<p>This thesis describes separate studies of high-energy Rydberg and ion-pair states in small molecules using resonant multi-photon ionisation spectroscopy.</p><p>* OODR/REMPI study of ungerade Rydberg states in O<sub>2</sub></p><p>The energy region between 75000 and 99900 cm<sup>-1</sup> of O<sub>2</sub> has been studied using optical-optical double resonance (OODR) with resonance enhanced multi-photon ionisation (REMPI). Three-photon excitation via single rotational levels of the b(<sup>1</sup>Σ<sup>+</sup><sub>g</sub> ) valence state was used to study <i>n</i>p (<i>n</i>=3–10) and <i>nf </i>(<i>n</i>=4–9) Rydberg states converging on O<sub>2</sub><sup>+</sup>X(<sup>2</sup>Π<sub>1/2,g</sub>) and X(<sup>2</sup>Π<sub>3/2,g</sub>). The excitation pathway picks out non-predissociated states that are singlet in the (Λ,S) coupling scheme – suitable for np states for n ≥8, or are linear combinations of equal weight of singlet and triplet-spin states in the (Ω,ω) coupling scheme which was found to be suitable for nf states for all values of n.</p><p>* OTR/RI study of Rydberg and ion-pair states in I<sub>2 </sub></p><p>Optical triple resonance (OTR) together with resonance ionisation (RI) has been used to study the ungerade manifold of molecular iodine between 57000 and 73000 cm<sup>-1</sup> via the E 0<sub>g</sub><sup>+</sup>(<sup>3</sup>P<sub>2</sub>) ion-pair state. Two 6s Rydberg states with 0 +u symmetry based on excited states of the ion core have been observed.</p><p>During this study we also observed electric-field-induced mixing of nearly isoenergetic rovibrational levels of the E0<sub>g</sub>P<sup>+</sup>(<sup>3</sup>P<sub>2</sub>) and D0<i>u</i><i>+</i>(<sup>3</sup>P<sub>2</sub>) ion-pair states. Detectable mixing with an applied field of 1kV/cm occurs over a range of energy level separations of ≤0.3 cm<sup>-1</sup>.</p><p>* (2+1)and (3+1) REMPI study of pyrrole (C<sub>4</sub>H<sub>5</sub>N) The two- and three-photon REMPI spectra of Rydberg states of pyrrole (C<sub>4</sub>H<sub>5</sub>N) have been recorded using circularly and linearly polarised light. The spectra were compared to the single-photon absorption spectrum of pyrrole and a similar study of furan (C<sub>4</sub>H<sub>4</sub>O). Although the ionisation spectra of pyrrole were considerably weaker than corresponding furan spectra, a strong propensity for excitation of d series with two photons and p and f series with three photons was observed for both molecules. The totally symmetric nd-Rydberg series associated with the first ionisation energy, [A<sub>2</sub><i>]n</i>d;A<sub>1</sub>, was identified from <i>n</i>=3 to <i>n</i>=15 and extrapolated to obtain IE1.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:kth-409 |
| Date | January 2005 |
| Creators | Sjödin, Marica |
| Publisher | KTH, Physics |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Trita-FYS, 0280-316X ; 2005:36 |
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