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The last column of the periodic table is a class of \"dampened\" elements that are collectively referred to as inert gases. The atoms of most elements share electrons with other atoms, forming chemical bonds that make up the molecules, while the outermost electrons of the inert gas atoms themselves have reached a \"full\" state, so that they themselves are extremely stable, have little chemical reaction and are difficult to combine with other atoms to form molecules.


On earth, no naturally occurring inert gas compounds have been found. Since the last century, scientists have tried to synthesize molecules of atoms in inert gases in the laboratory. In 1925, scientists managed to get helium (He) and hydrogen ions (H? ) shared an electron and synthesized the first helium-hydrogen ion (HeH? )。 Astronomers call helium-hydrogen ions "molecules," but because they are not electrically neutral, chemists prefer to call them" molecular ions."


In 1962, chemist Neil Bartlett induced a combination of xenon (Xe), fluorine and platinum to produce a mustard-yellow compound, xenon hexafluoroplatinum, an electrically neutral molecule and the first electrically neutral inert gas compound.


But in the universe, things can be very different. Space is a great place to find molecules of inert gas compounds. The inert gas elements are abundant in the universe. helium is the second-richest element in the universe after hydrogen, with neon (ne) abundance roughly ranked fifth or sixth. In interstellar space, temperatures and densities often reach extremes, and inert gases may react differently to Earth under such conditions, forming molecules as one of them.


Argon (ar) is an easily neglected element. in fact, in the earth ' s atmosphere, no matter the volume ratio or mass ratio, the ratio of argon is much higher than the often mentioned carbon dioxide, which is the third highest proportion of gas in the air, second only to nitrogen and oxygen. But in the past few scientists seem to be searching for an interstellar molecule that contains argon. When the team led by astrophysicist Mike Barlow found the argon hydrogen ions, he also modestly said," It was an unexpected discovery."


Ar H? The discovery cannot be separated from the Herschel Space Observatory. Launched in 2009, it is an observatory that observes far infrared and submillimeter waves. The Herschel Space Observatory is equipped with ultra-low temperature superfluid helium refrigerant, which allows it to observe far-infrared wavelengths from distant objects without being disturbed by its own temperature. Because many molecules absorb and emit far-infrared light, this spectrum is well suited to finding new interstellar molecules. As the refrigerant ran out, Herschel ended its observation career in 2013 and gave up its superior observational location. But before it retired, it made a huge contribution to observations of interstellar hydride.


In the year since Herschel took off, several groups of astronomers have begun to notice that there is something in interstellar space that absorbs far-infrared light at a wavelength of 485 microns, a line that has never been observed before. Barlow's team is one of them. At the time, they were using Herschel's data to study the Crab Nebula. In addition to the line of 485 microns, they noticed another line that happened to be half the wavelength of the former, marking a molecule of two atoms. Barlow team finally confirmed ArH? and published the discovery in the journal Science in 2013.


Many scientists "missed" ArH? Is it because they think they know ArH? The wavelength. previous arh created in the laboratory? contains ar-40, the most common isotope of argon on earth, but the abundance of ar-36 is much higher in interstellar media, and exactly 36 arh with slightly different wavelengths found in the universe? 。


Arh in the stars? the synthesis requires two steps. First, cosmic rays let the argon atom lose an electron and form an argon ion (ar? ), then Ar? And steal a hydrogen atom from a hydrogen molecule to form arh? However, argon hydrogen ions are so fragile that their synthesis cannot be separated from hydrogen molecules, but the presence of excess hydrogen molecules also undermines their stability.


In ArH? Once found, scientists are still struggling to find a \"simpler\" inert gas molecule, HeH? Although this molecule has long been synthesized in the laboratory, it is even more important to confirm its existence in the universe because scientists believe that after 100,000 years of the Big Bang, neutral helium atoms (He) and protons (actually positively charged hydrogen ions, H? ) will begin to react and form the first molecules in the universe, the HeH? .This is the first step in the evolution of the universe.


In the 1970s, theorists suggested that such molecules were likely to form in planetary nebulae, where physical conditions were similar to those of the early universe. After more than 40 years of searching, the young planetary nebula NGC 7027 finally gives the answer. In 2019, the likes of Rolf Gusten first detected HeH in NGC 7027? confirmed the existence of this material in interstellar space and put a perfect end to this long \"legend \".


There may be more inert gas molecules in the universe waiting for scientists to discover. In space, for example, there are more neon atoms than argon, so there should be neon-hydrogen ions. If they are found, the number of neon-hydrogen ions and where they exist will further reveal the nature of the interstellar medium.


Krypton (Kr) and xenon in the universe, on the other hand, are relatively rare, and the likelihood of the presence of krypton or xenon should be relatively low. But in the vast universe, the temperature and density vary so widely that, perhaps in the corner of a distant interstellar cloud, atoms combine to form more unexpectedly strange molecules. In the future, more sophisticated technology will help us explore the far, more mysterious depths of space, and perhaps more surprises await us.


Reference source: https:\/\/article\/physical-world\/2019\/noble-gas-molecules-in-space https:\/\/doi\/abs\/annurev-astro-081915-023409? Journal Code = astro