Pressure dependence of waman scattering in sulphur nitrides

The pressure and temperature dependence of Raman scattering in S4N4 in the 0-10 kbar range at 295 K and in the 10-295 K range at 0 pressure, have been studied in detail. S4N4 behaves like a typical molecular crystal under pressure except that the pressure dependences of the external mode frequencies are non-linear. The translational mode at 102 cm-1 shows an appreciable positive pressure coefficient and the lowest frequency rotational mode shows a temperature dependent softening which may be related to the thermochromic transition at -270 K. Correlation of the observed data with theexpected behaviour of (SN), is made. However, we have been unable to observe Raman scattering in (SN), under both ambient and high pressure conditions.