Molecular Beams of Macroions

Abstract

By means of electrospraying a dilute polymer solution into an evaporation chamber, negative macroions can be produced and a molecular beam formed by sampling the gaseous mixture of macroions, solvent, and nitrogen molecules with a nozzle‐skimmer system of the Kantrowitz–Gray type. The macroion current can be detected by a Faraday cage after the light ions have been repelled from the beam by negative voltages on a repeller grid. Theoretical repeller voltages which best agree with the observed are those calculated by assuming a macroion velocity within 2% of the estimated supersonic beam velocity of 743 m sec⁻¹. Polystyrene macroions of 51 000 weight‐average amu tend to form dimers and trimers in the beam while larger polystyrene macroions of 411 000 weight‐average amu appear mostly to be multiply charged single species. The results demonstrate that definite mass/charge states can be formed by the electrospray technique, that a considerable monochromatization of macroion velocities in the beam takes place, and that the macroions become highly concentrated relative to low‐molecular‐weight solvent and nitrogen ions during the transit time in the supersonic beam.