Studies on the application of laser photoionization in supersonic-jets for the generation of intense ionic clusters.

Navea, Juan G.
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Pulsed photoionization in a supersonic expansion was investigated for the production of intense ionic cluster beams from seeded organic molecules. Neutral clusters were photoionized in a pulsed system and studied by means of an optic ion array; the molecular beam design was optimized and is described as a mean to investigate ionic clusters. Neutral clusters were generated and directed to an acceleration region where ionization occurred via a focused 266 nm pulsed laser beam. A set of static voltage plates in the acceleration region provide the ionic clusters with the kinetic energy required for mass separation and detection. Optimization of the parameters involved in the molecular beam apparatus are discussed as well as the calibration of the Time of Flight-Mass Spectrometer (TOF-MS). Low order clusters were recorded and cluster cations of (C6H5CH3)n+, (n-C6H14)n+, (ClC6H5)n+ were produced by a multiple photon photoionization process in the acceleration region. The observed cluster mass spectra for (C6H5CH3)n+,(n-C6H14)n+, (ClC6H5)n+ presented characteristic features that are discussed. Cationic and neutral toluene clusters were computationally minimized by Density Functional Theory (DFT) and Hartree-Fock (HF) Theory. The geometry and potential energy of observed toluene clusters was calculated using Gaussian 98 system of programs by the method DFT B3LYP 6-31 (G)*. Conformational switching was found to have a predominant role in the stability of ionic clusters as well as favored the frontier orbital interaction of the toluene ionic dimer. The photoionization potential energy surface was calculated, involving the conformation switching for toluene dimer and trimer. Chlorobenzene dimer was also minimized and its conformational switching is presented. A perpendicular conformation structure (T-shaped) is favored for the chlorobenzene neutral dimer, instead of the antiparallel structure observed for toluene neutral dimer.

Includes bibliographical references (p. 201-208).
Molecular beams., Photoionization.