The analysis of the microwave absorption spectrum of trans-ethyl methyl ether in the skeletal torsion v₃₀ = 2 state

The microwave absorption spectrum of the trans-ethyl methyl ether in the skeletal torsional v₃₀ = 2 state was analyzed for the first time. The trans-ethyl methyl ether molecule has two inequivalent methyl group internal rotors. Splitting due to the methyl group connected to the oxygen was dominant and observed in the v₃₀ = 2 state. This result was supported by considering the torsional force field in the same way as in the ground and the v₃₀ = 1 states. Over 800 lines up to J = 55 and K_a = 6 were assigned. The spectrum was analyzed using an IAM-like matrix formulation. Three rotational constants, eight centrifugal distortion constants, and four O-CH₃ internal rotation tunneling parameters were determined for the v₃₀ = 2 state. It was also made clear in the present analysis that the tunneling parameter dominant concerning the splitting due to the O-CH₃ internal rotation has the same sign as that of the v₃₀ = 1 state, and the sign opposite to that of the ground state.