New type of chemical bond may exist in the extreme magnetic fields of stars

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New type of chemical bond may exist in the extreme magnetic fields of stars

The atoms we’re familiar with are held together with a sort of an electric force. But in the extreme magnetic fields of stars, far more powerful than we could ever produce on Earth, could be a new kind of magnetic chemical attraction, resulting a new breed of molecules.

As described in a new Science paper, Kai K. Lange, E. I. Tellgren, M. R. Hoffmann, and T. Helgaker performed detailed quantum mechanical calculations for two atoms in exceedingly strong magnetic fields. While previous work had shown that a relatively weak bond could form when the molecule is parallel to the magnetic field, Lange and colleagues discovered an additional stronger bond might result when the molecule is perpendicular. Their calculation relied on very few assumptions, so it is useful for determining the properties of the molecules formed. Intriguingly, their model also described a magnetic molecule could be made from helium, which is famously inert and doesn’t form stable electric bonds.

The authors used a common method in molecular chemistry and physics known as an full configuration-interaction (FCI) calculation, in which atoms are modeled directly with a minimum of assumptions. In this way, they were able to obtain all the possible molecular binding configurations. They focused on hydrogen, which has the twin advantages of being simple (one electron per atom) and common. At low temperatures and negligible electric or magnetic fields, hydrogen forms the two-atom molecule H2 through covalent bonding, where the electrons are shared equally between the two atoms. However, the environment around white dwarfs and neutron stars is too hot for this bond to survive, and the molecules dissociate.

Intense magnetic fields could change that, based on the FCI analysis. As the magnetic field strength increased, the researchers found the electron orbitals (the patterns of the electron cloud of an atom) distorted, making the atoms themselves magnetic. This effect, known as paramagnetism, is seen in many materials: they are magnetic only in the presence of an external field (as opposed to ferromagnets—”permanent magnets”—which don’t require an external field). In the case of hydrogen atoms in extreme magnetic fields, the result of the paramagnetism was the formation of an H2 molecule that’s held together through magnetic bonding.

While previous calculations had found magnetic bonding when the two atoms were oriented perpendicular to a magnetic field, they didn’t show bonding in other orientations. The new results revealed the bonds persist when the atoms are rotated by any angle relative to the field, though the perpendicular orientation was still preferred. Additionally, in the earlier results, bonding was due to motion of the electrons, not a paramagnetic effect. The differences arise because of the approximations used in the earlier work used, which are not present in the current one.

Via