Low-energy Charge Exchange Collisions Research Articles

High-Resolution Probe of Coherence in Low-Energy Charge Exchange Collisions with Oriented Targets

The trapping lasers of a magneto-optical trap have been used to bring Rb atoms into well defined oriented states. Coupled to recoil-ion-momentum spectroscopy, this provided a unique MOTRIMS setup which was able to probe scattering dynamics, including the coherence features, with unprecedented resolution. The technique was applied to the low-energy charge exchange reactions Na+ + Rb(5p±1)→Na(3p,4s)+Rb+. The measurements revealed detailed features of the collisional interaction which were employed to improve the theoretical description. As such, it was possible to ascertain the validity of the intuitive models used to predict the most likely capture transitions.

Plasma‐induced clearing and redistribution of material embedded in planetary magnetospheres

Charge exchange collisions between the ions trapped in a planetary magnetosphere and the ambient neutrals are a principal material loss process in evolving planetary systems (Johnson, 2004). Here we show that low energy charge exchange collisions, in which orbiting occurs, can drastically modify the redistribution and loss of materials in evolving planetary disks. Using Saturn as an example, these collisions can account for the fact that water products, produced primarily in the inner magnetosphere, are found to be the dominant ions throughout Saturn's magnetosphere.

X-Ray emission following low-energy charge exchange collisions of highly charged ions

K-shell x-ray emission following low-energy charge exchange collisions ( </=11 eV/amu) has been measured for ten bare and hydrogenic ions up to U91+. The data resolve capture into angular momentum states with l = 1 and provide a stringent test of theory. The assumption of Stark mixing of angular momentum states is inappropriate at such energies. Results from detailed calculations give a better description of the data, but significant discrepancies are noted. The measurements show that the hardness ratio of charge-exchange induced K-shell x-ray emission represents a diagnostic of the dynamics of ion-atom interactions in situations where the energy is below 1 keV/amu, e.g., in solar wind collisions.

Charge exchange and cluster formation in an rf Paul trap: interaction of alkali atoms with C +60

A Paul ion trap was used to study the formation of clusters under controlled temperature and pressure conditions. Exposure of cold C + 60 ions to Li flux leads to the formation of Li n C + 60 clusters ( n = 1–18) occurring by the sequential association of Li atoms. Cluster formation dependence on He pressure displayed a competition between vibrational relaxation and unimolecular dissociation. Collisions with Na, K, Rb and Cs atoms resulted in dissociative charge exchange. Decay rates of C + 60 ions resulting from these low-energy charge exchange collisions were consistent with Langevin capture rates.

Spectroscopy of Mg-like Ar produced in low-energy charge exchange collisions

After the single-electron capture collision Ar7++He to Ar6++He+ a measurement of Ar VII transition intensities in the region 100< lambda <1000 AA shows that the projectile captures the electron into the n=4 level of the Ar VII ion. A configuration interaction calculation of Ar VII energy levels is used to interpret and identify observed transitions. It is underlined that population of (Ar6+)3L states rather than (Ar6+)1L states is favoured.

VUV spectroscopy of charge exchange processes in collisions of multiply charged ions

We present some of our results concerning the VUV spectroscopic study of low energy charge exchange collisions. Metastable beam fractions for C 4+ and N 5+ have been measured and absolute cross sections for corresponding emission lines have been deduced. Two-electron change has been observed for N IV and Ne VII, where two processes (single capture with one core electron change and transfer ionisation) are involved. The charge exchange excitation method has also been applied to pure spectroscopic investigation of Kr VIII and to polarisation measurements on O III.

Spectroscopy of doubly excited Ne VII produced in low-energy charge exchange collisions

The spectroscopy of emitted radiation following double electron capture by low-energy Ne8+ from He shows state-selective capture into the n=2, n'=3 and 4 energy levels. These levels appear to favour radiative decay, whereas double capture to n=3, n'>or=3 will stabilise mostly via autoionisation.

Charge exchange process with low energy multicharged ions: n, l populations

Theoretical models for low energy charge exchange collisions of highly charged ions are reviewed in connection with populated final states. A simple experimental method is presented which provides the most populated n level, the percentage of p substates and the mean l value. Results are reported for 10 keV q Al 12+ collisions on H 2 and He.

Radiative decay following low energy charge exchange collisions at the Agrippa facility

From radiative decay observed in the X and VUV domain, it is possible to determine the ( n, l) substate populations and deduce their excitation cross sections. We consider here the case of different projectiles of charge +8. For some of them, we show σ nl for single capture from H 2 and He, as a function of energy. From the spectra it is recognized that double capture followed by radiative decay is effective. Observed transitions — of the same nature as dielectronic recombination satellites — are the signature of this process. Finally, in the case where energy levels are not known since the capture is a selective process, radiative decay appears thus as a means for basic spectroscopic studies.

Photon emission spectroscopy of highly charged ions following low energy charge exchange collisions

The theory of charge exchange is discussed in the framework of the quasi-molecular model. The classical one electron model indicates a specific state population. The Landau-Zener model is applied to charge exchange collision, two specific interaction appear : (a) radial coupling induced by the radial motion, (b) excitation effect due to rotational motion of the internuclear line during a collision. An example of n,1 distribution is given through the multi-channel Landau-Zener theory. The various radiative processes resulting from initial alignment suggest that polarization measurements make possible the differentiation of radial and rotational coupling.