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Title: Photodissociation dynamics and UV spectroscopy of ozone
Author: O'Keeffe, Patrick
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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The UV adsorption and photodissociation dynamics have been extensively studied by spectroscopic analysis of both the atomic and diatomic photofragments. Central to the study is the UV absorption which consists of the extremely intense Hartley band (200 - 310nm) and the less intense structured tail to lower energy called the Huggins bands (310 - 360 nm). The dissociation channels along with their thermodynamic thresholds for the dissociation of vibrationally relaxed ground state ozone are as follows: (A) O3 + hn (r) O(3PJ) + O2 (X 3 S-g) (1178 nm) (B) (r) O(3PJ) + O2 (a 1 Dg) (612 nm) (C) (r) O(3PJ) + O2 (b 1 S+g) (463 nm) (D) (r) O(1D) + O2 (X 3 S-g) (411 nm) (E) (r) O(1D) + O2 (a 1 Dg) (310 nm) The contribution of the spin-forbidden channels to Huggins band photodissociation was quantified using Resonance Enhanced Multiphoton Ionisation (REMPI) detection of the O (3P0) fragments combined with a delayed pulsed field extraction technique. The translational angular properties of the photofragments were measured as part of this technique. The observed trimodal velocity distribution of the O (3 P0) fragments was suggested to be a result of the different amounts of internal energy taken from the dissociation event by the diatomic co-fragments of channels (A), (B) and (C). However, a bimodal vibrational distribution of one of the channels could not be excluded at this stage as the slowest velocity peak of the O (3P0) fragments may be due to formation of high vibrational levels of the diatomic fragments of channels (A) or (B). REMPI spectroscopy was used to detect the diatomic photofragments in a rotationally and vibrationally selective manner. In these experiments ozone was photolysed with tunable UV radiation and the fragments were state selectivity ionised using (2 + 1) REMPI via the O2 (d 3ssg 1IIg) state using a second probe laser. This Rydberg state was found to be heavily perturbed by nearby valence state, yet it was possible to identify O2 (b 1 S+g, v = 0) fragments produced via spin-forbidden dissociation from a singlet state of ozone excited by absorption in the Huggins band region.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available