Description
Interatomic Coulombic decay (ICD) is an ultrafast
non-radiative electronic decay process for excited atoms
embedded in a chemical environment. Via ICD, the excited
system can get rid of the excess energy and this excess
energy is transferred to one of the neighbors and ionizes
it. Whereas the same excited atom when isolated relaxes only
by emitting a photon in a time range of picoseconds to
nanoseconds, ICD takes place in the femtosecond range. Thus,
ICD is generally the most favorable decay process. Through
ICD, the energy transfer between the two involved atoms can
take place over large distances. A question which arises is
how far can atoms exchange energy? The giant extremely
weakly bound helium dimer is a perfect candidate to
investigate this issue. After simultaneous ionization and
excitation of one helium atom, the excited ion can relax
through ICD and thus ionize the neighboring neutral helium
atom. The resulting two He$^+$ then undergo a Coulomb
explosion and fly apart. As it will be shown, the two helium
atoms can exchange energy via ICD over distances of more
than 45 times their atomic radius. Oscillatory structures in
the kinetic energy release spectra reflect the nodal
structures of vibrational wavefunctions involved in the
decay process.
