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Title: Vacuum ultraviolet laser spectroscopy of diatomic halogen and interhalogen molecules
Author: Flexen, Alexander C.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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The Rydberg and ion-pair states of Cl2, Br2, I2, ICl and IBr have been studied using a range of laser-based spectroscopic techniques, in the vacuum-ultraviolet (VUV) energy region. The [2+1] resonance enhanced multiphoton ionization (REMPI) spectrum of Br2 has been re-examined in the region 56 000-86 000 cm-1. Rydberg series, previously assigned to components of the ns Rydberg states have been reassigned to components of the (n-2)d Rydberg states, for n≥6. The lowest 5s Rydberg state components on each ionic core remain unchanged, based on energetic considerations. The Ω values of the Rydberg states were deduced from rotational band contour analysis and from intensity ratios under linear and circular polarization. A propensity rule for assignments based on two Ω components with significant singlet character (Ω=0 and Ω=2), on each ionic core, was determined in terms of the microconfigurations for the Hund's case (c) states. As an exception, triplet components (Ω=1) are also observed for the lowest n in a particular Rydberg series (n=4 for the d-series in Br2). This reassignment prompted a reinvestigation of the one- and two-photon spectra of the halogen and interhalogen molecules, Cl2 I2 , ICl and IBr in terms of the propensity rules developed for Br2. The one-photon spectra of I2 and ICl were recorded using VUV laser radiation, generated by four-wave mixing in Kr gas. Ion-pair formation (X++Y-) via predissociation of Rydberg states was observed from all states seen in the one-photon absorption spectrum of each molecule. Spectra were recorded from the ion-pair threshold up to the ionization limit. The field-lowering effect induced by the high electric field in the extraction region of the time-of-flight mass spectrometer was investigated with I2. Predissociation in I2 and ICl is discussed in terms of a two-electron exchange mechanism connecting the electronic configurations of the Rydberg and ion-pair states.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available