Spin–rotation measurements and magnetic shielding in CH2CF2

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Abstract
Rotational transitions 101→000, 212→111, 211→212, and 321→322 of 1,1 difluoroethylene were studied using a molecular beam maser spectrometer. Emission transitions were observed with 6 kHz linewidth (FWHM) and hyperfine structure due to fluorine and hydrogen interactions was resolved. The diagonal elements of the fluorine spin–rotation tensor are Maa=−13.4±3.6 kHz, Mbb=−10.94±0.68 kHz and Mcc=−6.06±0.68 kHz. This data is used to determine paramagnetic contributions to the fluorine chemical shift tensor. Analysis of the data yielded line centers for the rotational transitions of 15 774 348±3 kHz for 101→000, 26 465 055±5 for 212→111, and 14 419 906±3 kHz for 321→322, and 15 250 615±3 kHz for 211→212. Results of semiempirical calculations of diamagnetic contributions to the shielding tenors are presented for CH2CF2 and other molecules. Comparisons of total shielding tensors are made for related molecules.