Fourier transform microwave spectroscopy of some metal-containing compounds produced by laser ablation
Creators: name: Walker, Kaley Anne
Publisher: name: University of British Columbia
Year: 2009

description: A laser ablation source has been constructed for a pulsed jet cavity Fourier transform microwave (FTMW) spectrometer. This source is mounted in one of the microwave cavity mirrors and includes a mechanism for rotating and translating the target metal rod. Seven metal-containing species, namely MgS, MgBr, AlBr, MgNC, A1NC, Y F and YBr, have been prepared using this apparatus and their pure rotational spectra have been measured by FTMW spectroscopy. The first laser ablation-FTMW measurement of a metal sulfide, MgS, has been made. The J = 1 — 0 transition near 16 GHz has been measured for 4 isotopomers in the ground vibrational state, as well as for the main isotopomer in the first excited vibrational state. ²⁵Mg nuclear hyperfine structure has been observed and the nuclear quadrupole coupling constant has been determined. The pure rotational spectra of magnesium monobromide and aluminium monobromide have been measured between 9.3 and 20.1 GHz. For MgBr, this is the first report of such a spectrum. Rotational, fine structure and several Br hyperfine parameters have been obtained for this radical and an accurate equilibrium bond length has been determined. From the nuclear quadrupole and magnetic hyperfine constants MgBr has been found to be highly ionic, with the unpaired electron residing almost entirely on Mg. For AlBr, accurate hyperfine parameters have been obtained, including the first values for the Al⁸¹ Br isotopomer. These, too, are consistent with highly ionic bonding. The calculated ionic characters follow trends predicted from electronegativity values: MgBr exhibits more covalent character than Ca and heavier alkaline earth monobromide species and AlBr shows less covalent character than GaBr. Pure rotational spectra of aluminium isocyanide and magnesium isocyanide have been measured in the frequency range 11.9 - 23.9 GHz. The hyperfine structure in MgNC caused by the 1 4 N nucleus has been measured and the nuclear quadrupole coupling, Fermi contact and dipole-dipole interaction constants have been obtained. From the measured transitions of A1NC, nuclear quadrupole coupling constants and nuclear spin-rotation constants have been determined for both the ¹⁴N and the ²⁷A1 nuclei along with an Al-N nuclear spin-spin constant. The degree of sp-hybridisation of the bonding orbitals of A1NC and MgNC have been estimated from the nuclear quadrupole coupling constants. Comparisons have been made to similar linear metal isocyanide and metal monohalide species. The first high resolution spectrum of yttrium monobromide has been measured between 7.4 and 22.5 GHz. In addition, nuclear spin-rotation splitting has been observed in the spectrum of yttrium monofluoride. Equilibrium rotational parameters have been determined for YBr and used to calculate an equilibrium bond distance. Hyperfine structure due to the bromine nuclei has been observed and nuclear quadrupole and nuclear spin-rotation constants have been determined. From them, YBr has been found to be highly ionic and very similar in behaviour to the alkali metal bromide species. The FTMW results for Y F have been combined with data from other pure rotational studies to determine the nuclear spin rotation constant.