The phenomenon of collision-induced electronic energy transfer in selectively excited diatomic radicals has been investigated experimentally. Direct laser excitation of initial rovibronic states and dispersed, temporally-resolved fluorescence analysis of both parent <I>and</I> collisionally populated levels has allowed the collisional encounter to be quantified at a <I>state-specific </I>level. Theoretical modelling of these results allows the form of the potential energy surfaces which control the dynamics to be established. In an extended series of experiments, collision-induced C<SUP>2</SUP>Δ-B<SUP>2</SUP>Σ<SUP>+</SUP> transfer in the SiF radical has been investigated. It was observed that the product B<SUP>2</SUP>Σ<SUP>+ </SUP>state vibrational distributions were well correlated with the Frank-Condon overlap between vibronic wavefunctions of the two states. Dominant channels were found to involve Δ<I>v</I>=0, which corresponds to the energy defect of ~5000 cm<SUP>-1</SUP>. Rotationally resolved investigation of the C<SUP>2</SUP>Δ, <I>v</I>=0→B<SUP>2</SUP>Σ<SUP>+</SUP>, <I>v</I>'=0 channel revealed a significant fraction of this energy to be released as product state rotation. A limiting impulsive model of the energy release reproduced the main features of the observed behaviour. Polarisation resolved investigation of the transfer event revealed significant depolarisation of the product B<SUP>2</SUP>Σ<SUP>+</SUP> state compared to the initial C<SUP>2</SUP>Δ state. This observation was rationalised within two dynamically distinct models of rotational energy transfer. It is believed that all these observations may be explained by the valence-Rydberg nature of the electronic states involved. In a related set of experiments, novel measurements of collision-induced transfer between the A<SUP>2</SUP>Δ and B<SUP>2</SUP>Σ<SUP>-</SUP> states of the CH radical have been obtained.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660922 |
| Date | January 1998 |
| Creators | Randall, Colin James |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12833 |
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