Heating of ions moving in a gas under the influence of a uniform and constant electric field

A simple model for estimation of the internal temperature of ions, moving I n 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 coll isions are considered as elastic In which no energy is transferred to the i nternal 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 o f 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 mo del 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 resul t the significant discrepancies in activation energies for dissociation of protonated leucine enkephalin, measured by different methods, are qualitati vely explained. Copyright (C) 1999 John Whey & Sons, Ltd.