Equations have been derived that allow for the dependence of intermolecular potential on the level of vibrational excitation of an absorbing molecule in calculations of the spectral line shifts. The intermolecular potential in the form of a sum of atom-atom Lennard-Jones intermolecular potentials is used. Equations for calculation of matrix elements of the intermolecular potential with the allowance made for the vibrational dependence are obtained for diatomic and triatomic molecules. The contribution coming from the vibrational addition of the intermolecular potential to the Ar-pressure induced shift of HF spectral lines is assessed.