SENSITIZED FLUORESCENCE IN VAPORS OF ALKALI METALS: VIII. ENERGY TRANSFER BETWEEN THE 4 ²<i>P</i> LEVELS IN POTASSIUM INDUCED BY INELASTIC COLLISIONS

Abstract

Sensitized fluorescence in potassium vapor and its mixtures with inert gases was investigated in order to determine cross sections for the inelastic collisions leading to excitation transfer between the 4 2 P 1/2 and 4 2 P 3/2 states in potassium. The study was carried out at potassium vapor pressures of about 10 −6 mm Hg, which were not formerly accessible to such experiments, and in the absence of radiation trapping. The cross sections Q 1 (4 2 P 1/2 → 4 2 P 3/2 ) and Q 2 (4 2 P 1/2 → 4 2 P 3/2 ) are as follows: for K–K collisions: 370 and 250 Å 2 ; for K–He: 60 and 41 Å 2 ; for K–Ne: 14 and 9.5 Å 2 ; for K–A: 37 and 22 Å 2 ; for K–Kr: 61 and 41 Å 2 ; for K–Xe: 104 and 72 Å 2 . These values supersede those published previously (Chapman, Krause, and Brockman 1964; Chapman and Krause 1965). The cross sections for collisions between potassium and inert gas atoms do not increase monotonically with the polarizabilities of the inert gases but behave similarly to the electron – inert gas elastic scattering cross sections. This behavior is interpreted on the basis of a semiclassical model for the interaction, which involves overlap forces.