Supplemental fields, quadrupole

Forces of Adsorption. Adsorption may be classified as chemisorption or physical adsorption, depending on the nature of the surface forces. In physical adsorption the forces are relatively weak, involving mainly van der Waals (induced dipole-induced dipole) interactions, supplemented in many cases by electrostatic contributions from field-dipole or field-gradient-quadrupole interactions, By contrast, in chemisorption there is significant electron transfer, equivalent to the formation of a chemical bond between the sorbate and the solid surface. Such interactions are both stronger and more specific than the forces of physical adsorption and are obviously limited to monolayer coverage. 

Comprehensive summaries of ion activation methods can be found in Volume 3 of this series [31,32]. In all of the above methods, precursor ions are mapped at a fixed -value for the duration of the activation period. However, the non-ideal quadrupole field and space charge will cause the ion species secular frequency to deviate away from its theoretical value such that it no longer matches the frequency of the supplemental electric field calculated for the fixed value of q. Due to the lack of a technique... 

Nuclei that have a nuclear electric quadrupole moment have energy levels that arc split in the presence of an electric field gradient. Such a gradient does not have to be applied externally, but is a molecular property, and is almost always non-zero, the exceptions being in perfectly octahedral or tetrahedral environments. Transitions between these energy levels are observed in nuclear quadrupole resonance (NQR) spectroscopy, described in the on-line supplement for Chapter 4 on NQR. 

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