Predicted infrared spectra in the HF stretching band of the H₂-HF complex

The infrared spectra with hydrogen fluoride (HF) and deuterium fluoride (DF) (v₂ = 1 ← 0) for eight isotropic species of H₂-HF complex are predicted, based on our newly constructed high-accuracy ab initio potential energy surface [D. Yang et al., J. Chem. Phys. 148, 184301 (2018)]. The radial discrete variable representation/angular finite basis representation method and Lanczos algorithm were used to determine the ro-vibrational energy levels and wave functions for eight species of H₂-HF complex (para-H₂-HF, ortho-H₂-HF, para-D₂-HF, ortho-D₂-HF, para-H₂-DF, ortho-H₂-DF, para-D₂-DF, and ortho-D₂-DF) with separating the inter- and intra-molecular vibrations. Bound states properties including their dissociation energies and rotational constants were presented. The calculated band origins are all red shifted to the isolated HF molecule and in good agreement with available experimental values. The frequencies and line intensities of ro-vibrational transitions in the HF stretching band were further calculated, and the predicted infrared spectra are consistent with available observed spectra. Among them, the spectra for three isotopic species of H₂-HF (para-H₂-DF, para-D₂-DF, and ortho-D₂-DF) were predicted for the first time.