Bond Moments and Derivatives in CF4, SiF4, and SF6 from Infrared Intensities

The absolute intensities of the fundamental infrared absorption bands of SiF₄, CF₄, and SF₆ were measured utilizing the pressure broadening technique. The effective bond moments, μ₀, and bond moment derivatives, ∂u/∂r, are calculated as a function of the most general potential constants. Based on a valence force field plus repulsion between nonbonded atoms, the most probable values (first column) and the alternatives (second column) are as follows: $$\begin{array}{ccc}& {\mu }_0\text{=2.3\hspace{0.17em}d}& \text{\hspace{0.17em}\hspace{0.17em}3.3\hspace{0.17em}d}\\ {\mathrm{SiF}}_4& \text{\hspace{0.17em}\hspace{0.17em} ∂u/∂r=−7.49\hspace{0.17em}d/A}& \text{\hspace{0.17em}\hspace{0.17em}3.66\hspace{0.17em}d/A}\\ & & \\ & {\mathrm{\hspace{0.17em}\; \mu }}_0\text{=1.12\hspace{0.17em}d}& \text{\hspace{0.17em}\hspace{0.17em}2.36\hspace{0.17em}d}\\ {\mathrm{CF}}_4& \text{∂u/∂r=4.88\hspace{0.17em}d/A}& \text{\hspace{0.17em}\hspace{0.17em}3.35\hspace{0.17em}d/A}\\ & & \\ & {\mathrm{\hspace{0.17em}\; \mu }}_0\text{=2.65\hspace{0.17em}d}& \text{\hspace{0.17em}\hspace{0.17em}0.65d}\\ {\mathrm{SF}}_6& \text{∂u/∂r=3.85\hspace{0.17em}d/A}& \text{−6.58\hspace{0.17em}d/A}\end{array}$$ The results are discussed.