PhD defence Sanders Lemmens: ‘Polycyclic aromatic hydrocarbons: laboratory infrared signatures of astrochemical evolution’

On Thursday 10 March, Sander Lemmens successfully defended his thesis, which is all about carbon in our universe. Lemmens focused on three questions: what is the organic inventory in the universe, how do molecules form in the interstellar medium, and how do they interact?

Light still offers the most direct probe of the structure and quantum mechanical nature of molecules. Lemmens used the FELIX infrared light to probe the potential energy surface and intrinsic spectroscopic properties of large carbon molecules that occur in interstellar space, the Milky Way and other galaxies: Polycyclic Aromatic Hydrocarbons (PAHs).

The results suggest that far-infrared light might provide an answer to the question what the organic inventory in the universe is. The common assumption that interpreting the far-infrared bands is difficult and unreliable is, quite unexpectedly, partly refuted, which is good news for astronomers. On how molecules form in the interstellar medium, the thesis really uncovers the full complexity and provides initial handles to construct reliable models describing the formation of PAHs. While investigating the last question, the interaction of molecules, Lemmens provided new evidence in a long-standing discussion about the structure of PAH complexes.

Sander Lemmens (left) explains his work to the former minister of Education, Culture and Science, Ingrid van Engelshoven (right). Opening HFML-FELIX, July 2019

Lemmens studied Chemistry, and started at FELIX Laboratory in 2015 with his Master Internship. His promotion is part of a project on chemical reactions in space, led by prof. Wybren Jan Buma. Lemmens spent most of his time doing experiments at HFML-FELIX. “I enjoyed the research, experiments and above all, the people of my research group and at the lab. I learned a lot from working with others, like a project with a fellow PhD, or helping visiting scientists with their experiments. Science is best when shared! It’s also very motivating. At the lab, we would often share thoughts during coffee and lunch breaks. And I said this before: these breaks are the basis of every progress.
Of course, not every experiment ran smoothly. When I was at a dead end, I would usually start with another task I was sure I could do. That gave me some confidence again. And I could always rely on the skilled technicians, which is pretty unique.”

One thing that sets out in his thesis is: wonder. ‘However small the details that were uncovered in this thesis, one has to remember: no detail is too small. After all, the rules that govern the behavior of small matter on earth are the same that rule the rest of the universe. To discover these rules, we will have to keep testing theory with (laboratory) experiments and continue doing fundamental research, but above all: keep wondering.’

Lemmens is  going to continue his scientific career abroad.

The defence took place on Thursday 10 March

Supervisors: Prof. W.J. Buma and Prof. A.M. Rijs.
Commission includes dr. S. Brünken