Knowledge Bank

The interhalogens, $ClF3$ and $BrF3$, were originally assigned a pyramidal structure of symmetry $C3v$ on the basis of electron diffraction studies. Early vibrational spectra were also interpreted in terms of this model. More recently, however, investigation of $ClF3$ by x-ray diffraction and microwave spectroscopy, indicates that this molecule is plane and of symmetry $C2v$; the angles being nearly right angles. We have studied the infrared spectrum of $ClF3$ vapor from 3 to 38$\mu$ and its Raman spectrum. These data provide a strong confirmation for the plane structure. The fundamental frequencies obtained in the present work, together with the moments of inertia from the microwave results lead to a calculated entropy in good agreement with that obtained from thermal measurements. The spectral data obtained for $BrF3$ are less complete but the similarity of its infrared spectrum to that of $ClF3$ suggests that it also has the plane $C2v$ structure.