Low energy (0–10 eV) electron driven reactions in the halogenated organic acids CCl3COOH, CClF2COOH, and CF3CHNH2COOH (trifluoroalanine)

Negative ion formation following resonant electron attachment to the three title molecules is studied by means of a beam experiment with mass spectrometric detection of the anions. All three molecules exhibit a pronounced resonance in the energy range around 1 eV which decomposes by the loss of a neutral hydrogen atom thereby generating the closed shell anion (M–H)− (or RCOO−), a reaction which is also a common feature in the non- substituted organic acids. The two chlorine containing molecules CCl3COOH and CClF2COOH exhibit an additional strong and narrow resonance at very low energy (close to 0 eV) which decomposes by the cleavage of the C–Cl bond with the excess charge finally localised on either of the two fragments Cl− and (M–Cl)−. This reaction is by two to three orders of magnitude more effective than hydrogen loss. Apart from these direct bond cleavages (C–Cl, O–H) resonant attachment of subexcitation electrons trigger additional remarkably complex unimolecular decompositions leading, e.g., to the formation of the bihalide ions ClHCl− and ClHF− from CCl3COOH and CClF2COOH, respectively, or the loss of a neutral CF2 unit from trifluoroalanine thereby generating the fluoroglycine radical anion. These reactions require substantial rearrangement in the transitory negative ion, i.e., the cleavage of different bonds and formation of new bonds. F− from both chlorodifluoroacetic acid and trifluoroalanine is formed at comparatively low intensity (more than three orders of magnitude less than Cl− from the chlorine containing molecules) and predominantly within a broad resonant feature around 7–8 eV characterised as core excited resonance

Low energy (0–10 eV) electron driven reactions in the halogenated organic acids CCl3COOH, CClF2COOH, and CF3CHNH2COOH (trifluoroalanine)

Negative ion formation following resonant electron attachment to the three title molecules is studied by means of a beam experiment with mass spectrometric detection of the anions. All three molecules exhibit a pronounced resonance in the energy range around 1 eV which decomposes by the loss of a neutral hydrogen atom thereby generating the closed shell anion (M–H)− (or RCOO−), a reaction which is also a common feature in the non- substituted organic acids. The two chlorine containing molecules CCl3COOH and CClF2COOH exhibit an additional strong and narrow resonance at very low energy (close to 0 eV) which decomposes by the cleavage of the C–Cl bond with the excess charge finally localised on either of the two fragments Cl− and (M–Cl)−. This reaction is by two to three orders of magnitude more effective than hydrogen loss. Apart from these direct bond cleavages (C–Cl, O–H) resonant attachment of subexcitation electrons trigger additional remarkably complex unimolecular decompositions leading, e.g., to the formation of the bihalide ions ClHCl− and ClHF− from CCl3COOH and CClF2COOH, respectively, or the loss of a neutral CF2 unit from trifluoroalanine thereby generating the fluoroglycine radical anion. These reactions require substantial rearrangement in the transitory negative ion, i.e., the cleavage of different bonds and formation of new bonds. F− from both chlorodifluoroacetic acid and trifluoroalanine is formed at comparatively low intensity (more than three orders of magnitude less than Cl− from the chlorine containing molecules) and predominantly within a broad resonant feature around 7–8 eV characterised as core excited resonance

Reactions in the radiosensitizer misonidazole induced by low-energy (0–10 ev) electrons

PD/BD/114452/2016 UID/FIS/00068/2019 PD/00193/2012 ANR-10-LABX-0066 ANR-11-IDEX-0007Misonidazole (MISO) was considered as radiosensitizer for the treatment of hypoxic tumors. A prerequisite for entering a hypoxic cell is reduction of the drug, which may occur in the early physical-chemical stage of radiation damage. Here we study electron attachment to MISO and find that it very effectively captures low energy electrons to form the non-decomposed molecular anion. This associative attachment (AA) process is exclusively operative within a very narrow resonance right at threshold (zero electron energy). In addition, a variety of negatively charged fragments are observed in the electron energy range 0–10 eV arising from dissociative electron attachment (DEA) processes. The observed DEA reactions include single bond cleavages (formation of NO2−), multiple bond cleavages (excision of CN−) as well as complex reactions associated with rearrangement in the transitory anion and formation of new molecules (loss of a neutral H2O unit). While any of these AA and DEA processes represent a reduction of the MISO molecule, the radicals formed in the course of the DEA reactions may play an important role in the action of MISO as radiosensitizer inside the hypoxic cell. The present results may thus reveal details of the molecular description of the action of MISO in hypoxic cells.publishersversionpublishe

Electron stimulated desorption of Cl– from adsorbed and condensed Cl2: Effects of environment and orientation

Electron stimulated desorption (ESD) of Cl– from condensed molecular chlorine in the energy range 0–15 eV is studied. Cl2 is deposited in either multilayer amounts directly on a cryogenically cooled gold crystal or in sub-monolayer quantities on rare gas films (Xe, Kr) or ammonia ice films. Cl– desorption from multilayer films shows an intense resonance peaking at 5.5 eV and a comparatively smaller feature at 3 eV in qualitative agreement with an earlier ESD experiment. The desorption signal is enhanced by about one order of magnitude when a 0.2 monolayer (ML) Cl2 is adsorbed on a multilayer rare gas film. In this case, the desorption signal shows two clearly separated resonances peaking at 2.5 and 5.5 eV closely resembling dissociative electron attachment (DEA) from gas phase Cl2. These resonances can be associated to the transitions Cl2(1+g) Cl2–(2g) and Cl2(1+g) Cl2–(2u), respectively, both final states representing core excited resonances. The shape of the resonance around 5.5 eV splits into different peaks when changing from grazing incidence of the electron beam to an impact angle of 45° with respect to the surface normal. On the basis of the pronounced angular dependence of the Cl– intensity reported from gas phase DEA this observation is compatible with a situation in which the molecules are oriented along the surface normal. Compared to the noble gas films, ESD from sub-monolayer Cl2 on top of a multilayer NH3 film is suppressed while the overall shape of the yield function is approximately preserved. None of the present experiments show a Cl– desorption signal below 2 eV while the charging behaviour of the film indicates that electron attachment is still operative in this energy domain. This suggests that the transient anion in its electronic ground state (Cl2–#(2+u)) is still formed by low energy electron attachment but is subjected to effective energy dissipation creating either stabilized ions (Cl2–(2+u)) or fragment ions (Cl–(2P)) with insufficient kinetic energy to leave the surface