FUNDAMENTAL PROPERTIES OF HELIUM INDUCTIVELY-COUPLED PLASMAS MEASUREDBY HIGH-RESOLUTION FOURIER-TRANSFORM SPECTROMETRY

Intensities and widths of atomic spectral lines of He, H, and Fe, exci ted in an atmospheric-pressure helium inductively coupled plasma (He I CP) were measured with a high-resolution Fourier transform spectromete r. These data along with measured intensities of rotational bands, suc h as B2SIGMA(u)+ --> X2SIGMA(g)+ of N2+ and A2SIGMA+ --> X2PI(i) of OH , were used to estimate excitation, rotational, and Doppler temperatur es, and electron number densities. Similar to an Ar ICP, the widths of Fe lines ranged from 3 to 4 pm. The line widths of H and He lines in the spectra from a dry He ICP generally were larger than those observe d from a wet plasma. The line-width data for H were used to evaluate e lectron number densities in wet and dry He ICP discharges. The excitat ion temperature of He ICP was dependent upon the energy levels of the selected thermometric species. The rotational temperatures measured fr om OH (3000 K) and N2+ (2200 K) were substantially different from thos e of an Ar ICP. The presence of water in the aerosol resulted in an in crease in the excitation temperature of the He ICP, similar to the tre nd observed earlier for the Ar ICP. The implications of these results in He ICP spectrochemical analysis are discussed.