The Detection of Negative Ions and Their Stabilities

Abstract

A description was given of the construction and operation of a quadrupole mass filter system. This was used to identify negative ions emitted from a hot polycrystalline tantalum surface. The ionisation of various interhalogens and cyanogen halides were studied using the mass filter system. The kinetic methods of Page were applied to the results and the difference in electron affinity, of two radicals ionising simultaneously (halogens and cyanide) was evaluated. At pressures higher than 5 x 10-5 mm Hg., anomalous results were obtained and were explained quantitatively on the basis of positive ion formation, by negative ion collisions with the sample vapour, in the mass filter. The ionisation of various substituted pyridines were studied. Only fragment negative ions were observed (m/e values 24, 25, 26, and 27) for these compounds. In the case of 2-6-dimethyl-pyridine, the observed ions, ( m/e values, 24, 25 and 26 ) were shewn to be produced upon the tantalum surface. The appearance of intense positive ion peaks in the mass spectra of these compounds was again explained by negative ion collisions with the sample gas in the mass filter.