Amorphous silicon carbide (a-Si1-xCx:H) samples having x less-than-or-equal-to 0.4 were studied by infrared and visible spectroscopy. Treatment by factor analysis of the 2000-2100 cm-1 absorption band of the spectra allows us to interpret this particular vibrational mode in terms of only two independent contributions. The analysis shows that polarization inductive shifting is not significant. An IR study of the evolution of this band during oxidation of porous samples was also performed. All the experimental evidence indicates that the growth of free volumes induced by the presence of carbon plays the most important role in the behavior of the 2000-2100 cm-1 band upon stoichiometric variations.691178057811