STRUCTURE DETERMINATION AND CH…F INTERACTIONS IN H2C=CHF…H2C=CF2 BY FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY

The structure of the weakly bound dimer between fluoroethylene (FE) and 1,1-difluoroethylene (DFE) has been determined using a combination of chirped-pulse and resonant-cavity Fourier-transform microwave spectroscopy over a 7.5 to 19 GHz range. The rotational constants of the most abundant isotopomer were determined to be $A$ = 6601.14(35) MHz, $B$ = 833.3336(5) MHz and $C$ = 744.0217(5) MHz, and are in excellent agreement with $ab$ $initio$ predictions at the MP2/6-311++G(2d,2p) level. Observation of all four unique $^{13}$C isotopologues in natural abundance allowed for a full structure determination, showing that the dimer takes on a planar configuration with the H--C--F end of FE aligned with one of the F--C=C--H sides of DFE, forming two inequivalent CH$cdots$F contacts. The dipole moment components ($mu$$_{a}$ = 0.9002(18) D, $mu$$_{b}$ = 0.0304(80) D) were determined using Stark effect measurements and confirm the observed structure