Influence of halogen variation on structure and interactions in vinyl halide (H2C=CHX)…CO2 (X = F, Cl, Br) complexes

Chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy have been used to investigate dimers of CO$_2$ with vinyl fluoride (VF), vinyl chloride (VCl) and vinyl bromide (VBr). For all three complexes, CO$_2$ is aligned adjacent to the X--C--H end (X = F, Cl, Br) of the ethylene subunit, with C--X$\cdots$C and C--H$\cdots$O contacts. For VF$\cdots$CO$_2$, a second isomer is also observed, with CO$_2$ roughly parallel to the H--C=C--F side of VFhowever, there is no spectroscopic indication that similar structures are present for VCl$\cdots$CO$_2$ or VBr$\cdots$CO$_2$. For vinyl fluoride$\cdots$CO$_2$, a full structural analysis has previously been published,\footnote {C. L. Christenholz, R. E. Dorris, R. A. Peebles, S. A. Peebles, {\it J. Phys. Chem. A}, {\bf 118}, (2014), 8765-8772.} while for the Cl- and Br-containing species, insufficient data are presently available for complete structure determinations. However, structural information from ab initio calculations, $^{35}$Cl/$^{37}$Cl and $^{79}$Br/$^{81}$Br isotopic substitution, and analysis of chlorine and bromine nuclear quadrupole coupling constants will be presented. In addition, for this series of dimers containing C--H$\cdots$O contacts, further insight into the nature of the weak interactions may be obtained from Quantum Theory of Atoms in Molecules (QTAIM) and other {\it ab initio} analyses that are presently in progress