Geometry and Vibrational Spectra of the Alkaline-Earth Dihalides. I. MgF2

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Abstract
The infrared spectra of vaporized MgF2 isolated at liquid‐hydrogen temperatures in both argon and krypton matrices are reported. Six major regions of absorption have been found, viz., 240, 450, 477, 483, 740, and 840 cm−1. On the basis of corresponding matrix spectra of nMgF2, 26MgF2 and a 1:1 mixture of nMgF2–26MgF2, it is possible to demonstrate unequivocally that the 240‐, 477‐, 740‐, and 840‐cm−1 absorptions are due to molecular species containing one magnesium atom. The 450‐ and 483‐cm−1 features are clearly attributable to polymeric species. From the magnitude of the measured isotope shifts the 740‐cm−1 and 477‐, 240‐, and 840‐cm−1 absorptions have been assigned to MgF and v1, v2, v3 of MgF2, respectively. The observation of v1 shows that MgF2 is bent. The higher resolution and precise frequency measurement employed in this work have been used to calculate the apex angle. This lies on the range 145° to 160° the most probable value being 150°.