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| Author(s): |
Tatiana Giroldo
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2002-04-22 |
| Examining board members: |
Jose Manuel Riveros;
Harrald Victor Linnert;
Luiz Alberto Beraldo de Moraes
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| Advisor: | Jose Manuel Riveros |
| Abstract | |
Fragmentation processes are explored in mass spectrometry to identify structures of ions and neutral molecules. The study of ion dissociation reaction in the gas phase induced by infrared absorption also provides energetic data related to the fragmentation processes. The mechanism of the dissociation by infrared radiation involves sequential photon absorption that progressively raises the internal energy of the ion population until the dissociation threshold. In the present work, the blackbody radiation emitted by a heated tungsten wire is used to promote ion dissociation in gas phase. The reaction is observed in a Fourier transform mass spectrometer. The molecular ions of o-methylacetophenone, m-methylacetophenone, p-methylacetophenone and o-chloroacetophenone were studied with this technique. The dependency of the dissociation rates with the radiation temperature was explored, providing Arrhenius activation energies values. The ions cited above and the molecular ion of acetophenone displayed similar behavior, with the exception of the ion produced by o-methylacetophenone. This ion has dissociation rates much smaller than the others and higher activation energy. This behavior raised the idea of isomerization of the molecular ion to the more stable enolic form. The ion was then investigated with theoretical calculation and with specific reaction with neutral molecules. The results show that the isomerization is possible and this explains the observed slowness of the dissociation reaction. (AU) | |