Capturing electrons in space

Interstellar clouds are the birthplace of new stars, but they also play an important role in the origins of life in the Universe through regions of dust and gas in which chemical compounds form. The Molecular Systems research group, led by ERC Prize winner Roland Wester at the Institute for Ionic Physics and Applied Physics at the University of Innsbruck, set out to better understand the development of elementary molecules in space. “Simply put, our ion trap allows us to recreate the conditions of space in our lab,” explains Roland Wester. “This device allows us to study in detail the formation of chemical compounds.” Scientists working with Roland Wester have now found an explanation for the formation of negatively charged molecules in space.

An idea built on theoretical foundations

Before the discovery of the first negatively charged carbon molecules in space in 2006, it was assumed that interstellar clouds contained only positively charged ions. Since then, the question of how negatively charged ions are formed has remained open. Italian theorist Franco A. Gianturco, who has worked as a scientist at the University of Innsbruck for eight years, developed a theoretical framework a few years ago that could provide a possible explanation. The existence of weakly bound states, called dipole bound states, should improve the attachment of free electrons to linear molecules. Such molecules have a permanent dipole moment which enhances the interaction at a relatively large distance from the neutral nucleus and increases the rate of capture of free electrons.

Observation of states linked to dipoles in the laboratory

In their experiment, physicists from Innsbruck created molecules made up of three carbon atoms and one nitrogen atom, ionized them, and bombarded them with laser light in the ion trap at extremely low temperatures. . They continually changed the frequency of light until the energy was large enough to eject an electron from the molecule. Albert Einstein described this so-called photoelectric effect 100 years ago. An in-depth analysis of the measurement data by junior researcher Malcolm Simpson from the doctoral training program, Atoms, Light and Molecules at the University of Innsbruck has finally shed light on this difficult to observe phenomenon. A comparison of the data with a theoretical model ultimately provided clear evidence for the existence of dipole-bound states. “Our interpretation is that these dipole bound states represent a kind of gate opening for the binding of free electrons to molecules, thus contributing to the creation of negative ions in space,” explains Roland Wester. “Without this intermediate step, it would be very unlikely that the electrons actually bind to the molecules.”