Pulsed laser photolysis-probe techniques have been used to investigate the nascent internal state distributions of OH(X<SUP>2</SUP>Π) produced in reactions of the type: O(<SUP>3</SUP>P) + RH → OH(X<SUP>2</SUP>Π) + R RH is a saturated hydrocarbon, which is chosen to contain representative primary, secondary or tertiary C-H bonds. Reactive superthermal O(<SUP>3</SUP>P) atoms are generated by photolysis of NO<SUB>2</SUB> at either 337, 308 or 248 nm. By changing the wavelength of photolysis of NO<SUB>2</SUB>, the collision energy of the reaction can be effectively altered. The OH product is detected in a state-specific manner by laser-induced fluorescence (LIF) on the A<SUP>2</SUP>Σ<SUP>+</SUP> ←X<SUP>2</SUP>Π transition. The delay between the photolysis and probe pulses is kept short enough to allow the partitioning of the available energy amongst the possible vibrational, rotational and fine-structure states to be determined from collisionally unmodified OH LIF spectra. The OH product, from the reaction between O(<SUP>3</SUP>P) and RH, is found to be rotationally cold. It is also apparent that the rotational distribution is largely independent of the nature of the R group. These findings have been interpreted as evidence that the reaction exhibits a strong preference for collinear approach of the O(<SUP>3</SUP>P) atom to the C-H bond from which the H atom is abstracted. In contrast, the degree of vibrational excitation depends strongly on both the type of C-H bond and the collision energy. These observations are consistent with the shift towards an "earlier" reaction barrier with increasing reaction exothermicity, which occurs as the H atom being abstracted is changed from primary to secondary to tertiary. The OH spin-orbit state distribution is non-statistical. The correlations between the spin-orbit states of the O(<SUP>3</SUP>P) reactant and OH product have been clarified. A purely adiabatic correlation does not correctly predict the observed product spin-orbit state distribution but a model, which includes non-adiabatic coupling of surfaces with the same projection of total electronic angular momentum, gives much improved agreement. This model has interesting but yet unstudied corollaries for the differential reactivity of the O(<SUP>3</SUP>P<SUB>j</SUB>) states.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662660 |
| Date | January 1997 |
| Creators | Sweeney, Gillian Michelle |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13060 |
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