Spatially resolved temperature measurements in a furnace atomization plasma excitation spectrometry source

Spatially resolved atomic emission intensities from helium, and molecular emission intensities from OH and N-2(+) have been measured in a furnace atomization plasma excitation spectrometry (FAPES) source. He I emission at 388.86 nm was used to monitor the spatial structure of the plasma in the source while increasing the radio frequency (r.f.) power applied to its center electrode. At higher r.f. power the He I emission intensity increased significantly while its spatial structure remained relatively unchanged. The He I emission was found to be most intense adjacent to the center electrode. Some less intense emission was observed adjacent to the graphite cuvette wall and some very weak emission was seen throughout the volume of the source. These observations suggest that the FAPES source operates as an r.f. glow discharge. Emission intensities from the OH (0-0) rotational A (2) Sigma(+) –> X (2) Pi(i) and N-2(+) (0-0) rotational B (2) Sigma(u)(+) –> X (2) Sigma(g)(+) bands were used to monitor the effects of increasing the r.f. power applied to the center,electrode of the source. From these measurements, rotational temperatures for these molecules were calculated. The intensity measurements showed that there is a significant thermal gradient in the source with OH rotational temperatures ranging between 680 and 1050 K and N-2(+) rotational temperatures ranging between 580 and 1920 K with 60 W r.f. power applied to the center electrode. At higher r.f. powers there is an increase in rotational temperatures and an increase in the dissociation of molecular species in the FAPES source. Lead excitation temperatures were calculated using the line ratio method by measuring the emission of the Pb I 280.119 and 283.306 nm lines at different r.f. powers. The temperature was found to increase monotonically with r.f. power over the range of 35 to 75 W.