Physical Basis of Line Enhancement in Argon and Krypton*

Abstract

The enhancement of certain metallic ion lines, obtained from the dc arc in atmospheres of argon, krypton, and helium has been examined. The ratios of the intensities of these lines in argon to their intensities in helium and krypton are maximal for those whose excitation potentials (E.P.) lie in the vicinity of the E.P. of the lower excited energy levels of argon. This observation is accounted for by the following mechanism: The noble gas is energized to its lowest excited levels by the arc discharge through collisions of the second kind. This energy is transferred to neutral metal atoms volatilized in the arc. The metal atoms are thus ionized and excited; they then fall to the ground state emitting their characteristic radiation. The maximum energy is transferred from argon to metal atoms when the energy of the excited noble gas atom equals the E.P. of the metal ion line, resulting in the selective enhancement observed.