The interstellar iron is not lacking, it is hidden just in the sight

Astrophysicists know that iron (chemical symbol: Fe) is one of the most abundant elements in the universe, after the light elements such as hydrogen, carbon and oxygen. Iron is most often in gaseous form in stars such as the Sun and more condensed in planets such as the Earth.

Iron in interstellar environments should also be common, but astrophysicists only detect low gaseous levels. This implies that the missing iron exists in a solid form or in a molecular state, but that one's hiding place has remained elusive for decades.

A team of cosmochemists from Arizona State University, with the support of the W. M. Keck Foundation, now claims that the mystery is simpler than it seems. Iron is not lacking, they say. Instead, he hides in the sight of all. Iron is associated with carbon molecules to form molecular chains called iron pseudocarbynes. The spectra of these chains are identical to those of chains of carbon molecules, much more common, long known to be abundant in the interstellar space.

The work of the team was published at the end of June in the Astrophysical Journal.

"We are proposing a new class of molecules likely to be widespread in the interstellar medium," said Pilarasetty Tarakeshwar, associate professor of research at the ASU School of Molecular Sciences. His co-authors, Peter Buseck and Frank Timmes, are both at the School of Earth Exploration and Space USS, Buseck, Professor of ASU Regents , is also at the School of Molecular Sciences of Tarakeshwar.

The team examined how clusters containing only a few metallic iron atoms could associate with chains of carbon molecules to produce molecules that combine the two elements.

Recent evidence obtained from star dust and meteorites indicates the widespread presence of clusters of iron atoms in the cosmos. At extremely cold temperatures in interstellar space, these clusters of iron act as freezing particles, allowing carbon chains of different lengths to stick to them, producing molecules different from those that can occur with gaseous phase of iron.

Tarakeshwar said, "We have calculated what the spectra of these molecules would look like, and we found that they had spectroscopic signatures almost identical to the carbon chain molecules without any iron." He added that because of this, "previous astrophysical observations could have overlooked these more carbon molecules of iron".

According to the researchers, this means that the missing iron in the interstellar medium is actually visible, but masquerades as a common molecule of the carbon chain.

The new work could also solve another long-standing puzzle. Carbon chains with more than nine atoms are unstable, says the team. However, observations have detected more complex carbon molecules in the interstellar space. How nature builds these complex carbon molecules from simpler carbon molecules has been a mystery for many years.

Buseck explained: "The longer carbon chains are stabilized by the addition of iron clusters." This opens a new path for the construction of more complex molecules in space, such as polyaromatic hydrocarbons, of which naphthalene is a familiar example, being the main ingredient of mothballs.

Timmes said, "Our work provides new information to bridge the gap between molecules containing up to nine carbon atoms and complex molecules such as the C60 buckminsterfullerene, better known as" buckyballs. "