Positive and negative ion formation via slow electron collisions with 5-bromouridine

Cation and anion formation is studied experimentally upon inelastic low energy electron interactions with 5-bromouridine (BrUrd) using a crossed electron/neutral beams set-up combined with a quadrupole mass spectrometer. The BrUrd molecule belongs to the class of radiosensitizers that increase the sensitivity of DNA (or RNA) to ionizing radiation. In the case of positive ion formation the ionization efficiency curves are measured near the threshold and the corresponding appearance energies are determined using a non-linear least square fitting procedure. The anion yields are investigated in the electron energy range from about 0 to 14 eV. From the comparison of the present results for negative and positive ions information concerning the underlying mechanism of radiosensitizers is deduced

Dynamics of the Penning Ionization of Fullerene Molecules by Metastable Neon Atoms

The collisional energy dependence of the cross section for the Penning ionization of C60 mols. by metastable neon atoms was measured in the 0.035-0.5 eV range in a crossed beam expt. The results show a decreasing trend (.apprx.20%) in the low-energy range up to 0.06 eV, with a slightly increasing dependence in the higher energy range. This behavior is interpreted in terms of the characteristics of the intermol. interaction: an electron transfer can be possible from the metastable rare gas atom to the C60 mol. with the formation of an ion-pair collision complex. At low collisional energy the system evolves mainly adiabatically and the ionization occurs mainly from the ion-pair complex. However, at higher collision energies, nonadiabatic transitions become possible and the systems can remain partially \"trapped\" within the higher adiabatic state with a consequent increase of the ionization probability. [on SciFinder (R)

Energy dependence of the Penning ionization electron spectrum of Ne

A crossed beam experiment is carried out to measure the energy of electrons emitted in Penning ionization processes by Ne*(3P2,0)–Kr collisions. The electron energy spectra have been measured at four different collision energies: 0.050, 0.140, 0.190, 0.460 eV. The analysis of the results allows the separation of spin orbit contributions both in the entrance and in the exit channels providing the related cross-section ratios. Some theoretical considerations have been made to clarify nature and role of interatomic potentials driving the collisions and some general features about the role of atomic fine structure in the Penning ionization processes

Dissociative double photoionization of CO2 molecules in the 36-49 eV energy range: angular and energy distribution of ion products

Dissociative double photoionization of CO2, producing CO+ and O+ ions, has been studied in the 36–49 eV energy range using synchrotron radiation and ion–ion coincidence imaging detection. At low energy, the reaction appears to occur by an indirect mechanism through the formation of CO+ and an autoionizing state of the oxygen atom. In this energy range the reaction leads to an isotropic distribution of products with respect to the polarization vector of the light. When the photon energy increases, the distribution of products becomes anisotropic, with the two ions preferentially emitted along the direction of the light polarization vector. This implies that the molecule photoionizes when oriented parallel to that direction and also that the CO2 2+ dication just formed dissociates in a time shorter than its typical rotational period. At low photon energy, the CO+ and O+ product ions separate predominantly with a total kinetic energy between 3 and 4 eV. This mechanism becomes gradually less important when the photon energy increases and, at 49 eV, a process where the two products separate with a kinetic energy between 5 and 6 eV is dominant