Infrared and Raman Studies of Crystalline HCl, DCl, HBr, and DBr

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Abstract
The infrared and Raman spectra of crystalline samples of HCl, DCl, HBr, and DBr have been recorded in the temperature range 77°—10°K. The Raman results are most interesting in that four components are clearly resolved in the stretching region at low temperature. This indicates that the zigzag chains forming these crystals are probably not planar as was previously thought. Force-constant calculations based on the observed frequencies show that although the main interaction is between molecules in the same chain, there is also appreciable interaction between molecules in adjacent chains. The asymmetry of the two bands observed in the infrared persists at low temperatures. Certain anomalous features in the latter spectra are believed to originate from metastable phases.