A study of the formation of the excess kinetic energy CH₃⁺ ion occurring in the fragmentation of cis-2-butene

Includes bibliographical references.Includes illustrations.This study has been concerned with the mechanism(s) for formation of the excess kinetic energy CH₃⁺ ion occurring in the fragmentation of cis-2-butene, The study centered on determining the process(es) producing the CH₃⁺ ions by observation of metastable transitions. The Hitachi RMU-7 Mass Spectrometer was modified to permit observation of metastable transitions using the ion kinetic energy spectrometry (IKES) technique. Further investigation proved mass-analyzed ion kinetic energy spectrometry (MIKES) to be more useful in this particular work, A total of five doubly charged and two singly charged metastable decompositions were shown to produce the CH₃⁺ ion. Of these, the doubly charged decompositions from C₄H₈⁺⁺, C₄H₇⁺⁺, C₄H₆⁺⁺, C₄H₅⁺⁺, and C₄H₄⁺⁺ were observed to occur with release of about 3 eV energy. The most intense signal resulted from decomposition of the C₄H₄⁺⁺ ion. Syntheses of two deuterated cis-2-butene analogs, cis-2-butene-1,1,1,4,4,4-d₆, and cis-2-butene-2,3-d₂, were accomplished. Investigation of the hexadeutero species using MIKES suggested that extensive hydrogen and deuterium migrations were occurring. Calculated probabilities for randomization of hydrogen and deuterium in the productions showed good agreement with experimentally observed metastable peak intensities. This randomization process precluded determining the actual mechanism(s) responsible for producing the CH₃⁺ ion with excess translational energy. Additional data was obtained by measuring the excess energy of the satellite peak observed at m/e 15 by lowering the accelerating voltage. This excess energy was found to be 2.50 + 0,05 eV, For the hexa-deutero species, satellite peaks were observed at m/e 16, 17 and 18 vith excess energies of 2.49 ± 0.05, 2.49 ± 0.05 and 2.61 ± 0.05 respectively. The satellite peaks observed were well defined indicating the process(es) responsible produced ions with relatively homogeneous energy. Attempts to measure the appearance potential of the excess energy CH₃⁺ ion were made but proved unsuccessful. In general, the results of this study show the feasibility of examining metastable transitions by defocusing techniques (MIKES and IKES) and the use of the RMU-7 mass spectrometer for operation in these modes. The observations obtained in this work are consistent with an intermediate doubly charged species decomposing to yield products with excess translational energy.M.S. (Master of Science