Low energy electron impact spectra of the van der Waals clusters Xe2 and Xen (n approximately 3,4)

The energy loss spectrum of electrons scattered at 90' has been measured for Xe emanating from a 30 mu m diameter nozzle, in the 8.0-8.9 eV energy loss range, at 2 eV residual energy, and at stagnation pressures between 0.2 and 1.3 bar. Weak satellite bands of the 3P2 and 3P1 atomic lines have been observed at a stagnation pressure of 0.6 bar and assigned to electronic transitions of the van der Waals dimer Xe2. An additional shoulder emerging at even higher stagnation pressures has been attributed to larger clusters. The energy dependence of the excitation of the Xe 3P2 and 3P1 atomic lines exhibits a number of narrow doubly excited Feshbach resonances. These features are much less pronounced or absent in the excitation functions of the Xe2 and Xen bands, indicating energy broadening and lifetime shortening of the doubly excited resonances in the clusters.