Atomic and molecular spectra of vapours evolved in a graphite furnace. Part 1. Alkali halides

Molecular Absorption Spectrometry (MAS) with erectrothermal vaporization was applied to the measurement of absorption by alkali halides. The MAS system, consisting of a deuterium lamp primary source, a tubular graphite furnace, a grating polychromator and a linear array of Charge-Coupled-Device (CCD) detectors, allowed the simultaneous determination of atomic and molecular absorption in the range 200-400 nm. Vaporization was carried out in a pyrocoated graphite tube and absorption was measured during the heating of the furnace from 500 degrees C to 2000 degrees C in 100 s. Alkali halides vaporize as molecular compounds which absorb radiation in the whole ultraviolet range. The complexity of the molecular bands as well as the extent of the absorption increases from fluorides to iodides. The limit of absorption at long wavelengths is 254nm for NaF, 287nm for NaCl, 320nm for NaBr and 370nm for NaI. The appearance of vapors was observed between 680 degrees C (RbI) and 1220 degrees C (LiF), while the maximum absorption was reached between 800 degrees C (CsI) and 1440 degrees C (LiF); the characteristic temperatures of the vaporization peak were shifted towards lower values going from fluorides to iodides. (C) 1999 Elsevier Science B.V. All rights reserved.