  Linear Paul r.f. ion traps (LPT) are used in many experimental studies such
as mass spectrometry, atom-ion collisions and ion-molecule reactions. Mass
selective resonant quenching (MSRQ) is implemented in LPT either to identify a
charged particle's mass or to remove unwanted ions from a controlled
experimental environment. In the latter case, MSRQ can introduce undesired
heating to co-trapped ions of different mass, whose secular motion is off
resonance with the quenching ac field, which we call off-resonance energy
absorption (OREA). We present simulations and experimental evidence that show
that the OREA increases exponentially with the number of ions loaded into the
trap and with the amplitude of the off-resonance external ac field.
