Specific-ionization-density effect on the time dependence of luminescence in liquid xenon

We have investigated the influence of specific ionization density on the time dependence of luminescence in liquid xenon. The experiments have revealed that the luminescence decay is governed by the decay rates of two excited molecular states (${}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$) for alpha-particle excitation (high specific-ionization density) and by the recombination rate of free electrons and molecular ions for high-energy electron excitation (low specific-ionization density). A significant enhancement of the formation of ${}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ states was observed for alphaparticle excitation.