15min:

STEPHEN G. KUKOLICH, Department of Chemistry, University of Arizona, Tucson, AZ 85721; MICHAEL H. PALMER, School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom; PETER GRONER, Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110; AND CHAKREE TANJAROON, Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.

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The keys to successfully analysing the high-resolution rotational spectra for manganese-rhenium decacarbonyl and for o-benzyne were the results of extensive and accurate theoretical calculations. Obtaining the microwave spectrum of the dinuclear complex MnRe(CO)₁₀ was made difficult by the low rotational constant (200 MHz) resulting in fairly high J values for transitions in the normal Flygare-Balle spectrometer region. The assignments were further complicated by the presence of ¹⁸⁵Re, ¹⁸⁷Re isotopes with eQq = 391 and 370 MHz and ⁵⁵Mn with eQq = -16.5 MHz. Large Gaussian orbital basis calculations by Palmer and Guest provided sufficiently accurate predicted molecular constants to assign and fit the spectrum. Although the spectrum for the normal isotopomer of o-benzyne could be obtained with reasonable S/N, assigning the single-substitution ¹³C isotopomer spectra, even with an enriched sample, proved to be difficult. The accurate and precise rotational constants for the 7 measured isotopomers for o-C₆H₄ could not be accurately fit using a planar structure due to the vibrational averaging effects. Using ab initio vibrational averaging corrections calculated by Groner, an accurate, near-equilibrium structure was obtained for o-benzyne.