Negative Surface Ionization and Electron Affinity by Mass Spectrometry

Abstract

The negative surface jonizations of some halogens, metal hexafluorides, carbon tetrachloride, benzene and dime thy mercury have been studied over polycrystalline platinum, tungsten and tantalum filaments by mass spectrometry. A description is given of the construction and operation of the V. G. Micromass Q9 quadrupole mass spectrometer. A negative surface ionization source and suitable detection system has been designed. The kinetic methods of Page were applied to the results, and from non-zero gradients of the plots of the ratio the electron to jon current E', the apparent electron affinity was evaluated. The values of E, the actual electron affinity were then calculated from Page's relationship: E'(0) = E + Qr - D Although this study shows that some of the ions assumed to be present in the magnetron were not observed in the quadrupole mass spectrometer, yet the electron affinity of the ions observed were found to be in good agreement with those obtained in magnetron and by optical methods. Thus a valid estimate of the electron affinity of an observed Species may be determined from the temperature coefficient of the ratio of the electron to total ion current, provided the mechanism of the rate determining process is known and the criteria of surface ionization (temperature dependence) is applied.