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Metallic species are deposited into the Earth's upper atmosphere by the ablation of approximately 50 tonnes of interplanetary dust that enters the atmosphere each day. The dust undergoes frictional heating to its melting point (approx. 1800 K), after which metallic species ablate and are deposited in the mesosphere-lower thermosphere (MLT) region of the atmosphere (70-120 km). Magnesium is one of the most abundant metals in the MLT, with layers of Mg+ being observed by rocket-borne mass spectrometry and satellite observations of the earth's dayglow., The original document contains color images.

Carbonyl oxides, which are formed from alkenes through ozonolysis, play an important role in atmospheric chemistry. This study examined their rearrangement into carboxylic acids with the aid of another molecule that acts as a catalyst. Because carbonyl oxides are very unstable, computation is useful in studying this reaction. The bimolecular pathways for the reaction of formaldehyde oxide with CO2, SO2, NO2 and NO were studied. The geometries of all structures involved and their energies were calculated using several computational methods: BB1K/6-31+G(d,p), B3LYP/6-31+G(d,p), CBS-QB3, G3 and CBS-APNO. In each pathway, the carbonyl oxide and catalyst molecule formed a cyclic adduct, which then broke apart into a carboxylic acid and the catalyst. Depending on the catalyst used, the adduct could form and break apart in one or more steps or other pathways forming different products were possible. These reactions were also studied with a methyl group on the carbonyl oxide. The relative energies for the reaction were similar to the non-methylated pathways, although the placement of the methyl group on either the syn or anti position affected the reaction mechanism and energy. Transition state theory was used to determine the rate of the first step in each reaction and indicated that the SO2 reaction should occur at the highest relative rate. RRKM theory was used to determine branching ratios for the reactions.

Elementary statistical mechanics; transport properties; kinetic theory; solid state; reaction rate theory; and chemical reaction dynamics.

Elementary statistical mechanics; transport properties; kinetic theory; solid state; reaction rate theory; and chemical reaction dynamics.

An analytical study of the effect of pressure on the rate constant for the unimolecular decomposition of n-propyl nitrate is given. The Rice- Ramsperger-Kassel-Marcus theory is reviewed, and the present application is discussed in detail. Limitations on application of this model are also discussed. It is concluded that the initial decomposition reaction of nitrate esters cannot be the rate determining step for the observed variation of burning rate with pressure.

A priori theoretical predictions for the decomposition rate of the formyl and the methoxy radicals have been made by application of the Rice- Ramsperger-Kassel-Marcus Theory. An Arrhenius rate coefficient expression is derived for the formyl radial decomposition, and a modified Arrhenius type rate coefficient expression that includes pressure dependence is derived for the methoxyl radical decomposition

During the initiation of an explosion and subsequent reaction, molecules can acquire energy by a variety of mechanisms. The manner in which these molecules assimilate this energy will determine their subsequent behavior. A study on energy redistribution within a molecule is initiated in the present report. Different cases in which a statistical or a dynamical theory is preferable for treating the rate of decomposition of molecules caused by chemical or thermal activation are described. Experimental evidence is considered from this point of view. Current studies on the dynamical treatment of classical, quantum and semiclassical methods are summarized. (Modified author abstract)

Die erfolgreiche Erzeugung ultrakalter atomarer Quantengase, die den Zustand der Entartung erreicht haben, hat die Atomphysik, Molekülphysik und auch die optische Physik regelrecht revolutioniert und zu einer Vielzahl von neuen Erkenntnissen geführt. Hierdurch wurde zudem die Zusammenarbeit zwischen vormals stärker getrennten Forschungsbereichen inspiriert und verstärkt. Ein ähnlicher Antrieb der Forschung kann von der Erzeugung von Proben ultrakalter Moleküle in einem wohldefinierten Quantenzustand mit hoher Teilchenzahldichte erwartet werden. Die zusätzlichen Freiheitsgrade, die ein Molekül bietet, und die langreichweitigen Dipolkräfte zwischen heteronuklearen Molekülen können genutzt werden, um Licht auf ungelöste Rätsel, wie beispielsweise den genauen Mechanismus der Hochtemperatur-Supraleitung, zu werfen. In dieser Arbeit werden Experimente mit homonuklearen Cäsiummolekülen im rovibronischen Grundzustand vorgestellt, die sich mit deren Stoßeigenschaften beschäftigen. Die Moleküle werden in einem dreidimensionalen optischen Gitter erzeugt, dessen Geometrie für die Messungen so verändert werden kann, dass die Moleküle in einer ein- oder zweidimensionalen Umgebung miteinander wechselwirken können. Alternativ kann durch das vollständige Entfernen der Gitterstruktur auch die Stabilität des molekularen Gases in einer gekreuzten Dipolfalle untersucht werden. Wir können die Moleküle in verschiedenen Rotations- oder Vibrationszuständen erzeugen, was uns erlaubt, das Verhalten von Molekülen in energetisch angeregten Zuständen, bei denen Zerfall in energetisch niedrigere Zustände möglich ist, mit dem Verhalten von Molekülen im energetisch niedrigsten Zustand zu vergleichen. Eine Verbesserung des Lasersystems, das für den Grundzustandstransfer verwendet wird, hat die Effizienz des Transfers auf mehr als 80% erhöht. Die molekularen Gase haben damit eine Reinheit erreicht, die erlaubt, aussagekräftige Stoßexperimente durchzuführen. In einer ersten Reihe von Experimenten unte, The successful production of samples of ultracold atoms that have reached quantum degeneracy has revolutionized the field of atomic, molecular and optical physics and enforced collaborations between researchers from different fields of studies. A comparable effect on current and future research can be expected from the production of high-density samples of ultracold molecules in a defined quantum state. Here, the additional degrees of freedom available in molecular systems in addition to the long-range dipolar interaction between two heteronuclear molecules are expected to elucidate long-standing puzzles, such as the inner workings of high-temperature superconductivity. This thesis presents a series of experiments that investigate the scattering behavior of a sample of homonuclear cesium molecules in the rovibronic ground state. We employ a threedimensional optical lattice potential for the creation of the molecules. The lattice potential can be altered for the measurements, such that the molecules are either confined in twodimensional traps, or in one-dimensional tubes. Alternatively, the lattice structure can be removed completely to allow for a study of the stability of the molecular sample in a crossed optical dipole trap. Furthermore, the molecules can be prepared in different rotational and vibrational states, allowing us to compare the behavior of molecules in excited states, where internal-state relaxation to energetically lower-lying states can take place, to the behavior of molecules in the energetically lowest state of the ground-state potential. An improvement of the laser system that is used for molecule-state transfer helped to increase the efficiency of the transfer to more than 80%, thereby setting the stage for collision measurements. In a first set of measurements we investigate the interaction properties of molecules in a two-dimensional trapping geometry. We observe a strong and immediate loss of particles, irrespective of magnetic-field value an, by Dipl.-Phys. Katharina Jag-Lauber, Zusammenfassung in deutscher Sprache, Dissertation University of Innsbruck 2018

Die erfolgreiche Erzeugung ultrakalter atomarer Quantengase, die den Zustand der Entartung erreicht haben, hat die Atomphysik, Molekülphysik und auch die optische Physik regelrecht revolutioniert und zu einer Vielzahl von neuen Erkenntnissen geführt. Hierdurch wurde zudem die Zusammenarbeit zwischen vormals stärker getrennten Forschungsbereichen inspiriert und verstärkt. Ein ähnlicher Antrieb der Forschung kann von der Erzeugung von Proben ultrakalter Moleküle in einem wohldefinierten Quantenzustand mit hoher Teilchenzahldichte erwartet werden. Die zusätzlichen Freiheitsgrade, die ein Molekül bietet, und die langreichweitigen Dipolkräfte zwischen heteronuklearen Molekülen können genutzt werden, um Licht auf ungelöste Rätsel, wie beispielsweise den genauen Mechanismus der Hochtemperatur-Supraleitung, zu werfen. In dieser Arbeit werden Experimente mit homonuklearen Cäsiummolekülen im rovibronischen Grundzustand vorgestellt, die sich mit deren Stoßeigenschaften beschäftigen. Die Moleküle werden in einem dreidimensionalen optischen Gitter erzeugt, dessen Geometrie für die Messungen so verändert werden kann, dass die Moleküle in einer ein- oder zweidimensionalen Umgebung miteinander wechselwirken können. Alternativ kann durch das vollständige Entfernen der Gitterstruktur auch die Stabilität des molekularen Gases in einer gekreuzten Dipolfalle untersucht werden. Wir können die Moleküle in verschiedenen Rotations- oder Vibrationszuständen erzeugen, was uns erlaubt, das Verhalten von Molekülen in energetisch angeregten Zuständen, bei denen Zerfall in energetisch niedrigere Zustände möglich ist, mit dem Verhalten von Molekülen im energetisch niedrigsten Zustand zu vergleichen. Eine Verbesserung des Lasersystems, das für den Grundzustandstransfer verwendet wird, hat die Effizienz des Transfers auf mehr als 80% erhöht. Die molekularen Gase haben damit eine Reinheit erreicht, die erlaubt, aussagekräftige Stoßexperimente durchzuführen. In einer ersten Reihe von Experimenten unte, The successful production of samples of ultracold atoms that have reached quantum degeneracy has revolutionized the field of atomic, molecular and optical physics and enforced collaborations between researchers from different fields of studies. A comparable effect on current and future research can be expected from the production of high-density samples of ultracold molecules in a defined quantum state. Here, the additional degrees of freedom available in molecular systems in addition to the long-range dipolar interaction between two heteronuclear molecules are expected to elucidate long-standing puzzles, such as the inner workings of high-temperature superconductivity. This thesis presents a series of experiments that investigate the scattering behavior of a sample of homonuclear cesium molecules in the rovibronic ground state. We employ a threedimensional optical lattice potential for the creation of the molecules. The lattice potential can be altered for the measurements, such that the molecules are either confined in twodimensional traps, or in one-dimensional tubes. Alternatively, the lattice structure can be removed completely to allow for a study of the stability of the molecular sample in a crossed optical dipole trap. Furthermore, the molecules can be prepared in different rotational and vibrational states, allowing us to compare the behavior of molecules in excited states, where internal-state relaxation to energetically lower-lying states can take place, to the behavior of molecules in the energetically lowest state of the ground-state potential. An improvement of the laser system that is used for molecule-state transfer helped to increase the efficiency of the transfer to more than 80%, thereby setting the stage for collision measurements. In a first set of measurements we investigate the interaction properties of molecules in a two-dimensional trapping geometry. We observe a strong and immediate loss of particles, irrespective of magnetic-field value an, by Dipl.-Phys. Katharina Jag-Lauber, Zusammenfassung in deutscher Sprache, Dissertation University of Innsbruck 2018