Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

<p> The thermolysis of 2-diphenylmethylenehydrazono-5,5-dimethyl-Δ^3-1,3,4-oxadiazoline in vacuum and in chlorobenzene was studied. In both cases a stable 1-(diphenylmethylene)-4, 4-dimethyl-3-oxo-1,2-diazetidinium inner salt was obtained as the major product. The corresponding imino-oxirane, an isomer of the diazetidinium inner salt, is believed to be a precursor of the above product. Thermolysis of the same oxadiazoline in methanol gave benzophenone methyl carbazate and methyl isopropyl ether, probably involving the initial formation of an isocyanate as an intermediate.</p> / Thesis / Master of Science (MSc)

<p> The photo-addition of 2-cyclohexenone to norbornadiene has been investigated. A substantial proportion of the products formed were α, β unsaturated ketones. The structure of these has been assigned and a rationale is presented to explain the formation of these products. </p> / Thesis / Master of Science (MSc)

In recent years, thousands of exoplanets have been discovered around a variety of stellar hosts. The disks of gas and dust surrounding young stars are the location and source of material for planet formation. The properties of these protoplanetary disks therefore directly affect the planetary systems that may form. However, the details of the planet formation process are still unclear. In this dissertation, I constrain planet formation mechanisms by measuring the properties of protoplanetary disks, focusing on mass, dust grain growth, and dust settling. I use physically-motivated models and an Artificial Neural Network along with a Markov Chain Monte Carlo (MCMC) fitting procedure to obtain these and other disk properties. This dissertation compiles the largest sample to date of consistently-modeled protoplanetary disks, probing how disk properties vary with host mass and age. The occurrence of planetary companions increases as stellar mass decreases. Thus, brown dwarfs (BDs), with smaller masses than pre-main-sequence stars, may commonly host planets. Studying properties of BD disks and comparing them to pre- main-sequence star disks is therefore important for constraining their planet-forming potential. I present spectral energy distribution (SED) models for BD and pre-main- sequence star disks in four star-forming regions. The SEDs consist of archival photometry data spanning optical to millimeter wavelengths. I model the BD disk SEDs using physically-motivated radiative transfer code; pre-main-sequence star SEDs are modeled using a newly-developed MCMC fitting procedure that allows for a more complete analysis of the disk properties. I compare disk masses and dust settling in these two disk categories to gauge how host mass affects these properties. Typical disk lifetimes are a few tens of millions of years; planet formation likely occurs within the first few million years or less. Comparing how disk properties vary between star-forming regions of different ages can help pinpoint the timeline for planet formation. I present SED models for BDs in four star-forming regions and pre-main-sequence stars in eleven star-forming regions. I obtain the disk masses, dust grain sizes, and amount of dust settling in the disks and discuss the differences and similarities of these properties across regions of varying age.

Note:

Star cluster formation involves the conversion of molecular gas into stars inside giant molecular clouds (GMCs). Such a process involves many dynamical evolution mechanisms, including mergers between smaller star clusters (subclusters) on which we focus in this thesis. We take results of simulations performed by Howard et al. 2018 (H18) which found that young massive cluster (YMC) formation is heavily dependant on the process of subcluster mergers, and we simulate said mergers at higher resolution. Subclusters inside such GMC simulations are modelled using the sink particle prescription which does not resolve individual star particles or gas parcels inside the subcluster they represent. We employ a more controlled method in simulating subcluster mergers to better understand the response of the stellar and gas components of a subcluster from the merger process. To do this, we take the parameters of the sink particles created in H18 and set up spheres of stars and gas. We use the AMUSE framework to couple the N-body evolution of the stars to the smoothed particle hydrodynamics (SPH) evolution of the gas such that both components of a given cluster can realistically react to each other. We model 15 of these mergers and find that once the velocity at which the two clusters collide (collisional velocity) exceeds $\approx 10$kms$^{-1}$, the resultant cluster is not monolithic (i.e. it still contains two separate stellar components) while all other simulations merge into one monolithic stellar and gas component cluster. We also find that, regardless of the collisional velocity of masses of the component clusters, all resultant clusters lose a fraction of their stellar and gas mass. This fraction is directly proportional to the collisional velocity and is a discrepancy between the sink particle prescription (where all mass is contained inside a constant sink particle accretion radius) and real cluster mergers. A further discrepancy we find is that all simulations result in a cluster whose outermost regions are expanding and that the rate of this expansion is somewhat proportional to the collisional velocity of the merger. These results point to the inaccuracy of the sink particle prescription and allow us to develop tools to improve on it in future simulations. Next, we fit commonly used analytical density profiles to both the stellar and gas component of our resultant clusters and find that, while they do not provide particularly excellent fits, they provide constraints on what is an acceptable fit. Lastly, we analyze the amount by which gas with potentially star forming densities increase due to the merger and we find that all mergers increase their star forming gas mass fraction by roughly 50 per cent implying that mergers may be an effective tool for triggering star formation. / Thesis / Master of Science (MSc)

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