Interstellar clouds are the birthplaces 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 research group, molecular
systems, led by ERC prize winner Roland Wester at the Institute for ion
physics and applied physics at the University of Innsbruck, has set itself
the task of better understanding the development of elementary molecules in
space.
“Put simply, our ion trap allows us to recreate the conditions in space in
our laboratory,” explains Roland Wester. “This apparatus allows us to study
the formation of chemical compounds in detail.” The scientists working with
Roland Wester have now found an explanation for how negatively charged
molecules form 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 only contained
positively charged ions. Since then, it has been an open question how
negatively charged ions are formed. The Italian theorist Franco A.
Gianturco, who has been working 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, so-called dipole-bound states, should enhance the attachment of free
electrons to linear molecules. Such molecules have a permanent dipole moment
which strengthens the interaction at a relatively great distance from the
neutral nucleus and boosts the capture rate of free electrons.
Observing dipole-bound states in the laboratory
In their experiment, the Innsbruck physicists created molecules consisting
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
continuously changed the frequency of the 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 the early-stage researcher
Malcolm Simpson from the doctoral training program, atoms, light, and
molecules at the University of Innsbruck finally shed light on this
difficult-to-observe phenomenon. A comparison of the data with a theoretical
model finally provided clear evidence of the existence of dipole-bound
states.
“Our interpretation is that these dipole-bound states represent a kind of
door opener for the binding of free electrons to molecules, thus
contributing to the creation of negative ions in space,” says Roland Wester.
“Without this intermediate step, it would be very unlikely that electrons
would actually bind to the molecules.”
Reference:
“Influence of a Supercritical Electric Dipole Moment on the Photodetachment
of C3N−” by Malcolm Simpson, Markus Nötzold, Tim Michaelsen, Robert Wild,
Franco A. Gianturco and Roland Wester, 19 July 2021, Physical Review
Letters. DOI:
10.1103/PhysRevLett.127.043001