Effect of Isotopic Substitution on the Mass Spectra of Molecules. II. Oxygen and Carbon Dioxide, Experimental

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Abstract
The relative changes in the probability of bond breaking following electron impact have been studied for the molecules O16O16 and O16O18; O16C12O16, O16C13O16, and O16C12O18. The experimental results were obtained with a 60° mass spectrometer employing a source designed to equalize the collection efficiency of the fragment ions formed. The relative changes were studied systematically as a function of the various ion source voltages. In the case of oxygen the ratio of bond breaking in O16O18 divided by that in O16O16 is 0.98. The formation of C+ from O16C13O16 is 1.022 times the formation of C+ from O16C12O16 while the formation of C+ from O16C12O18 is 0.997 times the formation of C+ from O16C12O16. The formation of CO+ from O16C13O16 is 0.974 times that from O16C12O16 while the relative formation of C12O18+ from O16C12O18 is 1.03 times and that of C12O16+ is 0.97 times the formation of CO+ from O16C12O16. Finally the relative formation of O16+ is 1.05 times and that of O18+ is 0.98 times the formation of O+ from O16C12O16. The values for O16C13O16 are compared to previous values in the literature.

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