Fhag Frank Fey

Instantaneous and delayed responses of line intensities to interruption of the RF power in an argon inductively coupled plasma

Abstract Instantaneous and delayed responses of line intensities to the sudden interruption of the RF power have been studied in an argon inductively coupled plasma (ICP). The instantaneous responses are caused by equilibrium shifts in the balances of elementary processes that control the populations of the excited states. It has been found that excited levels of Ar and H are predominantly populated by recombination of free electrons with ionic species, while most levels of metals such as Mg, Cd, Na, Fe, Al and Cu are populated by excitation from the ground state atom. Also charge transfer between Mg 1 and Ar 1 has been observed in the temporal behaviour of line intensities of two Mg + states, quasi-resonant for charge transfer. Furthermore, we observed that in the inner part of the plasma the temperature remains constant during the recombination decay time, after an initial cooling of the electrons to the heavy particle temperature. When the power is switched on again, the electron temperature seems to increase temporarily to a value that is higher than the steady state value. The delayed responses are caused by disturbances created in the expansion zone of the plasma during and after the interruption. It was found that these disturbances travel through the plasma with a velocity of 12 m s −1 .

The effect of evaporation on the analyte emission intensities during power interruption in an inductively coupled plasma

Abstract A power interruption technique is used to study the population balances of excited states of analytes in an inductively coupled plasma (ICP). Measurements on Li analyte emission show that the Boltzmann balance of excitation of and de-excitation to the ground state is the dominant population process for the lower excited levels. During the power interruption, changes in the excitation and de-excitation flows are visible and it turns out that the ionization degree of Li depends strongly on position, central flow and plasma power. The results cannot be explained unless evaporation of analyte is assumed to have an important impact on the excitation flow in the Li system.