Hitherto Unrecognized Intermolecular Coulombic Decay Mechanism in Gases

Excited atoms and molecules can utilize their excess energy to ionize a neighboring system by a process named interatomic and intermolecular Coulombic decay (ICD). ICD is ultrafast, in the femtosecond regime, and has many modes of appearance. Ample applications of ICD have been reported spanning a wide range of fields and it is expected to be ubiquitous in nature. Essentially all the investigations on ICD were for weakly bound systems, like clusters and fluids. We demonstrate that, unexpectedly, ICD can be efficiently active in atomic and molecular gases in spite of the very large distances between the units. We uncover the underlying mechanism which is due to retardation and differs from the standard dipole-dipole interaction prevailing in weakly bound systems. The dynamics of ICD in gases is analyzed. The results considerably broaden the impact of ICD and open the gateway to new kinds of applications.