New Light Shed on Charge Transfer in FundamentalH++H2Collisions

Abstract

There is no consensus on the magnitude and shape of the charge transfer cross section in low-energy H þ þ H 2 collisions, in spite of the fundamental importance of these collisions. Experiments have thus been carried out in the energy range 15 E 5000 eV. The measurements invalidate previous recommended data for E 200 eV and confirm the existence of a local maximum around 45 eV, which was predicted theoretically. Additionally, vibrationally resolved cross sections allow us to investigate the evolution of the underlying charge transfer mechanism as a function of E.

Ab initiocalculation of electron-capture cross sections inH++BeHcollisions

“…It must be noted that, although Eqs. ( 19) and ( 33) are formally similar, the former one has been derived by using the centrifugal sudden approximation while the Coriolis couplings are not neglected in the semiclassical calculation [see (35)]. This di erence precludes that quantal and semiclassical treatments lead in general to the same results.…”

“…This di erence precludes that quantal and semiclassical treatments lead in general to the same results. The validity of this approximation has been discussed in previous works for H + +H 2 collisions [35], where it was found that the cross sections obtained from quantal (IOS) and eikonal semiclassical calculations agree in the range of collision energies 200 eV< E < 400 eV, and therefore both trajectory e ects and centrifugal sudden approximation are not relevant. In general, it is expected that the semiclassical treatment, including rotational couplings, is more accurate at high energies than the IOS one.…”

“…The validity of the sudden approximation for rotation and vibration has been discussed for the benchmark system H + +H 2 in [33], where it was shown that it is not appropriate at low collision energies (E 200 eV), because the transitions leading to the EC process take place between quasi-degenerate vibronic levels, as suggested in [34], and a method beyond the sudden approximation must be applied as in the calculations of [35]. In order to compare with beam experiments with gas-phase targets, the cross section must be averaged with respect to the molecule orientation (see [20]).…”

Lattice description of electron loss in high-energy H++H2O collisions

“…Previous calculations on ion-diatom collisions ( [35] and references therein) indicates that the approximation is valid for energies above 1 keV/u. In order to describe the electron-target interaction, we have used a threecenter model potential:…”

Photodissociation as a probe of the H 3 + avoided crossing seam

“…Numerous measurements of the cross section of reaction (1) exist, albeit with H 2 in its vibrational ground state and at collision energies well above 10 eV [3]. Our recent work on charge transfer in proton H 2 collisions down to 15 eV [4] demonstrated the decisive role * Electronic address: xavier.urbain@uclouvain.be of the avoided crossing seam connecting the ground and first excited potential energy surfaces of H + 3 . The vibrational population of the H + 2 products was shown to peak at v + = 0 at a collision energy of 45 eV, evolving from a Franck-Condon distribution at keV energies.…”