Photodissociation and photochemistry of silicon containing cluster ions
Jaeger, Jared Benjamin
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Silicon-ligand gas phase complexes of the form Si+(CO2)n and Si+(C6H6)n are produced by laser vaporization in a pulsed nozzle cluster source. These complexes are generated by utilizing a cutaway rod holder source which promotes the stabilization of weakly bound complexes. Metal-silicon cluster ions of the form MSin+ (M=Cu, Ag, Cr) are produced with the same laser vaporization pulsed nozzle cluster source. However, a rod holder with a growth channel is employed to promote the growth of large, strongly bound clusters consisting of many atoms. This growth channel facilitates multiple collisions that result in atom recombination allowing for the growth of large clusters. Laser photodissociation techniques are used to examine fragmentation patterns, elucidate structures, and obtain vibrational spectra to understand the nature of bonding via vibrational shifts of ligand based modes. Fixed frequency photodissociation at 355 nm is used to investigate the photochemistry of the Si+(C6H6)n complexes and MSin+ clusters. The complexes and clusters follow photofragmentation pathways including ligand elimination, atom elimination, decomposition or rearrangement, and photo- induced charge transfer. Vibrational spectra for the Si+(CO2)n complexes and Si+(C6H6)n complexes are obtained via Infrared Resonance Enhanced Photodissociation (IR-REPD)spectroscopy with a tunable optical parametric oscillator/amplifier (OPO/OPA). The Si+(CO2)n complexes are probed near the 2350 cm-1 region of the 3 asymmetric stretch, and the Si+(C6H6)n complexes are probed near the 3000 cm-1 region of the 12 C-H stretch. The complexes fragment by the loss of intact ligands and the photodissociation yield is enhanced on resonances. Monitoring the fragment yield versus the infrared excitation wavelength generates a vibrational spectrum for each size selected complex. Density functional theory calculations are employed to determine structures, energetics, and vibrational frequencies of these complexes. The comparison between theory and experiment provides insight into the bonding of these complexes.