Excitation Mechanism of Silver Ionic Lines Through Collisions with Metastable Atoms of Plasma Gas in a Glow-Discharge Plasma

Abstract

ABSTRACT Emission spectra of silver from glow-discharge plasmas using argon, krypton, and a krypton–argon gas mixture were analyzed to elucidate the excitation phenomenon of silver ionic lines occurring in collisions with the plasma gases. The intensities of the ionic lines that were assigned to the 4d95p–4d95s transition were largely different between argon and krypton; for instance, the intensity of the Ag II 243.78-nm line (9.94 eV) emitted from the krypton plasma was five times larger than that from the argon plasma, while the Ag II 228.00-nm line (11.14 eV) yielded much larger intensity in the argon plasma by a factor of 70. This effect can be explained by an excitation process through collisional energy transfer from the metastable atom of argon or krypton to the silver ion in the ground state (Penning excitation). This type of collision requires both matching in the excitation energy between the colliding partners and conservation in the total spin before and after the collision. The 3p54s metastable state of argon (11.72 eV for the singlet and 11.55 eV for the triplet) and the 4p55s metastable state of krypton (10.56 eV for the singlet and 9.92 eV for the triplet) would take part in the collision and principally determine the population of the 4d95p excited levels of the silver ion.