Desorption processes in the measurement of weak currents

It was previously shown that the experimental meas„urement of the lifetime of gas-phase negative ions formed in autoionization states during resonant electron capture by molecules is inherently fraught with inaccuracy due to adsorption of ions on the walls of the ionization chamber, with some of them surviving there and staying stabilized as ‘eternal’ till they eventually desorb back into the vacuum and merge with the total ion flow; this leads to an upward distortion of lifetime measurements. This paper describes a technique for removing desorbed ions from the total flow using an ion filter that lets only gas-phase ions pass into the detection system but detains the de„sorbed ions due to the differences among their kinetic energies.