Molecular-Beam Electric-Resonance Optothermal Spectroscopy Study of the Rotational Spectrum of the Less Stable Conformer of Methyl Vinyl Ether.

The pure rotational spectrum of the less stable conformer of methyl vinyl ether has been measured in an electric-resonance optothermal spectrometer. Analysis of the microwave spectrum shows that the less stable conformer is effectively planar with a low barrier between two gauche forms of the conformer. The rotational constants for the high-energy conformer, obtained from a least-squares fit to a threefold barrier internal rotation Hamiltonian are A = 39 192.490(26) MHz, B = 4527.5496(39) MHz, and C = 4181.2146(43) MHz. The threefold barrier to internal rotation is determined to be V3 = 427.516(71) cm-1. The dipole moment for the conformer has been measured using the Autler-Townes splitting of states in a strong, resonant microwave field. The dipole moment is µtot = 1.9(2) D [µa = 1.3(1) D, µb = 1.4(1) D]. The effectively planar structure of the conformer and the magnitude of the dipole moment are in good agreement with previous ab initio calculations. The experimentally determined threefold barrier to methyl rotation of the present study also agrees well with the value calculated from ab initio methods, 515 cm-1. Copyright 1999 Academic Press.