The vibrational coherence of the H-Cl oscillator in the monomer as well as in small clusters ((HCI)(x) and (HCl)(x)(N-2)(n)) trapped in argon and nitrogen matrices is explored by means of time-resolved one color degenerate four wave mixing experiments. The time and spectral resolution of the laser source, a picosecond OPO laser, enables the measurement of the vibrational dephasing time of HCl in various well defined (HCI),(N2). structures. The results highlight the environment effect on the dephasing processes. (c) 2005 Elsevier B.V. All rights reserved.