Date of Award
Doctor of Philosophy
High-resolution pulsed field ionization photoelectron (PFI-PE) measurements have been achieved using monochromatized multibunch synchrotron radiation. By employing a simple electron time-of-flight (TOF) spectrometer, we show that PFI-PEs produced by the PFI in the dark gap of a synchrotron ring period can be cleanly separated from prompt background photoelectrons. We have demonstrated instrumental resolutions of 1.0 cm-1 (FWHM) and 1.9 cm -1 (FWHM) in the PFI-PE bands at ionization energies of Xe +(2P3/2) and Ar+( 2P3/2), respectively. Using this scheme, we have obtained rotationally resolved PFI-PE bands of O2+(X 2pi3/2,1/2g, v+ = 0--38), O 2+(A2piu, v+ = 0--12) and O2+(a4pi u, v+ = 0--18) in the energy range of 12.05--18.2 eV and NO+(a3Sigma+, v + = 0--16), NO+(A'1Sigma -, v+ = 0--17), and NO+(b 3pi, w3Delta, b3Sigma- , W1Delta and A1pi) in the energy range of 15.6--20.4 eV. The analysis of many of these highly excited rovibronic states provides accurate spectroscopic constants for the first time.;Another novel scheme is the energy-selected high-resolution pulsed field ionization photoelectron photoion coincidence (PFI-PEPICO) measurement of the dissociation of small molecules using two and multi-bunch synchrotron radiation. We show that this technique provides an ion internal state (or energy) selection limited only by the PFI-PE measurement. Employing a shaped pulse for PFI and ion extraction, a resolution of 0.6 meV (FWHM) is observed in the PFI-PEPICO bands for Ar+(2P3/2,1/2 ). As demonstrated in the PFI-PEPICO study of the process, O2 + hnu → O2+(b4Sigma g-, v+ = 4, N+) + e- → O+(4S) + O( 3P) + e-, the dissociation of O2 +(b4Sigmag-, v + = 4) in specific rotational N+ levels can be examined. The PFI-PEPICO study of the dissociation of CH3+ from CH4 also reveals the lifetime effect on the intensities for CH3+ and CH4+, which was characterized by a step-like feature observed in the PFI-PE measurement. The high-resolution for PFI-PEPICO measurements, along with the ability to distinguish the CH3+ fragments due to the supersonically cooled CH4 beam from those formed by the thermal CH4 sample, has allowed the determination of a highly accurate dissociation threshold for CH3+ from CH4. Similar studies are performed for C2H2, C2H5Br, iso-C 3H7X (X = Br, I), CH3X (X = Br, I), NH3 and CD4 so that highly accurate themochemical quantities related to these systems can be derived with unprecedented precisions.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Yang, Song, "Rotational-resolved photoelectron spectroscopy and energy-selected photoelectron-photoion coincidence spectroscopy using synchrotron radiation " (2001). Retrospective Theses and Dissertations. 676.