Using infrared and Raman spectroscopics, we have Studied the effects induced by ion irradiation on icy mixtures at low temperature (T = 12 K) and after warm up to room temperature. In particular, we have considered mixtures made of H2O, CO, CH4, and N-2. These mixtures have been irradiated with 30 keV He+ and 60 keV Ar2+ ions. After ion irradiation at low temperature, several new absorption features appear in the infrared spectra, some of which may be due to N-bearing molecular species. A refractory organic residue is left over after warm-up to room temperature. After further irradiation of the residue at room temperature, the intensity of all infrared absorption features decreases. Raman spectroscopy of similar mixtures has shown that ion irradiation causes a modification of the structure of the samples which evolve towards an amorphous carbon. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.