Effect of Inelastic Energy Loss on Ion Mobility

At low E/N, all internal and translational modes of both ions and gas molecules are equilibrated at T. Hence collisions, though inelastic individually, must be elastic on average (1.4.1). The internal modes of an ion and a molecule remain in equilibrium at their average translational ternperamres at any E/N, but at high E/N those temperatures (Tef and T, respectively) are unequal ions heat up and the gas does not. A miniscule firaction of ions in the IMS gas means a nil number of ion-molecule collisions compared to that of intermolecular ones, and all molecules 

Instead of infinitely raising at higher E/N, the ion temperature asymptotically approaches maximum 7ef by Equation 2.66. Its value appears related to the 

FIGURE 2.19 Inelasticity fraction [ measured for Cl (solid line), NO (long dash), N02 (medium dash), and NOs (short dash) ions in N2 at P = 0.12-45 Torr and Na+ in SFe at P = 0.1 Torr (dotted hne), and some derivative quantities, log-log plots. The of hnear regressions to aU data are 0.95 for (h) and 0.96 for (c). 

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