The Dimethyl Ether−OCS Dimer: Rotational Spectrum, Structure, and Ab Initio Calculations

The rotational spectra of the normal species and four isotopically substituted species of the dimethyl ether−OCS dimer have been measured by Fourier transform microwave spectroscopy, thereby allowing a structural
determination of this weak complex. The normal isotopic species rotational constants are A = 4069.4106(23)
MHz, B = 1431.7413(7) MHz, and C = 1074.2925(5) MHz, and the experimental dipole moment components
are μa = 1.3046(28) D, μb = 0.8134(37) D, with μtotal = 1.5374(30) D. Rotational constants, dipole moment
components, and planar moments are all consistent with a geometry in which the OCS molecule is located
in the heavy-atom plane of dimethyl ether, making an O···CS angle of 96.5(2)°, and with an O···C separation
of 2.916(3) Å. Ab initio calculations at the MP2/6-311++G(2d,2p) level reproduce the structure accurately,
predicting rotational constants of A = 4065 MHz, B = 1450 MHz, and C = 1083 MHz.