Fig. 2
From: Lattice Dynamics of the Rhenium and Technetium Dichalcogenides
The calculated zone-centre phonon modes of ReS2 (black squares), ReSe2 (red circles) and TcS2 (green triangles) plotted in order of increasing frequency. All modes are either IR- or Raman-active. The vertical dotted line indicates the position in frequency of the gap in the phonon spectrum between modes 9 and 10. Note, modes 1–3 are zero-frequency rigid displacements of the unit cell and are not plotted