Thin films of copper phthalocyanine have been deposited on KBr and glass substrates by thermal evaporation method and characterized by the X-ray diffraction and optical absorption techniques. The observed X-ray pattern suggests the presence of alpha crystalline phase of copper phthalocyanine in the as-deposited thin films. Infrared spectra of thin films on the KBr pallet before and after exposure to the vapours of ammonia and methanol have been recorded in the wavenumber region of 400-1650 cm(-1). The observed infrared bands also confirm the alpha crystalline phase. On exposure, change in the intensity of some bands is observed. A new band at 1385 cm(-1), forbidden under ideal D-4h point group symmetry, is also observed in the spectra of exposed thin films. These changes in the spectra are interpreted in terms of the lowering of molecular symmetry from D-4h to C-4v. Axial ligation of the vapour molecules oil fifth coordination site of the metal ion is responsible for lowering of the molecular symmetry. (C) 2008 Elsevier B.V. All rights reserved.