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

Abstract

The infrared emission spectrum of Xe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> of width 900 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 0.1 MPa. The spectrum shape is consistent with a bound-free molecular transition between 0 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and 0 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> 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.