Microwave spectra and quadrupole coupling measurements for methyl rhenium trioxide

Microwave rotational transitions for J′ ← J = 1 ← 0 and 2 ← 1 were measured in the 6–14 GHz range for methyl rhenium trioxide using a Flygare-Balle type, pulsed-beam spectrometer. The rotational constants for the most abundant isotopomers are B(187Re) = 3466.964(2) MHz and B(185Re) = 3467.049(3) MHz. The quadrupole coupling strengths are eQq(187Re) = 716.55(2) MHz and eQq(185Re) = 757.19(3) MHz. Transitions were also observed for 13C isotopomers and 18O isotopomers. The value for the ReC bond length obtained from a Kraitchman analysis is R(ReC) = 2.080 Å. The rhenium quadrupole coupling strengths are about 20% smaller than those obtained for HRe(CO)5.