| Abstract |
In this thesis, the kinetic investigation of the gas-phase reaction of chlorine atoms with the entire series of methyl disiloxanes, Me3SiOSiMe3, Me2HSiOSiHMe2, and MeH2SiOSiH2Me was performed in the temperature range 273-363 K. The rate constants of the reactions were found to be temperature independent, indicating a zero activation energy. The values of the absolute rate constants were found to be (in cm3 molecule-1 s-1, 2σ uncertainties): k1 = (1.00 * 0.10) ΄ 10-10, k2 = (1.98 * 0.13) ΄ 10-10, and k3 = (2.42 * 0.28) ΄ 10-10 respectively. The experiments were performed with a very low-pressure reactor (VLPR) in a molecular flow system, by simultaneously monitoring both reactants and products with a quadrupole mass spectrometer. The reaction mechanism involves the direct transfer of a hydrogen atom to a chlorine atom, leading to the formation of HCl and the corresponding organosilicon free radical. In the case of Me2HSiOSiHMe2 and MeH2SiOSiH2Me, the branching ratio of the two possible pathways, namely methyl versus silyl hydrogen atom abstraction, was not possible to be determined, due to the inability of detection of the organosilicon free radical. Therefore, the reaction enthalpies were calculated at five different levels of theory employing Gaussian94, and the abstraction of the hydrogen atom bonded to silicon was found to be 30 to 40 kJ mol-1 more exothermic than the abstraction of a methyl hydrogen. Finally, the bond dissociation energies (BDE) for all kinds of bonds for the three disiloxanes were calculated, for the first time, employing DFT methods and MP2 perturbation theory using triple-zeta basis sets. The BDE's obtained at the B3P86/6-311++G(3df,2p), B3P86/6-311++G(2df,p) and ΜP2/6-311++G(3df,2p) levels of theory for 9 different bonds for 6 well-studied molecules were found to be in good agreement with the experimental data.
|
Κινητική μελέτη των αντιδράσεων ατομικού χλωρίου με σειρά μεθυλιωμένων δισιλοξανίων στην αέρια φάση
