THE MICROWAVE-SPECTRUM OF TRANS-2,3-DIMETHYLOXIRANE IN TORSIONAL EXCITED-STATES

The microwave spectrum of trans-2,3-dimethyloxirane (CH3CHOCHCH3) in t he excited torsional states v(17) = 1 and v(33) = 1 has been measured in the range from 8 to 26 GHz and assigned. An analysis of internal ro tation splittings of the observed rotational transitions was performed using the internal axis method (or ''combined axis method'') with a n ewly developed program accounting for the top-top coupling. The threef old hindering potential V-3 and the direction cosines lambda(g,l) of t he 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 V-6 was found to be -0.2600(12) kJ/mo l. The value of the parameter V-12(') describing the top-top coupling in the potential function (via V-12(') sin 3 tau(1) sin 3 tau(2)), was determined to -0.4240(6) kJ/mol.