Date

Thursday 11 Jun 2026

Time

15:15 - 15:45

Location

BW017

Supervisor

Thanja Lamberts

2nd reviewer

Katharina Doblhoff-Dier

Jury

Jaco Geuchies

The detection of several pre-biotic molecules in the interstellar medium (ISM) and throughout the star-formation cycle compels investigation into underlying chemical formation pathways. Small species, such as CCN, lie at the base of these pathways, which act as precursors to complex organic molecules. These molecules are believed to originate from dense regions within the ISM, where nano- to micrometer-sized dust grains effectively attenuate UV radiation and reduce photo-destruction of molecules. The icy surfaces of such dust grains catalyze chemical reactions and act as third bodies that dissipate excess reaction energies, emphasizing the importance of representative ice-surface models. Furthermore, calculations on initial reactions of simple progenitor molecules such as CCN tend to be electronically complex, requiring accurate quantum-chemical treatment. Therefore, this work presents a computational study of a previously unexplored evolutionary path on water-ice, where the CCN radical serves as a precursor molecule in the effective generation of several molecules of pre-biotic relevance. Within these calculations, geometry optimizations were performed with density functional theory using the BHandHLYP-D4 exchange–correlation (xc) functional and the ma-def2-TZVP basis set, providing a balance between accuracy and efficiency. All energetic refinements were obtained with DLPNO-CCSD(T)-F12 single-point calculations, and any open-shell singlet calculations employed a broken-spin-symmetry formalism. For all reactions, the chemical system includes a water trimer that represents a minimal model of an ice surface, where water is the dominant species, enabling the exploration of a large chemical network. The resulting data indicate that HCCN, H2CCN, acetonitrile (H3CCN), ketenimine (H2CCNH), ethanimine (H3CCHNH), vinylamine (H2CCHNH2) and ethylamine (H3CCH2NH2) can form on icy dust grain surfaces via a common hydrogenation pathway. In addition, the water trimer was shown to actively participate in the formation paths of ethanolamine (HOCH2CH2NH2) and glyconitrile (HOCH2CN). All of the aforementioned molecules have previously been detected in the ISM, and the calculated activation energies are low enough to suggest the efficient formation of these pre-biotic species on icy dust grain surfaces. These findings motivate further investigation of larger representative ice models and reaction-type-dependent xc-functionals, and propose potential target species for observational detection in the ISM.