Infrared high temperature spectra of aluminium chloride and related species

Abstract

Isothermal cells of nickel with diamon windows were used to study various melts and vapours by infrared emission, transmission and reflectance techniques in the 860 to 300 K range with an evacuable Fourier transform spectrometer. IR vapour spectra of AlX 3 (X = Cl, Br, I) and GaCl 3 in transmission and emission were measured between 700 and 50 cm −1. A comparable signal/noise ratio between the transmission and emission spectra was obtained above 200 cm −1, below 200 cm −1 the transmission spectra had better quality. The dimer and monemer spectra were assigned in terms of D 2h and D 3h symmetry, respectively, and compared with earlier Raman and IR matrix isolation data. Emission spectra of chloroaluminates AlkAlCl 4 (Alk = Li, Na, K, Rb, Cs) were recorded as melts between 1500 and 50 cm −1. Increasing distortion of the tetrahedral AlCl − 4 ion in the series Cs<Rb<K<Na<Li was observed. Emission spectra of AlkAl 2Cl 7 (Alk = Li, Na, K, Cs) indicate D 3d symmetry for Al 2Cl − 7 with a linear Al-Cl-Al bridge as proposed from earlier Raman data. As a demonstration of reflectance technique an IR spectrum of ZnAl 2Cl 8 at ambient temperature is presented.