Metastable Atoms and Molecules. I. Metastable States Produced in Charge-Exchange Processes

A beam of ions of energy between 25 and 360 eV was formed, and permitted to pass through the parent gas at pressures between 5 and 100 \ensuremath{\mu}. The beam then emerged into a highly evacuated space (2 to 9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ Torr) and impinged on a target of Mo. When the ions of the beam were deflected and prevented from reaching the target, a target current of secondary electrons or ions to the housing surrounding the target disclosed that neutral particles, formed by charge exchange, were reaching the target, and that these neutrals were excited with long lives compared with a microsecond. The behavior was tested in ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, Ne, and Ar, all of which were found to contain excited states in the neutral beam. A new variant of the charge-exchange process thus appears to be occurring in the production of excited neutrals. The essential technique is to cause the charge-changing collisions to occur directly in the source. It is believed that different mechanisms are active in different gases, but that collisions between ions and excited atoms or molecules occur commonly under the experimental conditions existing in this study, where very short times exist between electron-atom collisions and ion-atom-exchange collisions.