MULTIWAVELENGTH MONITORING OF PHOTOFRAGMENT FLUORESCENCE AFTER 193-NM PHOTOLYSIS OF NACL AND NAOH - APPLICATION TO MEASURING THE SODIUM SPECIES RELEASED FROM COAL AT HIGH-TEMPERATURES

Excimer laser photodissociation of gas-phase NaCl and NaOH, and monitoring of the subsequent Na photofragment fluorescence, are used to determine the concentration of the species in coal-derived gaseous environments. Detection limits lower than 1 ppb of NaCl have been achieved under atmospheric conditions using 193 nm photodissociation. It is shown that monitoring two Na emission wavelengths (at 819 and 589 nm) allows speciation between NaOH and NaCl in the gas phase. In particular, emission from the Na 3(2)D levels (at 819 nm) has been unambiguously attributed to photodissociation of NaOH. This emission results from hot-band absorption of the excimer laser, and thus its intensity is temperature dependent and weaker than 3(2)P (589 mm) emission. The technique has been applied to the detection of NaCl and NaOH released during the pyrolysis and gasification of samples of Loy Yang (Australian brown) coal.