The Microwave Spectrum of trans-2,3-E>imethyloxirane in Torsional Excited States

The microwave spectrum of trans-2,3-dimethyloxirane ( C H 3 C H O C H C H 3 ) in the excited torsional states u17 = 1 and vi3 — 1 has been measured in the range from 8 to 26 G H z and assigned. An analysis of internal rotat ion splittings of the observed rotational transitions was performed using the internal axis method (or "combined axis method") with a newly developed program accounting for the top-top coupling. The threefold hindering potential V3 and the direction cosines /.g of the internal rotation axes i with respect to the principal inertia axes g are in a good agreement with the ground state values. Additionally, the sixfold hindering parameter Vt was found to be — 0.2600(12) kJ/mol. The value of the parameter V[2 describing the top-top coupling in the potential function (via V[2 s i n 3 r ! s in3 i 2 ) , was determined to —0.4240(6) kJ/mol.