Infrared absorption of (NH4)(3)WO3F3 compound has been studied. Profile of asymmetric band in 600-1000 cm (1) range associated with polar W-O vibrations of WO3F33- ions is explicable on the basis of multi-oscillatory dynamics with account of damping. Complex profile with Evans holes proves that internal modes of WO3F33- anions in the fluorine-oxygen octahedron interact due to the effects of the local field. (C) 2011 Elsevier B. V. All rights reserved.