The raman spectra of sulphur and phosphorus - Part I. Polarisation and molecular structure
The polarisation of Raman lines of sulphur and phosphorus is investigated with reference to their molecular structures. An intense Raman spectrum of liquid phosphorus has yielded three lines the state of polarisation of which conforms to the Raman-active vibrations of a tetrahedral molecule. The molecule of sulphur is considered to be a symmetrical puckered ring made up of two squares of four atoms each, one square placed at 45° with respect to the other. To explain the strong infra-red absorptions, the neighbouring atoms in the plane of each square are assumed to be connected with co-ordination bonds which give rise to electric dipoles causing absorption. The two lines 470 and 216 which are well-polarised are assigned to two symmetrical oscillations of such a model, 470 to the vibration in which the four atoms in each square move towards or away from the centre of the square and 216 to the vibration in which the two squares move towards or away from each other. The lines at 150 and 434 are completely depolarised and belong to anti-symmetric vibrations. The well-known changes of sulphur on heating are explained on the basis of this new molecular structure. A method of distilling high-boiling-point substances is also described in the paper.