Reactions in small clusters studied by time-resolved laser spectroscopy

Citation

Peng, Lawrence Weiman (1991) Reactions in small clusters studied by time-resolved laser spectroscopy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3cw7-7w07. https://resolver.caltech.edu/CaltechETD:etd-04042008-130407

Abstract

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Molecular solute/solvent clusters are an ideal medium for studying solvent effects from the van der Waals complex to the solution bulk limit. Such clusters are conveniently produced using molecular beams. Thus, a new apparatus for making time-resolved measurements of large neutral clusters was constructed and is described in detail herein. The apparatus consists of a molecular beam interrogated by two picosecond lasers. Detection is by laser-induced fluorescence and resonance-enhanced multiphoton ionization. The laser and molecular beam combination permits the study of the role of solvation on the solute's excited electronic-state dynamics for a specific cluster size.

Picosecond time-resolved laser spectroscopy is applied to neutral solute/solvent clusters to study the effect of solvation on charge-transfer reactions in real-time. p(Dimethylamino)benzonitrile (4-DMABN) and [...]-naphthol ([...]-NpOH) are used as model systems since the charge-transfer is solvent dependent. The S[...] excited state dynamics of gas-phase 4-DMABN has been studied both in a supersonic jet expansion and in a thermalized vapor. The jet studies show that 1:1 complexes with water, ammonia, methanol, and acetonitrile do not undergo charge-transfer. At higher jet temperatures, emission is observed from 4-DMABN self-complexes. Charge-transfer fluorescence from 4-DMABN self-complexes is observed in a thermalized vapor. Studies have been done on the S[...] excited state dynamics of gas phase [...]-NpOH clustered with ammonia, piperidine and water. The measurements reveal cluster-size dependent dynamics for [...]-NpOH clustered with ammonia and piperidine, but not with water. The fast-time dynamics in the ammonia and piperidine clusters indicates the occurrence of proton-transfer reactions in these solute/solvent clusters. The cluster size, solvent dependence and the timescale for the reactions serve to emphasize the importance of the local solvent environment.

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