Neutral dissociation of hydrogen following photoexcitation of HCl at the chlorine K edge

Time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K edge (similar to 2.8 keV) using monochromatic synchrotron radiation. At the lowest resonant excitation to the 6 sigma* antibonding orbital, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cln+ ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very short lifetimes (1 fs).