Optical and Raman studies of explosives under varying pressure and temperature

Recent studies of the effect of pressure and temperature on the optical and Raman spectra of the azides of potassium, thallium, silver and lead have been made using a diamond anvil cell, helium low temperature cryostat and high temperature furnace. With increasing temperature or decreasing pressure potassium azide was found to show stiffening of the lattice modes. Thallium azide however, shows both pressure and temperature induced phase changes which lead to a doubling of the unit cell in the c direction. Silver azide does not show any phase change with temperature although some of its Raman modes stiffen and some soften with temperature. Optical absorption at low temperatures in silver azide show strong excitonic features near the band edge and with pressure the crystals are found to darken irreversibly. Some recent results on the Raman and optical spectra of pure and sensitised nitromethane are also reported.