15min:
FOURIE TRANSFORM MICROWAVE SPECTRUM OF DIMETHYL ETHER DIMER.

YOSHIO TATAMITANI, BINGXIN LIU, JUN SHIMADA, T. OGATA, Department of Chemistry,
Faculty of Science, Shizuoka University, Shizuoka, Japan 422-8529.

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 leftarrow3, J = 5 leftarrow4, and J = 6 leftarrow5 transitions of (DME)2. The microwave spectrum of the six isotopomers (DME)2, (DME-d6)2, (DME-13C2)2, (DME-d6) cdots(DME), (DME-13C2) cdots(DME), (DME) cdots(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 cdotsHC hydrogen bonds.The barrier height to internal rotation of the methyl group has been determined from the observed A-E splitting.