Daniël Rap, PhD student
Daniël Rap started September 2019 with his PhD, focusing on Astrochemistry.
Rap studied Chemistry and did his Bachelor ánd Master internship at FELIX. He is fascinated by spectroscopy, the technique that uses light to discover the structure of molecules. “And then preferably molecules, that occur in space. Spectroscopy is a very powerful technique to discover molecules in space and see how all the atoms are connected to each other.”
October 2020 Rap’s first ‘first-author paper’ was published, on stable isomeric structures of the pyridine cation and protonated pyridine. Many molecules have been observed in astronomical environments. Some smaller species are considered to function as building blocks for larger molecules. Pyridine is one of those building blocks. Calculations predicted the structure of pyridine cation, but is was never experimentally elucidated. How did Rap and his colleagues succeed? They started by tagging pyridine ions with a rare gas atom. With infrared light resonant with the vibration of the molecule, energy was brought in that broke the weak bond between the ion and the rare gas atom. Then,they counted the difference of ions with and without this tag at different wavelengths. This gave the information to accurately determine the spectrum of the pyridine cation. “This technique provides the fingerprint spectrum of cold and reactive ionic species using the very intense and tuneable light of the free electron laser FELIX.” Their findings are essential for future studies and infrared observations in astronomical sources.
Rap moved on to chemical reactions now, to see if he can form PAH’s - polycyclic aromatic hydrocarbons. Strong evidence suggests that these molecules are present in interstellar space, but they haven’t been identified individually. Several theories exist on how they are formed. Some think that they are fragmented by the radiation of stars. Another theory is that they are formed by smaller molecules, like pyridine. Rap now tries to add a second ring to pyridine, by studying how small molecules like acetylene gas (C2H2) react by collisions with the pyridine cation.
“Astrochemistry involves a lot of different research areas. And we all need each other. Astronomers observe in space. Their observations are compared to microwave/infrared frequencies and transitions that experimental scientists have measured. The information gained is used by more fundamental researchers to generate a model, that can predict for example how many of a certain molecule occurs in a nebula or other astronomical environments. Astronomers can check that again."
In his free time Rap looks at the sky in a different way; he makes photos of nebulae, interstellar clouds of dust, hydrogen, helium and other ionized gases. “You will be amazed by how ‘easy’ you can make spectacular images from objects in space using only a few tricks.”
Magazine cover with a photo of Daniël Rap