Vibrational spectroscopy at high pressures.

A review is given with over 100 references of equipment for and results obtained in the field of vibrational spectroscopy at high pressures in the period June, 1975 to June, 1977. The device used in this thesis, the Diamond Anvil Cell (DAC), is analysed in detail and redesigned. A full discussion is given of earlier designs. The complex problems that arise in optical coupling of the DAC to i.r. and Raman spectrometers are also studied. Pressure calibration using the R fluorescence lines of Ruby is fully discussed and the problems of low temperature high pressure experiments investigated, and a calibration proposed. Three classes of compound are investigated: (i) organic (benzene), (ii) inorganic molecular (mercuric halides), and (iii) inorganic ionic (CsNiCl3). For benzene the same sample held under hydrostatic pressure in a gasketed DAC was examined by Raman, far-i.r. and mid-i.r. spectroscopy. Spectra of the solid phases of I and II were recorded and evidence for the elusive phase III obtained. The Raman spectra compared well with those obtained by Nicol using a much larger sample in a Drickamer cell whilst the i.r. results are entirely new. HgX2 (X = Cl, Br, I) have been studied in detail up to ca. 40 kbar and almost all known phases characterised by Raman and i.r. spectroscopy and structures proposed for several phases of hitherto unknown structure. In particular the high pressure form of yellow Hgl2 is shown to differ from the yellow high temperature modification. Raman and i.r. spectra of CsNiCl3 at various temperatures and pressures have been obtained and analysed, using compressibility and thermal expansion data determined as part of the study, in terms of anharmonic parameters.