Abstract
The time dependence of the luminescence due to the recombination process of electrons and ions in liquid argon, krypton, and xenon excited by $^{207}\mathrm{Bi}$ internal-conversion electrons has been studied by considering the difference curve of two decay curves, the one in the absence of electric field and the one with such a high electric field that all of the observed decay characteristics can be attributed to self-trapped exciton luminescence. The time dependence is well explained by using the kinetic equation for electrons and the recombination process, without diffusion. This provides good evidence for the existence of a strong Coulomb interaction of thermalized electrons and ions. Two excited molecular states $^{1}\ensuremath{\Sigma}_{u}^{+}$ and $^{3}\ensuremath{\Sigma}_{u}^{+}$ are formed through the recombination process, as in the case of self-trapped exciton luminescence. The recombination cross sections, in units of ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$, are 7000\ifmmode\pm\else\textpm\fi{}2000 for liquid argon, 120\ifmmode\pm\else\textpm\fi{}30 for liquid krypton, and 10\ifmmode\pm\else\textpm\fi{}2 for liquid xenon. The considerably small values for liquid krypton and xenon compared with that for liquid argon are explained by the unfavorable crossing of the ${{R}_{2}}^{+}$ and repulsive ${{R}_{2}}^{**}$ potential curves in the liquid, based on the theory of dissociative recombination ${{R}_{2}}^{+}+e\ensuremath{\rightleftarrows}{{R}_{2}}^{**}\ensuremath{\rightarrow}{R}^{**}+R$ in the gaseous state.
Published Version
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