The molecular structure of difluoroisocyanato silane: A combined microwave spectral and theoretical study

The calculated SiNC angles for the cis-HSiNC conformer are: 171.2 (B3LYP), 167.7 (MP2), 154.9 (MP4) and 154.6° (CCSD(T)), with differences up to 9° (MP2) in the trans-series. The potential energy (PE) surface for SiNC bending (x) is unsymmetrical, but the differences from a symmetric form are very small. A B3LYP study leads to a polynomial fit of the SiNC angle (x, radians) with the energy (E, cm−1), where E = 1993(536)x2 − 422(134)x4 + 27(10)x6 − 0.5(2)x8; the alternating signs indicate a double minimum potential. We have re-determined the PE surfaces for silyl group rotation for several other isocyanates using similar methods.