Kinetic energy of fragment ions in a radiofrequency mass spectrometer

Abstract

A radiofrequency mass spectrometer has been used, with slight modification, to measure the kinetic energy of fragment ions from polyatomic molecules. Selected ions from CO 2 , CH 3 OH, C 2 H 5 OH, C 3 H 7 OH, i-C 3 H 7 OH, CH 3 I and C 2 H 5 I were examined for excess kinetic energy by means of retarding potential analysis before mass analysis. The excess kinetic energy for any given ion was always greater for 70 V electron impacts than for 50 V. Such ions as m/g 31 and 29 from ethanol have an excess of about 0·45 V kinetic energy for 50 and 70 V electrons; m/q 29 and 27 from isopropanol also have about 0·45 excess energy for 70 V electrons; CH + 3 ions from the alcohols and from the iodides showed excess kinetic energy while m/q 27 from ethyl iodide had 0·9 V excess energy for 70 V electrons. The results are interpreted as evidence of a significant num ber of dissociations from electronic states which are not in effective competition with one another. The existence of non ­ competing dissociation paths for a given molecular ion complex would preclude the application of the statistical theory of mass spectra to predict the breakdown scheme of that complex.