Complete empirical assignment of vibrational spectra

Returning to the expected tetrahedral form, we can assign the polarized Raman bands to three of the four expected modes. The corresponding IR bands have B-type contours. Without calculating moments of inertia about three Cartesian axes we cannot be sure which band type corresponds to which of the three IR-active symmetry species, but we know that the B axis is assoeiated with aj vibrations (Section 8.6.2), and is therefore the z axis. The axis of greatest moment of inertia must be x, as it is perpendicular to the plane eontaining the three heavy atoms. This is confirmed by the observation that one of the Ge-H stretching modes 

IR(gas) Raman (liquid) Calculated (B3LYP/6-311G ) Assignment 

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