Knowledge Bank

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 $Cs$ symmetry, CH$2$ClF$\cdots$propyne has $C1$ symmetry, with the fluorine and chlorine atoms straddling the propyne. \vspace{1em} Investigation of four single $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C and the DC$\equiv$CCH$3$ isotopologues in CH$2$F$2\cdots$propyne has allowed a detailed structural determination, while only the $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}$Cl and $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$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 $Cs$ symmetry structures, with double C--H$\cdots \pi$ interactions.