COMPARATIVE-STUDY OF ENERGY DEPOSITION IN GASEOUS ORGANIC IONS PERFORMED USING LIMONENE AS A MODEL-COMPOUND

Limonene, 1-methyl-4-(1-methylethenyl)cyclohexene, is chosen as a representative organic compound and its dissociation is studied using different ionization and activation methods. The fragmentation of limonene is principally controlled by the average magnitude of the internal energy lodged in the molecular ion, although substantial effects due to the range of internal energies represented are observed, especially for the retro Diels-Alder process. The effects of internal excitation of the neutral molecule prior to electron impact, and of the ion prior to collisional activation, are shown to be small. The internal energy can be selected by appropriate choice of the agent and/or conditions emloyed for ionization (in MS experiments) and activation (in MS-MS experiments). There are no substantial effects of differing observation time scales. Good agreement is recorded between data collected using a triple quadrupole and a Fourier transform ion cyclotron resonance (FT-ICR) spectrometer when using low energy collisional activation and for charge exchange with selected reagents. Photodissociation data are compared with collisional activation data for the FT-ICR method. The internal energy distribution associated with electron excitation of the molecular ion is characterized and found to resemble qualitatively the distribution lodged in the ion upon electron impact ionization of the neutral molecule.