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Title: Near-threshold photodissociation and photoionization of triatomic molecules.
Author: Matthews, Sarah Jane
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2007
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Multichannel quantum defect theory (MQDT) has been used to simulate the doubleresonant autoionization spectra of HCO, produced following the photodissociation of acetaldehyde (CH3CHO). Vibrational angular momentum has been incorporated into these calculations for the first time. Simulations are produced for HCO involving Rydberg series with up to six quanta of ion-core bending mode (1I2) excitation. The simulation of resonances converging to the (0310) state of HCO+ is compared with our own experimentally recorded spectrum, while all other simulations are compared with spectra recorded by Grant et al. A good agreement between experimental and simulated spectra is reached, and values for both diagonal and off-diagonal quantum defect matrix elements for 1I2 = 0 - 6 are obtained and compared. A fully state selective velocity-map ion imaging (VMI) study of N02 photodissociation was carried out over a range of photolysis wavelengths. Images were recorded for three different rotational channels of NO (JII = 3/2, 11/2 and 21/2) and different spin-orbit states of the 0 atom (3P2,1), at photolysis energies ranging from 0 to 1000 cm-1 above the dissociation threshold. The angular anisotropy parameter (fJ) was then obtained as a function of both excess energy Eexc (energy above threshold) and available energy Eavl (Eexc - Erot ). The observed variation in the angular anisotropy parameter fJ close to the dissociation threshold is explained by considering the dissociation mechanism of N02 • After initial excitation to the A state, non-adiabatic coupling means that dissociation actually occurs on the ground potential energy surface. The reaction rate constants fluctuate rapidly in this energy region and level out at higher excess energies. These fluctuations in reaction rates have a strong effect on the angular distribution of the photofragments and translate directly into the wide variations of fJ observed in this work. The range of lifetimes derived from these spectra are in agreement with the range observed in picosecond pump-probe experiments.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available