Environment influence on the IR fluorescence of Xe$_{2}^{*}$ molecules   in electron beam excited Ar--Xe mixture at high density
  We report new measurements of the near infrared (NIR) Xe$_2^*$ excimer fluorescence in an electron--beam--excited Ar (90%)--Xe (10 %) mixture at room temperature. Previous measurements up to a density $N\approx 2\times 10^{26}$ m$^{-3}$ discovered a broad excimer fluorescence band at $\approx 7800$ cm$^{-1},$ whose center is red--shifted by increasing $N$ (A. F. Borghesani, G. Bressi, G. Carugno, E. Conti, and D. Iannuzzi, {\em J. Chem. Phys.}, {\bf 115}, 6042 (2001)). The shift has been explained by assuming that the energy of the optical active electron in the molecule is shifted by the density--dependent Fermi shift and by accounting for the solvation effect due to the environment. We have extended the density range up to $N\approx 6\times 10^{26}$ m$^{-3}, $ confirming the previous measurements and extending the validity of the interpretative model. A detailed analysis of the width of the fluorescence band gives a value of 2.85 nm for the size of the investigated excimer state. Such a large value lends credence to the validity of the proposed explanation of the experimental findings. 
A.F.Borghesani, G. Carugno, D. Iannuzzi, I. Mogentale