Calculation of rate constants for asymmetric charge transfer, and their effect on relative sensitivity factors in glow discharge mass spectrometry

For this paper, we have calculated the rate coefficients for asymmetric charge transfer between Ar+ ions and all elements of interest in analytical glow discharges, based on a semi-classical approach. These values were then used to make predictions on the relative sensitivity factors (RSFs) in glow discharge mass spectrometry (GDMS) (VG9000 discharge cell) for various elements. The RSFs were calculated based on a transport factor, and an ionization factor, which comprises asymmetric charge transfer, Penning ionization and electron impact ionization. The ionization rates of these three processes were calculated explicitly, based on our earlier computer simulations, in combination with the rate coefficients and cross sections of the ionization processes for different elements. In this way, we are able to offer a rationalization of the experimental RSFs. It is demonstrated that variations in RSFs are largely determined by the occurrence of asymmetric charge transfer in the glow discharge plasma.