Evidence of the existence of exciton states in liquid argon and exciton-enhanced ionization from xenon doping

Experimental investigations have been performed on the ionization yield in rare-gas-doped liquid Ar excited by ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ conversion electrons. The enhanced ionizaiton yield (13% relative to the ionization yield in pure liquid Ar) is observed for Xe-doped (1.6%) liquid Ar and is attributed to the ionizing excitation transfer process from Ar excitons to doped Xe. The saturated value of the enhanced ionization is in good agreement with the theoretical value obtained under the assumption that the same electron band structure and the same exciton states as those in solid Ar exist in the liquid, too. This provides strong evidence for the existence of the exciton states in liquid Ar. No significant increase in ionization is observed with Kr-doped liquid Ar. The relaxation processes in liquid Ar are discussed.