Force Fields for Group IV Tetrafluorides and Group V Trifluorides

Abstract

The Coriolis zeta constants of the degenerate modes of SiF₄, GeF₄, NF₃, PF₃, and AsF₃ were obtained from infrared‐band contour measurements. These Coriolis coupling data provided the necessary constraints for determining unique force fields for the F₂ and E symmetry species of the XF₄ and XF₃ molecules, respectively. In an attempt to limit the force field for the A₁ species of the XF₃ molecules, the rotational distortion constants, which are functions of both the A₁ and E species force constants, were calculated for a range of values of the F₁₂ interaction force constant. For the purpose of this calculation, the E species force constants that were determined from Coriolis coupling data were held fixed. For NF₃, a satisfactory value of F₁₂ was obtained using the rotational distortion data. However, the rotational distortion data were not useful in fixing the A₁ species force fields for PF₃ and AsF₃.