Radial distribution function analyses of polythiohydroquinone

Abstract

In recent years, the RDF analysis [1-4] of X-ray diffraction patterns has become a powerful tool for studying the structures of non-crystalline disordered materials. This technique may be applied to systems for which the average radial distribution function is spherically symmetrical, such as pure liquids, solutions, glasses and finely divided powders. It yields information not only about structural parameters but also many physical parameters such as Debye temperature, coupling coefficients, coordination numbers and interatomic potentials. The polymer, polythiohydroquinone, reported here does not crystallize and therefore single crystal techniques cannot be used to obtain structural information. Hydroquinone and excess sulphur were mixed thoroughly and poured into a glass tube. The tube was flushed several times with nitrogen and placed in a furnace in a nearly horizontal position. The issuing hydrogen sulphide gas was trapped in a lead acetate solution. After several hours the tube was removed and allowed to cool. The material was washed with concentrated sulphuric acid, followed by concentrated alkali solution to remove low molecular weight products and finally with hot carbon disulphide solutions to remove excess sulphur. The yield was about 70%. X-ray diffraction patterns for the present sample were recorded with the help of a Phillips diffractometer on a strip chart, the scanning rate being 2 ° min -1 , using MoK~ radiation in the range s = 0.77 to s = 8.96 (where s = 4re sin 0/4). The background radiation was suppressed with the aid of a discriminator by running the diffractometer once without sample. Then the sample was mounted and the intensities recorded. Other corrections for polarization and absorption were carried out using procedures described by Kaelble [2]. Tubulated values of atomic scattering factors [5] and incoherent scattering factors [6] were used for obtaining independent scattering curves. The corrected intensities were scaled to electron units by the method described by Kroughmoe [7]. The contribution of the flat-faced diffractometer sample in the small-angle region and that due to multiple scattering were subtracted following the method described by Warren [8]. Following the procedure described by Kaelble, the radial distribution function for polyatomic samples, 47t?2~0(r) is given by