[en] The Penning and associative ionization cross sections were measured as functions of the relative velocity of the particles for the systems He(2³S)+Ar and He(2¹S)+Ar, in the 0.03-0.04eV range (1200-4500m/s)

[en] The velocity dependence of both the Penning and associative ionization cross section of Ar atoms by He(2³S) and He(2¹S) metastable atoms, and of their sum is measured in the velocity range 1200-4500m/sec (30-400MeV) in a crossed-beam experiment by a time-of-flight technique. Characteristic cross-section ratios associative/total and singlet/triplet are reported along with the relative magnitude of the associative, Penning and total cross-sections. The measurements clearly show a difference in the reaction mechanisms involving He(2³S) and He(2¹S). This difference appears not only in the ratio associative/total, whose magnitude reaches 19% and 38% for He(2³S) and He(2¹S) respectively at the velocity v=1200m/sec (30MeV), and in the ratio singlet/triplet, which increases from 0.5 to 3.8 for velocity decreasing from 4500m/sec to 1200m/sec, but also in the different shapes of the associative and Penning cross sections for He(2³S) and He(2¹S)

[en] The velocity dependence of both Penning and associative ionization cross sections sigma(Pe) and sigma(As) or Ar atoms by the He(2³S) and He(2¹S) metastable atoms, and their sum sigma(Pe)+sigma(Ar) was measured in the velocity range 1200-4500m/sec (30-400MeV) in a crossed-beam experiment using time-of-flight techniques

[en] A time-of-flight technique has been developed for the study of the velocity dependence of the cross section for Penning ionization of D atoms by metastable He atoms: He(2¹S)+D→He(1¹S)+D⁺+e^-, He(2³S)+D→He(1¹S)+D⁺e^-

[en] The application limits of the free electron model are tested. Experiments on polar molecules and on molecules of high electronical affinity are effectuated. The experiments are carried out in a three crossed beam geometry: a He(2^1S, 2^3S) metastable atom beam, a continuous and monomode laser UV beam (316 nm), and a gas target beam. The main results are: high cross sections are observed on NH3, SO2 and C3H6O; the σ''exp'' behavior, as a function of v_r, is v_r^-2; a monotone σ''exp'' (v_r) behavior is observed for SF6 and NO2. The experimental data can not be justified by means of the free electron model

No abstract available

[en] We have studied the fragmentation of thymidine and deoxyadenosine induced by slow multiply charged ions. The measured mass spectra specify as an important reaction channel the separation of the molecules into their basic and osidic parts, combined with some structural modifications. In particular for higher projectile charges singly and doubly charged small-size fragments (m<100) are produced, but also the formation of large molecules (modified dimers or trimers) occurs in the sputtering process. The sputtering yield increases with the charge state, the grazing angle as well as the kinetic energy of the projectile

[en] Interaction between radiative excited rare gas atoms of low n ground state atoms or molecules has been studied either in discharges or in crossed beam experiments. Results of recent work on Hesup(*)-rare gas systems and their comparison with the existing theoretical prediction are discussed. (Author)

[en] The velocity dependence of the associative ionization (He(5³P)+He → He₂⁺ + e) cross section has been investigated at thermal energies. We report the first experimental evidence of structures arising in the cross section, which are well interpreted in the framework of a theoretical model. (Author)

[en] The velocity dependence of both the Penning and associative ionization cross sections sigma/sub PI/ and sigma/sub AI/ of Ar atoms by He(2 ³S) and He(2 ¹S) metastable atoms, and of their sum sigma/subT/ = sigma/sub PI/ + sigma/sub AI/, is measured in the velocity range 1200--4500 m/sec (30--400 meV) in a crossed-beam experiment by a time-of-flight technique. Characteristic cross-section ratios sigma/sub AI//sigma/subT/ and sigma/subT/(singlet)/sigma/subT/(triplet) are reported along with the relative magnitude of the cross sections sigma/sub AI/, sigma/sub PI/, sigma/subT/. The measurements clearly show a difference in the reaction mechanisms involving He(2 ³S) and He(2 ¹S). This difference appears not only in the ratio sigma/sub AI//sigma/subT/, whose magnitude reaches 19% and 38% for He(2 ³S) and He(2 ¹S), respectively, at the velocity v = 1200 m/sec (30 meV), and in the ratio sigma/subT/(singlet)/sigma/subT/ (triplet), which increases from 0.5 to 3.8 for velocity decreasing from 4500 m/sec to 1200 m/sec, but also in the different shapes of the sigma/sub AI/ and sigma/sub PI/ cross sections for He(2 ³S) and He(2 ¹S). The experimental results for He(2 ³S) are also compared to theoretical calculations made in the classical impact parameter formulation. The model gives a total ionization cross section sigma/subT/ and partial ionization cross sections sigma/sub AI/ and sigma/sub PI/ in good agreement with the data. Information on both the coupling width and the He + Ar⁺ interaction potential well are obtained