"NATURALISM is a philosophical viewpoint according to which everything arises from natural properties, and supernatural explanations are just excluded. This proposal is a by-product of this definition. It will contribute to the understanding of the origin of life in the universe by unravelling experimentally the chemical reaction schemes leading to large and complex molecules in interstellar ice analogues. Interstellar chemistry is governed by a complex interaction between gas phase and solid-state processes. These provide a universal starting point for a prebiotic chemistry. Several observational facilities have become operational recently, and more will in the near future, probing this chemistry through the detection of spectral rotational lines related to a large diversity of new and complex species. The availability of detailed laboratory data is a prerequisite for a proper interpretation of these observational data.This proposal addresses both the characterisation and the formation of large complex species in interstellar ice analogues. Laboratory studies will be carried out at the Leiden Observatory, using MATRIICES, a worldwide unique and highly sensitive setup capable to address the question of molecular complexity in processed interstellar ice analogues. Large complex species relevant to the field of astrobiology are expected to be detected in situ during irradiation of N-bearing and O-bearing interstellar ice analogues. In a second step, millimeter and submillimeter data of complex or transient species will be analysed. The results will be included in databases within a collaborative work in the Cologne Laboratory Astrophysics Group.The outcome of this proposal will provide qualitative and quantitative data for astrochemical solid-state processes, a key to assist in developing astrochemical models, and give spectroscopic data that are strongly needed to steer and interpret astronomical observations and to predict abundances of complex species in space."