N. Bischof

Dependence of the desorption yield for valine on the charge state of the primary ions

Abstract The yield for molecular ions desorbed from a valine sample has been measured as a function of the charge state of the incident fast heavy ions. The data can be interpreted in the following way: (i) the yield depends on the square of the primary ion charge, and (ii) desorption takes place not only at the sample surface but also within a layer underneath. The depth of this layer is smaller than the depth needed to achieve charge state equilibrium for the primary ions.

Fast heavy ion induced desorption: Dependence of the yield on the angle of incidence of the primary ions

Abstract The yield for secondary ions desorbed from organic samples (amino acids) by 9 MeV oxygen ions has been investigated for different angles of incidence θ of the primary ions. Primary ions with definite charge states and an equilibrium charge state distribution have been used. The yield increases rapidly with θ and deviates strongly from a (cos θ) 1 distribution at large angles.

Energy dependence of fast heavy ion induced desorption of secondary ions

Abstract Yields for positive and negative secondary ions desorbed by 12C, 160 and 32S ions with velocities ν≳109cm s 1 and equilibrium charge state distributions have been measured. The data show that the yields depend on the charge and the velocity of the primary ions and the secondary ion species. They are independent of the primary ion mass.

Fast heavy ion induced desorption: Dependence of the yield on the primary ion energy

Abstract The dependence of the secondary ion yield on the energy of the fast primary ions has been investigated for several organic samples. We find different dependences for positive secondary ions desorbed from polar and ionic compounds as well as for positive and negative secondary ions desorbed from the same sample (polar compounds).

Molecular effects in the 12C + 13C exit channel of the reaction 16O + 9Be

Abstract Angular distributions for the reactions 9Be(16O, 17O)8Be and 9Be(16O, 12C)13C leading to the lowest-lying 1 2 − , 1 2 + and 5 2 + states in 13C have been measured at energies close to the Cou barrier. The angular distributions of the transitions to the 1 2 − and 1 2 + states in 13bit fast variations within small energy intervals. It was attempted to reproduce the data by means of EFR-DWBA calculations performed up to second order. These attempts failed, particularly for the low-energy data. It is concluded that this failure is due to the formation of single-particle molecular orbitals in the 12+13C exit channel and that nucleon promotion at avoided crossings causes the fast variations in the angular distributions.

Molecular orbital formation and Landau-Zener transitions in the 13C+12C collision

Abstract Angular distributions of the elastic and inelastic 13C + 12C scattering leading to excited states in 13C have been measured at eight energies at Coulomb barrier energies. The data are compared with DWBA calculations performed up to second order and with coupled-reaction-channels calculations using a molecular wave function basis. The result of these calculations allows the conclusion that molecular orbital formation takes place in the 13C + 12C collision. This mechanism is most important at the lowest measured energies, where rapid changes in the angular distributions of the 13 C ∗ ( 1 2 + ) state are observed at energies just above the barrier. They cannot be described by standard second-order DWBA calculations and are interpreted as being due to Landau-Zener transitions.

Multi-step processes and molecular effects in the reaction 14C(13C, 12C)15C at Coulomb barrier energies

Abstract Angular distributions for the 13 C+ 14 C elastic scattering, the inelastic scattering 14 C( 13 C, 13 C ∗ ( 1 2 + )) and the reactions 14 C( 13 C, 12 C) 15 C g.s , 14 C( 13 C, 12 C) 15 C( 5 2 + ) have been measured at Coulomb barrier energies. With the exception of the ground-state transfer data all other data could be reasonably reproduced with EFR-DWBA calculations performed up to third order. The failure of the calculations in case of the ground-state transfer is interpreted as being due to the existence of molecular effects namely nucleon promotion at avoided crossings.

Yield measurements of organic molecules desorbed by energetic heavy ions as a function of the ionic charge state

Abstract Energetic 16 O ions having different well defined charge states at one particular incident energy have been used to bombard the surface of a Valine sample. The experiments were performed at two different incident energies, 20 MeV and 25 MeV. The yield of the desorbed secondary ions [Valine+H] + , [Valine+Na] + , and [Valine-COOH] + has been measured. It is roughly proportional to the charge state of the primary ions and is proportional to the inverse square of the primary ion velocity.

Nuclear glory scattering in the 16O + 16O collision

Abstract Elastic 16O + 16O scattering data have been analyzed by means of a phase shift analysis with regard to the possible existence of nuclear glory scattering. The data contain all features necessary for a nuclear glory.

Intermediate-structure resonances in the /sup 16/O+/sup 16/O total reaction cross section

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