AbstractRaman spectra are described for the three crystalline modifications of polybutene‐1. The Raman frequencies are compared with infrared results and give good agreement. A normal‐coordinate analysis for A‐mode vibrations is presented for five possible helical conformations. The behavior of several calculated helix‐sensitive bands is characterized. These results are applied to the experimental Raman frequencies and lead to the prediction of a 103 helix for the orthorhombic form III modification.