Radiative stabilization of double-Rydberg states formed in slow Xeq+-Xe (15 ⩽q⩽ 35) collisions

Electron capture process, in which the projectile charge ( q ) is lowered by one unit, have been recorded by means of high-resolution energy-gain spectroscopy for 4 q keV Xe q + -Xe (15 ⩽ q ⩽ 35) collisions. The ratios, R , between the cross sections for the transfer ionisation and single-electron capture were extracted from the measured spectra. The quantity R increases slowly for charges up to q = 25 and decreases rapidly for higher q . Relying on the extended classical over-barrier model we relate R to the branching ratio for autoionisation, F , through R = k · F , and estimate the variation in k as a function of q . On the basis of the extended classical over-barrier model we ascribe the decrease in R at high q to an increase in radiative stabilization of double-Rydberg states formed in slow Xe q + -Xe, q > 25, collisions.