The microwave spectra of six isotopic species of dimethyl ether were investigated from 8ndash;48 Gc. From the changes in moments of inertia with C13and O18substitutions the CO distance and COC were found to be 1.410plusmn;0.003 Aring; and 111deg;43prime;plusmn;20prime;, respectively.The conformation of the methyl groups was determined from the (CH2D) (CH3)O species. Dimethyl ether hasC2vsymmetry and the methyl groups are staggered with respect to the opposite CO bonds.The data from deuterium substitutions could only be satisfactorily fit by a structure containing asymmetric methyl groups. The two CH distances in this structure differ by 0.009 Aring;, the HCH by 49prime;, and the angle between the CO internuclear line and a perpendicular to its respective hydrogen plane is 2deg;31prime;plusmn;40prime;. If an average CH distance of 1.0956Aring; is assumed the average HCH is 109deg;29prime;. The structure of the asymmetric methyl groups is shown to be consistent withsandphybridization of the carbon orbitals. In this scheme the carbons form ``bent bonds'' with the oxygen.From the Stark effect the dipole moment of dimethyl ether was determined to be 1.31plusmn;0.01times;10mdash;18esu.
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