Abstract
The structure of fluoroethylene dimer ((C2H3F)(2), (FE)(2)) has been determined using chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy. Although the most stable structure was expected to be nonpolar, a planar, polar configuration was observed with sufficient intensity to measure spectra for four unique C-13 substituted isotopologues in natural abundance. This allowed a least-squares fit of the structural parameters of the dimer to observed moments of inertia. The resulting structure has a T-shaped arrangement of C=C bonds, similar to the recently studied FE center dot center dot center dot 1,1-difluoroethylene complex. Both dimers contain a cyclic arrangement of CH center dot center dot center dot F contacts between the H-C-F end of one monomer and the H-C=C-F side of the second monomer. omega B97X-D/6-31+G(d,p), MP2/6-311++G(2d,2p) and MP2/aug-cc-pVDZ calculations give the expected nonpolar end-to-end structure, ranging from 9 cm(-1) (DFT) to 63 cm(-1) and 57 cm(-1) (MP2/6-311++G(2d,2p) and aug-cc-pVDZ, respectively) more stable than the experimentally observed orientation. The omega B97X-D/6-31+G(d,p) calculations also indicate a nonplanar, polar configuration that is over 60 cm(-1) more favorable than the nonpolar structure; however, MP2 calculations predict significantly higher energy, and spectroscopic results provide no evidence of that structure's existence. The rotational constants of the observed T-shaped (FE)(2) structure are A = 6582.8323(12) MHz, B = 1256.6203(4) MHz, C = 1060.3474(3) MHz, and the dipole moment components, determined via Stark effect measurements, are mu(a) = 0.683 (3) D, mu(b) = 0.301 (5) D, mu(tot) = 0.746 (5) D. (C) 2020 Elsevier B.V. All rights reserved.