Charge Transfer Excitation in Glow Discharge Sources: the Spectra of Titanium and Copper with Neon, Argon and Krypton as the Plasma Gas

Abstract

There is increasing awareness of the importance of asymmetric charge transfer as a mechanism for the selective excitation of ionic energy levels in low pressure gas discharges. A Fourier transform spectrometer has been used to record the titanium spectrum from a microwave boosted glow discharge source (in dc and boosted modes) using neon, argon and krypton as the plasma gas. Analysis of the data produced shows clear evidence of charge transfer excitation by argon and krypton ions. The wider energy separation between the ground state ² P _3/2 ion and the metastable ² P _1/2 ionic state (0.75 eV) of krypton makes it clear that the metastable state is also responsible for charge transfer reactions. This observation, together with results obtained using krypton with a copper cathode, supports the earlier suggestion that the metastable argon ion is responsible for the selective excitation of the Cu II 224.70 nm line when a discharge with a copper cathode is operated in argon.