Insights into atomic orbital polarization in polyatomic dissociation from DC slice velocity map imaging
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT REQUEST OF AUTHOR.] This thesis presents the investigation of the dynamics of polyatomic photodissociation mainly focusing on the measurements of recoil angle dependent photofragment angular momentum polarization (v-j correlation). These measurements provide a deep understanding of the dissociation dynamics such as excited state symmetries, coherent effects and nonadiabatic interactions. The quantum mechanical treatment established for the analysis of the atomic orbital polarization utilizes a set of anisotropy parameters which describe unique dissociation mechanisms. This thesis demonstrates a complete quantum mechanical model developed for the interpretation of the orbital orientation and alignment for a planer polyatomic system applied to ozone photodissociation probed using dc slice imaging technique. The coherent alignment produced by circularly polarized photolysis is measured here for the first time in light of the ozone photodissociation experiment. This parameter in combination with the quantum mechanical model developed, unraveled interesting observations of the dissociation dynamics, in particular the contribution of vibronic interactions and association of the geometric phase effect. These results further emphasize the importance of studying the photofragment angular momentum polarization to gain deeper insight into dissociation dynamics. Photodissociation of other systems such as carbonyl sulfide (OCS) and ethylene sulfide (C₂H₄S) studied using the dc slice imaging technique are also presented. By looking into the energy disposal and the velocity anisotropy of the atomic photofragment, the dynamics of the dissociation process such as the electronic states that come into play and their symmetries are identified. Moreover, features of the detected photofragment can be use as a reporter for the dynamics of the undetected cofragment which is demonstrated in the C₂H₄S experiment where it reveals the formation of triplet ethylene. A further modification to the current dc sliced velocity map imaging technique is introduced by incorporating the 3D imaging method. This approach registers the time (t) at which the particle hits the detector in addition to the position (x, y). This method utilizes a fast frame camera and a high speed digitizer along with the other components used in conventional velocity map imaging apparatus. The multihit, multimass detection and 3D slicing capabilities of this technique are demonstrated by two experiments: OCS and dimethyl amine photodissociation.
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