The Effective Temperature of Ions Stored in a Linear Quadrupole Ion Trap Mass Spectrometer

The extent of internal energy deposition into ions upon storage, radial ejection, and detection using a linear quadrupole ion trap mass spectrometer is investigated as a function of ion size (m/z 59 to 810) using seven ion-molecule thermometer reactions that have well characterized reaction entropies and enthalpies. The average effective temperatures of the reactants and products of the ion-molecule reactions, which were obtained from ion-molecule equilibrium measurements, range from 295 to 350 K and do not depend significantly on the number of trapped ions, m/z value, ion trap q (z) value, reaction enthalpy/entropy, or the number of vibrational degrees of freedom for the seven reactions investigated. The average of the effective temperature values obtained for all seven thermometer reactions is 318 +/- 23 K, which indicates that linear quadrupole ion trap mass spectrometers can be used to study the structure(s) and reactivity of ions at near ambient temperature.