Electrical Engineering Department, Institute for Computer Science, Technical University of Czestochowa, Al. Armii Krajowej 17,PL-42200 Czestochowa, Poland~Received 24 July 2003; revised manuscript received 18 December 2003; published 30 April 2004!Acetonitrile has been condensed into porous Vycor glass. The dielectric response in a frequency range from0.1 Hz to 1 MHz and temperatures between 40 K and 220 K, has been studied for a complete filling and apartial filling of 20%. Thereby the response of the adsorbed layer on the pore walls could be separated from thequasibulk material in the pore center. The quasibulk component shows a conventional melting transition, but ata reduced temperature and with hysteresis. The solid-solid transition of bulk acetonitrile is replaced by arelaxor behavior. The adsorbed layer does not support the melting transition.DOI: 10.1103/PhysRevB.69.134207 PACS number~s!: 61.43.Gt, 64.70.Nd, 77.22.2dI. INTRODUCTION