Strong, Polarized Balmer- α Fluorescence after Resonant Core Excitation of HCl

Visible-UV fluorescence has been analyzed after resonant Cl 2p core excitation of HCl molecules. The dispersed fluorescence spectra are dominated by emissions from atomic fragments. In particular, an intense and polarized Balmer H_α line is observed after photoexcitation of the 2p^-1nl Rydberg states. The excited hydrogen atoms are efficiently produced in the resonant Auger process and the subsequent dissociation of high lying HCl⁺ states. The experimental results, complemented by a time-resolved measurement of the H_α decay, point to a universal mechanism for the production of H( n  =  3) atoms in the dissociation of innershell excited HCl molecules.