The Raman spectra of aragonite, strontianite and witherite

The Raman spectra of the three crystals are recorded using the λ 2536·5 radiation of mercury and eleven new lines of low intensity are reported. These include the appearance in the cases of SrCO3 and BaCO3 of the line corresponding to the Raman-inactive mode of the free-ion, this line being of progressively diminishing intensity in the three cases owing to the structures progressively approaching that of hexagonal symmetry. The similarities and the differences observed in the three spectra are also correlated with the details of the crystal structures

The Raman and infra-red spectra of some solid hydroxides. Part II. Correlation with crystal structure

The paper discusses the results reported in Part I in relation to the crystal structures of the substances. From a comparison of the facts with the theoretically expected picture of the spectrum, the salient features exhibited by the spectra have been explained, in addition to identification and assignment of the frequencies wherever feasible. The progressive variations in the hydroxyl shifts exhibited by the different hydroxides and their hydrates are explicable as due to the interactions of the hydroxyls with each other and also with their neighbouring water molecules in the case of the hydrates

The Raman and infra-red spectra of some solid hydroxides. Part 1. Raman effect data

This article does not have an abstract

The Raman spectrum of calcite and its interpretation

The paper reports the results of a study of the Raman spectrum of calcite recorded with prolonged exposures. (a) The principal Raman shift of 1086 cm.-1 is accompanied by much weaker satellites whose frequency shifts are 1067, 1072 and 1075 cm.-1 The o ctave of the principal mode is recorded as a sharp line with a frequency shift of 2173 cm.-1 with a diffuse companion of comparable intensity which is a superposition of the octaves of the three satellites. The 1436 cm.-1 Raman shift likewise has satellites at 1399, 1412 and 1418 cm.-1 and its octave is feebly recorded as a sharp line, while the octaves of the satellites are also observed in its vicinity. The origin of the satellite radiations is discussed and it is shown that they represent the superlattice vibration frequencies of the calcite structure which are feebly excited. (b) The appearance of a sharp Raman line with a frequency shift of ± 221 cm.-1 is confirmed and it is shown to arise from a normal mode usually considered as inactive. (c) The two intense Raman shifts of 155 and 282 cm.-1 exhibit a highly unsymmetrical broadening, as also wings of low intensity spread out over the whole range of frequency shifts between -300 cm.-1 to + 600 cm.-1 This spectrum is explicable as arising from a very feeble excitation of the whole group of forty lattice and superlattice frequencies of the calcite structure and their overtones and combinations. (d) Sixteen combinational frequency shifts have been recorded. Seven of them are explained as combinations with the 1086 cm.-1 Raman line and the the nine others as combinations with 875 cm.-1 Some of the observed combinations violate the selection rule

The Raman spectra of crystalline sulphates of Ni and Mn

The paper reports the results of investigations on the Raman spectra of NiSO4·6H2O (tetragonal and monoclinic forms), NiSO4·7H2O (orthorhombic) and MnSO4·4H2O (monoclinic). Using λ 2536·5 resonance radiation of mercury for excitation of the Raman effect, it has been possible to observe a large number of frequency shifts. The spectra exhibit striking differences between themselves and also a few characters of general similarity. These are largely explicable in terms of the crystal symmetry and structure of these substances. In all the cases studied, the internal frequencies of the sulphate ion exhibit multiplicities owing to the lowering of the symmetry of the SO4 ion in the crystalline state and due to the number of ions present in the unit cell

Evaluation of the four elastic constants of some cubic crystals

This article does not have an abstract

The structure and optical behaviour of pearls

The paper embodies a study of the structure of the material composing pearls and of the optical effects which they display. The following topics are dealt with: (1) Birefringence, (2) X-ray-diffraction patterns, (3) The reflection-diffraction spectra, (4) The diffusion haloes of reflection and transmission, (5) The whispering-gallery effect, (6) The spectral character of iridescence and the influence of birefringence thereon, (7) The transmission spectra. The most noteworthy result of the investigation is to show that the diffusive properties of nacre play a major role no less important than that of the reflection by its stratifications in the optics of pearls

On the iridescence of potassium chlorate crystals. Part III. Some general observations

This article does not have an abstract

On the iridescence of potassium chlorate crystals. Part I. Its spectral characters

This article does not have an abstract

Optics of the pearl

This article does not have an abstract