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43964-G6
Fourier Transform Microwave Spectroscopy of Gas Phase Metal-Containing Compounds, Complexes, and Clusters
We have constructed three Fourier transform microwave spectrometers which are currently being used to study the fundamental gas phase chemistries of metal-containing compounds, complexes and clusters. The first spectrometer accepts molecules prepared using a laser ablation source. This spectrometer has been used to study the microwave spectra of a series of metal-containing molecules including SrS, SnO, PbO and ThO. Our study on thorium monoxide represents the first rotational spectroscopic study of any actinide-containing compound. From hyperfine constants we have shown that the electronic structure of ThO strongly resembles that of the ZrO and HfO molecules. The spectrometer is of sufficient sensitivity oxygen-17 species could be observed. This allowed us to survey the oxygen-17 hyperfine structures of a series of metal-containing oxides for the first time.
Our second spectrometer has been adjusted to record pure rotational transitions at low frequencies (i.e. below 2 GHz). We have successfully recorded a transition for iodobenzene at 1.1 GHz, the lowest transition recorded with a FTMW spectrometer. This spectrometer will be of particular use in pursuing the rotational spectra of metal-containing species with small rotational constants.
Our last spectrometer uses a chirped pulse microwave source and is capable of observing 4 GHz spectral regions in one data acquisition event. This spectrometer also accepts molecules from a laser ablation source. We have demonstrated the use of this spectrometer by recording the pure rotational spectra of AgCl and AuCl. In the former case the J = 2 – 1 rotational transition for all 4 isotopologues, spanning 1 GHz, complete with chlorine hyperfine structure, was recorded. A signal-to-noise ratio of 1000:1 was achieved following 21 minutes of acquisition time. We estimate that this represents at least a 10-fold reduction in the time required to search through and measure spectral features in a region of that size. A second significant advantage of the instrument is that spectral features are observed with correct relative intensities. For example the chlorine-35 AgCl lines were 3 times stronger than the chlorine-37 AgCl lines. Also the hyperfine components in the AgCl spectra were of correct relative intensities which allow easy spectral assignment. We have called this instrument the Search Accelerated Correct Intensity Fourier Transform microwave (SACI-FTMW) spectrometer. This instrument will be of considerable use in future studies pertaining to our research goal.
