Rainer Hippler

An application of the branching ratio method for ion impact cross section measurements in the far ultraviolet

The branching ratio method is used to carry out a determination of the quantum efficiency of a vacuum UV spectrometer at discrete wavelengths between 37.9 nm and 73.6 nm. Branching ratios of ion impact excited Ne III and Ne IV are applied. Cross sections for the ion and electron impact induced 2s-vacancy production in neon are determined.

Direct and charge-exchange excitation of the 21P level in He+-He collisions

The direct and the charge-exchange excitation of the He 21P level in He+-He collisions has been studied in the impact energy range 150-1000 keV. The direct excitation cross section shows a maximum around 600 keV, whereas the charge-exchange cross section decreases monotonically with increasing impact energy by more than two orders of magnitude.

Cross sections for Ne-K X-ray production in Ne+-Ne collisions (100 keV to 1.2 MeV)

Abstract Absolute cross sections for Ne-K X-ray emission in collision of Ne + ions with Ne atoms have been measured at energies from 100 keV to 1.2 MeV. The cross section rises approximately linear with energy. The results are in satisfactory agreement with respective measurements at lower energies.

Negatively and positively charged oxygen ion formation in collisions of positively charged projectiles with O

Absolute cross sections for positive and negative ion fragments formed from O2 molecules following collisions with H+, H2+, He+, and Ar+ projectiles in the energy range 50–350 keV are presented. Cross sections for negatively charged secondary ions are much smaller ( cm2) compared to those for positively charged fragments. The non-dissociative formation of negatively charged O2− ions results from an electron transfer collision with the projectile. The impact energy dependence shows that the collision cross section for O2− formation strongly depends on the type of projectile involved.

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By measuring the 3s 1.3P1-2p6 1S0 emission of Ne, both direct excitation of the target and charge-exchange excitation of the projectile to the same level have been studied in the energy range from 150 keV to 1 MeV, corresponding to impact velocities between 0.5 and 1.5 au. Comparison of the measured cross sections with existing data for the excitation of resonance states in H++H and He++He collisions shows similarities in the relative magnitude of the direct and the charge-exchange processes which are discussed.

molecules in the energy range 50–350 keV

Absolute cross sections for production of the 1s22s2p5 and 1s22s02p6 configurations of neon in collisions of H+, He+, and Ne+ with Ne and He have been measured by observation of radiative transitions in the spectral range of the vacuum ultraviolet for energies between 50 keV and 1 MeV. Projectile and target emission have been separated. The dependence of the cross sections upon impact velocity is discussed and compared with theoretical calculations. The relative population of the1P1 and3P2, 1, 0 and the3P2, 1, 0 fine structure levels of the 1s22s2p5 configuration is measured as function of impact velocity for the different projectile target combinations.

Excitation of the Ne resonance transitions in Ne+-Ne collisions at intermediate velocities

The angular distribution of H+ fragment ions produced in 5–25 keV H+–H2 collisions was investigated in coincidence with Lyman-α photons. The observed photons arise from electron capture to the projectile H(2p) state and/or from the fragmentation of the H2 molecule via 2sσg, 2pσu or 2pΠ u states of the excited H+2* ion. An analysis of the measured angular distributions has been performed to distinguish the separate degenerate channels available to an emitted Lyman-α photon. The results show similarities to the data of Lindsay et al. (1987) who measured the non-coincident angular distribution of H+ fragment ions within the same energy range.

Multiple ionization of neon 2s- and 2p-electrons induced by ion atom collisions

Abstract The 3s vacancy production in Ar + -He and Ar + -Ar collisions has been studied at impact energies of 100 keV to 550 keV. A comparison is made for the Ar + -He system with theoretical calculations based on the quasi-molecular model.

Angular distribution of hydrogen fragment ions in H + -H 2 collisions

Abstract Ion impact excited spectra of Ne contain a line at 52.82 nm which has been identified as resulting from the decay of double 2s vacancies in NeIII via the transition 2s 0 2p 6 ( 1 S 0 )−2s 1 2p 5 ( 1 P 1 ).

3s vacancy production in Ar+-Ar and Ar+-He collisions

The outer s-shell ionization of neon, argon and krypton has been studied by N+ and Ne+ impact in the energy range of 100 keV to 1000 keV, and by Ne2+ on Ne from 300 keV to 1800 keV. For the Ne+-Ne system the 2s vacancy production has been studied for the projectile and target separately. In connection with theoretical calculations of Albat et al. (see ibid., vol.8, p.2520 (1975)), the Ne+-Ne measurements allow the statement that the quasi-molecule model holds for this process up to relative velocities of 0.7 au.