Laser spectroscopy of metal-containing free radicals
thesisposted on 15.12.2014, 10:35 by Gary Keith. Corlett
Laser-induced fluorescence (LIF) spectroscopy has been used to probe the properties of several metal-containing free radicals, prepared in a supersonic jet expansion by either an electrical discharge or by laser ablation/photolysis.;The first spectroscopic observation of the zinc monoethyl radical was carried out following an electrical discharge through a mixture of zinc diethyl and helium. The laser excitation spectra recorded contained extensive vibrational structure, and a partial assignment is presented with the aid of ab initio SCF calculations. This was the first time an electrical discharge had been used to prepare a binary organometallic intermediate in a supersonic jet.;LIF excitation and dispersed fluorescence spectra of the MgCCH free radical were obtained following laser ablation of magnesium metal in the presence of methane. This was the first observation of the electronic spectrum of MgCCH, and vibrational progressions in the metal-carbon stretching mode were assigned for both the XËœ2sum+ and A 2pi electronic states. Other weak vibrational structure attributable to metal-carbon bending and carbon-carbon stretching modes is also tentatively assigned. In addition, the rotational constant was found for the A 2pi state following a simulation of the observed rotational structure.;Laser ablation of calcium and strontium in the presence of benzene gave intense LIF spectra of several well-known and one unknown species. Subsequent analysis of the observed vibrational structure led to the conclusion that the CaCCCH3 and SrCCCH3 free radicals were the spectral carriers, respectively. This task was aided by a series of density-functional theory calculations. This is the first spectral observation of both species.;Initial attempts at characterising the alkali metal monoxides by LIF spectroscopy are also presented. These intermediates were to be prepared by laser ablation of the corresponding metal in the presence of N2O. Early experiments focused on the monoxides of Li and Na, and currently only Li + N2O has produced an LIF spectrum. The observed structure, which is quite complex and not amenable to any simple assignment, has been tentatively assigned to the C2pi -- X2pi and C2pi -- A2sum+ systems of LiO. These preliminary findings bode well for future studies of the heavier alkali monoxides.