Analysis of the pure-rotational spectrum in the ν28 = 1 excited torsional state and torsional couplings of trans-ethyl methyl ether

► The microwave spectra of trans-ethyl methyl ether in the ν28 = 1 state was assigned. ► Analysis was carried out based on a tunneling matrix formulation. ► A perturbation was found in the high J transitions. ► Interactions between the torsional excited states were examined.