Clustering of Gas Molecules on Ions and the Standard High-Field Effect

3 CLUSTERING OF GAS MOLECULES ON IONS AND THE STANDARD HIGH-FIELD EFFECT 

Clustering of gas molecules on ions greatly affects their mobility and thus has been topical to IMS since its early days, with focus on the declustering at higher T (1.3.8). When gas molecules adsorb on the ion starting from most 

The effect of clustering on high-field mobility may superficially seem nonstandard as it does not apparently affect K E/N) above a certain T depending on the ion/gas pair. However, the (de)clustering and the standard effect (2.2.3) are intimately related. Those are often viewed as unrelated (presumably additive) phenomena, but the capture of gas molecules to orbit around or adsorb on the ion is just 

FIGURE 2.11 Cross sections of ions solvated by gas molecules at low E/N (a) decrease upon declustering at high E/N (b). The outer boundary for hard-sphere collisions (dash-dot circles) assumes an average radius of nonspherical gas molecules. 

Polar molecules (i.e., those with a permanent dipole moment, Pm) bind to ions particularly strongly because of charge-dipole force. A fixed dipole interacts with an ion via 

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