Laser spectroscopy of small metal-containing free radicals
thesisposted on 15.12.2014, 10:35 by Matthew Simon. Beardah
The work presented in this thesis is concerned with the preparation of small supersonically-cooled alkaline-earth metal-containing polyatomic molecules by a laser ablation method, with subsequent detection using laser electronic spectroscopy. The results of spectroscopic studies involving three alkaline-earth metal-containing free radicals are presented. A new electronic transition, the D2T,+ -X2T,+ system, of the BaOH free radical is reported. The laser-induced fluorescence (LIF) spectrum is relatively straightforward, showing a simple vibrational progression in the Ba-0 stretching mode (v3). A re investigation of the C - X system of BaOH, carried out under supersonic jet conditions for the first time, is also presented. The LIF excitation spectrum is rather more complex than expected and possible explanations for these observations are considered. Five new electronic transitions of the SrOH free radical are reported for the first time. Three of these, the 52E+-r, Â£2S+-*2I+ and F2T1-X21,+ transitions, show simple structure in their vibrationally-resolved LIF excitation spectra. Another new transition, the C2TI- X2I,+ transition, is remarkably complex. It is proposed that a combination of Renner-Teller coupling and a 'reverse-polarised' n orbital in the C2TI electronic state is responsible for the added complexity in the LIF excitation spectrum. The 2'2S+ - X2I,+ electronic transition of SrOH shows evidence of vibronic interaction with the nearby C2Tl state. A dispersed fluorescence study of the ground state (X2I>+) of the MgCCH radical is also presented. The results of this study, in addition to a previous FTIR-matrix isolation study, have now accounted for four out of the five fundamental vibrational frequencies of ground state MgCCH. Finally, experiments involving a newly constructed REMPI-TOF mass spectrometer are discussed. Initial test experiments involving NO, CaOH, SrOH and SrCCH show that while the mass spectrometer detection aspect of the instrument is working well, supersonic cooling has proved elusive. Possible design aspects of the spectrometer which may be affecting the supersonic cooling are discussed, along with suggestions for future improvements.