79 zyxwvutsr International Journal of Mass Spectrurnetry and Ion Physics, 14 (1974) 79-88 Q zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Elsevier Scientific Publishing Company, Amsterdam - Printed in The -etherlands zyxwvutsrqponmlkjih A CESIUM IMPACT SOURCE FOR NEGATIVE-ION MASS SPECTRA S. Y. TANG, ERHARD W. ROTHE Research Institute for Engineering Sciences and Department of Chemical Engineering, Wayne State Uniuersity, Detroit, Mich. 48202 (U.S.A.). zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ GENE P. RECK Deparrment of Chemistry, Wayne State University, Detroit, Mich. 48-X72 (U.S.A.) (First received 25 July 1973; in final form 17 December 1973) ABSTRACT Negative ions are produced in a single-collision charge-transfer source. A beam of cesium atoms with kinetic energies which are variable between 10 and 350 eV intersects a beam of target molecules. Negative ions and Csi are formed. The energy dependence of these anion spectra are measured for SO,, CH,N02, SF,, and CF,Cl,. The observed cesium impact spectra are qual- itatively different from those produced by electrons. At the higher cesium-atom energies, they are relatively insensitive to energy. Large parent ion intensities are seen for SO2 and CH,NOz . For Cs+SF,, our ratios (SF,-/ SF,-) and (F-/ SF,-) are in agreement with those of Compton and Cooper for the limited range of Cs energy employed in both experiments. INTRODUCTION Negative-ion mass spectrometry the more familiar work with positive has shown promise zyxwvutsrqponmlkjihgfedcbaZYXW as a complement to ions and numerous negative-ion spectra have been described and interpreted. Interest has been limited, however, because of the following characteristics of electron-impact ion sources: (a) Intensities of negative ions are considerably less than those of positive ions. (b) Negative-ion spectra are highly dependent on electron energy, and upon the particular source configuration, because secondary electrons also produce negative ions. In. contrast, positive-ion spectra, above about 40 eV, are approximately independent of ener,gy.