Knowledge Bank

The microwave spectrum of dimethyl ether dimer $(DME)2$ has been observed using a Fourie transform microwave spectrometer at Shizuoka University from 5 to 18 GHz. The sample of 1% dimethyl ether in Ar was used to form the complex in a super sonic expansion. Sets of characteristic triplet lines with similar spectroscopic properties were found and assigned to be the $J=4\leftarrow 3$, $J=5\leftarrow 4$, and $J=6\leftarrow 5$ transitions of $(DME)2$. The microwave spectrum of the six isotopomers $(DME)2$, $(DME-d6)2$, $(DME-13C2)2$, $(DME-d6)\dots (DME)$, $(DME-13C2)\dots (DME)$, $(DME)...(DME-13C2)$ have been assigned, leading to the precise spectroscopic constants. From the rotational constants of these six isotopomers molecular structure of dimethyl ether dimer was determined, being found to have $Cs$ symmetry and to be bound with three $O\dots HC$ hydrogen bonds.The barrier height to internal rotation of the methyl group has been determined from the observed A-E splitting.