Vibrational Spectra of the Polymorphic Solids of Methylene Iodide

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Abstract
Polarized infrared spectra of single crystals of methylene iodide solid I and the laser–Raman spectra of polycrystalline solid I at 90°K have been measured. The absence of the a2 fundamental in the infrared spectrum and the lack of crystal-field splitting in both the infrared and Raman spectra suggest that the site group for the solid I phase is C2υ. The infrared polarization results confirm this assignment of the site group and further indicate that solid I belongs to the orthorhombic crystal system with either C2υ or D2h factor group symmetry. The laser–Raman spectrum of a polycrystalline film of methylene iodide solid II has also been recorded. The observed correlation splittings give new spectroscopic evidence for the previous assignment of the crystal structure as monoclinic C2h.