Abstract
The rotational spectrum of the weakly bound dimer CH2F2 center dot center dot center dot CO2 has been measured using chirped-pulse and resonant cavity Fourier-transform microwave spectrometers in the frequency range 7-15 GHz. Spectra for six isotopic species have allowed a determination of the structure for this complex, in which the fluorine atoms of the CH2F2 straddle the CO2 subunit with a C center dot center dot center dot C=O angle of 71.3(4)degrees, and an M center dot center dot center dot C center dot center dot center dot C angle of similar to 38 (where M is the center of mass of CH2F2). A doubling of all rotational transitions has been ascribed to rocking of the CH2F2 subunit between two equivalent positions via a C-2v, transition state, and this motion inverts the mu(c) dipole moment component of the dimer. Analysis of the tunneling splittings with a coupled Hamiltonian gives an energy difference between the 0(+) and 0(-) vibrational states of 115.1402(24) MHz in the parent isotopologue and use of a flexible 1-dimensional model provides an estimated barrier for this motion of similar to 137(14) cm(-1). Observed dipole moment components (mu(a), = 1.513(6) D, mu(b) = 0 D, mu(c) = 1.259(3) D, mu(tot) = 1.968(7) D) are consistent with the observed structure and with ab initio predictions. (C) 2013 Elsevier Inc. All rights reserved.