The Coulomb de-excitation (Table 1), where the transition energy is
shared between the colliding particles, is an important acceleration
mechanism producing 'hot' (
eV) exotic atoms (see
Fig. 4a).
The highly-energetic 
atoms were discovered experimentally in
[52], and a multicomponent structure of the energy distribution
was found in [46].
Recent experiments in liquid and gaseous hydrogen
[47,48] found the shape of the kinetic energy distribution to
be consistent with the Coulomb mechanism.
The cascade calculations [29] show that the atoms
with kinetic energy 
eV are not significantly decelerated
between the Coulomb de-excitation and the nuclear reaction. For the
atoms with 
eV the deceleration is important and the Coulomb
peaks are expected to be smeared out.
The earlier calculations of the Coulomb transitions [16,17,18,19] were rather controversial. The latest calculations [20,21,22] seem to clarify the theoretical picture. This removes one of the uncertainties in the cascade calculation of the past where a Coulomb rate-tuning parameter was used to normalize the calculated high-energy component to the measurements in pionic hydrogen [29]. It is not excluded that the Coulomb de-excitation can be part of a multistep process. For instance, the formation of excited molecular states can be followed by a Coulomb-like decay [2,54,55].