15min:

P. GRONER, Department of Chemistry, University of Missouri - Kansas City, Kansas City, MO 64110; S. ALBERT, E. HERBST AND F. C. DE LUCIA, Department of Physics, Ohio State University, Columbus, OH 43210.

An effective rotational Hamiltonian was used to analyze the rotational transitions in the vibrational ground state of dimethyl ether. Microwave and mm-wave measurements from the literature were combined with new measurements between 100 and 550 GHz in a global fit of all four torsional substates. Frequencies between 8 and 550 GHz were fit for transitions involving energy levels with J up to 40 and K_a up to 9. Only 22 spectroscopic parameters were necessary to fit 1499 frequencies to experimental precision (dimensionless standard deviation 0.67). The following parameters were determined in the least-squares fit: \rho=0.21665(19), ß=8.426(27) deg., parameters equivalent to the rotational, quartic and sextic distortion constants, the internal energy tunneling parameters \epsilon₀₁=-3.0392(43) MHz and \epsilon₀₂=0.0019(17) MHz and three tunneling constants related to the "rotational" constants.