This project centers around the investigation of molecular mobility in solid layers by a truly multidisciplinaryapproach: combining the expertise from crystal growth, astrophysics, and chemistry. We aim toanswer long standing questions in the context of two cross-disciplinary applications: the formation andevolution of interstellar ices and the solid state transition from one crystal structure — polymorph —to another. The first is important for fundamental questions dealing with the origin of life, specificallyconcerning the delivery of molecules—like H2O, CO2 and organic molecules—to habitable planets.The second application is of great interest to the pharmaceutical industry where polymorph control iscrucial. The polymorphic form controls the solubility of the compound and is therefore key in dosedetermination.The goal of the investigation is to obtain an understanding of mobility in molecular layers on themolecular level in order to (i) understand the processes in interstellar ices leading to the meeting of tworeactive species, (ii) identify the trapping mechanisms in interstellar ices, (iii) predict which molecules can survive in ices in the harsh environment of star and planet forming regions, (iv) determine which processes are fundamental to polymorphic conversion, and (v) design a way to inhibit or promote polymorphic conversion. I propose to study the mobility in molecular layers This project centers around the investigation of molecular mobility in solid layers by a truly multidisciplinary approach: combining the expertise from crystal growth, astrophysics, and chemistry. We aim to answer long standing questions in the context of two cross-disciplinary applications: the formation and evolution of interstellar ices and the solid state transition from one crystal structure - polymorph -to another. The first is important for fundamental questions dealing with the origin of life, specifically concerning the delivery of molecules -like H2O, CO2 and organic molecules - to habitable planets. The second application is of great interest to the pharmaceutical industry where polymorph control is crucial. The polymorphic form controls the solubility of the compound and is therefore key in dose determination.The goal of the investigation is to obtain an understanding of mobility in molecular layers on the molecular level in order to (i) understand the processes in interstellar ices leading to the meeting of two reactive species, (ii) identify the trapping mechanisms in interstellar ices, (iii) predict which molecules can survive in ices in the harsh environment of star and planet forming regions, (iv) determine which processes are fundamental to polymorphic conversion, and (v) design a way to inhibit or promote polymorphic conversion. I propose to study the mobility in molecular layers using a combination of simulation techniques. The fundamental difficulty is to cover processes that take place over a large range of timescales: from picoseconds to years. Advances in numerical simulations have only recently made this research possible. Using Molecular Dynamics and Monte Carlo simulations we will study the interactions and processes in molecular layers on different lengthscales and covering a timescale range of roughly 20 orders of magnitude.This ambitious research project will be carried out in the Institute for Molecules and Materials at the Radboud University in Nijmegen, but will also benefit from existing and new collaborations with local, national and international colleagues.