Determination of quenching coefficients in a hydrogen RF discharge by time-resolved optical emission spectroscopy

In gas discharges at elevated pressure, radiation-less collisional de-excit ation (quenching) has a strong influence on the population of excited state s. The knowledge of quenching coefficients is therefore important for plasm a diagnostics and simulations. A novel time-resolved optical emission spect roscopic (OES) technique allows the measurement of quenching coefficients f or emission lines of various species, particularly of noble gases, with mol ecular hydrogen as collision partner. The technique exploits the short elec tron impact excitation during the field reversal phase within the sheath re gion of a hydrogen capacitively coupled RF discharge at 13.56 MHz. Quenchin g coefficients can be determined subsequent to this excitation from the eff ective lifetime of the fluorecence decay at various hydrogen pressures. The measured quenching coefficients agree very well with results obtained by m eans of laser excitation. The time-resolved OES technique based on electron impact excitation is not limited - in contrast to laser techniques - by op tical selection rules and the energy gap between the ground state and the o bserved excited level.