The microwave spectra of several isotopic species of difluorosilane, SiH2F2, have been investigated in the region from 12 000 to 38 000 mc. Rotational constants have been determined and the following structural parameters calculated for SiH2F2: rSiH=1.471±0.007 A, rSiF=1.5767±0.001 A, ∠HSiH=112°1′±30′, ∠FSiF=107°56′±6′. An independent determination of the structure of SiD2F2 was also carried out with the following results: rSiD=1.469±0.010 A, rSiF=1.5764±0.001 A, ∠DSiD=113°11′±45′, ∠FSiF=107°57′±10′. Rotational constants for the vibrationally excited state ν4 have been determined for both SiH2F2 and SiD2F2, and certain structural parameters determined. The variation of effective structure upon isotopic substitution is discussed.
Measurements on the Stark effect of the ground vibrational state of SiH2F2 give a value of 1.54±0.02D for the dipole moment. Values for the excited state v4=1 and for SiD2F2 were also measured and agree within the experimental error with the SiH2F2 ground‐state value.