A simple model for estimation of the internal temperature of ions, moving in a monoatomic gas under the influence of an electric field, is considered. The basic assumption of the model is formation of ion-atom complexes in a quasi-equilibrium state for some of the ion-atom collisions, and other collisions are considered as elastic in which no energy is transferred to the internal energy of the ion. For Langevin collision cross sections, the model allows coinciding equations to be obtained for internal and translational or effective temperatures of ions, in cases where the polarization energy of the atom in the local electric field of the ion is not taken into account. The influence of this polarization energy leads, in the context of the model considered here, to an increase of internal ion temperature by a factor of 1.3-1.5 compared to its effective temperature (which coincides with the buffer gas temperature for zero external electric field). Using this result the significant discrepancies in activation energies for dissociation of protonated leucine enkephalin, measured by different methods, are qualitatively explained.

© 1998 by John Wiley & Sons, Ltd.