The story behind a recent paper on fullerene ions began over a decade ago when a facility called ELISA — which stands for electrostatic ion storage ring, Aarhus — was built in Denmark. At the time Klavs Hansen was a postdoc working with Jens Ulrik Andersen, a physics professor at Aarhus University, on the cooling of hot clusters and molecules in the storage ring. In 2001 they published a paper showing that negative fullerene ions and metal clusters cool as 1/t, where t is time, but they were not able to determine a lifetime or absolute cooling rate, and they moved on to work on other problems.

The work picked up again years later when Sophie Canton, a postdoc at Lund University in Sweden, discussed the storage ring data with Hansen, who is now at the University of Gothenburg, also in Sweden. These discussions led to a new method for measuring absolute cooling rates in storage rings, so Hansen took his student, Erika Sundén, to the newly commissioned electrostatic storage ring at Tokyo Metropolitan University (TMU) to make the measurement.

Together with a team of chemists and physicists from TMU, Sundén and her Scandinavian colleagues were able to measure the absolute cooling rate of negative fullerene ions, and also track the relative importance of radiative and non-radiative contributions to cooling (Phys. Rev. Lett. 103, 143001; 2009). The new approach could prove to be an important tool for studying the thermodynamics and optical absorption of large molecules or clusters, including several of astrophysical interest.

Hansen and co-workers did a lot of background work before they headed east. “We knew exactly what we were going for when we went to Tokyo,” he says. Although the visiting team found themselves in a unique part of the world, work was the focus: “Cultural exchange is a plus, but you spend most of your waking time in a confined space in a lab,” says Hansen. And what is his advice for anyone thinking about starting a collaboration? “Just do it”.