Mössbauer Studies of Iodine Bond Hybridization in Iodomethanes

The Mössbauer effect of the 57.6 keV transition in 127I has been used to investigate the iodine bonding in CH3I, CH2I2, CHI3, and CI4 at 4.2°K. The data unambiguously imply the existence of a small amount of s hybridization in the iodine bonding orbitals. This hybridization increases approximately linearly through the series from ∼0% in CI4 to ∼8% in CH3I. The ionic character of the C–I bond also increases from CI4 to CH3I. The results are compared with several semiempirical predictions based on iodine NQR data. Separate experiments using the Mössbauer effect of the 27.8-keV transition in 129I have yielded consistent results in a CH129I3 absorber.