The molecular structure of methyl(difluoro)silyl chloride as determined by broadband microwave spectroscopy

Abstract

The rotational spectrum of methyl(difluoro)silyl chloride, CH3SiF2Cl, has been obtained using chirped-pulse Fourier transform microwave spectroscopy. The spectrum is complicated by hyperfine structure contributed by the chlorine, as well as transition doubling by the internal rotation of the methyl group. The spectrum was analyzed by simultaneously fitting both the hyperfine and internal rotation contributions using the Internal Axis Method (IAM), and the resulting fit rotational constants are A=3780.570(6), B=2423.8177(16), and C=2317.9254(13) MHz.Additionally, the singly-substituted isotopologue spectra corresponding to 13C, 37Cl, 29Si and 30Si, as well as the 37Cl/29Si and 37Cl/30Si double isotopologues, were observed. This abundance of isotopic data enabled calculation of both an experimental substitution structure (rs) and an effective ground state fit structure (r0) for CH3SiF2Cl in excellent agreement with the ab initio results.The ab initio structure was calculated using the MP2/aug-cc-pVTZ level of theory and a potential energy surface was calculated for the methyl rotor using the MP2/6–311++g(d,p) level of theory. These calculations predict a torsional barrier of 435.835cm−1, in agreement with the experimental barrier height of 468(3)cm−1.