A liquid nitrogen cooled, carbon monoxide laser magnetic resonance spectrometer was used to study mid-infrared vibration-rotation transitions in the gaseous free radical NCO, in its ̅X<sup>2</sup>Π state, at very high resolution. The use of an intracavity absorption cell made possible the observation of some transitions with sub-Doppler resolution. Developments to the spectrometer extended the range of operation of the CO laser. Most importantly, a CO laser operating on overtone transitions, Δν = 2, was operated in Oxford. The Δν = 2 CO laser operates over the range 2450-3800cm<sup>-1</sup> (4.08-2.63 μm), and the Δν = 1 CO laser over the range 1200-2100 cm<sup>-1</sup> (8.33-4.76 μm). NCO exhibits a Renner-Teller effect in its ground electronic state, an interaction between the motion of the electrons and the bending motion of the nuclei. Vibration-rotation transitions were observed in a sequence of bands involving the excitation of the out-of-phase stretching vibration, in the region of 1900cm<sup>-1</sup>. Some of the bands involved the excited bending vibration. The Zeeman effect behaviour of the molecular energy levels, particularly in the <sup>2</sup>Σ vibronic states, clearly showed the manifestation of the Renner-Teller effect. The Zeeman effect in the <sup>2</sup>Σ vibronic states was considered in detail. Many of the <sup>2</sup>Σ LMR spectra were recorded at sub-Doppler resolution. NCO is complicated to model, and unassigned LMR spectra remain. A harmonic Renner-Teller model was developed for the analysis. It was implemented by constructing an explicit matrix representation of the single electronic state N<sup>2</sup> effective Hamiltonian, which was diagonalised exactly. A new term in this Hamiltonian, describing centrifugal distortion corrections to the Renner-Teller coupling term, was developed for the <sup>2</sup>Σ vibronic states in order to account for anharmonic vibronic interactions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:318521 |
| Date | January 1994 |
| Creators | Gillett, David Alan |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:038bdb7e-1f8c-4112-bcea-4a0ca7ab7bcf |
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