  We present a realistic molecular-dynamics treatment of laser-cooled ions in
radiofrequency ion traps which avoids previously made simplifications such as
modeling laser cooling as a friction force and combining individual heating
mechanisms into a single effective heating force. Based on this implementation,
we show that infrequent energetic collisions of single ions with background gas
molecules lead to pronounced heating of the entire ion ensemble and a
time-varying secular ensemble temperature which manifests itself in a
superstatistical time-averaged velocity distribution of the ions. The effect of
this finding on the experimental determination of ion temperatures and rate
constants for cold chemical reactions is discussed.
