The Rydberg and ion-pair states of Cl<SUB>2</SUB>, Br<SUB>2</SUB>, I<SUB>2</SUB>, 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 Br<SUB>2</SUB> has been re-examined in the region 56 000-86 000 cm<SUP>-1</SUP>. Rydberg series, previously assigned to components of the <I>ns</I> Rydberg states have been reassigned to components of the (<I>n</I>-2)d Rydberg states, for <I>n</I>≥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 <I>n</I> in a particular Rydberg series (<I>n</I>=4 for the d-series in Br<SUB>2</SUB>). This reassignment prompted a reinvestigation of the one- and two-photon spectra of the halogen and interhalogen molecules, Cl<SUB>2</SUB> I<SUB>2 </SUB>, ICl and IBr in terms of the propensity rules developed for Br<SUB>2</SUB>. The one-photon spectra of I<SUB>2</SUB> and ICl were recorded using VUV laser radiation, generated by four-wave mixing in Kr gas. Ion-pair formation (X<SUP>+</SUP>+Y<SUP>-</SUP>) <I>via </I>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 I<SUB>2</SUB>. Predissociation in I<SUB>2</SUB> and ICl is discussed in terms of a two-electron exchange mechanism connecting the electronic configurations of the Rydberg and ion-pair states.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:650974 |
| Date | January 1999 |
| Creators | Flexen, Alexander C. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13824 |
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