The densities of ionic liquid compound EMIGaCl4 and its mixtures with EMIC were measured by pycnometry in the temperature range from 308.15 to 343.15 K. The values of apparent molar volume of the mixture, partial molar volume and apparent molar expansibilities of EMIC were determined. Both Raman scattering and ab initio calculations were performed. All results show that GaCl4- is sole anion in ionic liquid compound EMIGaCl4 and is predominant one in the mixture composed of EMIC and ionic liquid compound EMIGaCl4. (C) 2004 Elsevier B.V. All rights reserved.