This Thesis shows discoveries in non-linear astrochemical kinetics as well as a deeper analysis of dark clouds chemistry. It is concluded that autocatalysis in interstellar gas-phase chemistry... Show moreThis Thesis shows discoveries in non-linear astrochemical kinetics as well as a deeper analysis of dark clouds chemistry. It is concluded that autocatalysis in interstellar gas-phase chemistry leads to bistability but when coupled with the gas-grain exchange of key species, the system can show Hopf bifurcation and lead to the appearance of complex chemical oscillations. The results and discussion of the five chapters allow further understanding of the chemical evolution in a gas phase system and in a gas-grain environment, providing better predictions to compare with future observations. Show less
Artur de la Villarmois, E.; Guzmán, V.V.; Jørgensen, J.K.; Kristensen, L.E.; Bergin, E.A.; Harsono, D.; ... ; Yamamoto, S. 2022
Large areas of space are filled by molecular clouds that consist of gas and dust grains that are the remnants of dead stars. When these clouds start collapsing, the decreasing temperature and... Show moreLarge areas of space are filled by molecular clouds that consist of gas and dust grains that are the remnants of dead stars. When these clouds start collapsing, the decreasing temperature and increasing density cause gas particles to start accreting onto dust grain surfaces. This results in layered geometries of partially mixed ices on top of the grains that act as molecule reservoirs and cryogenic catalysts on which both simple and complex molecules form in surface reactions. These grains form the material from which celestial bodies form. A good understanding of the elementary processes taking place in dark interstellar clouds, therefore, is necessary to understand the chemical inventory of stellar systems, like our own Solar system.This thesis focuses on laboratory studies investigating the surface chemistry of CO-rich ices on dust grains at temperatures as low as 10 K. The formation mechanisms of complex organic molecules (COMs) are investigated by non-energetic processes (e.g., hydrogenation) and energetic processes (e.g., photolysis). Moreover, the net transfer of the newly formed hydrogenated species from grain surfaces into the gas phase through non-thermal desorption is investigated to link the detection of COMs in the gas phase to their formation in the solid state. Show less
Polycyclic aromatic hydrocarbons (PAHs) are the most abundant class of organic compounds in space. The PAH field evolves from the constant interaction between experimentalists, theorists,... Show morePolycyclic aromatic hydrocarbons (PAHs) are the most abundant class of organic compounds in space. The PAH field evolves from the constant interaction between experimentalists, theorists, modellers and observers. While laboratory research and quantum chemical calculations together set up the molecular properties of PAH species, astronomers on the other hand, retrieve as much information as possible from the space observations. Nowadays, the PAH field is advanced enough to start implementing all these results into astronomical models, in order to study PAHs from a molecular groundwork. In this regard, the research projects presented in this thesis do precisely that. They constitute a first attempt to gather the vast current knowledge available on specific PAH molecules (not using generic properties), and put it in an astrophysical context, and with it, target some of the key subjects of the field such as: the existence of the so-called grandPAHs in space; the role of PAHs in the formation of molecular hydrogen in photodissociation regions; the abundance of superhydrogenated PAHs and their contribution as a carrier of the 3.4 micron band observed in photodissociation regions; and the deuterium fractionation in PAHs, and their consequent role in explaining the observed deuterium abundance in the local interstellar medium. Show less
This thesis presents the results from the analysis and characterisation of the water and mid-J (J<11) 12CO, 13CO and C18O observations for a large sample of low-, intermediate-, and high-mass... Show moreThis thesis presents the results from the analysis and characterisation of the water and mid-J (J<11) 12CO, 13CO and C18O observations for a large sample of low-, intermediate-, and high-mass young stellar objects (YSOs). The studied molecular transitions have been observed with the HIFI instrument on board of Herschel Space Observatory and within the context of the Herschel key programme __WISH__. These species and transitions constitute unambiguous tracers of specific physical conditions within the inner and warmer regions of the YSO environment. The sample of sources, composed by more than 120 YSOs, covers a large range of bolometric luminosities, several evolutionary stages within the embedded phase, and different physical scales. The aim of this work is to explore the differences and similarities between low- and high-mass star-forming regions. In particular, this study focuses on investigating the physical and dynamical structure of dense warm gas within protostellar environments by characterising the velocity-resolved H2O and CO spectra in terms of line profile and line luminosity. The ultimate goal is to contribute to the understanding of the star formation process without imposing luminosity boundaries, and to put in context these processes on Galactic and extragalactic scales. Show less
