Ionization and Excitation of Argon with Alpha Particles

Abstract

Experimental data on alpha‐particle ionization of binary mixtures of gases involving argon suggest that two states of electronic excitation persist long enough after the passage of the charged particle to allow collisions of the type Ar^*+X→Ar+X⁺+e^— to occur. One of these states is near the metastable levels in argon, approximately 11.6 eV, and the other is at approximately 14 eV. Examination of electron energy loss data and spectroscopic data leads to a tentative identification of these states as resonance levels; thus, their lifetimes are due to the trapping of photons in the apparatus. Ionization yield data are fitted to a kinetic model representing the above suggested mechanism with good agreement between the model and the experimental data. Other evidence for the existence of excited states of long lifetimes is derived from light emission experiments with argon in which continuous emission spectra suggest Franck—Condon transitions in excited argon molecules.