Unlike many other molecules having local modes, the highly excited C-H stretching states of
CHD_3 show well resolved experimental spectra and simple Fermi resonance behavior. In this
paper the local mode features in this prototype molecule are examined using a curvilinear
coordinate approach. Theory and experiment are used to identify the vibrational state coupling.
Both kinetic and potential terms are employed in order to characterize the coupling of the C-H
stretch to various other vibrational modes, notably those including D-C-H bending. Predictions
are also made for CHT_3 and the role of dynamical coupling on the vibrational states of CH_3D
explored. Implications of these findings for mode-specific and other couplings are discussed
