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Title: Laser based studies of transient species in a discharge flow apparatus
Author: Singleton, Scott
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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This thesis is concerned with spectroscopic and dynamical studies of transient species in a flow reactor. For the SiCl radical various studies using Laser Induced Fluorescence were performed. The excitation spectra detailed the band positions of the lower lying vibrational levels of the B2Σ+ and B'2Δ states, with the bands appearing to be unperturbed but suffering from spectral congestion. Dispersed fluorescence studies of these bands enabled measurement of the vibrational transition probabilities between the ground and excited states. By comparing these probabilities with calculated values, estimates of the transition dipole moment functions for the B-X and B'-X transition were made: with the conclusion that the B-X moment was nearly constant with internuclear separation, while the B'-X moment was a strongly decreasing function with increasing internuclear separation. A simple, yet consistent, molecular orbital argument was presented as an explanation of the form of the transition moment functions. Because of the longer radiative lifetime of the B' state (im 1.0μs compared to im 10ns for the B state) collision induced energy transfer of the B' state was readily observed experimentally. Total quenching cross sections for removal of v' = 0 and 1 of the B'-state are reported for a variety of nonpolar molecular colliders, with the magnitude of the cross sections appearing to be correlated with long range attractive forces between the collision pair. Partial cross sections for transfer from initially populated B' state to the B states are also reported, in this case, the cross sections may be influenced by specific resonant energy transfer processes. However, for transfer to v' = 2 of the B state (for which no resonant processes were obvious) the magnitude of the partial cross sections again appeared to be correlated with long range attractive forces. Resonance Enhanced Multiphoton Ionisation studies were performed on the HI molecule, formed as a result of the reaction:H+ I2 → HI+ I. Spectroscopic observations on this molecule are reported at selected positions between 67500 and 73500 cm^-1. Wherever possible effective molecular constants were calculated from the observed spectra. While various transitions were evident from ground state hot bands, observation of nascent rotational or vibrational product state distributions, of the reaction, were not made in these relatively slow flow conditions. The complementary nature of the single photon (vuv) and two photon absorption techniques was highlighted by the apparent inversion of intensities with which bands were observed by the two techniques. Bands previously unobserved in the single photon absorption work are reported. The bands are assigned as transitions to the i^3Δ(2) and d3Πo(0±) states.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available