Helium hydride ion

Helium hydride ion (HeH+) is the chemical name for a positively charged ion formed by the reaction of a helium atom with a hydrogen atom. It is considered the first molecule to have formed in the universe, making it of significant interest in astrophysics and cosmochemistry. The helium hydride ion is believed to play a crucial role in the chemistry of the early universe, acting as a precursor to the formation of more complex molecules.

Formation

The formation of HeH+ is primarily through the association of helium (He) and protonated hydrogen (H+), a process that can occur in the high-energy environment of the early universe or in modern astrophysical settings such as planetary nebulae and H II regions. The reaction is as follows: \[ \text{He} + \text{H}^+ \rightarrow \text{HeH}^+ + \text{photon} \]

Properties

HeH+ is notable for its strong dipole moment and its role as a potential coolant in the early universe. Its existence helps in understanding the cooling processes that allowed for the formation of the first stars. The ion has a bond length of approximately 0.77 Å, and it is one of the strongest known acids, surpassing the acidity of the hydronium ion (H3O+).

Astrophysical Significance

The detection of HeH+ in space has been a significant goal for astronomers, as its presence would provide evidence supporting theories about the chemical evolution of the early universe. In 2019, astronomers reported the first detection of the helium hydride ion in space, specifically in the planetary nebula NGC 7027, confirming long-standing theoretical predictions about its role in the chemistry of the universe.

Research and Applications

Beyond its astrophysical importance, research into HeH+ also has implications for understanding quantum chemistry and potential applications in plasma physics. The study of its properties, such as its spectroscopic signatures, helps refine models of molecular formation and interaction under extreme conditions.

See Also

• Molecular astrophysics
• Chemical evolution
• Planetary nebula
• H II region