ is real science.

It is not a mystery element.

Its laboratory story started in 1925. Its secure space detection came in 2019. Researchers are still checking its chemistry and spectroscopy today.

The reason it stands out is simple.

Early-Universe models place this helium-hydrogen ion near the opening stage of molecular chemistry, where the first molecular bond could form.

A tiny ion.

A very old story.

FAQ

What does Helonium mean?

Helonium is another name for the helium hydride ion, HeH⁺. It is a positively charged molecular species made from hydrogen and helium.

Is Helonium a real element?

No. It is a molecular ion, not an element. It has no atomic number or separate periodic-table position.

What is the chemical formula?

The formula is HeH⁺, also written HHe⁺.

What is its electrical charge?

Its net charge is +1.

When was it first found?

Laboratory evidence was published in 1925 by T. R. Hogness and E. G. Lunn.

When was it found in space?

The first unambiguous interstellar detection was published on April 17, 2019.

Where was it found in space?

Astronomers detected it in the planetary nebula NGC 7027 using SOFIA’s GREAT/upGREAT instrument.

Why is HeH⁺ called the first molecule?

Early-Universe models place it among the first molecular species to form. Researchers describe its bond as the Universe’s first molecular bond.

What did the 2025 study find?

A cryogenic experiment using deuterium found that an HeH⁺ reaction stayed fast at low temperatures instead of slowing sharply as older calculations predicted.

What did scientists find in 2026?

Researchers refined the fundamental rotational transition to 2010.183312(8) GHz, giving astronomers a more exact spectral target.

Can HeH⁺ be made on Earth?

Yes. Scientists can produce and study the ion in laboratories, including inside cryogenic ion traps.

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