We have performed classical molecular dynamics simulations of 3 keV Ar + (C24H12)n(C60)m collisions where (n,m) = (3,2),(1,4),(9,4) and (2,11). The simulated mass spectra of covalently bound reaction products reproduce the main features of the corresponding experimental results reported by Domaracka et al., Phys. Chem. Chem. Phys., 2018, 20, 15052-15060. The present results support their conclusion that molecular growth is mainly driven by knockout where individual atoms are promptly removed in Rutherford type scattering processes. The so formed highly reactive fragments may then bind with neighboring molecules in the clusters producing a rich variety of growth products extending up to sizes containing several hundreds of atoms, and here we show examples of such structures. In addition, knocked out atoms may be absorbed such that e.g. hydrogenated coronene and fullerene molecules are formed.

Fullerenes and PAHs (polycyclic aromatic hydrocarbons) are two families of carbon based molecules. These are both present in the interstellar medium, and are there believed to play important roles in various processes, including the formation of stars in the case of PAHs. This thesis presents studies on the structures and dynamics of fullerenes and PAHs and their weakly bound clusters, that all have relevance in an astrophysical context. Here, the focus is on knockout driven reactions in which a single atom is knocked out of a molecule or a molecular cluster as a result of Rutherford-like scattering processes. These are modelled by means of classical molecular dynamics simulations.

The first study investigates knockout processes where a C₆₀ molecule is collided with helium atoms at 166 eV in the centre-of-mass-frame, similar to the velocities in interstellar shocks. Using a combination of experimental measurements and molecular dynamics simulations we find that highly reactive C₅₉ fragments can be created sufficiently cold to stabilise and survive indefinitely inisolation.

Following the first study, we model the structures and stabilities of mixed clusters of C₆₀ and C₂₄H₁₂ (coronene) molecules. We find that the two molecular species do not mix very well, but that they like to be in compact formations. For larger pure coronene clusters, we find that the most stable clusters contain two interacting stacks, forming a shape that looks similar to a “handshake”. These results are consistent with earlier modelling studies. Here, we show that such stacks also show up as subclusters in large mixed clusters.

Finally, we use the most stable clusters from the second study as targets in collisions with 3 keV argon atoms. We find that the simulated mass spectra strongly resemble the corresponding experimental ones. These show that many various forms of new molecular structures, both fragments and large new molecules, are being formed, as a result of the collisions. Here, the simulations give information on the reaction pathways and on the structures of these new species. There are also examples of hydrogenated, but otherwise intact, fullerene and coronene molecules being formed.

The mechanisms we have studied mimic inter- and circumstellar conditions where shockwaves and stellar winds drive particles (atoms and ions) at velocities similar to those studied here. The reactions covered in this work are thus likely to take place in such environments when carbon-based molecules and grains are energetically processed.

We have studied the stability of C₅₉ anions as a function of time, from their formation on femtosecond timescales to their stabilization on second timescales and beyond, using a combination of theory and experiments. The C^-₅₉ fragments were produced in collisions between C₆₀ fullerene anions and neutral helium gas at a velocity of 90 km s⁻¹ (corresponding to a collision energy of 166 eV in the center-of-mass frame). The fragments were then stored in a cryogenic ion beam storage ring at the DESIREE facility, where they were followed for up to 1 minute. Classical molecular dynamics simulations were used to determine the reaction cross section and the excitation energy distributions of the products formed in these collisions. We find that about 15% of the C^-₅₉ ions initially stored in the ring are intact after about 100 ms and that this population then remains intact indefinitely. This means that C₆₀ fullerenes exposed to energetic atoms and ions, such as stellar winds and shock waves, will produce stable, highly reactive products, like C₅₉, that are fed into interstellar chemical reaction networks.

The branch of condensed matter physics focusing on topological phases of matter has rapidly grown into a major part of the research field. A common feature of topological models is their robust edge and corner states, that are robust against perturbations of the Hamiltonian. This work studies such edge and corner states experimentally.

The method of using a femtosecond laser to write waveguide patterns in glass has, since its introduction, opened many experimental doors. Most prominently it has the potential to be used to design and create intrinsic photonic integrated systems. Here, it is used to experimentally explore non-Hermiticity of Hamilto- nians, that up until recently only had been investigated theoretically.

Partly dissipative Su-Schrieffer-Heeger chains and Kagome lattices are written in borosilicate glass samples of and excited with 720-780 nm light to simulate the time evolution of the corresponding non-Hermitian Hamiltonians. This way, the edge and corner states of the models are distilled.

Den gren av kondenserade materiens fysik som fokuserar på topologiska materiefaser har snabbt vuxit till vad som idag kan räknas som en huvudsaklig del av forskningsfältet. En gemensam egenskap hos topologiska modeller är deras robusta kant- och hörntillstånd som är okänsliga för störningar av Hamiltonianen. Det här arbetet studerar sådana kant- och hörntillstånd experimentellt.

Att använda en femtosekundlaser för att skriva vågledarmönster i glas är en metod som, sedan den introducerades, öppnat många experimentella dörrar. Kanske mest lovande är dess potential att användas för att skriva intrinsiska integrerade fotonsystem. Här används den för att experimentellt undersöka icke-hermiticitet hos hamiltonianer, som fram till nyligen bara undersökts på ett teoretiskt plan.

Delvis dissipativa Su-Schrieffer-Heeger-kedjor och Kagomegitter skrivs i borosilikatglasbitar och exciteras med 720-780 nm-ljus för att simulera tidsutvecklingen av motsvarande icke-hermitska hamiltonianer. På detta sätt destilleras modellernas kant- och hörntillstånd.

We have performed classical molecular dynamics simulations of 3 keV Ar + (C₂₄H₁₂)_n(C₆₀)_m colli- sions where (n,m) = (3,2), (1,4), (9,4) and (2,11). The simulated mass spectra of covalently bound reaction products reproduce the main features of the corresponding experimental results reported by Domaracka et al., PCCP, 2018, 20, 15052. The present results support their conclusion that molecular growth is mainly driven by knockout where individual atoms are promptly removed in Rutherford type scattering processes. The so formed highly reactive fragments may then bind with neighboring molecules in the clusters producing a rich variety of growth products extending up to sizes containing several hundreds of atoms, and here we show examples of such structures. In addition, knocked out atoms may be absorbed such that e.g. hydrogenated coronene and fullerene molecules are formed.

We have studied the stability of C₅₉ anions as a function of time, from their formation on femtosecond timescales to their stabilization on second timescales and beyond, using a combination of theory and experiments. The C₅₉ fragments were produced in collisions between C₆₀ fullerene anions and neutral helium gas at a velocity of 90 km/s (corresponding to a collision energy of 166 eV in the center-of-mass frame). The fragments were then stored in a cryogenic ion-beam storage ring at the DESIREE facility where they were followed for up to one minute. Classical molecular dynamics simulations were used to determine the reaction cross section and the excitation energy distributions of the products formed in these collisions. We found that about 15 percent of the C₅₉ ions initially stored in the ring are intact after about 100 ms, and that this population then remains intact indefinitely. This means that C₆₀ fullerenes exposed to energetic atoms and ions, such as stellar winds and shock waves, will produce stable, highly reactive products, like C₅₉, that are fed into interstellar chemical reaction networks.

We have performed molecular dynamics simulations on the formation of mixed molecular clusters of buckminster- fullerene and coronene, (C₂₄H₁₂)_n(C₆₀)_N−n. We report on our findings on the structures and their relative stabilities for cluster sizes N = 5 and 13 and for all possible combinations of the two species within these sizes, including the pure clusters of each type. Generally, we see that the two species mix rather poorly and that compactly bound clusters are favoured over spatially extended ones. For a given ratio of coronene and fullerene, clusters with one or two coronene stacks tend to be more stable than those with a larger number of stacks. In the case of small clusters, the coronene and fullerene molecules tend to separate into two different cluster parts. For larger clusters, this is often but not always the case.