The Rotational Spectrum of Tricarbonyl(trans,trans-2,4-hexadiene) Iron

The microwave spectrum of tricarbonyl(trans,trans-2,4-hexadiene) iron has been recorded in the range from 3 to 22 GHz using a Balle-Flygare type Fourier transform microwave spectrometer. The b- and c-type spectrum for the (56)Fe and the (54)Fe isotopomer could be assigned. The internal rotation of the two equivalent methyl groups results in a fine structure of the rotational transitions which is analogous to that of 2,2-dimethyloxirane [H. Hartwig and H. Dreizler, Z. Naturforsch., A: Phys. Sci. 47, 1063-1066 (1992)] and cis-2,3-dimethyloxirane [H. Hartwig and H. Dreizler, Z. Naturforsch., A: Phys. Sci. 47, 1051-1057 (1992)]. Analyzing this fine structure yields the internal rotation barrier in addition to the rotational constants and the quartic centrifugal distortion constants. Copyright 2000 Academic Press.