Charge measurement vibrating probe method

Another type of feedback electrometer works in a quite different manner, aiid Fig. 7.5 illustrates the method of using it to measure charge density on the surface of an insulating sheet or film lying on an earthed base. The probe peeps at the surface in question through a hole in a metal box, and, in addition, the field to the probe is interrupted by a vibrating shutter. The periodic signal on the probe is amplified and phase-sensitively detected, and the output used to drive an amplifier whose own output in turn raises the potential of the metal box and the shutter. 

The most detailed probe of an ion-molecule reaction is the state-to-state cross section. The measurement of angularly resolved state-to-state cross sections has been achieved only for reactants in their ground state, but true state-to-state total cross sections have now been measured in a few favorable cases. A particularly novel method for product state determination with reactant state selection has been developed by Ng. In the differential reactivity method, product vibrational states are distinguished by their differing cross sections for charge transfer with selected molecules. The charge transfer reaction... 

---