Isotopic studies and refined structure for the dimethyl ether-CS2 dimer

Rotational spectra of two additional isotopomers of the 1:1 dimer between dimethyl ether (DME) and carbon disulfide (CS2) have been measured by Fourier-transform microwave spectroscopy, allowing an inertial fit of the structure of this complex. The isotopic data are consistent with a structure in which the CS2 is aligned nearly perpendicular to the plane of the heavy atoms in DME, with internal motion of the CS2 from one side of the DME to the other leading to an inversion splitting, ΔE, of 90.34 MHz. This corresponds to a barrier to the tunneling motion of 69(10) cm−1. Ab initio calculations give two structures that are fairly consistent with the experimental rotational constants. One of these is similar to the experimental structure derived from the moments of inertia of three isotopic species, while in the other the CS2 is aligned roughly along the lone pair direction of the DME, similar to previously observed hydrogen bonded complexes.