UC San Diego
An experimental probe of electronic interactions in excited molecules produced by charge exchange
- Author(s): Savee, John David
- et al.
The electronic structure and fundamental electronic interactions of sym-triazine, HN₂, and HOCO were probed using translational spectroscopy coupled with coincidence detection techniques. The neutral species were prepared in excited vibronic states by neutralization of the corresponding parent cation with cesium, and full kinematic descriptions of the resulting dissociation dynamics were measured and used as a basis for identifying the accessed states and describing the mechanisms leading to dissociation. This dissertation begins with a brief introduction to the production of neutral species via neutralization with cesium, followed by a general overview of the experimental apparatus and data analysis methods. The dissertation concludes with detailed accounts of the experiments performed on sym-triazine, HN₂, and HOCO. A rich history of mechanistic debate is associated with the dissociation of sym-triazine. A collaborative experimental and theoretical investigation into the three-body dissociation dynamics (sym-triazine\[right arrow\]3HCN) resulting from excitation of sym-triazine into the \[pi\]*\[left arrow\]n and 3s Rydberg electronic manifolds established the working theory and treatment of experimental data that was carried over to later experiments. It was found that the topology of the electronic manifold into which sym-triazine is excited is consistent with the observed dissociation mechanism; sym- triazine dissociates to 3HCN via a concerted mechanism when excited to the highly symmetric \[pi\]*\[left arrow\]n electronic manifold, and via a stepwise mechanism when produced in the Jahn-Teller distorted 3s Rydberg electronic manifold. A two-body channel (\[right arrow\]HCN+ C₂N₂H₂) was also observed, and shares many correlations with the stepwise three-body dissociation mechanism. HN₂ and HOCO are reaction intermediates in important physical processes, and were both studied alongside their deuterated isotopologs to aid interpretation of the observed dissociation dynamics. HN₂ is believed to be a transient intermediate in thermal De-NOx processes, but has thus far eluded direct experimental detection. The CE experiments described here accessed three different dissociative vibronic states of HN₂ and use the observed dissociation dynamics to describe possible interactions between potential energy surfaces that ultimately lead to H/D+N₂ products. HOCO is a transient reaction intermediate in combustion processes, and, similar to HN₂, is difficult to isolate for spectroscopic investigation. The study described in this dissertation marks the first direct probe of excited electronic states of this species and describes possible mechanisms leading from the 1² A" electronic state of trans-HOCO to the observed H/D+CO₂ and OH/OD+CO product channels.