Sympathetic cooling of trapped negative ions by self-cooled electrons in a fourier transform ion cyclotron resonance mass spectrometer

Hot electrons confined in a Penning trap at 3 tesla self-cool to near room temperature in a few seconds by emission of cyclotron radiation. Here, we show that such cold electrons can “sympathetically” cool, in ～10 s, laser desorbed/ionized translationally hot Au^? or C₇₀ ^? ions confined simultaneously in the same Penning trap. Unlike “buffer gas” cooling by collisions between ions and neutral gas molecules, sympathetic cooling by electrons is mediated by the mutual long-range Coulomb interaction between electrons and ions, so that translationally hot ions can be cooled without internal excitation and fragmentation. It is proposed that electrosprayed multiply charged macromolecular ions can be cooled sympathetically, in the absence of ion-neutral collisions, by self-cooled electrons in a Penning trap.