Collisional Studies of Alkoxide Ions.

This thesis is concerned with the application of collisional activation methods to negative ions. Several alkoxides ions have been studied: methoxide, methoxide -d_3, ethoxide, ethoxide-d _2, ethoxide-d_5, n-propoxide, n-propoxide-d_7, i -propoxide, i-propoxide-d_6, i-propoxide -d_7, n-butoxide, i-butoxide, s-butoxide, t-butoxide, 1-pentoxide, 2-pentoxide, 3-pentoxide, 2-methyl -1-butoxide, 3-methyl-1-butoxide, 2,2-dimethyl-1-propoxide, 2-methyl-2-butoxide, 2-methyl-3-buten-2-oxide, 2-phenyl -2-propoxide, and 2-trifluoromethyl-2-propoxide. The alkoxide ions were generated by proton abstraction from the appropriate alcohol by OH^- chemical ionisation. The collisionally induced dissociation (CID) spectra of these ions at 5-100 eV collision energy (lab scale) were obtained using the quadrupole portion of a hybrid tandem mass spectrometer. A plot of the fractional fragment ion abundances against collision energy (breakdown graph) was produced by varying the collision energy. It was found that the fragmentation of the alkoxides could be accounted for by a mechanism involving initial formation of an ion/dipole complex followed by proton transfer within the complex to form the final products, 1,2-elimination of H_2 and/or alkane(s). The identities of the secondary and tertiary alkoxide ions were unambiguously determined by the low-energy CID spectra. Primary alkoxide isomers cannot be differentiated from one another by this technique. The CID spectra of the C_2 through C_5 alkoxide ions have been obtained at 8 keV collision energy using the sector portion of the hybrid instrument. A comparison of the CID spectra at 30 eV and 8 keV reveals that the distribution of fragment ions corresponds to a higher internal energy in the 30 eV CID spectra than in the 8 keV CID spectra. The difference is attributed to a change in excitation mechanism between the two energy regimes. The charge inversion (RO^- to M^+ + N + 2e) and neutralisation-reionisation (RO^ - to RO + e to M^+ + N + e) spectra of the C_1 to C_4 alkoxides were obtained at 8 keV collision energy using the sector portion of the instrument. The two techniques yield similar spectra for most isomers. The propoxide and butoxide isomers can be differentiated on the basis of the distribution of 1,1-elimination products, which are characteristic of the alkoxide structure.