Role of the induced dipole moment in the collisional interference in the pure rotational spectrum of HD-He and HD-Ar

The parameters describing the interference between allowed and collision-induced transitions in the far-infrared spectrum of HD-He and HD-Ar are computed following the formalism of Gao et al. [Phys. Rev. A 44, 7379 (1991)] and the calculational procedure of Gao et al. [Phys. Rev. A 46, 5781 (1992)]. The contribution from each component of the induced-dipole moment is identified. The interference between the induced-dipole component having the same symmetry as the allowed moment and the allowed moment itself has the largest single contribution to the intensity interference effect. The mixing of rotational levels by an anisotropic intermolecular interaction introduces other components into the interference mechanism. The overall effect is usually to decrease the magnitude of the interference and to permit line broadening and asymmetry to occur. This interaction is most effective in causing the anisotropic overlap-induced pair dipole moment ${\mathit{B}}_2$(21) to play a role in the interference mechanism. The effect of the isotropic overlap-induced dipole moment is usually negligible.