H. Fröhlich

Desorption of organic compounds from solid surfaces by bombardment with heavy ions from a tandem accelerator

Abstract It is shown that heavy ion beams from a 5 MV tandem accelerator are capable to induce desorption of organic compounds from solid surfaces. The observed mass spectra of the desorbed secondary ions are comparable with those obtained from the bombardment with fission fragments. The unique features of the accelerator beam, such as known mass and well defined energy, have been used in order to study the desorption mechanism. Relative yields and energy distributions of H + , Na + , [valine + H] + , and [valine -COOH] + desorbed from a valine sample have been measured as a function of the incident energy of the primary ions. For increasing energy loss in the sample surface the secondary ion yield increases, whereas the yield ratios of different ions desorbed from the same surface remain unchanged. Evidence has been found that only a certain portion of the energy loss contributes to the desorption process.

Heavy ion induced desorption of organic compounds

Abstract The desorption of organic compounds has been studied using 16 O and 32 S ions as primary ion beam in the energy range from 8 to 40 MeV. The observed mass spectra are comparable to those obtained by bombardment with heavier ions at higher energies ( 252 Cf-fission products). Using the amino acid valine as sample the energy distributions and the yield of desorbed ions like H + , Na + , [valine+H] + and [valine-COOH] + were measured as a function of the stopping power in the sample, which is also called linear energy transfer (LET). For increasing LET the secondary ion yield increases too, but the ratio of the yields of different ions desorbed from the same surface remains unchanged. There are indications that only a certain portion of the LET contributes to the desorption process. The ratio of that portion to the total LET (as calculated by the Bragg rule) seems to be an universal function of ζ = ν ν 0 Z , where ν is the velocity of the primary ion and ν 0 Z is the Bohr velocity of a K-electron of the primary ion.

Oscillations in the excitation function for complete fusion of 6O+12C at low energies

Abstract The excitation function of the complete fusion of 16 O + 12 C has been measured in the range E c.m. =8.5−12.9 MeV. It contains oscillations which have already been observed at higher energies. Some of these oscillations are tentatively in terms of a rotational band.

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.

Experimental investigations of fast heavy ion induced desorption

Abstract Yields of secondary ions desorbed by energetic (1 MeV/amu) heavy ions from different solid samples have been measured as a function of the primary ion energy. The results are compared with predictions of models for the desorption mechanism.

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).

Formation of covalent nuclear molecules in the 13C + 12C system

Abstract Angular distributions of the elastic scattering of 13 C on 12 C and the inelastic scattering leading to the lowest-lying 1 2 + and 5 2 + states in 13 C have been measured at energies close to the Coulomb barrier. Analyses carried out in the framework of a complete coupled-reaction-channel theory show that extremely polarized single-particle molecular orbits (hybridization) are formed during the scattering process which give rise to a multiple-step interaction of the valence nucleon, i.e. the formation of a covalent nuclear molecule.

Simple method for yield measurements of secondary ions desorbed by fast heavy ions of variable energy

Abstract A new method for yield measurements of secondary ions desorbed by fast heavy ions is presented which reduces the data collecting time in cases where the energy dependence of the yield on the primary ion energy is of interest. The method allows yield measurements to be carried out at accelerators with fixed energy.