MICROWAVE SPECTROSCOPIC INVESTIGATIONS OF THE C--H$\cdots\pi$ CONTAINING COMPLEXES CH$_2$F$_2\cdots$PROPYNE AND CH$_2$ClF$\cdots$PROPYNE

Abstract

The spectra of the CH$_2$F$_2\cdots$propyne and CH$_2$ClF$\cdots$propyne complexes have been studied by chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy and by {\em ab initio} calculations at the MP2/6-311++G(2d,2p) level. Both complexes contain C--H$\cdots\pi$ contacts, with the halogen atoms angled towards the methyl group end of the propyne. While CH$_2$F$_2\cdots$propyne has $C_s$ symmetry, CH$_2$ClF$\cdots$propyne has $C_1$ symmetry, with the fluorine and chlorine atoms straddling the propyne. \vspace{1em} Investigation of four single $^{13}$C and the DC$\equiv$CCH$_3$ isotopologues in CH$_2$F$_2\cdots$propyne has allowed a detailed structural determination, while only the $^{35}$Cl and $^{37}$Cl isotopologues have so far been assigned for CH$_2$ClF$\cdots$propyne. Experimental data will be compared with {\em ab initio} results and with the analogous acetylene complexes, both of which have $C_s$ symmetry structures, with double C--H$\cdots\pi$ interactions.