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Hyperfine and internal rotation effects in the microwave spectra of some gaseous molecules

University of British Columbia

The microwave spectra of the following gaseous molecules have been observed and analyzed, using Stark-modulated microwave spectroscopy and cavity microwave Fourier transform (MWFT) spectroscopy. Bromine ¹⁸O-isocyanate, BrNC¹⁸O The microwave spectrum or BrNC¹⁸O has been measured in the frequency region 23-52 GHz, using a Stark-modulated microwave spectrometer. Because the spectrum is that of a prolate near-symmetric rotor with strong a-type and weak b-type transitions, perturbations in the quadrupole hyperfine patterns of Br were used to improve the precision of A₀. The geometry of the molecule has been determined; in particular, the NCO chain has been found to have a bend of ~8° away from Br. Dichiorosilane, SiH₂Cl₂ The b-type rotational spectrum of ²⁸SiH₂³⁵Cl₂ has been re- measured in the frequency region 10-16 GHz (J=1-10) using a cavity MWFT spectrome ter. The MWFT technique has permitted resolution of the complex hyperfine patterns observed for this molecule, which in turn has allowed the precise determination of the Cl nuclear quadrupole coupling constants. In particular, perturbations in the 9₁₈-8₂₇ transition have been analyzed to obtain a value for Xab . The quadrupole coupling tensor has been diagonalized to yield principal values, and the results are discussed in terms of the bonding in SiH₂Cl₂. Tetrolyl fluoride, CH₃⁻C≡C-COF The microwave spectrum of the unstable molecule tetrolyl fluoride has been observed for the first time. The a-type rotational spectrum observed with a Stark-modulated microwave spectrometer is very dense, owing to internal rotation of the methyl group. The spectrum has also been measured in the frequency range 9-17 GHz using a pulsed jet cavity MWFT spectrometer. Cooling in the jet has removed all internal rotation states other than⃒m ⃒= 0 and⃒m⃒=1, permitting assignment of the microwave spectrum. The threefold barrier to internal rotation has been confirmed to be very low =(V₃=2.20(12) cm⁻¹.) Metal Halides: AgCI, AlCl, CuCl, InCl, InBr, InF, YCl An apparatus has been constructed to produce metal compounds using laser ablation and to investigate their rotational spectra with a microwave Fourier transform (MWFT) cavity spectrometer. Metal halides have been produced by ablation of metal rods in the presence of a halogen-containing gas, using a Q-switched Nd:YAG laser (532 nm). The first seven such compounds that have been studied are silver chloride, aluminum (I) chloride, copper (I) chloride, indium (I) chloride, indium (I) bromide, indium (I) fluoride, and yttrium (I) chloride; the pure rotational spectrum of YCl is reported here for the first time. Nuclear spin-rotation coupling constants have been determined for the first time for AlCl, CuCl, InCl, InBr, and YCl, as has eQq(Cl) of YCl. Where possible, nuclear spin-rotation coupling constants have been used to examine the electronic structures of the molecules, and eQq(Cl) of YCl has been interpreted in terms of the ionicity of the Y-Cl bond. Values of the rotational and nuclear quadrupole coupling constants have also been improved for the metal halides.

Thesis/Dissertation

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2009-04-09

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http://hdl.handle.net/2429/7003

Chemistry

University of British Columbia

UBCV

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