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The investigation of molecular vibrations through non-linear classical mechanics has achieved considerable success in accounting for the transition from the normal mode to the local mode regime(1). We have recently proved the existence of some peculiar type of modes, which differ from both local and normal modes, in a system of two coupled Morse oscillators $A-B-A\prime$ (2). In this work we analyze the Fourier transform of some vibrational autocorrelation functions derived from numerical integration of the classical equations of motion(3). We applied these theoretical calculations to gain insight into the quasiperiodic vibrational motions of $CH2$-type oscillators. Eventually we intend to use these results to further understand observed overtone absorption spectra of molecules containing methylenic groups.