Microwave spectrum of divinyl ether: Analysis of doublet splittings in b and c type transitions and internal rotation of vinyl groups

Microwave spectrum of cis, trans-divinyl ether has been remeasured and doublet splittings were observed in most of the b and c type lines and also in a few of the a type transitions. The splittings were analyzed in terms of tunneling motion of the two vinyl groups through the planar configuration in which a steep potential barrier exists due to the repulsion between the α and β hydrogen atoms of trans and cis vinyl groups, respectively. An effective Hamiltonian the form $\text{G}{}_{\mathrm{a}}\text{P}\text{?}{}_{\mathrm{v}}\text{J}\text{?}{}_{\mathrm{a}}\text{+(α}{}_{\mathrm{v}}\text{J}\text{?}{}^2{}_{\mathrm{a}}\text{+β}{}_{\mathrm{v}}\text{J}\text{?}{}^4{}_{\mathrm{a}}\text{+γ}{}_{\mathrm{v}}\text{J}\text{?}{}^2{}_{\mathrm{a}}\text{J}\text{?}{}^2\text{)}$ was used for the analysis where terms in parenthesis apply only for the upper levels of the tunneling doublet. The values of G_a = 2.764, α_v = ?0.391, β_v = ?0.0067, and γ_v = +0.00065 (all in MHz) were derived in addition to the tunneling doubling Δ_v as 27.28 MHz and the refined rotational and centrifugal distortion constants. The potential barrier was approximated by a Gaussian function of the form $\text{V = A}\text{exp}\text{?a}{}^2\text{(?}{}_1{}^2\text{+ ?}{}_2{}^2\text{)]}$ and its height, A, was estimated to be 580 cm^?1 (1.6 kcal/mole) by way of WKB approximation.The definitions of large-amplitude vibrations in non-planar and non-linear molecules were discussed and a criterion to distinguish internal rotation, pseudo-rotation, inversion, and puckering from each other was derived. The motion reported in this paper was classified as internal rotation by this criterion.