Espectrometria de massa a temperaturas próximas a 0 K e simulações em mecânica molecular no estudo de espécies de interesse astrofísico e astroquímico

Abstract

Alcohols and fullerenes are among the species observed in the interstellar medium (ISM) to date. Methanol is one of the most studied molecules detected in space and its importance as an organic molecule is well known. The fullerene molecule (carbon 60) could be responsible for carrying compounds along different regions of space and could also serve as a reaction matrix for organic molecules such as alcohols. The investigation of the possible chemical reactions of different compounds in ISM could help to understand the formation and transport of molecules around the universe. In this thesis experiments were performed where pure methanol and etanol clusters as well as C60 clusters doped with those alcohols were formed upon pickup of individual molecules by superfluid He nanodroplets with an isothermic temperature of 0.37 K achieved by evaporative cooling of Helium (He) atoms. After pickup, the clusters were ionized by a 70 eV electron beam and then accelerated through a set of electrostatic lenses to a time-of-flight (TOF) analyzer, where the ion yield was recorded as a function of the mass to charge ratio. Molecular mechanics calculations with the MM2 force field as well as molecular dinamics simulations were performed to interpretate the spectra. Herein we report a chemical reaction occurring within the doped clusters upon ionization, where the alcohol molecules dehydrate forming water (H2O), dimethyl or diethyl ethers and also possibly ethene. There is evidence that the reaction is triggered by a proton coming from the fragmentation of one of the alcohol molecules due to the ionization process. The product ethers tend to leave the cluster after their formation while the H2O remains inside, solvated by alcohols. Magic numbers are also observed at the spectra for different number of C60 and alcohol molecules.