Geometry and vibrational spectra of the alkaline earth dihalides. III. MgCl2, CaCl2, SrCl2, and BaCl2

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Abstract
The infrared spectra of MgCl2, CaCl2, SrCl2, and BaCl2 trapped in solid krypton matrices at 20 °K are reported. From precise measurements of changes in the vibrational modes on isotopic substitution, a linear configuration for MgCl2 and CaCl2 is confirmed and an apex angle of 120° is established for SrCl2. For BaCl2 the bond angle has been estimated at 100°. Using a valence force field we have obtained a set of force constants from the measured fundamental frequencies as well as approximate values for the anharmonic corrections to some of the vibrational modes. The statistical entropies calculated from the vibrational frequencies and molecular geometries are in excellent agreement with the thermodynamic measurements.