Abstract
Couplings between inter‐ and intramolecular vibrations have been investigated. In normal‐mode calculations a program has been used which allows all possible couplings between molecular and crystal vibrational modes. Several low‐frequency molecular modes coupled to lattice vibrations have been isolated. A complete assignment of the phenanthrene crystal spectrum is presented and the intermode mixing occurring in the region from 1550 to 1250 cm−1 is discussed.