We compare geometry configurations, vibrational properties, and electronic structures of Ž . HF in a free state and inside argon atom shells Ar . the argon atoms closest to the trapped dimer. We conclude that the hydrogen-bonded Ž . complex HF gains some extra stability inside the argon shells, originating primarily 2 from a decrease of intermolecular distance R . Electronic structure calculations are in FF accord with the changes in dynamical properties, namely, a noticeable increase in the Ž y1 . vibrational frequency assigned to the F-F stretching mode q25 cm and decrease in rms deviations for the corresponding coordinate ␦ . In addition to these changes, the FF argon atoms of the nearest solvent shell donate a small fraction of electron charge which is spent for an increase of population of the antibonding orbital U of the free H -F f f monomer unit and shift orbital energies primarily of the lone-pair fluorine species. These shifts are greater than the changes due to geometry alterations and the possible inaccuracies of the calculation scheme.