Multi photon spectroscopy of some short-lived molecules

Tabrizchi, Mahmoud (1996) Multi photon spectroscopy of some short-lived molecules. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

In this work three molecules, HOCI, NF and NCI were studied by multiphoton ionisation spectroscopy. The nascent chlorine atom (²P) relative spin-orbit state population resulting from UV photolysis of HOCI has been measured by MPI in single laser experiments. The ratio of (0.30±0.07) for Cl^*:Cl has been obtained, indicating a higher preference for production of ground-state Cl(²P_3/2) than expected from statistical weights. Also, the Cl⁺ arrival time spectra show that most of the energy available in the photolysis is converted into kinetic energy of the photofragments.

In the NF case, transitions to previously unobserved 3dδ and 4dδ Rydberg states have been reported and assigned to ¹φ ← a¹Δ and ³φ ← a¹Δ transitions. The forbidden ³φ ← a¹Δ two-photon transition was found to derive its intensity from spin-orbit and spin-uncoupling interactions in the ¹φ₃, ³φ₄, ³φ₃ and ³φ₂ upper states.

The NCI work includes the observation of three ¹∑ states, and ¹II_v=0,1, (3dδ)¹φ_v=0,1,2,3, (4dδ)¹φ_v=0 and ³II_v=1,2,3,4 Rydberg states via MPI transitions from the X³∑^- or a¹Δ state. The observed bands were assigned and the rotational constants for each band were obtained. Also two experimental bands were observed and assigned as the (0,0) and (1,0) vibrational components of an NCI ³Δ ← X³∑^- transition.

Also a time-of-flight (TOF) mass spectrometer was constructed for use as a mass analyser in some MPI spectroscopic experiments. It employs a supersonic expansion together with laser ablation to generate samples. The main aim of this apparatus was to produce rotationally cold metal containing species such as metal oxides and hydroxides (e.g. AlO and AlOH) for study by MPI.

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