Electronic Energy Transfer Phenomena in Rare Gases

In this paper we present the results of an experimental study of electronic energy transfer in xenon‐argon, krypton‐argon, and xenon‐krypton gaseous mixtures excited by a pulsed electric discharge. Spectroscopic evidence for electronic energy transfer is based on the decrease in the intensity of the vacuum ultraviolet emission of the excited diatomic homonuclear rare gas molecules in the presence of small amounts (10–1000 ppm) of a foreign rare gas atom, while the visible emission spectrum of the host gas is parctically unmodified under these conditions. The relative contributions of two energy transfer mechanisms involving atom‐atom and molecule‐atom energy transfer were established by a kinetic analysis of the dependence of the energy transfer efficiency on the host pressure. We have determined the cross sections for energy transfer from the lowest metastable Ar and Kr excited states, and from the lowest excited state of ${\mathrm{Ar}}_2*$ and ${\mathrm{Kr}}_2*$ to ground state Xe, and from metastable excited Ar and from ${\mathrm{Ar}}_2*$ to ground state Kr. The molecule‐atom energy transfer process is characterized by large ${\text{∼ 10}}^{\text{−14}}\hspace{0.17em}{\mathrm{cm}}^2$ cross sections. A simplified theoretical treatment of excited molecule‐ground state atom collisions provides a proper rationalization of these large cross sections in terms of long range dipole‐dipole coupling.