B P Marinković

The electronic states of pyrimidine studied by VUV photoabsorption and electron energy-loss spectroscopy

The electronic state spectroscopy of pyrimidine C(4)H(4)N(2) has been investigated using both high resolution VUV photoabsorption in the energy range 3.7 to 10.8 eV (335 to 115 nm) and lower resolution electron energy loss in the range 2 to 15 eV. The low energy absorption band, assigned to the (pi*) <-- 7b(2)(n(N)) (1(1)B(1)<-- 1(1)A(1)) transition, at 3.85(4) eV and the vibrational progressions superimposed upon it have been observed for the first time, due to the availability of a high-resolution photon beam (0.075 nm), corresponding to 3 meV at the midpoint of the energy range studied. Vibronic coupling has been shown to play an important role dictating the nature of the observed excited states, especially for the lowest (1)B(1) state. The 2(1)B(1) state is proposed to have its origin at 7.026 eV according to the vibrational excitation reported in this energy region (7.8-8.4 eV). New experimental evidence of 4(1)A(1) state with a maximum cross section at 8.800 eV is supported by previous ab initio quantum chemical calculations. Rydberg series have been assigned converging to the three lowest ionisation energy limits, 9.32 eV ((2)B(2)), 10.41 eV ((2)B(1)) and 11.1 eV ((2)A(1) + (2)A(2)) with new members reported for the first time and classified according to the magnitude of the quantum defects (delta). Additionally, the absolute differential cross section for inelastic electron scattering has been measured for the most intense band from 6.9 to 7.8 eV assigned to (1)pipi* (3(1)A(1) + 2(1)B(2)).

Elastic and inelastic electron scattering by cadmium

Relative elastic scattering and excitation cross-sections of cadmium, up to the first ionization potential, are obtained from spectroscopic measurements on electrons with initial energies ranging from 3.4 to 85 eV. Relative differential cross sections are reported for excitation of the 55 0 (elastic), 53 P1 , 53 P)2 , 51 P1 , 63 S1 , 61 S0 , 51 D2 , 61 P1 , 71 S0 , (61 D2 -71 P1 ), 81 S0 and (71 D2 -81 P1 ) levels. Relative integrated scattering cross sections as well as momentum transfer and viscosity cross sections are also given.

Experimental determination of the differential cross-section surface for elastic electron?atom (molecule) scattering

A crossed-beam experimental set-up, which allows independent measurement of differential electron–atom (molecule) elastic scattering cross section as a function of both scattering angle and incident electron energy, is described. The experimental system utilizes an electron gun and a double cylindrical mirror analyser, which are described in detail. A procedure for obtaining constant scattering geometry, transmission function and detection efficiency, in a wide range of the incident electron energies (40–250 eV), was tested experimentally and by means of electron trace simulations. The present experimental procedure allows determination of a two-dimensional relative differential cross-section surface, which can be calibrated to the absolute scale via normalization to a single point.

Low-energy electron transmission through high aspect ratio Al2O3 nanocapillaries

Electron transmission through insulating Al2O3 nanocapillaries of different diameters (40 and 270 nm) and 15 mu m length has been investigated for low-energy electrons (2-120 eV). The total intensity of transmitted current weakly depends on the incident electron energy and tilt angle defined with respect to the capillary axis. On the other hand, the intensity of elastically transmitted electrons significantly varies with the alteration of electron energy and tilt angle. In addition, we measured an energy distribution of electrons transmitted both in the straightforward direction and at large tilt angle. The measured spectra show that inelastic processes dominate and, in particular, a large amount of low-energy electrons. These low-energy electrons can be either inelastically scattered projectiles or secondary electrons emitted within the capillaries. Furthermore, a change of the tilt angle appears to influence significantly only the intensity of the elastic transmission. The present results suggest a more complex nature of low-energy electron transport through insulating nanocapillaries than proposed for positive ions. Copyright (C) EPLA, 2009

Absolute cross sections for elastic electron scattering from 3-hydroxytetrahydrofuran

The results of measurements and calculations of absolute cross sections for elastic electron scattering from the 3-hydroxytetrahydrofuran (3hTHF) (C4H8O2) molecule are reported. The measurements were performed using a crossed beam experimental setup, for an incident electron energy range of 40-300eV and an overall scattering angle range of 10 -110 . Relative differential cross sections (DCSs) were measured both as a function of the angle and theincident energyand theabsolute DCSswere determinedusing therelative flow technique. The calculations of molecular cross sections are based on a corrected form of the independent-atom method, known as the screen corrected additivity rule (SCAR) procedure and using an improved quasifree absorption model. Additional calculations are also done to investigate the influence of rotational excitations and low-angular behavior of SCAR DCSs. The calculated dataset includes differential, integral and total cross sections in the energy range from 5eV to 10000eV. The present results are discussed regarding the most recent low-energy elastic DCSs for 3hTHF (Vizcaino et al 2008 New J. Phys. 10 053002), as well as the recent DCSs for molecules of similar structure (tetrahydrofuran and tetrahydrofurfuryl alcohol).

Normalization of the measured relative electron differential cross sections for 2 ^1Sigma+ and ^1Pi states of N2O

The measured relative electron differential cross sections (DCSs) for excitation of the 2 + and states of N2O (Marinkovic et al 1986 J. Phys. B: At. Mol. Phys. 19 2365) have been normalized through a recent forward scattering function for the generalized oscillator strength. Measurements were obtained at electron impact energies of 15, 20, 30, 50 and 80 eV, using the electron spectrometer with crossed electron-molecule beam arrangement. Measured data are corrected at and near zero scattering angles following the analytic behaviour of the momentum dispersion method. Absolute DCS values for the state are compared with the only available set of theoretical data, while for the 2 + state results are presented for the first time.

Electron-impact excitation of the (n- 1)d9ns2np autoionizing states of cadmium (n = 5) and zinc (n=4)

Electron-impact excitation of the 53P 1 (12.062 eV) and 51P 1 (12.810 eV) 4d95s25p autoionizing states of Cd has been experimentally investigated at incident electron energies (E0) from 15 to 60 eV and scattering angles (θ) up to 40° (at E0 = 40 eV, θ = 2°–150°). The absolute differential cross sections (DCSs) at E0 = 40 eV were determined through normalization to the optical oscillator strengths. These DCSs were extrapolated to 0° and 180° and numerically integrated to yield integral, momentum transfer and viscosity cross sections. Energy-loss spectra for Cd were recorded from 11 to 18 eV, and 22 autoionizing states were identified at different impact energies. Electron-impact excitation of the 3d94s24p autoionizing states was observed in energy-loss spectra of Zn at E0 = 20, 60, 80 and 100 eV (θ up to 10°). The DCSs for Cd could not be compared with other results, because there are no available data in literature. The autoionizing energy levels and line widths are in good agreement with existing experimental and calculated values.

Radiation damage of biomolecules (RADAM) database development: current status

Ion beam therapy offers the possibility of excellent dose localization for treatment of malignant tumours, minimizing radiation damage in normal tissue, while maximizing cell killing within the tumour. However, as the underlying dependent physical, chemical and biological processes are too complex to treat them on a purely analytical level, most of our current and future understanding will rely on computer simulations, based on mathematical equations, algorithms and last, but not least, on the available atomic and molecular data. The viability of the simulated output and the success of any computer simulation will be determined by these data, which are treated as the input variables in each computer simulation performed. The radiation research community lacks a complete database for the cross sections of all the different processes involved in ion beam induced damage: ionization and excitation cross sections for ions with liquid water and biological molecules, all the possible electron – medium interactions, dielectric response data, electron attachment to biomolecules etc. In this paper we discuss current progress in the creation of such a database, outline the roadmap of the project and review plans for the exploitation of such a database in future simulations.

Absolute cross sections for electron scattering from furan

We report results of measurements and calculations of absolute cross sections for electron scattering from furan molecules (C(4)H(4)O). The experimental absolute differential cross sections (DCSs) for elastic electron scattering were obtained for the incident energies from 50 eV to 300 eV and for scattering angles from 20° to 110°, by using a crossed electron-target beam setup and the relative flow technique for calibration to the absolute scale. The calculations of the electron interaction cross sections are based on a corrected form of the independent-atom method, known as the screening corrected additivity rule (SCAR) procedure and using an improved quasifree absorption model. The latter calculations also account for rotational excitations in the approximation of a free electric dipole and were used to obtain elastic DCSs as well as total and integral elastic cross sections which are tabulated in the energy range from 10 to 10 000 eV. All SCAR calculated cross sections agree very well with both the present and previously published experimental results. Additionally, calculations based on the first Born approximation were performed to calculate both elastic and vibrationally inelastic DCSs for all the modes of furane, in the energy range from 50 eV to 300 eV. The ratios of the summed vibrational to elastic DCSs are presented and discussed. Finally, the present results for furan are compared with previously published elastic DCSs for the tetrahydrofuran molecule and discussed.

Electron scattering by ytterbium: I. Excitation of the 4f146s6p 1P1 resonance state and elastic collision

Differential cross sections (DCSs) for electron-impact excitation of the 4f 14 6s6p 1 P1 resonance state of ytterbium were measured at 10, 20, 40, 60 and 80 eV incident electron energies (E0) and scattering angles (θ ) between 2 ◦ and 150 ◦ . The absolute DCS scale for the 1 P1 state was determined through normalization of its relative DCSs to the optical oscillator strength using the forward scattering function method. DCSs for elastic electron scattering by ytterbium were measured at the same energies for θ between 10 ◦ and 150 ◦ . Elastic-to-inelastic intensity ratios were obtained from energy-loss spectra recorded with overall energy resolution of 65 meV (FWHM) and angular resolution of 1.5 ◦ . Both inelastic and elastic DCSs were extrapolated to 0 ◦ and 180 ◦ and numerically integrated to yield integral, momentum transfer and viscosity cross sections. Our results are compared with scarce experimental and theoretical data.