MULTIWAVELENGTH MONITORING OF PHOTOFRAGMENT FLUORESCENCE AFTER 193-NMPHOTOLYSIS 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 monito ring of the subsequent Na photofragment fluorescence, are used to dete rmine the concentration of the species in coal-derived gaseous environ ments. Detection limits lower than 1 ppb of NaCl have been achieved un der atmospheric conditions using 193 nm photodissociation. It is shown that monitoring two Na emission wavelengths (at 819 and 589 nm) allow s speciation between NaOH and NaCl in the gas phase. In particular, em ission from the Na 3(2)D levels (at 819 nm) has been unambiguously att ributed to photodissociation of NaOH. This emission results from hot-b and absorption of the excimer laser, and thus its intensity is tempera ture 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.