Raman study on para nitroaniline single crystal. II: Internal Vibrations

The assignment of the Raman frequencies from 200 to 1800 cm −1 has been made taking into account the values calculated by Brandmüller et al. for a planar molecule since only the H atoms of NH 2 are out of the plane. In the crystal the V line is unusually weak and the 1276–1284 cm −1 broad band is extremely strong: its complexity is explained by a Fermi resonance whose development can be followed with temperature variations. On the other hand the line of the deuterated pNA is always sharp because the resonant combination is related to a NH 2 vibration. The observation of this Fermi resonance confirms the non‐planar structure of the molecule in the crystal.