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We report on the experimental determination of absolute, total cross sections for electron-impact double ionization of helium in its metastable 1s2s 3S state and of the helium negative ion He􀀀(1s2s2p 4P). Cross sections are measured for impact energies ranging from threshold to 1000 eV using the animated crossed beams technique. The fast, pure beam of metastable helium required for the experiment is produced by photodetachment of fast He􀀀 ions. Results for He(1s2s 3S) are compared to those for He(1s2 1S), and exhibit similar magnitude and behaviour. The cross section for He􀀀 is large compared to other negative ions and indicates the predominance of indirect ionization channels at large impact energies.

We present an experimental determination of the electron-impact ionization cross section of the $1s2s\phantom{\rule{0.16em}{0ex}}^{3}S$ state of helium, for which there is a serious long-lasting discrepancy between theory and experiment. A technique for the production of a fast, intense beam of helium in the $1s2s\phantom{\rule{0.16em}{0ex}}^{3}S$ state only has been developed for this purpose, based on photodetachment of the ${\mathrm{He}}^{\ensuremath{-}}$ anion. The cross section is measured using the animated crossed beam technique. The present results are much lower than the experimental data of Dixon et al. [J. Phys. B 9, 2617 (1976)] and are in excellent agreement with the calculation of Fursa and Bray [J. Phys. B 36, 1663 (2003)].

Absolute cross sections for electron-impact single ionization, dissociative excitation and dissociative ionization of the ethynyl radical ion (C(2)D(+)) have been measured for electron energies ranging from the corresponding reaction thresholds to 2.5 keV. The animated crossed electron-ion beam experiment; is used and results have been obtained for the production of C(2)D(2+), C(2+), C(2)(+), CD(+), C(+) and D(+). The maximum of the cross section for single ionization is found to be (2.01 +/- 0.02) x 10(-17) cm(2), at the incident electron energy of 105 eV. Absolute total cross sections for the various singly charged fragments production are observed to decrease by a factor of almost three, from the largest cross-section measured for C(+), over C(2)(+) and CD(+) down to that of D(+) The maxima of the cross sections are obtained to be (14.5 +/- 0.5) x 10(-17) cm(2) for C(2)(+) (12.1 +/- 0.1) x 10(-17) cm(2) for CD(+) (27.7 +/- 0.2) x 10(-17) cm(2) for C(+) and (11.1 +/- 3.8) x 10(-17) cm(2) fo D(+). The smallest cross section is measured to be (1.50 +/- 0.04) x 10(-18) cm(2) for the production of the doubly charged ion C(2+). Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic energy release distributions of dissociation fragments are seen to extend from 0 to 6 eV for the heaviest; fragment C(2)(+), up to 11.0 eV for CD(+) 14.2 eV for C(+) and 11.2 eV for D(+) products.

Absolute cross-sections for electron-impact dissociative excitation of C2H (2) (+) and C2D (2) (+) to C2D+, CH+, C+, C (2) (+) , H+ and CH (2) (+) singly-charged fragments have been estimated. The animated crossed-beams method is applied in the energy range from the corresponding reaction threshold up to 2.5 keV. Individual contributions for dissociative excitation are determined from the analysis of the total absolute cross-sections measured for each detected product. The dissociative excitation cross-sections are seen to decrease for more than an order of magnitude, from C2D+ (12.6 +/- 0.3) x 10(-17) cm(2) over CH+ (6.37 +/- 0.12) x 10(-17) cm(2), C+ (4.09 +/- 0.13) x 10(-17) cm(2), C (2) (+) (3.5 +/- 0.2) x 10(-17) cm(2) and H+ (1.57 +/- 0.11) x 10(-17) cm(2) to CH (2) (+) (3.6 +/- 0.5) x 10(-18) cm(2). Cross-section values and threshold energies are compared with the data which are available from the literature.

Absolute cross-sections for electron-impact dissociative ionization of C2 H 2 + and C2 D 2 + to CH+, C+, C 2 + , H+, CH 2 + and C2D+ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH+ (5.37±0.10) × 10-17 cm2 over C+ (4.19± 0.16) × 10-17 cm2, C2D+ (3.94±0.38) × 10-17 cm2, C 2 + (3.82±0.15) × 10-17 cm2 and H+ (3.37±0.21) × 10-17 cm2 to CH 2 + (2.66±0.14) × 10-18 cm2. Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C2H 2 + $\left( {\rm C}_2 {\rm D}_2^+ \right)$ , the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.

Absolute cross sections for electron-impact dissociative excitation and ionization of CD4+ leading to formation of ionic products (CD42+, CD3+, CD2+, CD+, C+, D-3(+), D-2(+), and D+) have been measured. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections are found to be (3.8 +/- 0.2) x 10(-1)9 cm(2), (10.8 +/- 1.5) x 10(-17) cm(2), (7.1 +/- 0.8) x 10(-17) cm(2), (9.0 +/- 0.8) x 10(-17) cm(2) and (3.7 +/- 0.4) x 10(-17) cm(2) for the heavy carbonaceous ions CD42+, CD3+, CD2+, CD+ and C+ respectively. For the light fragments, D-3(+), D-2(+), and D+, the cross sections around the maximum are found to be (5.0 +/- 0.6) x 10(-19) cm(2), (1.7 +/- 0.2) x 10(-17) cm(2) and (10.6 +/- 1.0) x 10(-17) cm(2), respectively. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. The analysis of ionic product velocity distributions allows determination of the kinetic energy release distributions which are seen to extend from 0 to 9 eV for heavy fragments, and up to 14 eV for light ones. The comparison of present energy thresholds and kinetic energy release with available published data gives information about states contributing to the observed processes. Individual contributions for dissociative excitation and dissociative ionization are determined for each detected product. A complete database including cross sections and energies is compiled for use in fusion application.

Absolute cross sections for electron-impact dissociative excitation and ionization of CD+ 4 leading to formation of ionic products (CD2+ 4, CD+ 3, CD+ 2, CD+, C+, D+ 3, D+ 2, and D+) have been measured. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections are found to be (3.8±0.2) ×10-19 cm2, $(10.8\,\pm\,1.5) \times~10^{-17}$ cm2, (7.1±0.8) ×10-17 cm2, (9.0±0.8) × 10-17 cm2 and (3.7±0.4) ×10-17 cm2 for the heavy carbonaceous ions CD2+ 4, CD+ 3, CD+ 2, CD+ and C+ respectively. For the light fragments, D+ 3, D+ 2, and D+, the cross sections around the maximum are found to be (5.0±0.6) ×10-19 cm2, (1.7± 0.2) ×10-17 cm2 and (10.6±1.0) ×10-17 cm2, respectively. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. The analysis of ionic product velocity distributions allows determination of the kinetic energy release distributions which are seen to extend from 0 to 9 eV for heavy fragments, and up to 14 eV for light ones. The comparison of present energy thresholds and kinetic energy release with available published data gives information about states contributing to the observed processes. Individual contributions for dissociative excitation and dissociative ionization are determined for each detected product. A complete database including cross sections and energies is compiled for use in fusion application.

Absolute cross sections for electron impact dissociative excitation and ionization of CD+ leading to the formation of ionic products ( D+, C+, C2+ and C3+) are reported in the energy range from their respective thresholds to 2.5 keV. Around the maximum, cross sections are found to be ( 10.5 +/- 1.0) x 10(-17) cm(2), ( 20.6 +/- 3.5) x 10(-17) cm(2), ( 1.20 +/- 0.11) x 10(-17) cm(2) and ( 8.2 +/- 1.5) x 10(-20) cm(2) for D+, C+, C2+ and C3+, respectively. In the very low- energy region, dissociative excitation leading to the C+ formation dominates over the D+ one. The cross section for dissociative ionization ( C+ + D+ formation) is found to be ( 6.9 +/- 1.3) x 10(-17) cm(2) around 105 eV and the corresponding threshold energy is ( 22.1 +/- 0.5) eV. The animated crossedbeams method is used and the analysis of ionic product velocity distributions allows the determination of the kinetic energy release distributions. They are seen to extend from 0 to 15 eV both for C+ and for D+, and up to 40 eV both for C2+ and for C3+. For singly charged products, the comparison of the present energy thresholds and kinetic energy release with published data allows the identification of states contributing to the observed processes. In particular, contributions from primary ions formed in the a(3)Pi metastable state are perceptible. At fixed electron energy, the cross sections for the various ionization channels are seen to reduce exponentially with the potential energy of each dissociated ion pair. Anisotropies are estimated to be in the range 8 +/- 2% for both C+ and D+. The total CD+ single ionization cross section calculated by application of the Deutsch - Mark formalism is found to be in good agreement with experimental results.

Absolute cross sections for electron impact ionization of CO+ leading to the formation of doubly and triply charged products (CO2+, C2+ and O2+, C3+ and O3+) are reported in the energy range from their respective thresholds to 2500 eV. Around the maximum, cross section values are found to be ( 13.36 +/- 0.56) x 10(-18) cm(2), ( 5.58 +/- 0.55) x 10(-18) cm(2) and (1.37 +/- 0.14) x 10(-18) cm(2) for CO2+, C2+ and O2+, respectively, and (28.3 +/- 7.0) x 10(-21) cm(2) and (2.4 +/- 0.7) x 10(-21) cm(2) for C3+ and O3+, respectively. The analysis of ionic product velocity distributions, obtained by means of a crossed electron-ion beam set-up, allows the determination of the kinetic energy release distributions. They are seen to extend from 0 to 50 eV both for C2+ and O2+. The mean kinetic energy releases for C3+ and O3+ are found to be 33 +/- 5 eV and 39 +/- 9 eV, respectively. The cross sections are seen to depend exponentially on the potential energy of each dissociated ion pair. The total single CO+ ionization cross section calculated by application of the Deutsch-Mark ( DM) formalism is found to be in good agreement with the experimental results.

A crossed electron-ion beam experimental set-up has been upgraded for the study of electron impact ionization and dissociation of molecular ions by means of ionic product detection. Both the experimental set-up and the data analysis procedures are described in detail for the estimation of ( i) absolute cross sections, ( ii) kinetic energy release distributions ( KERD) and ( iii) anisotropies of angular distributions. Absolute cross sections are obtained separately for dissociative excitation ( DE) and for dissociative ionization ( DI). A double focusing magnetic field analyser is used for the observation of product velocity distributions, in the laboratory frame, at selected electron energies. The KERD in the centre of mass frame is calculated from the measured velocity distribution as well as the anisotropy of the angular distribution with respect to the initial orientation of the molecular ions. Results are reported for dissociative ionization and dissociative excitation of CO+ to C+ and O+ fragments in the energy range from about 5 eV to 2.5 keV. Absolute cross sections for DE at maximum, i. e. for an electron energy around 35 eV, are found to be ( 9.69 +/- 2.08) x 10(-17) cm(2) and ( 6.24 +/- 1.33) x 10(-17) cm(2), for C+ and O+, respectively, and the corresponding threshold energies are found to be ( 8.5 +/- 0.5) eV and ( 14.8 +/- 0.5) eV. The DE process leading to C+ production is seen to dominate at low electron energies. For DI, the absolute cross section is found to be ( 12.56 +/- 2.38) x 10(-17) cm(2) around 125 eV and the corresponding threshold energy is ( 27.7 +/- 0.5) eV. KERDs, which extend from 0 to 24 eV both for C+ and O+, exhibit very different shapes at low electron energy but similar ones above 100 eV, confirming the role observed respectively for DE and DI. The groups of states contributing to the different processes are identified by comparing present energies thresholds values and the KERDs with theoretical values. Anisotropies are estimated to be in the range 3-6% for both C+ and O+.

Applying the animated beam method the total cross sections (TCS) for double ionization (DI) of helium by electrons are measured in the collision energy region from threshold to 3 keV. The TCS for the same process are calculated at intermediate and high incident energies in the first Born approximation (FBA). The radial and angular correlations between the bound electrons and repulsion between the ejected electrons are accounted. In order to go beyond the FBA the scattered electron is considered as a particle being in the Coulomb field of the nucleus, the charge of which is screened by the ejected electrons. On the basis of the obtained results some conclusions concerning the behaviour of the TCS in the intermediate and high-energy regions are drawn.

Absolute total cross sections have been measured for electron impact dissociative excitation and dissociative ionization of H-2(+) and D-2(+) in the energy range 5-3000 eV. The vibrational population of the primary H-2(+) beam has been analysed by dissociative charge exchange on a potassium target, and is in good agreement with the measurements of von Busch and Dunn (1972 Phys. Rev. A 5 1726). Kinetic energy release (KER) distributions have been extracted from momentum analysis of the released protons and deuterons at selected impact energies. A model calculation has been performed to interpret the different spectra. Below 100 eV, the distributions exhibit a sharp peak in the range 0-1 eV that is attributed to the dissociative excitation of high vibrational levels to the 2psigma(u) repulsive state in the vicinity of their outer turning point. This observation is consistent with the measured vibrational population extending up to upsilon = 13, as confirmed by the appearance threshold of the dissociative ionization (DI) channel. The KER distributions exhibit a second contribution peaking between 1 and 5 eV, resulting from the admixture of the (1ssigma(g) --> 2psigma(u)), (1ssigma(g) --> 2ppi(u)) and (1ssigma(g) --> 2ssigma(g)) electronic transitions. A distinctive hump is also present around 9 eV, that coincides both with the maximum of the DI contribution, and with the high-energy shoulder of the 2ppi(u) and 2ssigma(g) contributions. The present measurements are in qualitative agreement with the previous results of Caudano and Delfosse, and are fairly well reproduced by our first-order model.

The absolute cross section for associative ionization in H(1s) + H(3s) and D(1s) + D(3s) collisions has been measured, in the energy range 0.006-3.6 eV, in a merged beam apparatus. The 3s state is populated by exciting metastable atoms, with CW laser radiation, in a static field. For both isotopes, the cross section exhibits an E-1 behaviour at low energy, and a faster decrease above the ionization threshold of the 3s state. In the intermediate energy region, isotope-dependent oscillations of the cross section are observed, which we attribute to interferences between several reaction pathways.

Absolute cross sections for electron impact ionization, dissociative excitation (DE) and dissociative ionization of N-2(+) ions are measured in the energy range from threshold to 2500 eV. The animated crossed electron-ion beam method has been employed. The individual contributions of ionization products (N-2(2+)) and dissociation fragments (N+), which have both identical mass-to-charge ratio and average velocity, are deduced from the analysis of product velocity distributions. Particular attention was paid to determining the transmission efficiency for dissociation fragments, since their collection was incomplete during the measurements. Threshold energies and kinetic energy released to dissociation fragments are measured. The role of states contributing to different reactions is discussed. For DE, the present results are found to be much smaller than the results of Peterson et al (1998). For ionization (single and dissociative), a satisfactory agreement with their result is obtained as well as with the prediction of Kim et al (2000) obtained in the binary-encounter Bethe approximation.

First absolute cross sections for electron impact single ionization of H3O+, HD2O+ and D3O+ and for dissociative excitation (DE) producing H+ and D+ are reported. The animated crossed electron-ion beam method has been employed in the energy range from threshold to 2500 eV. The maxima of these cross sections are found to be unusually small (

Absolute cross sections for electron impact ionization and dissociation of CO2+ to form C+ and O+ fragments are measured in the energy range from threshold to 2500 eV. The animated crossed-beams method has been employed. The ionization cross section shows a maximum of 4.79 x 10(-17) cm(2) at 130 eV and the corresponding threshold is found in good agreement with previous measurements. Both dissociation cross sections are shown to exhibit wide plateaux which are of the same order of magnitude. In addition, these cross sections almost coincide above 100 eV. The threshold energy and kinetic energy released are determined for both the production of C+ and O+. They are found in good agreement with the previously published data obtained in electron impact ionization experiments of neutral CO2.

The iodine molecule has been investigated by a threshold electron spectrometer in the incident electron energy range from 1.00 eV to 3.5eV. From the threshold electron spectrum contributions for excitation of three states known from optical spectrometry have been subtracted. The remaining signal has been interpreted by four curves similar in shape to those in absorption optical spectroscopy into antibonding energy states. The detected maxima have been attributed to the following valence excited states of the iodine molecule: 3?2u(2u), 3?0u-(0u-), 3?2g(2g), and 3?1g(1g), respectively. With the knowledge of the energy ranges within which the signal from a particular state appears, the predicted values of equilibrium distances of iodine atom nuclei and estimated values of vibrational transition frequency potential energy curves have been constructed, too.

The wavelength dependence of the two-photon ionisation of metastable D(2s) by a laser beam has been measured near the 2s - 3p resonant frequency. A sharp structure is observed in the broad resonance profile at quite moderate intensity. Its origin is shown to be the spontaneous decay of the 3p state that competes with photoionisation.

We describe a new experiment dealing with the multiphoton ionization of metastable atomic hydrogen H(2s). The ion yield has been measured in a relative way but it provides absolute photoionization rates. In the present contribution, the wavelength is tuned in the vicinity of the 2s-3p transition and the laser intensity is in the 10(7)-5 x 10(10) W cm(-2) range. Experimental photoionization rates and resonance width are found to be in agreement with theoretical predictions.

Absolute cross sections for electron impact ionization and dissociation of OH+ and OD+ leading to the formation of the OH2+, O+, O2+, O3+ and D+ ions have been measured by applying the animated electron-ion beam method in the energy range from the respective reaction thresholds up to 2.5 keV. The maximum of the single ionization cross section is found to be (0.95 ± 0.02) × 10-19 cm2 at 155 eV. The maximum total cross sections for O+ and D+ fragments production are observed to be (15.7 ± 0.2) × 10-17 cm2 at 95 eV and (10.8 ± 0.5) × 10-17 cm2 at 95 eV, respectively. The cross sections for O2+ and O3+ are much smaller, (5.37 ± 0.04) × 10-18 cm2 at 135 eV and (7.95 ± 0.23) × 10-20 cm2 at 315 eV, respectively. The collected data are analyzed in details in order to determine separately the contributions of dissociative excitation and of dissociative ionization to the O+ and D+ fragments production.

International audience; Absolute cross sections have been measured using the crossed electron-ion beams method for electron-impact dissociation of the D 2 H + molecular ion yielding H +, D +, HD + and + 2 D fragments. The collision energy ranges from a few eV up to 2.5 keV. Around the maximum, cross sections are found to be of similar amplitude: (3.25±0.08)×10 -17 cm 2 for H +, (3.56±0.15)×10 -17 cm 2 for HD + and (3.33±0.11)×10 -17 cm 2 for + 2 D ; except for D + for which the maximum cross section is (4.62±0.09)×10 -17 cm 2. Individual contributions for dissociative excitation and for dissociative ionization are determined for each product. Close analysis of present data brings into evidence isotope effects in the fragmentation pattern of the D 2 H + target. Ejection of the lightest isotope is generally favored: for resonant dissociative excitation (H + over D +), for dissociative excitation (molecular ions + 2 D and HD +, associated with ejection of H and D, respectively) and for dissociative ionization, but not for H + and D + produced via dissociative excitation. Present dissociative excitation cross sections for D 2 H + are found to be significantly lower than those measured for + 3 D, although those of DI agree well together.

International audience; Absolute cross sections for electron-impact dissociation and ionization of NH + leading to the formation of N + and N 2+ products have been measured by applying the animated electron–ion beam method, in the energy range from the respective thresholds up to 2.5 keV. The maximum total cross sections are observed to be (15.7±0.7)×10 -17 cm 2 and (11.1±0.2)×10-18 cm 2 for N + and N 2+, respectively. Absolute cross sections are determined separately for dissociative excitation and for dissociative ionization processes. The measurements for slow N + ions show a noticeable contribution in the low incident electron energy range ; these data are attributed to excitation processes. Dissociative excitation is assumed to play a significant role in the collision energy region close to the vertical excitation energies for the lowest electronic transitions in the Franck-Condon region. The yields of fast N + ions have also been measured ; these energetic dissociations are generally ascribed to ionization processes. Kinetic energy release distributions are seen to extend from 0eV to 15eV for the N + fragments and up to 20eV for the N 2+ ones. Present energy thresholds and kinetic energy release results are compared with available published data, allowing in some cases identification of fragmentation patterns and of molecular states contributing to observed processes. The possibility of dissociative excitation of the molecular ion which could occur via a mechanism involving autoionizing resonances is discussed.

New absolute cross section measurement for the reaction H- + e --> H+ + 3e- is reported for interaction energies from threshold to 2 keV by using the animated crossed beam method. The present results confirm the disagreement between the previous results of this laboratory and the results of Peart et al.

Absolute total cross sections have been measured for the reaction H(2s) + H(2s) --> H2+ + e- in the collison energy range 0.004-0.65 eV. Single beam measurements yield a cross section of 2.1 x 10(-15) cm2 at an average collision energy of 4.1 meV. Relative measurements performed with merged beams indicate, together with the absolute measurements, an overall E-1 energy dependence.

The first absolute cross section measurements for single and double electron impact ionization of sodium-like Ar7+ are reported. The animated crossed beams method has been employed in the energy range from threshold to 3000 eV. The measured cross sections for single ionization are higher than the theoretical and semi-empirical predictions by about 20-50%. This discrepancy has been associated with the contribution of the indirect ionization processes. The double ionization cross section is only 1% of the single one.

International audience; Absolute cross sections for electron impact dissociative excitation and ionization of NeD+ leading to the formation of singly and multiply charged products (D+, Ne+, Ne2+ and Ne3+) are reported, in the energy range from their respective thresholds to 2.5 keV. The animated crossed-beams method is used. For singly charged fragments, absolute cross sections are obtained separately for dissociative excitation and for dissociative ionization. Dissociative excitation is seen to be restricted to the low-energy range (

Measured cross sections for single ionisation of Li-like N4+, O5+ and Ne7+ by electron impact are reported for energies from threshold to 2500 eV. The animated crossed beams method has been employed. In addition to direct ionisation, the 1s22s to 1s2l2l' excitation followed by autoionisation is shown to give a significant contribution to the total cross section, and its magnitude has been estimated for all three ions. Comparisons are made with other experimental results and different theoretical predictions. Cross sections for N4+ and O5+ are in a good agreement with previous results and the first result on Ne7+ ionisation is well reproduced by the Coulomb-Born calculations.

H2 molecules were ionized by Ti:sapphire (45 fs, 800 nm) and Nd-doped yttrium aluminum garnet lasers (6 ns, 1064 nm). The relative populations of the vibrational levels of the H+2 ions were determined and found to be concentrated in the lowest vibrational levels. Tunneling ionization calculations with exact field-modified potential curves reproduce the experimental results. The reason for the departure from conventional Franck-Condon-like distributions is the rapid variation of the ionization rate with internuclear distance.

Associative ionization (AI): A + B* → AB+ + e− and dissociative recombination (DR) share the same reaction channels, although the precise dynamics depend on the actual collision taking place. The large angular momentum put into the system by heavy particle collisions does indeed obliterate the subtle role of closed Rydberg channels, as these resonances are displaced by the centrifugal energy. However, the systematic study of AI processes at low energy provides us with additional information on the reaction channels, their branching into atomic products, and the preferred symmetries of DR. The effect of isotope substitution on total cross sections, together with the development of a new diagnostic tool to measure the internal energy of AI products, give an unambiguous identification of the reaction pathways.

Absolute cross sections have been measured for electron-impact dissociative excitation and ionization of the helium-hydride ion (HeH+) leading to the formation of helium ions Heq+ (q = 1–2). Measurements have been performed for electron energies ranging from the respective thresholds up to 2.5 keV. For He+ production, the maximum absolute cross section for dissociative excitation is found to be (2.5 ± 0.2) ×10−17 cm2 (around 40 eV), while for dissociative ionization, it is found to be (2.1 ± 0.1) ×10−17 cm2 (around 135 eV). For He2+ production, only the inclusive absolute cross section is presented, without attempting to isolate any distinct contribution, and it is measured to be (2.6 ± 0.2) ×10−19 cm2 (around the maximum, 195 eV). Appearance energies for He+ and He2+ are determined to be (11.2 ± 0.5) eV and (66.5 ± 1.0) eV, respectively. Kinetic energy release and angular distributions are obtained, at specific incident electron energies.

Electron-impact dissociation and ionization of NH+ and ND+ ions leading to formation of D+, N+ and N2+ products have been measured by applying the animated electron-ion beam method in the energy range from respective thresholds up to 2.5 keV. Absolute cross sections are determined separately for dissociative excitation (DE), dissociative ionization (DI) and for asymmetric dissociative ionization (ADI) processes.

Absolute cross sections results are reported for electron impact dissociative excitation and ionization of HD2+ in the electron energy range from threshold to 2.5 keV. Direct and resonant dissociative excitation is found to dominate the production of possible ionic products in the low energy region. Dissociative ionization is observed for H+ and D+ products only. The lowness of dissociative ionization signals both for HD+ and for D2+ indicate that molecular ions are dominantly formed in dissociative states, a situation which totally contrasts with the D3+isotopomer case.

Measurements of NeD+ dissociative excitation cross section were obtained in Louvain-la-Neuve (UCL, Belgium) by using the animated crossed electron-ion beam method. The electronic structure of the system was calculated by using quantum chemistry calculations for the NeD+ ion and ab initio electron scattering calculations using the complex Kohn variational method for the resonant NeD neutral complex formed by the temporary capture of the electron by the ion. The cross section for dissociative excitation are then calculated below the second excitation thresholds of the ion where the process is dominated by a series of doubly-excited resonance states. Theory and experiment are then compared.

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 electron-impact dissociation of D-3(+) leading to the formation of D+ and D-2(+) products have been measured by applying the animated electron-ion beam method in the energy range from the respective thresholds up to 2.5 keV. The maximum total cross-sections are observed to be (13.9 +/- 1.1) x 10(-17) cm(2) and (8.2 +/- 0.1) x 10(-17) cm(2) (around 50 eV) for D+ and for D-2(+) fragments, respectively. The present results are in a satisfactory agreement with those of experiments performed at storage ring facilities in the low energy range (

The Bethe-Born theory is applied to estimate the effective charges experienced by the ejected electrons at single, double and triple ionization of neon by fast electrons. The expansion coefficients appearing in the asymptotic expressions for total cross sections sigma(n+) similar to[a(n+) In(E-i/In+) + b(n+)]/E-i are determined by fitting to these expressions the experimental data for single and multiple ionization of neon. Coefficients a(n+) and b(n+) are seen to decrease exponentially with increasing number of ejected electrons. Empirical formulae are found to describe this behaviour. Analytical expressions for coefficients a(n+) are derived within the Bethe-Born approximation for single, double and triple ionization of neon. The effective charges are determined by assuming that the derived analytical expressions for a(n+) can be reduced to the empirical formula. It is shown that, in order to obtain the reasonable values for the effective charges, coefficient b(n+) should be taken into consideration. It is also revealed that the inclusion of interaction between the ejected electrons in the final state in calculation improves the results.

Absolute cross sections for electron-impact single and multiple ionization of Ne+ leading to the formation of Neq+ (q = 2-5) are reported. The animated crossed beams method is applied in the energy range from the respective thresholds up to 2.5 keV. The maximum cross sections are found to be (4.12 +/- 0.21) x 10(-17) cm(2), (1.42 +/- 0.07) x 10(18) cm(2), (2.57 +/- 0.14) x 10(-20) cm(2), (8.78 +/- 0.54) x 10(-22) cm(2) for the multiply-charged products Neq+ (q = 2-5), respectively. The corresponding threshold energies are measured to be (41.0 +/- 0.5) eV, (105 +/- 1) eV, (205 +/- 5) eV and (345 +/- 15) eV. Present data are compared with available experimental and theoretical results.

Cross sections for electron capture by H(2s) atoms in collision with H2, He, Ne, Ar, Kr, and Xe have been measured in the energy range 1.6-5 keV. The results are compared with those of Dose and Gunz (1972), Roussel et al. (1977) and Hill et al. (1979).

A method of producing an intense beam of H(3p) atoms is described. The 3p hydrogen atoms are formed by laser excitation of metastable H(2s) atoms and efficiencies of the order of 0.3 to 0.4 are easily obtained. The metastables themselves are formed by the charge exchange of protons in a Cs vapour. Cross sections for electron loss from H(3p) atoms and H(2s) atoms in collision with H2 molecules and rare-gas atoms have been measured in the energy range 1260-3600 eV in the forward direction (10 mrad acceptance). The results are normalised to absolute cross sections obtained by Roussel et al. (1977) for electron loss from ground-state hydrogen atoms in collision with the same targets. Comparison with other measurements is only possible for electron loss from H(2s) atoms and a good agreement with other authors is found.

Reports absolute cross section measurements of the ion pair production HA(2s)+HB(1s) to HA++HB- using a merged beams experiment. Four centre-of-mass energies have been investigated between 85 and 325 eV. The results are found to be in good agreement with recent theoretical predictions. This work also confirms the important distinction made between 'direct' (like the reaction studied) and 'indirect' (i.e. HA(2s)+HB(1s) to HA-+HB+) charge exchange.

Absolute electron impact ionization cross-sections have been measured for the neonlike Ar 8+ in the energy range from below the threshold for the metastable state to 2500 eV. No contribution of metastable states is observed. The results are well reproduced by the distorted wave Born approximation.

A new crossed beams apparatus for measuring absolute electron impact ionization cross-sections of multiply charged ions is described. First measurements are also reported which deal with N/sup 4+/ and N/sup 5+/. The results are in good agreements with those previously obtained by the Oak Ridge group, For N/sup 5+/ a non-negligible signal is observed below the ground state ionization threshold. It is attributed to the presence of ions in metastable states. From the semi-empirical Lotz formula the population of ions in those states is estimated to be approximately 3%.