Vibrational spectra and trapping sites of HArF in solid argon are studied by using the original hybrid approach, combining quantum mechanical (QM) description of HArF at the MP2/6-311++G(2d,2p) level and non-empirical diatomics-in-molecules (DIM) method for guest-host interactions. Three types of structures for trapping sites within the C-4v (DS-I), C-2v (DS-II) and C-3v (DS-III) local symmetries are found. The calculated differences in harmonic frequencies of the H-Ar stretching and H-Ar-F bending vibrations between these sites are in quantitative agreement with the experimental data. The results indicate that the thermally stable solid-state configuration of HArF can be best described by the DS-III structure, while the unstable configuration refers to DS-I. (c) 2005 Elsevier B.V. All rights reserved.