Event by event analysis of collision induced cluster ion fragmentation: sequential monomer evaporation versus fission reactions

IP

Fragmentation processes of ionized 5-fluorouracil in the gas phase and within clusters

We have measured mass spectra for positive ions produced from neutral 5-fluorouracil by electron impact at energies from 0 to 100 eV. Fragment ion appearance energies of this (radio-)chemotherapy agent have been determined for the first time and we have identified several new fragment ions of low abundance. The main fragmentations are similar to uracil, involving HNCO loss and subsequent HCN loss, CO loss, or FCCO loss. The features adjacent to these prominent peaks in the mass spectra are attributed to tautomerization preceding the fragmentation and/or the loss of one or two additional hydrogen atoms. A few fragmentions are distinct for 5-fluorouracil compared to uracil, most notably the production of the reactive moiety CF+. Finally, multiphoton ionization mass spectra are compared for 5-fluorouracil from a laser thermal desorption source and from a supersonic expansion source. The detection of a new fragment ion at 114 u in the supersonic expansion experiments provides the first evidence for a clustering effect on the radiation response of 5-fluorouracil. By analogy with previous experiments and calculations on protonated uracil, this is assigned to NH3 loss from protonated 5-fluorouracil

Theoretical study of charge transfer dynamics in collisions of C

A theoretical approach of the charge transfer dynamics induced by collision of C6+ ions with biological targets has been performed in a wide collision energy range by means of ab-initio quantum chemistry molecular methods. The process has been investigated for the target series thymine, uracil and 5-halouracil corresponding to similar molecules with different substituent on carbon C5. Such a study may be related to hadrontherapy treatments by C6+carbon ions and may provide, in particular, information on the radio-sensitivity of the different bases with regard to ion-induced radiation damage. The results have been compared to a previous analysis concerning the collision of C4+ carbon ions with the same biomolecular targets and significant charge effects have been pointed out

Détermination des courbes de potentiel non-adiabatiques à partir de fonctions d’onde obtenues par interaction de configurations

Nous avons développé une méthode de calcul réalisant le passage des surfaces de potentiel adiabatiques à des surfaces non-adiabatiques. Cette méthode consiste à projeter les voies ouvertes du calcul adiabatique sur un sous-espace [math] de référence et à y définir un hamiltonien effectif qui redonne les projections sur [math] des fonctions propres et les valeurs propres du calcul adiabatique. Nous avons étudié l’influence du choix de la base de référence sur l’exemple du système (ArH)+. La méthode donne de bons résultats pour des distances supérieures à 4 ua environ