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The amazing stability of the helium hydride ion: Why can't it be stored in a conventional environment?
Helium hydride ion (HeH+) is a positive ion composed of helium and hydrogen and has amazing stability. The compound is thought to be the first molecule created at the birth of the universe and was first created in a laboratory in 1925. Although its stability allows this ion to be maintained in isolation, it is extremely reactive under normal conditions, making it impossible to store or use in conventional environments.
Helium hydride ions are considered to be the strongest acid, even stronger than fluoroantimonic acid.
The reactivity of helium hydride ions causes them to react violently with any molecules they come into contact with, making them impossible to store in containers. This strong reactivity means that laboratories need specific methods to study its chemistry, and it usually needs to be generated on site and cannot be stored.
It is noteworthy that the polar nature of the helium hydride ion makes its identification relatively simple in spectroscopy, and it has the same electronic structure as molecular hydrogen (H2). The dipole moment of the helium hydride ion is about 2.26 D, showing the inhomogeneity of its electron cloud distribution. About 80% of the electron density is near the helium nucleus, which makes helium hydride ions exhibit unique behavior in chemical reactions.
The presence of helium hydride ions in the interstellar medium was suspected as early as the 1970s and was first detected in the NGC 7027 nebula in 2019.
Despite the unique physical and chemical properties of helium hydride ions, stable storage in containers is impossible. Specifically, this ion can accept protons from molecules such as oxygen, ammonia, sulfur dioxide and water to form a range of new substances. During this process, any molecules that come into contact with it will be protonated and will not be able to maintain stability at all.
Research Methods and Technical Challenges
The chemistry of helium hydride ions is usually explored using special experimental techniques, such as replacing hydrogen in an organic compound with tritium and then observing the behavior of the resulting helium hydride ions. This process can produce helium hydride ions [TR → 3He+ + R•] and react with organic matter, but the process It is still accompanied by great uncertainties and challenges.
When hydrogen in organic compounds is replaced by tritium, a mixture with helium hydride ions can be generated, which is one of the research approaches for helium hydride.
Since the 1980s, scientists have begun to predict the behavior of helium hydride ions in the spectrum and tried to set their detection wavelength in the infrared range. These efforts finally produced preliminary results in the 2019 experiment.
The importance of interstellar and cosmic chemistry
Helium hydride ions are believed to be an important factor in the formation of the early universe and are crucial to understanding the chemical processes in the early universe. The formation of this compound can affect the formation and evolution of stars, and plays an important role in helium-rich white dwarfs, changing the opacity of the gas and affecting the cooling rate of the star.
While helium hydride ions are extremely difficult to preserve in laboratories on Earth, they can form in the interstellar medium from collisions of cooling gases, making them an important proxy for the observed universe. However, its reactivity means that observing it in an interstellar environment will be a challenging task for scientists.
Helium hydride ions are not only a cutting-edge topic in scientific research, but also an important part of our future understanding of the universe.
Against this background, will helium hydride ions continue to be an important object of cosmochemical research and advance our understanding of chemical processes in the universe?
