Density-induced modifications of the IR emission spectrum of Xe2 excimers in dense gas

The infrared emission spectrum of Xe₂ excimers produced by irradiating Xe gas with high-energy electrons has been monitored as a function of density up to 3.3 MPa at room temperature. Excimer decay yields a broad continuum centered around 7800 cm^-1 of width 900 cm^-1 at 0.1 MPa. The spectrum shape is consistent with a bound-free molecular transition between 0_u ⁺ and 0_g ⁺ states correlated with 6p and 6s atomic limits. Upon increasing density, the spectrum is strongly red-shifted and broadened. The present measurements confirm preliminary results obtained in a smaller density range. The shift is explained by the dielectric screening exerted by the gas atoms on the optically active electron-ionic molecular core interaction, and by quantum multiple scattering effects of the electron scattered off the gas atoms. The latter effect links this experiment to electron transport experiments in non-polar gases. The different spectrum broadening in pure Xe and in an Ar-Xe mixture is believed to be due to quantum indistinguishability of identical particles.