Ion content of cold cathode glow discharges in iodine†

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Abstract
An r.f. mass spectrometer has been used to obtain the positive and negative ion spectra of a cold cathode low-pressure (about 07ndash;2 torr) glow discharge in. iodine. The relative abundances of I3 −, I2 −, I −, and I3 +, I2 +, I +, I + + have boon measured at the anode mid at the tube wall bounding the negative glow and positive column for a range of discharge currents. The dominant positive ion was I2 + . I + + was only found in the negative glow. The most intense negative ion was usually I − . Negative ions of uncertain nature were recorded, with mass number 640 a.m.u. and above, but the reality of some of these is doubtful. The ion production processes arc discussed briefly and difficulties in the interpretation of results arising from discharge instability mentioned.