Aspects of vibrational spectroscopy at high pressure.

The thesis is divided into two major areas of study. Part 1 consists of a computer-aided design study of the stress patterns and deflections experienced by diamond anvils. The aim is to understand and to learn how to control potentially-destructive stresses which limit the performance of anvils in high pressure diamond anvil cells. Twenty-three calculations were performed using two different finite-element analysis programs. Anvil shape, loading and support conditions and support material are all varied. The results are presented in the form of stress contour plots and tables of maximum stresses and deflections. The results are compared semi-quantitatively. The mechanisms of anvil failure are discussed and illustrated with photographs of actual failure. In particular, the importance of radial cracking in anvil failure is highlighted. Fatigue is seen to be associated with surface cracking of anvils. Suggestions for the better design of anvils and their supports are made. Part 2 contains Raman and mid-infrared studies of various molecular crystals at pressures up to 40 kbar. Major transitions were observed in Re2(CO)10 and Mn2(CO)10 at 5 kbar and 8 kbar respectively. These almost certainly involve a change from a staggered to an eclipsed molecular configuration. Studies were also performed on Cr(CO)6, Mo(CO)6 and W(CO)6. It is tentatively suggested that a transition occurs in W(CO)6 at about 10 kbar. A transition at 0.8 kbar was clearly seen in C10F8, but no evidence was found for a supposed transition at higher pressure. A transition was almost certainly observed in (PNCl2)3 at about 23 kbar but none was found in (PNCl2)4.