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HoC2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho is bonded in a distorted q4 geometry to ten equivalent C atoms. There are two shorter (2.44 Å) and eight longer (2.66 Å) Ho–C bond lengths. C is bonded in a 6-coordinate geometry to five equivalent Ho and one C atom. The C–C bond length is 1.30 Å.
The general problem of predicting infrared intensities is examined. The problem of predicting line intensities is discussed with attention focussed specifically on the problem of predicting vibrational strengths (or total band intensities). Two methods are considered: predictions based on ab initio quantum mechanical calculations, and predictions based on the transfer of atomic polar tensor parameters from small model molecules to the molecule of interest. Comparisons of predicted spectra with experimental spectra are shown for CH3OH, CH3OCH3, C2H5OH, and HOC2. It is suggested that the most important application of this work may be to the prediction of intensities for free radicals, ions, and reactive intermediates so that the infrared spectrum can be used in the quantitative analysis for these interesting species.