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We have revisited the still unresolved puzzle of the dispersion of the Ramandisordered-induced D band as a function of laser excitation photon energy E$_L$in graphite-like materials. We propose that the D-mode is a combination of anoptic phonon at the K-point in the Brillioun zone and an acoustic phonon whosemomentum is determined uniquely by the double resonance condition. The fit ofthe experimental data with the double-resonance model yields the reducedeffective mass of 0.025m$_{e}$ for the electron-hole pairs corresponding to theA$_{2}$ transition, in agreement with other experiments. The model can alsoexplain the difference between $\omega_S$ and $\omega_{AS}$ for D andD$^{\star}$ modes, and predicts its dependence on the Raman excitationfrequency.Comment: 4 figures in eps forma

Origin of the unusual dependence of Raman D band on excitation wavelength in graphite-like materials