Molecular beam Fourier transform microwave spectrum of the dimethylether–xenon complex: tunnelling splitting and 131Xe quadrupole coupling constants

The rotational spectra of three isotopomers of the complex dimethyl ether–Xe (132Xe, 129Xe, 131Xe) have been measured by molecular beam Fourier transform microwave spectroscopy. An evenly spaced doubling of ca. 0.2 MHz, due to the internal rotation of the dimethyl ether subunit in the complex, has been observed for the μc-type transitions. The corresponding vibrational spacing, Δ01, has been determined to be 105(1) and 106(1) kHz for the 132Xe and 129Xe species, respectively. This datum has been useful to size the tunnelling barrier of Xe from above to below the COC plane. The nuclear quadrupole coupling constants of the 131Xe (I=3/2) species have been precisely determined, χaa=4.57(3), χbb=−2.93(3), and χcc=−1.64(3) MHz, respectively. These values indicate that the nuclear contributions to the field electric gradient at the Xe nucleus are smaller than the electronic ones.