Microwave measurements on transition metal and weakly bound molecular complexes.

Abstract

High resolution microwave spectra for the transition metal compounds cobalt tri-carbonyl nitrosyl (Co(CO)₃NO), cyclopentadienyl cobalt di-carbonyl (CpCo(CO)₂), and cyclopentadienyl manganese tri-carbonyl (CpMn(CO)₃) were obtained for the first time using pulsed beam Fourier transform spectroscopy. An oblate symmetric top spectrum was measured for Co(CO)₃NO and the first gas phase value of the cobalt nuclear quadrupole coupling parameter was obtained. The asymmetric top hindered rotor spectrum for CpCo(CO)₂ was measured and a barrier to internal rotation was estimated from the spectrum. Analysis of the prolate symmetric top hyperfine spectrum of CpMn(CO)₃ yielded the first gas phase measurement of the rotational constant and the Mn nuclear quadrupole coupling. High resolution microwave spectra for the iron containing transition metal complexes cyclobutadiene iron tri-carbonyl (CbFe(CO)₃), cyclohexadiene iron tri-carbonyl (C-hexFe(CO)₃) were obtained and a Kraitchman analysis of the isotopic substitution data for the butadiene iron tri-carbonyl (BuFe(CO)₃) is also discussed. Structural parameters for the HCCH-CO were obtained from the various isotopomers for this complex. An analysis of the distortion parameter D(J) yielded an estimation of the binding energy for this weakly bound complex. Analysis of spectra for nitrosyl chloride (NOCl) and chlorine tri-fluoride (ClF₃) yielded the first high resolution low J data sets for these molecules. The quadrupole coupling data are interpreted using the Townes-Dailey model for quadrupole coupling and an improved ground state structure for ClF₃ was obtained. Microwave spectra reported here were obtained using a pulsed beam Fourier transform microwave spectrometer constructed at the University of Arizona. The design is similar to original Flygare-Balle apparatus with many modifications for improving signal sensitivity and data acquisition.